Publications by authors named "Christopher J Alteri"

28 Publications

  • Page 1 of 1

Lipopolysaccharide O structure of adherent and invasive Escherichia coli regulates intestinal inflammation via complement C3.

PLoS Pathog 2020 10 7;16(10):e1008928. Epub 2020 Oct 7.

Department of Pathology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.

Gut dysbiosis associated with intestinal inflammation is characterized by the blooming of particular bacteria such as adherent-invasive E. coli (AIEC). However, the precise mechanisms by which AIEC impact on colitis remain largely unknown. Here we show that antibiotic-induced dysbiosis worsened chemically-induced colitis in IL-22-deficient mice, but not in wild-type mice. The increase in intestinal inflammation was associated with the expansion of E. coli strains with genetic and functional features of AIEC. These E. coli isolates exhibited high ability to out compete related bacteria via colicins and resistance to the host complement system in vitro. Mutation of wzy, the lipopolysaccharide O polymerase gene, rendered AIEC more sensitive to the complement system and more susceptible to engulfment and killing by phagocytes while retaining its ability to outcompete related bacteria in vitro. The wzy AIEC mutant showed impaired fitness to colonize the intestine under colitic conditions, but protected mice from chemically-induced colitis. Importantly, the ability of the wzy mutant to protect from colitis was blocked by depletion of complement C3 which was associated with impaired intestinal eradication of AIEC in colitic mice. These studies link surface lipopolysaccharide O-antigen structure to the regulation of colitic activity in commensal AIEC via interactions with the complement system.
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http://dx.doi.org/10.1371/journal.ppat.1008928DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7571687PMC
October 2020

Optimization of an Experimental Vaccine To Prevent Escherichia coli Urinary Tract Infection.

mBio 2020 04 28;11(2). Epub 2020 Apr 28.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA

Urinary tract infections (UTI) affect half of all women at least once during their lifetime. The rise in the numbers of extended-spectrum beta-lactamase-producing strains and the potential for carbapenem resistance within uropathogenic (UPEC), the most common causative agent of UTI, create an urgent need for vaccine development. Intranasal immunization of mice with UPEC outer membrane iron receptors FyuA, Hma, IreA, and IutA, conjugated to cholera toxin, provides protection in the bladder or kidneys under conditions of challenge with UPEC strain CFT073 or strain 536. On the basis of these data, we sought to optimize the vaccination route (intramuscular, intranasal, or subcutaneous) in combination with adjuvants suitable for human use, including aluminum hydroxide gel (alum), monophosphoryl lipid A (MPLA), unmethylated CpG synthetic oligodeoxynucleotides (CpG), polyinosinic:polycytidylic acid (polyIC), and mutated heat-labile enterotoxin (dmLT). Mice intranasally vaccinated with dmLT-IutA and dmLT-Hma displayed significant reductions in bladder colonization (86-fold and 32-fold, respectively), with 40% to 42% of mice having no detectable CFU. Intranasal vaccination of mice with CpG-IutA and polyIC-IutA significantly reduced kidney colonization (131-fold) and urine CFU (22-fold), respectively. dmLT generated the most consistently robust antibody response in intranasally immunized mice, while MPLA and alum produced greater concentrations of antigen-specific serum IgG with intramuscular immunization. On the basis of these results, we conclude that intranasal administration of Hma or IutA formulated with dmLT adjuvant provides the greatest protection from UPEC UTI. This report advances our progress toward a vaccine against uncomplicated UTI, which will significantly improve the quality of life for women burdened by recurrent UTI and enable better antibiotic stewardship. Urinary tract infections (UTI) are among the most common bacterial infection in humans, affecting half of all women at least once during their lifetimes. The rise in antibiotic resistance and health care costs emphasizes the need to develop a vaccine against the most common UTI pathogen, Vaccinating mice intranasally with a detoxified heat-labile enterotoxin and two surface-exposed receptors, Hma or IutA, significantly reduced bacterial burden in the bladder. This work highlights progress in the development of a UTI vaccine formulated with adjuvants suitable for human use and antigens that encode outer membrane iron receptors required for infection in the iron-limited urinary tract.
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http://dx.doi.org/10.1128/mBio.00555-20DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7188996PMC
April 2020

The oxidative fumarase FumC is a key contributor for E. coli fitness under iron-limitation and during UTI.

PLoS Pathog 2020 02 27;16(2):e1008382. Epub 2020 Feb 27.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.

The energy required for a bacterium to grow and colonize the host is generated by metabolic and respiratory functions of the cell. Proton motive force, produced by these processes, drives cellular mechanisms including redox balance, membrane potential, motility, acid resistance, and the import and export of substrates. Previously, disruption of succinate dehydrogenase (sdhB) and fumarate reductase (frdA) within the oxidative and reductive tricarboxylic acid (TCA) pathways in uropathogenic E. coli (UPEC) CFT073 indicated that the oxidative, but not the reductive TCA pathway, is required for fitness in the urinary tract. Those findings led to the hypothesis that fumA and fumC encoding fumarase enzymes of the oxidative TCA cycle would be required for UPEC colonization, while fumB of the reductive TCA pathway would be dispensable. However, only UPEC strains lacking fumC had a fitness defect during experimental urinary tract infection (UTI). To further characterize the role of respiration in UPEC during UTI, additional mutants disrupting both the oxidative and reductive TCA pathways were constructed. We found that knock-out of frdA in the sdhB mutant strain background ameliorated the fitness defect observed in the bladder and kidneys for the sdhB mutant strain and results in a fitness advantage in the bladder during experimental UTI. The fitness defect was restored in the sdhBfrdA double mutant by complementation with frdABCD. Taken together, we demonstrate that it is not the oxidative or reductive pathway that is important for UPEC fitness per se, but rather only the oxidative TCA enzyme FumC. This fumarase lacks an iron-sulfur cluster and is required for UPEC fitness during UTI, most likely acting as a counter measure against exogenous stressors, especially in the iron-limited bladder niche.
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http://dx.doi.org/10.1371/journal.ppat.1008382DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7064253PMC
February 2020

Dietary L-serine confers a competitive fitness advantage to Enterobacteriaceae in the inflamed gut.

Nat Microbiol 2020 01 4;5(1):116-125. Epub 2019 Nov 4.

Division of Gastroenterology, Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA.

Metabolic reprogramming is associated with the adaptation of host cells to the disease environment, such as inflammation and cancer. However, little is known about microbial metabolic reprogramming or the role it plays in regulating the fitness of commensal and pathogenic bacteria in the gut. Here, we report that intestinal inflammation reprograms the metabolic pathways of Enterobacteriaceae, such as Escherichia coli LF82, in the gut to adapt to the inflammatory environment. We found that E. coli LF82 shifts its metabolism to catabolize L-serine in the inflamed gut in order to maximize its growth potential. However, L-serine catabolism has a minimal effect on its fitness in the healthy gut. In fact, the absence of genes involved in L-serine utilization reduces the competitive fitness of E. coli LF82 and Citrobacter rodentium only during inflammation. The concentration of luminal L-serine is largely dependent on dietary intake. Accordingly, withholding amino acids from the diet markedly reduces their availability in the gut lumen. Hence, inflammation-induced blooms of E. coli LF82 are significantly blunted when amino acids-particularly L-serine-are removed from the diet. Thus, the ability to catabolize L-serine increases bacterial fitness and provides Enterobacteriaceae with a growth advantage against competitors in the inflamed gut.
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http://dx.doi.org/10.1038/s41564-019-0591-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6925351PMC
January 2020

UTI patients have pre-existing antigen-specific antibody titers against UTI vaccine antigens.

Vaccine 2019 08 15;37(35):4937-4946. Epub 2019 Jul 15.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, USA. Electronic address:

Urinary tract infection (UTI) is most frequently caused by uropathogenic Escherichia coli (UPEC). Our laboratory has been developing an experimental vaccine targeting four UPEC outer membrane receptors involved in iron acquisition - IreA, FyuA, IutA, and Hma - to elicit protection against UTI. These vaccine targets are all expressed in humans during UTI. In the murine model, high titers of antigen-specific serum IgG or bladder IgA correlate with protection against transurethral challenge with UPEC. Our aim was to measure levels of pre-existing serum antibodies to UTI vaccine antigens in our target population. To accomplish this, we obtained sera from 64 consenting female patients attending a clinic for symptoms of cystitis. As a control, we also collected sera from 20 healthy adult male donors with no history of UTI. Total IgG and antigen-specific IgG titers were measured by ELISA. Of the 64 female patients, 29 had significant bacteriuria (>10 cfu/ml urine) and uropathogenic E. coli (UPEC). Thirty-five patients had non-significant bacteriuria (<10 cfu/ml). Antigen-specific IgG titers did not correlate with the presence or absence of the gene encoding the antigen in the infecting strain (when present), but rather titers were proportional to prevalence of genes encoding antigens among representative collections of UPEC isolates. Surprisingly, we obtained similar results when sera from healthy male patients without history of UTI were tested. Thus, unvaccinated adults have non-protective levels of pre-existing antibodies to UTI vaccine antigens, establishing an important baseline for our target population. This suggests that a UTI vaccine would need to boost pre-existing humoral responses beyond these background levels to protect from infection.
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http://dx.doi.org/10.1016/j.vaccine.2019.07.031DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6812515PMC
August 2019

Flexible Metabolism and Suppression of Latent Enzymes Are Important for Adaptation to Diverse Environments within the Host.

J Bacteriol 2019 08 24;201(16). Epub 2019 Jul 24.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA

Bacterial metabolism is necessary for adaptation to the host microenvironment. Flexible metabolic pathways allow uropathogenic (UPEC) to harmlessly reside in the human intestinal tract and cause disease upon extraintestinal colonization. intestinal colonization requires carbohydrates as a carbon source, while UPEC extraintestinal colonization requires gluconeogenesis and the tricarboxylic acid cycle. UPEC containing disruptions in two irreversible glycolytic steps involving 6-carbon (6-phosphofructokinase; ) and 3-carbon (pyruvate kinase; ) substrates have no fitness defect during urinary tract infection (UTI); however, both reactions are catalyzed by isozymes: 6-phosphofructokinases Pfk1 and Pfk2, encoded by and , and pyruvate kinases Pyk II and Pyk I, encoded by and UPEC strains lacking one or both phosphofructokinase-encoding genes ( and ) and strains lacking one or both pyruvate kinase genes ( and ) were investigated to determine their regulatory roles in carbon flow during glycolysis by examining their fitness during UTI and growth requirements. Loss of a single phosphofructokinase-encoding gene has no effect on fitness, while the double mutant outcompeted the parental strain in the bladder. A defect in bladder and kidney colonization was observed with loss of , while loss of resulted in a fitness advantage. The mutant was indistinguishable from wild-type , suggesting that the presence of Pyk II rather than the loss of Pyk I itself is responsible for the fitness defect in the mutant. These findings suggest that suppresses latent enzymes to survive in the host urinary tract. Urinary tract infections are the most frequently diagnosed urologic disease, with uropathogenic (UPEC) infections placing a significant financial burden on the health care system by generating more than two billion dollars in annual costs. This, in combination with steadily increasing antibiotic resistances to present day treatments, necessitates the discovery of new antimicrobial agents to combat these infections. By broadening our scope beyond the study of virulence properties and investigating bacterial physiology and metabolism, we gain a better understanding of how pathogens use nutrients and compete within host microenvironments, enabling us to cultivate new therapeutics to exploit and target pathogen growth requirements in a specific host environment.
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http://dx.doi.org/10.1128/JB.00181-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6657593PMC
August 2019

Can the Microbiome Deliver? A Proof-of-Concept Engineered E. coli PKU Therapeutic.

Cell Host Microbe 2019 04;25(4):473-474

Department of Natural Sciences, University of Michigan Dearborn, Dearborn, MI 48128, USA. Electronic address:

Phenylketonuria (PKU) is a rare genetic disorder that causes phenylalanine toxicity in the brain. Two studies, Crook et al. (2019), in this issue of Cell Host & Microbe, and Isabella et al. (2018), employ synthetic biology to develop a live bacterial therapeutic to treat PKU and potentially other metabolic diseases.
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http://dx.doi.org/10.1016/j.chom.2019.03.015DOI Listing
April 2019

Subtle variation within conserved effector operon gene products contributes to T6SS-mediated killing and immunity.

PLoS Pathog 2017 Nov 20;13(11):e1006729. Epub 2017 Nov 20.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.

Type VI secretion systems (T6SS) function to deliver lethal payloads into target cells. Many studies have shown that protection against a single, lethal T6SS effector protein requires a cognate antidote immunity protein, both of which are often encoded together in a two-gene operon. The T6SS and an effector-immunity pair is sufficient for both killing and immunity. HereIn this paper we describe a T6SS effector operon that differs from conventional effector-immunity pairs in that eight genes are necessary for lethal effector function, yet can be countered by a single immunity protein. In this study, we investigated the role that the PefE T6SS immunity protein plays in recognition between two strains harboring nearly identical effector operons. Interestingly, despite containing seven of eight identical effector proteins, the less conserved immunity proteins only provided protection against their native effectors, suggesting that specificity and recognition could be dependent on variation within an immunity protein and one effector gene product. The variable effector gene product, PefD, is encoded upstream from pefE, and displays toxic activity that can be countered by PefE independent of T6SS-activity. Interestingly, while the entire pef operon was necessary to exert toxic activity via the T6SS in P. mirabilis, production of PefD and PefE alone was unable to exert this effector activity. Chimeric PefE proteins constructed from two P. mirabilis strains were used to localize immunity function to three amino acids. A promiscuous immunity protein was created using site-directed mutagenesis to change these residues from one variant to another. These findings support the notion that subtle differences between conserved effectors are sufficient for T6SS-mediated kin discrimination and that PefD requires additional factors to function as a T6SS-dependent effector.
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http://dx.doi.org/10.1371/journal.ppat.1006729DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5714391PMC
November 2017

The Versatile Type VI Secretion System.

Microbiol Spectr 2016 04;4(2)

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109.

Bacterial type VI secretion systems (T6SSs) function as contractile nanomachines to puncture target cells and deliver lethal effectors. In the 10 years since the discovery of the T6SS, much has been learned about the structure and function of this versatile protein secretion apparatus. Most of the conserved protein components that comprise the T6SS apparatus itself have been identified and ascribed specific functions. In addition, numerous effector proteins that are translocated by the T6SS have been identified and characterized. These protein effectors usually represent toxic cargoes that are delivered by the attacker cell to a target cell. Researchers in the field are beginning to better understand the lifestyle or physiology that dictates when bacteria normally express their T6SS. In this article, we consider what is known about the structure and regulation of the T6SS, the numerous classes of antibacterial effector T6SS substrates, and how the action of the T6SS relates to a given lifestyle or behavior in certain bacteria.
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http://dx.doi.org/10.1128/microbiolspec.VMBF-0026-2015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4887148PMC
April 2016

Development of a Vaccine against Escherichia coli Urinary Tract Infections.

Pathogens 2015 Dec 31;5(1). Epub 2015 Dec 31.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.

Urinary tract infection (UTI) is the second most common infection in humans after those involving the respiratory tract. This results not only in huge annual economic costs, but in decreased workforce productivity and high patient morbidity. Most infections are caused by uropathogenic Escherichia coli (UPEC). Antibiotic treatment is generally effective for eradication of the infecting strain; however, documentation of increasing antibiotic resistance, allergic reaction to certain pharmaceuticals, alteration of normal gut flora, and failure to prevent recurrent infections represent significant barriers to treatment. As a result, approaches to prevent UTI such as vaccination represent a gap that must be addressed. Our laboratory has made progress toward development of a preventive vaccine against UPEC. The long-term research goal is to prevent UTIs in women with recurrent UTIs. Our objective has been to identify the optimal combination of protective antigens for inclusion in an effective UTI vaccine, optimal adjuvant, optimal dose, and optimal route of delivery. We hypothesized that a multi-subunit vaccine elicits antibody that protects against experimental challenge with UPEC strains. We have systematically identified four antigens that can individually protect experimentally infected mice from colonization of the bladder and/or kidneys by UPEC when administered intranasally with cholera toxin (CT) as an adjuvant. To advance the vaccine for utility in humans, we will group the individual antigens, all associated with iron acquisition (IreA, Hma, IutA, FyuA), into an effective combination to establish a multi-subunit vaccine. We demonstrated for all four vaccine antigens that antigen-specific serum IgG represents a strong correlate of protection in vaccinated mice. High antibody titers correlate with low colony forming units (CFUs) of UPEC following transurethral challenge of vaccinated mice. However, the contribution of cell-mediated immunity cannot be ruled out and must be investigated experimentally. We have demonstrated that antibodies bind to the surface of UPEC expressing the antigens. Sera from women with and without histories of UTI have been tested for antibody levels to vaccine antigens. Our results validate iron acquisition as a target for vaccination against UTI.
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http://dx.doi.org/10.3390/pathogens5010001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4810122PMC
December 2015

Metabolism and Fitness of Urinary Tract Pathogens.

Microbiol Spectr 2015 Jun;3(3)

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109.

Among common infections, urinary tract infections (UTI) are the most frequently diagnosed urologic disease. The majority of UTIs are caused by uropathogenic Escherichia coli. The primary niche occupied by E. coli is the lower intestinal tract of mammals, where it resides as a beneficial component of the commensal microbiota. Although it is well-known that E. coli resides in the human intestine as a harmless commensal, specific strains or pathotypes have the potential to cause a wide spectrum of intestinal and diarrheal diseases. In contrast, extraintestinal E. coli pathotypes reside harmlessly in the human intestinal microenvironment but, upon access to sites outside of the intestine, become a major cause of human morbidity and mortality as a consequence of invasive UTI (pyelonephritis, bacteremia, or septicemia). Thus, extraintestinal pathotypes like uropathogenic E. coli (UPEC) possess an enhanced ability to cause infection outside of the intestinal tract and colonize the urinary tract, the bloodstream, or cerebrospinal fluid of human hosts. Due to the requirement for these E. coli to replicate in and colonize both the intestine and extraintestinal environments, we posit that physiology and metabolism of UPEC strains is paramount. Here we discuss that the ability to survive in the urinary tract depends as much on bacterial physiology and metabolism as it does on the well-considered virulence determinants.
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http://dx.doi.org/10.1128/microbiolspec.MBP-0016-2015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4510461PMC
June 2015

Preferential use of central metabolism in vivo reveals a nutritional basis for polymicrobial infection.

PLoS Pathog 2015 Jan 8;11(1):e1004601. Epub 2015 Jan 8.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.

The human genitourinary tract is a common anatomical niche for polymicrobial infection and a leading site for the development of bacteremia and sepsis. Most uncomplicated, community-acquired urinary tract infections (UTI) are caused by Escherichia coli, while another bacterium, Proteus mirabilis, is more often associated with complicated UTI. Here, we report that uropathogenic E. coli and P. mirabilis have divergent requirements for specific central pathways in vivo despite colonizing and occupying the same host environment. Using mutants of specific central metabolism enzymes, we determined glycolysis mutants lacking pgi, tpiA, pfkA, or pykA all have fitness defects in vivo for P. mirabilis but do not affect colonization of E. coli during UTI. Similarly, the oxidative pentose phosphate pathway is required only for P. mirabilis in vivo. In contrast, gluconeogenesis is required only for E. coli fitness in vivo. The remarkable difference in central pathway utilization between E. coli and P. mirabilis during experimental UTI was also observed for TCA cycle mutants in sdhB, fumC, and frdA. The distinct in vivo requirements between these pathogens suggest E. coli and P. mirabilis are not direct competitors within host urinary tract nutritional niche. In support of this, we found that co-infection with E. coli and P. mirabilis wild-type strains enhanced bacterial colonization and persistence of both pathogens during UTI. Our results reveal that complementary utilization of central carbon metabolism facilitates polymicrobial disease and suggests microbial activity in vivo alters the host urinary tract nutritional niche.
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http://dx.doi.org/10.1371/journal.ppat.1004601DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4287612PMC
January 2015

Arginine promotes Proteus mirabilis motility and fitness by contributing to conservation of the proton gradient and proton motive force.

Microbiologyopen 2014 Oct 7;3(5):630-41. Epub 2014 Aug 7.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, 48104.

Swarming contributes to Proteus mirabilis pathogenicity by facilitating access to the catheterized urinary tract. We previously demonstrated that 0.1-20 mmol/L arginine promotes swarming on normally nonpermissive media and that putrescine biosynthesis is required for arginine-induced swarming. We also previously determined that arginine-induced swarming is pH dependent, indicating that the external proton concentration is critical for arginine-dependent effects on swarming. In this study, we utilized survival at pH 5 and motility as surrogates for measuring changes in the proton gradient (ΔpH) and proton motive force (μH(+) ) in response to arginine. We determined that arginine primarily contributes to ΔpH (and therefore μH(+) ) through the action of arginine decarboxylase (speA), independent of the role of this enzyme in putrescine biosynthesis. In addition to being required for motility, speA also contributed to fitness during infection. In conclusion, consumption of intracellular protons via arginine decarboxylase is one mechanism used by P. mirabilis to conserve ΔpH and μH(+) for motility.
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http://dx.doi.org/10.1002/mbo3.194DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4234256PMC
October 2014

PafR, a novel transcription regulator, is important for pathogenesis in uropathogenic Escherichia coli.

Infect Immun 2014 Oct 28;82(10):4241-52. Epub 2014 Jul 28.

Department of Microbiology and Molecular Genetics, IMRIC, The Hebrew University Faculty of Medicine, Jerusalem, Israel

The metV genomic island in the chromosome of uropathogenic Escherichia coli (UPEC) encodes a putative transcription factor and a sugar permease of the phosphotransferase system (PTS), which are predicted to compose a Bgl-like sensory system. The presence of these two genes, hereby termed pafR and pafP, respectively, has been previously shown to correlate with isolates causing clinical syndromes. We show here that deletion of both genes impairs the ability of the resulting mutant to infect the CBA/J mouse model of ascending urinary tract infection compared to that of the parent strain, CFT073. Expressing the two genes in trans in the two-gene knockout mutant complemented full virulence. Deletion of either gene individually generated the same phenotype as the double knockout, indicating that both pafR and pafP are important to pathogenesis. We screened numerous environmental conditions but failed to detect expression from the promoter that precedes the paf genes in vitro, suggesting that they are in vivo induced (ivi). Although PafR is shown here to be capable of functioning as a transcriptional antiterminator, its targets in the UPEC genome are not known. Using microarray analysis, we have shown that expression of PafR from a heterologous promoter in CFT073 affects expression of genes related to bacterial virulence, biofilm formation, and metabolism. Expression of PafR also inhibits biofilm formation and motility. Taken together, our results suggest that the paf genes are implicated in pathogenesis and that PafR controls virulence genes, in particular biofilm formation genes.
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http://dx.doi.org/10.1128/IAI.00086-14DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4187875PMC
October 2014

A conserved PapB family member, TosR, regulates expression of the uropathogenic Escherichia coli RTX nonfimbrial adhesin TosA while conserved LuxR family members TosE and TosF suppress motility.

Infect Immun 2014 Sep 16;82(9):3644-56. Epub 2014 Jun 16.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA

A heterogeneous subset of extraintestinal pathogenic Escherichia coli (ExPEC) strains, referred to as uropathogenic E. coli (UPEC), causes most uncomplicated urinary tract infections. However, no core set of virulence factors exists among UPEC strains. Instead, the focus of the analysis of urovirulence has shifted to studying broad classes of virulence factors and the interactions between them. For example, the RTX nonfimbrial adhesin TosA mediates adherence to host cells derived from the upper urinary tract. The associated tos operon is well expressed in vivo but poorly expressed in vitro and encodes TosCBD, a predicted type 1 secretion system. TosR and TosEF are PapB and LuxR family transcription factors, respectively; however, no role has been assigned to these potential regulators. Thus, the focus of this study was to determine how TosR and TosEF regulate tosA and affect the reciprocal expression of adhesins and flagella. Among a collection of sequenced UPEC strains, 32% (101/317) were found to encode TosA, and nearly all strains (91% [92/101]) simultaneously carried the putative regulatory genes. Deletion of tosR alleviates tosA repression. The tos promoter was localized upstream of tosR using transcriptional fusions of putative promoter regions with lacZ. TosR binds to this region, affecting a gel shift. A 100-bp fragment 220 to 319 bp upstream of tosR inhibits binding, suggesting localization of the TosR binding site. TosEF, on the other hand, downmodulate motility when overexpressed by preventing the expression of fliC, encoding flagellin. Deletion of tosEF increased motility. Thus, we present an additional example of the reciprocal control of adherence and motility.
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http://dx.doi.org/10.1128/IAI.01608-14DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4187811PMC
September 2014

SslE elicits functional antibodies that impair in vitro mucinase activity and in vivo colonization by both intestinal and extraintestinal Escherichia coli strains.

PLoS Pathog 2014 May 8;10(5):e1004124. Epub 2014 May 8.

Novartis Vaccines and Diagnostics Srl, Siena, Italy.

SslE, the Secreted and surface-associated lipoprotein from Escherichia coli, has recently been associated to the M60-like extracellular zinc-metalloprotease sub-family which is implicated in glycan recognition and processing. SslE can be divided into two main variants and we recently proposed it as a potential vaccine candidate. By applying a number of in vitro bioassays and comparing wild type, knockout mutant and complemented strains, we have now demonstrated that SslE specifically contributes to degradation of mucin substrates, typically present in the intestine and bladder. Mutation of the zinc metallopeptidase motif of SslE dramatically impaired E. coli mucinase activity, confirming the specificity of the phenotype observed. Moreover, antibodies raised against variant I SslE, cloned from strain IHE3034 (SslEIHE3034), are able to inhibit translocation of E. coli strains expressing different variants through a mucin-based matrix, suggesting that SslE induces cross-reactive functional antibodies that affect the metallopeptidase activity. To test this hypothesis, we used well-established animal models and demonstrated that immunization with SslEIHE3034 significantly reduced gut, kidney and spleen colonization by strains producing variant II SslE and belonging to different pathotypes. Taken together, these data strongly support the importance of SslE in E. coli colonization of mucosal surfaces and reinforce the use of this antigen as a component of a broadly protective vaccine against pathogenic E. coli species.
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http://dx.doi.org/10.1371/journal.ppat.1004124DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4014459PMC
May 2014

Multicellular bacteria deploy the type VI secretion system to preemptively strike neighboring cells.

PLoS Pathog 2013 5;9(9):e1003608. Epub 2013 Sep 5.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.

The Type VI Secretion System (T6SS) functions in bacteria as a contractile nanomachine that punctures and delivers lethal effectors to a target cell. Virtually nothing is known about the lifestyle or physiology that dictates when bacteria normally produce their T6SS, which prevents a clear understanding of how bacteria benefit from its action in their natural habitat. Proteus mirabilis undergoes a characteristic developmental process to coordinate a multicellular swarming behavior and will discriminate itself from another Proteus isolate during swarming, resulting in a visible boundary termed a Dienes line. Using transposon mutagenesis, we discovered that this recognition phenomenon requires the lethal action of the T6SS. All mutants identified in the genetic screen had insertions within a single 33.5-kb region that encodes a T6SS and cognate Hcp-VrgG-linked effectors. The identified T6SS and primary effector operons were characterized by killing assays, by construction of additional mutants, by complementation, and by examining the activity of the type VI secretion system in real-time using live-cell microscopy on opposing swarms. We show that lethal T6SS-dependent activity occurs when a dominant strain infiltrates deeply beyond the boundary of the two swarms. Using this multicellular model, we found that social recognition in bacteria, underlying killing, and immunity to killing all require cell-cell contact, can be assigned to specific genes, and are dependent on the T6SS. The ability to survive a lethal T6SS attack equates to "recognition". In contrast to the current model of T6SS being an offensive or defensive weapon our findings support a preemptive mechanism by which an entire population indiscriminately uses the T6SS for contact-dependent delivery of effectors during its cooperative mode of growth.
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http://dx.doi.org/10.1371/journal.ppat.1003608DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3764213PMC
April 2014

The multifunctional protein YdiV represses P fimbria-mediated adherence in uropathogenic Escherichia coli.

J Bacteriol 2013 Jul 10;195(14):3156-64. Epub 2013 May 10.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, USA.

YdiV, a degenerate EAL domain protein, represses motility by interacting with FlhD to abolish FlhDC interaction with DNA. Here, we demonstrate that deletion of ydiV dysregulates coordinate control of motility and adherence by increasing adherence of Escherichia coli CFT073 to a bladder epithelial cell line by specifically increasing production of P fimbriae. Interestingly, only one of the two P fimbrial operons, pap_2, present in the genome of E. coli CFT073 was upregulated. This derepression of the pap_2 operon is abolished following deletion of either cya or crp, demonstrating cyclic AMP (cAMP)-dependent activation of the P fimbrial operon. However, the absence of YdiV does not affect the gene expression of cya and crp, and loss of SdiA in the ydiV mutant does not affect the derepression of the pap_2 operon, suggesting that YdiV control of adherence acts in response to cAMP levels. Deletion of ydiV increases motility by increasing expression of fliA, suggesting that in E. coli CFT073, YdiV regulates motility by the same mechanism as that described previously for commensal E. coli strains. Furthermore, analysis of site-directed mutations found two putative Mg(2+)-binding residues of four conserved YdiV residues (E29 and Q219) that were involved in regulation of motility and FliC production, while two conserved c-di-GMP-binding residues (D156 and D165) only affected motility. None of the four conserved YdiV residues appeared to affect regulation of adherence. Therefore, we propose a model in which a degenerate EAL, YdiV, utilizes different domains to regulate motility through interaction with FlhD and adherence to epithelial cells through cAMP-dependent effects on the pap_2 promoter.
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http://dx.doi.org/10.1128/JB.02254-12DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3697638PMC
July 2013

Prophage induction is enhanced and required for renal disease and lethality in an EHEC mouse model.

PLoS Pathog 2013 Mar 28;9(3):e1003236. Epub 2013 Mar 28.

Department of Microbiology and Immunology, University of Michigan, Ann Arbor, Michigan, United States of America.

Enterohemorrhagic Escherichia coli (EHEC), particularly serotype O157:H7, causes hemorrhagic colitis, hemolytic uremic syndrome, and even death. In vitro studies showed that Shiga toxin 2 (Stx2), the primary virulence factor expressed by EDL933 (an O157:H7 strain), is encoded by the 933W prophage. And the bacterial subpopulation in which the 933W prophage is induced is the producer of Stx2. Using the germ-free mouse, we show the essential role 933W induction plays in the virulence of EDL933 infection. An EDL933 derivative with a single mutation in its 933W prophage, resulting specifically in that phage being uninducible, colonizes the intestines, but fails to cause any of the pathological changes seen with the parent strain. Hence, induction of the 933W prophage is the primary event leading to disease from EDL933 infection. We constructed a derivative of EDL933, SIVET, with a biosensor that specifically measures induction of the 933W prophage. Using this biosensor to measure 933W induction in germ-free mice, we found an increase three logs greater than was expected from in vitro results. Since the induced population produces and releases Stx2, this result indicates that an activity in the intestine increases Stx2 production.
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http://dx.doi.org/10.1371/journal.ppat.1003236DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3610611PMC
March 2013

Anaerobic respiration using a complete oxidative TCA cycle drives multicellular swarming in Proteus mirabilis.

mBio 2012 Oct 30;3(6). Epub 2012 Oct 30.

Department of Microbiology and Immunology, University of Michigan Medical School, West Medical Center Drive, Ann Arbor, MI, USA.

Proteus mirabilis rapidly migrates across surfaces using a periodic developmental process of differentiation alternating between short swimmer cells and elongated hyperflagellated swarmer cells. To undergo this vigorous flagellum-mediated motility, bacteria must generate a substantial proton gradient across their cytoplasmic membranes by using available energy pathways. We sought to identify the link between energy pathways and swarming differentiation by examining the behavior of defined central metabolism mutants. Mutations in the tricarboxylic acid (TCA) cycle (fumC and sdhB mutants) caused altered patterns of swarming periodicity, suggesting an aerobic pathway. Surprisingly, the wild-type strain swarmed on agar containing sodium azide, which poisons aerobic respiration; the fumC TCA cycle mutant, however, was unable to swarm on azide. To identify other contributing energy pathways, we screened transposon mutants for loss of swarming on sodium azide and found insertions in the following genes that involved fumarate metabolism or respiration: hybB, encoding hydrogenase; fumC, encoding fumarase; argH, encoding argininosuccinate lyase (generates fumarate); and a quinone hydroxylase gene. These findings validated the screen and suggested involvement of anaerobic electron transport chain components. Abnormal swarming periodicity of fumC and sdhB mutants was associated with the excretion of reduced acidic fermentation end products. Bacteria lacking SdhB were rescued to wild-type pH and periodicity by providing fumarate, independent of carbon source but dependent on oxygen, while fumC mutants were rescued by glycerol, independent of fumarate only under anaerobic conditions. These findings link multicellular swarming patterns with fumarate metabolism and membrane electron transport using a previously unappreciated configuration of both aerobic and anaerobic respiratory chain components. Bacterial locomotion and the existence of microbes were the first scientific observations that followed the invention of the microscope. A bacterium can swim through a fluid environment or coordinate motion with a group of bacteria and swarm across a surface. The flagellar motor, which propels the bacterium, is fueled by proton motive force. In contrast to the physiology that governs swimming motility, much less is known about the energy sources required for multicellular swarming on surfaces. In this study, we used Proteus mirabilis as a model organism to study vigorous swarming behavior and genetic and biochemical approaches to define energy pathways and central metabolism that contribute to multicellular motility. We found that swarming bacteria use a complete aerobic tricarboxylic acid (TCA) cycle but do not respire oxygen as the terminal electron acceptor, suggesting that multicellular cooperation during swarming reduces the amount of energy required by individual bacteria to achieve rapid motility.
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http://dx.doi.org/10.1128/mBio.00365-12DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3487771PMC
October 2012

Escherichia coli physiology and metabolism dictates adaptation to diverse host microenvironments.

Curr Opin Microbiol 2012 Feb 27;15(1):3-9. Epub 2011 Dec 27.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, United States.

Bacterial growth in the host is required for pathogenesis. To successfully grow in vivo, pathogens have adapted their metabolism to replicate in specific host microenvironments. These adaptations reflect the nutritional composition of their host niches, inter-bacterial competition for carbon and energy sources, and survival in the face of bactericidal defense mechanisms. A subgroup of Escherichia coli, which cause urinary tract infection, bacteremia, sepsis, and meningitis, have adapted to grow as a harmless commensal in the nutrient-replete, carbon-rich human intestine but rapidly transition to pathogenic lifestyle in the nutritionally poorer, nitrogen-rich urinary tract. We discuss bacterial adaptations that allow extraintestinal pathogenic E. coli to establish both commensal associations and virulence as the bacterium transits between disparate microenvironments within the same individual.
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http://dx.doi.org/10.1016/j.mib.2011.12.004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3265668PMC
February 2012

The broadly conserved regulator PhoP links pathogen virulence and membrane potential in Escherichia coli.

Mol Microbiol 2011 Oct 2;82(1):145-63. Epub 2011 Sep 2.

Department of Microbiology and Immunology, University of Michigan Medical School, 5641 West Medical Center Drive, Ann Arbor, MI 48109, USA.

PhoP is considered a virulence regulator despite being conserved in both pathogenic and non-pathogenic Enterobacteriaceae. While Escherichia coli strains represent non-pathogenic commensal isolates and numerous virulent pathotypes, the PhoP virulence regulator has only been studied in commensal E. coli. To better understand how conserved transcription factors contribute to virulence, we characterized PhoP in pathogenic E. coli. Deletion of phoP significantly attenuated E. coli during extraintestinal infection. This was not surprising since we demonstrated that PhoP differentially regulated the transcription of > 600 genes. In addition to survival at acidic pH and resistance to polymyxin, PhoP was required for repression of motility and oxygen-independent changes in the expression of primary dehydrogenase and terminal reductase respiratory chain components. All phenotypes have in common a reliance on an energized membrane. Thus, we hypothesized that PhoP mediates these effects by regulating genes encoding proteins that generate proton motive force. Indeed, bacteria lacking PhoP exhibited a hyperpolarized membrane and dissipation of the transmembrane electrochemical gradient increased susceptibility of the phoP mutant to acidic pH, while inhibiting respiratory generation of the proton gradient restored resistance to antimicrobial peptides independent of lipopolysaccharide modification. These findings demonstrate a connection between PhoP, virulence and the energized state of the membrane.
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http://dx.doi.org/10.1111/j.1365-2958.2011.07804.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3188958PMC
October 2011

Identification of in vivo-induced antigens including an RTX family exoprotein required for uropathogenic Escherichia coli virulence.

Infect Immun 2011 Jun 21;79(6):2335-44. Epub 2011 Mar 21.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.

Uncomplicated urinary tract infections (UTI) are caused most commonly by uropathogenic Escherichia coli (UPEC). Whole-genome screening approaches, including transcriptomic, proteomic, and signature-tagged mutagenesis, have shown that UPEC highly expresses or requires genes for translational machinery, capsule, lipopolysaccharide, type 1 fimbriae, and iron acquisition systems during UTI. To identify additional genes expressed by UPEC during UTI, an immunoscreening approach termed in vivo-induced antigen technology (IVIAT) was employed to identify antigens produced during experimental infection that are not produced during in vitro culture. An inducible protein expression library, constructed from genomic DNA isolated from UPEC strain CFT073, was screened using exhaustively adsorbed pooled sera from 20 chronically infected female CBA/J mice. Using this approach, we identified 93 antigens induced by UPEC in vivo. A representative subset of these genes was tested by quantitative PCR for expression by CFT073 in vivo and during growth in human urine or LB medium in vitro; proWX, narJI, lolA, lolD, tosA (upxA), c2432, katG, ydhX, kpsS, and yddQ were poorly expressed in vitro but highly expressed in vivo. Of these, tosA, a gene encoding a predicted repeat-in-toxin family member, was expressed exclusively during UTI. Deletion of tosA in UPEC strain CFT073 resulted in significant attenuation in bladder and kidney infections during ascending UTI. By screening for in vivo-induced antigens, we identified a novel UPEC virulence factor and additional proteins that could be useful as potential vaccine targets.
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http://dx.doi.org/10.1128/IAI.00110-11DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3125824PMC
June 2011

Mucosal immunization with iron receptor antigens protects against urinary tract infection.

PLoS Pathog 2009 Sep 18;5(9):e1000586. Epub 2009 Sep 18.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America.

Uncomplicated infections of the urinary tract, caused by uropathogenic Escherichia coli, are among the most common diseases requiring medical intervention. A preventive vaccine to reduce the morbidity and fiscal burden these infections have upon the healthcare system would be beneficial. Here, we describe the results of a large-scale selection process that incorporates bioinformatic, genomic, transcriptomic, and proteomic screens to identify six vaccine candidates from the 5379 predicted proteins encoded by uropathogenic E. coli strain CFT073. The vaccine candidates, ChuA, Hma, Iha, IreA, IroN, and IutA, all belong to a functional class of molecules that is involved in iron acquisition, a process critical for pathogenesis in all microbes. Intranasal immunization of CBA/J mice with these outer membrane iron receptors elicited a systemic and mucosal immune response that included the production of antigen-specific IgM, IgG, and IgA antibodies. The cellular response to vaccination was characterized by the induction and secretion of IFN-gamma and IL-17. Of the six potential vaccine candidates, IreA, Hma, and IutA provided significant protection from experimental infection. In immunized animals, class-switching from IgM to IgG and production of antigen-specific IgA in the urine represent immunological correlates of protection from E. coli bladder colonization. These findings are an important first step toward the development of a subunit vaccine to prevent urinary tract infections and demonstrate how targeting an entire class of molecules that are collectively required for pathogenesis may represent a fundamental strategy to combat infections.
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http://dx.doi.org/10.1371/journal.ppat.1000586DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2736566PMC
September 2009

Fitness of Escherichia coli during urinary tract infection requires gluconeogenesis and the TCA cycle.

PLoS Pathog 2009 May 29;5(5):e1000448. Epub 2009 May 29.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI, USA.

Microbial pathogenesis studies traditionally encompass dissection of virulence properties such as the bacterium's ability to elaborate toxins, adhere to and invade host cells, cause tissue damage, or otherwise disrupt normal host immune and cellular functions. In contrast, bacterial metabolism during infection has only been recently appreciated to contribute to persistence as much as their virulence properties. In this study, we used comparative proteomics to investigate the expression of uropathogenic Escherichia coli (UPEC) cytoplasmic proteins during growth in the urinary tract environment and systematic disruption of central metabolic pathways to better understand bacterial metabolism during infection. Using two-dimensional fluorescence difference in gel electrophoresis (2D-DIGE) and tandem mass spectrometry, it was found that UPEC differentially expresses 84 cytoplasmic proteins between growth in LB medium and growth in human urine (P<0.005). Proteins induced during growth in urine included those involved in the import of short peptides and enzymes required for the transport and catabolism of sialic acid, gluconate, and the pentose sugars xylose and arabinose. Proteins required for the biosynthesis of arginine and serine along with the enzyme agmatinase that is used to produce the polyamine putrescine were also up-regulated in urine. To complement these data, we constructed mutants in these genes and created mutants defective in each central metabolic pathway and tested the relative fitness of these UPEC mutants in vivo in an infection model. Import of peptides, gluconeogenesis, and the tricarboxylic acid cycle are required for E. coli fitness during urinary tract infection while glycolysis, both the non-oxidative and oxidative branches of the pentose phosphate pathway, and the Entner-Doudoroff pathway were dispensable in vivo. These findings suggest that peptides and amino acids are the primary carbon source for E. coli during infection of the urinary tract. Because anaplerosis, or using central pathways to replenish metabolic intermediates, is required for UPEC fitness in vivo, we propose that central metabolic pathways of bacteria could be considered critical components of virulence for pathogenic microbes.
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http://dx.doi.org/10.1371/journal.ppat.1000448DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2680622PMC
May 2009

Expression of flagella is coincident with uropathogenic Escherichia coli ascension to the upper urinary tract.

Proc Natl Acad Sci U S A 2007 Oct 9;104(42):16669-74. Epub 2007 Oct 9.

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, MI 48109-0620, USA.

Uropathogenic Escherichia coli (UPEC) cause most uncomplicated urinary tract infections (UTIs) in humans. Because UTIs are considered to occur in an ascending manner, flagellum-mediated motility has been suggested to contribute to virulence by enabling UPEC to disseminate to the upper urinary tract. Previous studies from our laboratory and others have demonstrated a modest yet important role for flagella during ascending UTI. To better understand the role of flagella in vivo, we used biophotonic imaging to monitor UPEC infection and temporospatial flagellin gene expression during ascending UTI. Using em7-lux (constitutive) and fliC-lux transcriptional fusions, we show that flagellin expression by UPEC coincides with ascension of the ureters and colonization of the kidney. The patterns of fliC luminescence observed in vitro and in vivo were also validated by comparative quantitative PCR. Because fliC expression appeared coincident during ascension, we reassessed the contribution of fliC to ascending UTI using a low-dose intraurethral model of ascending UTI. Although wild-type UPEC were able to establish infection in the bladder and kidneys by 6 hours postinoculation, fliC mutant bacteria were able to colonize the bladder but were significantly attenuated in the kidneys at this early time point. By 48 hours postinoculation, the fliC mutant bacteria were attenuated in the bladder and kidneys and were not detectable in the spleen. These data provide compelling evidence that wild-type UPEC express flagellin and presumably utilize flagellum-mediated motility during UTI to ascend to the upper urinary tract and disseminate within the host.
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http://dx.doi.org/10.1073/pnas.0607898104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2034267PMC
October 2007

Quantitative profile of the uropathogenic Escherichia coli outer membrane proteome during growth in human urine.

Infect Immun 2007 Jun;75(6):2679-88

Department of Microbiology and Immunology, University of Michigan Medical School, 5641 Medical Science Building II, 1150 West Medical Center Drive, Ann Arbor, MI 48109, USA.

Outer membrane proteins (OMPs) of microbial pathogens are critical components that mediate direct interactions between microbes and their surrounding environment. Consequently, the study of OMPs is integral to furthering the understanding of host-pathogen interactions and to identifying key targets for development of improved antimicrobial agents and vaccines. In this study, we used two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and tandem mass spectrometry to characterize the uropathogenic Escherichia coli (UPEC) outer membrane subproteome; 30 individual OMPs present on the bacterial surface during growth in human urine were identified. Fluorescence difference gel electrophoresis was used to identify quantitative changes in levels of UPEC strain CFT073 OMPs during growth in urine; six known receptors for iron compounds were induced in this environment, i.e., ChuA, IutA, FhuA, IroN, IreA, and Iha. A seventh putative iron compound receptor, encoded by CFT073 open reading frame (ORF) c2482, was also identified and found to be induced in urine. Further, the induction of these seven iron receptors in human urine and during defined iron limitation was verified by using quantitative real-time PCR (qPCR). An eighth iron receptor, fepA, displayed similar induction levels under these conditions as measured by qPCR but was not identified by 2D-PAGE. Addition of 10 microM FeCl(2) to human urine repressed the transcription of all eight iron receptor genes. A number of fecal-commensal, intestinal pathogenic, and uropathogenic E. coli strains all displayed similar growth rates in human urine, showing that the ability to grow in urine per se is not a urovirulence trait. Thus, human urine is an iron-limiting environment and UPEC enriches its outer membrane with iron receptors to contend with this iron limitation.
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http://dx.doi.org/10.1128/IAI.00076-06DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1932884PMC
June 2007

Mycobacterium tuberculosis produces pili during human infection.

Proc Natl Acad Sci U S A 2007 Mar 8;104(12):5145-50. Epub 2007 Mar 8.

Department of Immunobiology, University of Arizona, 1501 North Campbell Avenue, LSN 649, Tucson, AZ 85724, USA.

Mycobacterium tuberculosis is responsible for nearly 3 million human deaths worldwide every year. Understanding the mechanisms and bacterial factors responsible for the ability of M. tuberculosis to cause disease in humans is critical for the development of improved treatment strategies. Many bacterial pathogens use pili as adherence factors to colonize the host. We discovered that M. tuberculosis produces fine (2- to 3-nm-wide), aggregative, flexible pili that are recognized by IgG antibodies contained in sera obtained from patients with active tuberculosis, indicating that the bacilli produce pili or pili-associated antigen during human infection. Purified M. tuberculosis pili (MTP) are composed of low-molecular-weight protein subunits encoded by the predicted M. tuberculosis H37Rv ORF, designated Rv3312A. MTP bind to the extracellular matrix protein laminin in vitro, suggesting that MTP possess adhesive properties. Isogenic mtp mutants lost the ability to produce Mtp in vitro and demonstrated decreased laminin-binding capabilities. MTP shares morphological, biochemical, and functional properties attributed to bacterial pili, especially with curli amyloid fibers. Thus, we propose that MTP are previously unidentified host-colonization factors of M. tuberculosis.
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http://dx.doi.org/10.1073/pnas.0602304104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1817835PMC
March 2007