Publications by authors named "Elna M Buys"

26 Publications

  • Page 1 of 1

Ultraviolet-C inactivation and hydrophobicity of Bacillus subtilis and Bacillus velezensis spores isolated from extended shelf-life milk.

Int J Food Microbiol 2021 Jul 4;349:109231. Epub 2021 May 4.

Department of Consumer and Food Sciences, Faculty of Natural and Agricultural Sciences, University of Pretoria, Pretoria, South Africa. Electronic address:

Bacterial spores are important in food processing due to their ubiquity, resistance to high temperature and chemical inactivation. This work aims to study the effect of ultraviolet C (UVC) on the spores of Bacillus subtilis and Bacillus velezensis at a molecular and individual level to guide in deciding on the right parameters that must be applied during the processing of liquid foods. The spores were treated with UVC using phosphate buffer saline (PBS) as a suspension medium and their lethality rate was determined for each sample. Purified spore samples of B. velezensis and B. subtilis were treated under one pass in a UVC reactor to inactivate the spores. The resistance pattern of the spores to UVC treatment was determined using dipicolinic acid (Ca-DPA) band of spectral analysis obtained from Raman spectroscopy. Flow cytometry analysis was also done to determine the effect of the UVC treatment on the spore samples at the molecular level. Samples were processed for SEM and the percentage spore surface hydrophobicity was also determined using the Microbial Adhesion to Hydrocarbon (MATH) assay to predict the adhesion strength to a stainless-steel surface. The result shows the maximum lethality rate to be 6.5 for B. subtilis strain SRCM103689 (B47) and highest percentage hydrophobicity was 54.9% from the sample B. velezensis strain LPL-K103 (B44). The difference in surface hydrophobicity for all isolates was statistically significant (P < 0.05). Flow cytometry analysis of UVC treated spore suspensions clarifies them further into sub-populations unaccounted for by plate counting on growth media. The Raman spectroscopy identified B4002 as the isolate possessing the highest concentration of Ca-DPA. The study justifies the critical role of Ca-DPA in spore resistance and the possible sub-populations after UVC treatment that may affect product shelf-life and safety. UVC shows a promising application in the inactivation of resistant spores though there is a need to understand the effects at the molecular level to design the best parameters during processing.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ijfoodmicro.2021.109231DOI Listing
July 2021

Effects of vacuum packaging storage of minimally processed cassava roots at various temperatures on microflora, tissue structure, starch extraction by wet milling and granule quality.

J Sci Food Agric 2021 May 10. Epub 2021 May 10.

Department of Consumer and Food Sciences and Institute for Food, Nutrition and Well-being, University of Pretoria, Pretoria, South Africa.

Background: Vacuum package storage is commonly applied to reduce postharvest deterioration in minimally processed cassava roots. However, the influence of vacuum packaging conditions on root end-use quality is poorly understood. Hence, the effects of vacuum packaged storage at ambient, refrigerated and freezing temperatures on microflora, cassava tissue structure and starch extraction by wet milling were studied.

Results: Vacuum packaged storage temperature strongly affected cassava root quality. Minimal adverse effects were obtained with frozen storage. With refrigerated storage, there was negligible microbial growth but some disruption of the parenchyma cell wall structure suggestive of chilling injury. With ambient temperature storage, there was considerable Lactobacilli dominated fermentation. This caused substantial cell degradation, probably due to the production of extracellular cellulolytic and other cell wall degrading enzymes. A benefit of this cell wall breakdown was that it substantially improved starch extraction with wet milling from the stored cassava pieces; by 18% with pieces that had been ambient vacuum packaged and wet milled using a 2000 μm opening screen. However, ambient temperature storage resulted in some starch granule pitting due to the action of extracellular amylases from the fermenting microorganisms.

Conclusion: The best vacuum packaging storage conditions for minimally processed cassava depends on application and cost. For short-term storage, refrigeration would be best for vegetable-type products. For several months storage, freezing is best. For wet milling applications, this could be combined with subsequent short-term ambient temperature storage as it improves starch extraction efficiency and could reduce distribution energy costs. © 2021 Society of Chemical Industry.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jsfa.11305DOI Listing
May 2021

Invited review: Probiotic yogurt quality criteria, regulatory framework, clinical evidence, and analytical aspects.

J Dairy Sci 2021 Jan;104(1):1-19

Department of Consumer and Food Sciences, University of Pretoria, Pretoria 0028, South Africa. Electronic address:

Yogurt is a milk-based product manufactured by lactic acid fermentation enabled by symbiotic yogurt cultures. Yogurt is largely considered to be a health product, and it is employed to deliver probiotics and prebiotics to the consumer. However, not all yogurts are probiotic, neither are they all functional products. There is increasing demand for health-promoting beverages, which is prompting the dairy industry to develop functional probiotic yogurts to meet the demand. However, there seems to be a scarcity of reviews providing critical information on regulatory frameworks in regions of the world, clinical trial outcomes, and methodological approaches for enumerating multiprobiotic strains in yogurt. This review, relating to functional probiotic yogurt, covers the newest information on the topic for the period mostly between 2014 and 2019. Conformance to regulations is paramount and hence, global regulatory frameworks for probiotic yogurt and prebiotic and nonprebiotic ingredients included in yogurt are reviewed. The paper emphasizes the need for convincing clinical trial outcomes that provide the dairy industry with an opportunity to market products with substantiated beneficial claims. The paper also discusses probiotic strains in functional yogurt, which is required to have population levels above the recommended therapeutic minimum during shelf life. The multiprobiotic species added to yogurt may present challenges relating to methodological and analytical approaches needed to determine viability of each strain contained in such yogurt. Hence, the review also presents the pros and cons of the culture-dependent and culture-independent approaches for the enumeration of probiotic cells in yogurt. The review is arguably valuable to the dairy industry, functional food developers, related scientists, and researchers, as well as policy makers.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3168/jds.2020-19116DOI Listing
January 2021

Comparative Genome Analysis of with Its Closest Phylogenetic Neighbor, , and and Groups.

Microorganisms 2020 Aug 4;8(8). Epub 2020 Aug 4.

Department of Consumer and Food Sciences, University of Pretoria, Private Bag X20, Hatfield, Pretoria 0028, South Africa.

currently possesses one of the most highly heat-resistant spores (HRS), which can withstand ultra-high temperature (UHT) processing. Determination of multiple whole genome sequences of . provided an opportunity to perform the first comparative genome analysis between strains and with . , . , and . groups. In this study, five whole genome sequences of strains, including those belonging to the HRS clone (SAD and BR12) normally isolated from UHT milk, were compared with the aforementioned species for gene clusters responsible for heat resistance. In the phylogenomic analysis, , with its closest phylogenetic neighbor, . , clustered with . and . Heat shock proteins GrpE, GroES, GroEL, and DnaK presented identical sequences for all . strains, indicating that differences in functional efficiency are not involved in the thermal resistance variations. However, comparing all species evaluated, . exhibited a different gene configuration in the chromosomal region of the heat shock protein GrpE. Furthermore, only . strains presented the stage II sporulation protein P gene located in this region. Multisequence alignment and phylogenetic analysis of the ClpB protein showed differences for HRS and non-HRS strains. The study identified ClpC, ClpE, and ClpX as the three ATPases putatively involved in protein disaggregation in . . exhibits high homology with other species in the DnaK, DnaJ, GroEL, and GroES cluster of genes involved in heat resistance. The data presented here pave the way to select and evaluate the phenotypic effects of genes putatively involved in heat resistance.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3390/microorganisms8081185DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7464528PMC
August 2020

Consumers' perceptions of intrinsic and extrinsic attributes as indicators of safety and quality of chicken meat: Actionable information for public health authorities and the chicken industry.

J Food Sci 2020 Jun 29;85(6):1845-1855. Epub 2020 May 29.

Department of Consumer and Food Sciences, University of Pretoria, Pretoria, South Africa.

Understanding consumers' perceptions toward chicken meat safety and quality could provide valuable information to public health educators since it is the most consumed meat. This study explores perceptions of a group of South African consumers on the safety and quality of chicken meat based on intrinsic and extrinsic attributes and identifies related safety risks. Data were collected through a web-based survey (863 participants). A substantial proportion of consumers considered supermarkets as the most trusted outlets to sell safe and good quality chicken (compared with butcheries, wholesalers, farmers' markets, street vendors, or "other retailers"). The majority of respondents (53%) most trusted refrigerated chicken to be of good quality compared with 36% trusting frozen chicken or 11% chicken at room temperature. Frozen chicken was considered most safe by 48% of consumers while 43% regarded refrigerated chicken as most safe. At point of purchase and home, smell, use-by date, sell-by date, and color were perceived as important attributes when judging chicken safety and quality. Consumers considered the absence of brine use and growth-promoting hormones in chicken feed as relatively important. The majority of consumers can be classified as highly involved during purchasing. It is essential that consumers apply safe chicken handling practices from point of purchase to consumption, irrespective of the type of retailer, perceived sensory characteristics, and date labels to reduce or eliminate microbial risks. Addressing consumer's knowledge and expectations regarding factors such as growth-promoting hormones and free range may improve safety and quality perceptions. PRACTICAL APPLICATION: This study gives insight into perceptions of a group of South African consumers toward safety and quality of chicken meat. Understanding consumers' perceptions can provide valuable information to public health educators since chicken meat is a common vehicle for Salmonella spp. and Campylobacter spp., which are human pathogens. Additionally, this information can assist the chicken industry to meet consumer expectations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/1750-3841.15125DOI Listing
June 2020

Solid-State Fermentation of Cassava Roots Using Cellulolytic-Type Alkaliphilic Bacillus spp. Cultures to Modify the Cell Walls and Assist Starch Release.

Appl Biochem Biotechnol 2020 Aug 27;191(4):1395-1410. Epub 2020 Feb 27.

Institute for Food, Nutrition and Well-being and Department of Consumer and Food Sciences, University of Pretoria, Private Bag X 20, Hatfield, Pretoria, 0028, South Africa.

To improve cassava starch extraction by wet milling, solid-state fermentation of ground roots using cellulolytic-type alkaliphilic Bacilli spp., Bacillus akibai, B. cellulosilyticus and B. hemicellulosilyticus was investigated. Enzyme assay and scanning electron microscopy indicated that Bacillus spp. production of extracellular cellulase and polygalacturonase caused the formation of micropores through the root parenchyma cell walls and exposed the embedded cellulosic network. Gas chromatography data of the cell wall constituent sugars remaining after fermentation and Fourier transform infrared data indicated that the Bacillus treatments reduced the levels of pectin and, hemicellulose and to lesser extent cellulose. Wide-angle X-ray scattering data indicated that the Bacillus spp. cell wall degrading enzymes had partially hydrolysed the amorphous fractions of the cell wall polysaccharides. All the Bacillus spp. treatments improved starch extraction by 17-23% compared to fermentation with endogenous microflora. B. cellulosilyticus was most effective in disintegration of large root particles and as result, released marginally the most starch, probably due to it having the highest cellulase activity. Solid-state fermentation using cellulolytic-type Bacillus spp. is, therefore, promising to technology to improve the efficiency of cassava wet milling cell wall disintegration and consequent starch yield without use of commercial cell wall degrading enzymes or polluting chemicals.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1007/s12010-020-03286-xDOI Listing
August 2020

Dysbiosis Signatures of Fecal Microbiota in South African Infants with Respiratory, Gastrointestinal, and Other Diseases.

J Pediatr 2020 03 14;218:106-113.e3. Epub 2020 Jan 14.

Department of Consumer and Food Sciences, University of Pretoria, Hatfield, South Africa.

Objective: To determine the association between the fecal microbiota diversity of the infants with different disease conditions, and vitamin A supplementation, antibiotic, and deworming therapies.

Study Design: In this case-control study, the bacterial community variations and the potential pathogens were identified through 16S ribosomal RNA gene-based amplicon sequencing and quantitative insights into microbial ecology pipeline in fecal samples. The participants were South African infants (mean age, 16 ± 8 months; 17 male and 17 female) hospitalized and diagnosed with gastrointestinal, respiratory, and other diseases.

Results: The top phyla of the infants with respiratory disease were Proteobacteria, followed by Firmicutes, which were equally abundant in gastrointestinal disease. A significant difference in Shannon (alpha) diversity index (95% CI, 2.6-4.4; P = .008), among the microbiota of the fecal samples categorized by disease conditions, was observed. In beta diversity analysis of fecal microbiota, remarkable variations were found within the groups of deworming therapy (95% CI, 0.40-0.90; P = .033), disease conditions (95% CI, 0.44-0.86; P < .012) through unweighted and antibiotic therapy (95% CI, 0.20-0.75; P = .007), vitamin A intake (95% CI, 0.10-0.80; P < .033) and disease conditions (95% CI, 0.10-0.79; P = .006) through weighted UniFrac distances. The candidate pathogen associated with the disease groups were identified through analysis of the composition of microbiomes analysis.

Conclusions: This study provides preliminary evidence for the fecal microbiome-derived dysbiosis signature and pathobiome concept that may be observed in young children during illness.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.jpeds.2019.11.029DOI Listing
March 2020

Comparison of the microbial composition of African fermented foods using amplicon sequencing.

Sci Rep 2019 09 25;9(1):13863. Epub 2019 Sep 25.

Gut Microbes and Health Institute Strategic Programme, Quadram Institute Bioscience, Norwich Research Park, Norwich, United Kingdom.

Fermented foods play a major role in the diet of people in Africa, where a wide variety of raw materials are fermented. Understanding the microbial populations of these products would help in the design of specific starter cultures to produce standardized and safer foods. In this study, the bacterial diversity of African fermented foods produced from several raw materials (cereals, milk, cassava, honey, palm sap, and locust beans) under different conditions (household, small commercial producers or laboratory) in 8 African countries was analysed by 16S rRNA gene amplicon sequencing during the Workshop "Analysis of the Microbiomes of Naturally Fermented Foods Training Course". Results show that lactobacilli were less abundant in fermentations performed under laboratory conditions compared to artisanal or commercial fermentations. Excluding the samples produced under laboratory conditions, lactobacilli is one of the dominant groups in all the remaining samples. Genera within the order Lactobacillales dominated dairy, cereal and cassava fermentations. Genera within the order Lactobacillales, and genera Zymomonas and Bacillus were predominant in alcoholic beverages, whereas Bacillus and Lactobacillus were the dominant genera in the locust bean sample. The genus Zymomonas was reported for the first time in dairy, cereal, cassava and locust bean fermentations.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-019-50190-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6761159PMC
September 2019

Genome Sequences of Bacillus sporothermodurans Strains Isolated from Ultra-High-Temperature Milk.

Microbiol Resour Announc 2019 May 30;8(22). Epub 2019 May 30.

Department of Consumer and Food Sciences, University of Pretoria, Pretoria, South Africa

Here, we report the draft genome sequences of 3 strains isolated from ultra-high-temperature milk products in South Africa and Brazil and the type strain MB 581 (DSM 10599). The genomes will provide valuable information on the molecular dynamics of heat resistance in .
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1128/MRA.00145-19DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6544184PMC
May 2019

Persistence of foodborne diarrheagenic Escherichia coli in the agricultural and food production environment: Implications for food safety and public health.

Food Microbiol 2019 Sep 19;82:363-370. Epub 2019 Mar 19.

Department of Consumer and Food Sciences, University of Pretoria, Corner Lynnwood and Roper Roads, Hatfield, 0028, Pretoria, South Africa. Electronic address:

Diarrheagenic Escherichia coli (DEC) is a leading cause of foodborne illness associated with intestinal disease. While known over the years that contamination of food sources occurs via the oral faecal-route, the mechanisms underlying its persistence within the open environments including the food chain remains virtually unknown. Therefore, in this mini-review we will shed light on bacterial processes such as initial attachment, biofilm formation, horizontal gene transfer and response to environmental stresses. These factors may enable persistence of DEC as well as the emergence of potentially more virulent strains within the agricultural and food production environment. Mechanistic studies in clinical microbiology and immunology have elucidated infection pathways in the human and other animal bodies leading to diagnostic and treatment solutions. Therefore, understanding DEC behaviour in the agricultural and food production environment is crucial for ensuring food safety and public health by reducing the burden of foodborne illnesses.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.fm.2019.03.018DOI Listing
September 2019

Visualisation and quantification of fumonisins bound by lactic acid bacteria isolates from traditional African maize-based fermented cereals, ogi and mahewu.

Food Addit Contam Part A Chem Anal Control Expo Risk Assess 2019 Feb 24;36(2):296-307. Epub 2019 Jan 24.

b Department of Consumer and Food Sciences , University of Pretoria , Pretoria , South Africa.

Consumption of fumonisin-contaminated foods has a negative influence on the health of humans (carcinogen; oesophageal cancer in Eastern Cape in South Africa). Lactic acid bacteria (LAB) have emerged as a promising natural detoxification agent against mycotoxins. The aim of this study was to visualise the interaction between fumonisins (FB and FB) and LAB: Lactobacillus plantarum FS2, L. delbrueckii subsp. delbrueckii CIP 57.8T and Pediococcus pentosaceus D39, isolated from traditional fermented maize-based products (ogi and mahewu) using confocal laser scanning microscopy (CLSM) and to then quantify the LAB-bound fumonisin using high performance liquid chromatography (HPLC). The objective was to obtain a physically visible and quantifiable binding interaction between fumonisins and LAB strains with the aim of utilising LAB as a possible detoxifying agent. Fumonisins were derivatised using naphthalene-2,3-dicarboxaldehyde (NDA) and then combined with non-fluorescent LAB cells (viable and non-viable). For the quantification of bound fumonisins, viable and non-viable cells were incubated in the presence of predetermined concentrations of fumonisins and the level of fumonisin in the suspension was determined. CLSM showed the derivatised green fluorescent fumonisins binding to the surface of each of the LAB cells. For viable cells, L. plantarum FS2 bound FB most effectively while P. pentosaceus D39 bound the least level of FB. The highest levels of FB were bound by L. plantarum R 1096 and the least by L. delbrueckii CIP 57.8 T. For non-viable cells, L. plantarum FS2 was also the most effective for binding both fumonisins with P. pentosaceus D39 and L. delbrueckii CIP 57.8 T being the least effective for FB and FB, respectively. To our knowledge, this is the first study to visualise the interaction between LAB and fumonisins. We demonstrate that LAB isolates from indigenous fermented maize-based beverages bind fumonisins and thus present a potential strategy for their reduction in these traditional foods.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1080/19440049.2018.1562234DOI Listing
February 2019

Insights into the role of bacteria in vitamin A biosynthesis: Future research opportunities.

Crit Rev Food Sci Nutr 2019 13;59(19):3211-3226. Epub 2019 Jan 13.

Department of Consumer and Food Sciences, University of Pretoria, Hatfield Campus, Pretoria, South Africa.

Significant efforts have been made to address the hidden hunger challenges due to iron, zinc, iodine, and vitamin A since the beginning of the 21st century. Prioritizing the vitamin A deficiency (VAD) disorders, many countries are looking for viable alternative strategies such as biofortification. One of the leading causes of VAD is the poor bioconversion of β-carotene into retinoids. This review is focused on the opportunities of bacterial biosynthesis of retinoids, in particular, through the gut microbiota. The proposed hypothesis starts with the premise that an animal can able to store and timely convert carotenoids into retinoids in the liver and intestinal tissues. This theory is experimental with many scientific insights. The syntrophic metabolism, potential crosstalk of bile acids, lipocalins and lipopolysaccharides of gut microbiota are reported to contribute significantly to the retinoid biosynthesis. The gut bacteria respond to these kinds of factors by genetic restructuring driven mainly by events like horizontal gene transfer. A phylogenetic analysis of β-carotene 15, 15'-mono (di) oxygenase enzymes among a selected group of prokaryotes and eukaryotes was carried out to validate the hypotheses. Shedding light on the probiotic strategies through non-genetically modified organism such as gut bacteria capable of synthesizing vitamin A would address the VAD disorders.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1080/10408398.2018.1546670DOI Listing
February 2020

Short communication: Source tracking Bacillus cereus in an extended-shelf-life milk processing plant using partial sequencing of rpoB and multilocus sequence typing.

J Dairy Sci 2019 Jan 24;102(1):135-139. Epub 2018 Oct 24.

Department of Consumer and Food Sciences, University of Pretoria, Private Bag X20, Hatfield, Pretoria 0028, South Africa. Electronic address:

We used rpoB partial sequencing and multilocus sequence typing (MLST) to characterize 7 Bacillus cereus strains obtained at the following points: ESL milk during shelf life, pasteurized milk, raw milk, and filler nozzles after cleaning in place. The objective of the study was to determine relatedness among B. cereus isolates from several sampling points along an ESL processing plant with the aim of source tracking. The study revealed that isolates from filler nozzles shared 100% similarity with isolates from ESL milk and raw milk using rpoB sequencing. It also revealed that isolates from pasteurized milk shared 100% similarities with isolates from filler nozzles and ESL milk using MLST. We suggest 3 routes of B. cereus contamination in ESL milk. We showed that B. cereus contamination of ESL milk might be through raw milk and biofilms from filler nozzles. In addition, rpoB partial sequencing and MLST can be used as tools for source tracking in ESL milk processing.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.3168/jds.2018-14733DOI Listing
January 2019

The Impact of Cooling Rate on the Safety of Food Products as Affected by Food Containers.

Compr Rev Food Sci Food Saf 2018 Jul 30;17(4):827-840. Epub 2018 May 30.

School of Public Health, Faculty of Health Sciences, Curtin Univ., Bentley, Western Australia, 6102, Australia.

In recent decades, the demand for ready-to-eat (RTE) food items prepared by the food catering sector has increased together with the value of cook-serve, cook-chill, and cook-freeze food products. The technologies by which foods are cooked, chilled, refrigerated for storage, and reheated before serving are of prime importance to maintain safety. Packaging materials and food containers play an important role in influencing the cooling rate of RTE foods. Food items that are prepared using improper technologies and inappropriate packaging materials may be contaminated with foodborne pathogens. Numerous research studies have shown the impact of deficient cooling technologies on the survival and growth of foodborne pathogens, which may subsequently pose a threat to public health. The operating temperatures and cooling rates of the cooling techniques applied must be appropriate to inhibit the growth of pathogens. Food items must be stored outside the temperature danger zone, which is between 5 and 60 °C, in order to inhibit the growth of these pathogens. The cooling techniques used to prepare potentially hazardous foods, such as cooked meat, rice, and pasta, must be properly applied and controlled to ensure food safety. This paper critically reviews the effects of cooling and its relationship to food containers on the safety of RTE foods produced and sold through the food service industry.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/1541-4337.12357DOI Listing
July 2018

Enteroaggregative Escherichia coli is the predominant diarrheagenic E. coli pathotype among irrigation water and food sources in South Africa.

Int J Food Microbiol 2018 Aug 20;278:44-51. Epub 2018 Apr 20.

Department of Consumer and Food Sciences, University of Pretoria, South Africa. Electronic address:

Diarrheagenic E. coli (DEC) has been implicated in foodborne outbreaks worldwide and have been associated with childhood stunting in the absence of diarrhoea. Infection is extraordinarily common, but the routes of transmission have not been determined. Therefore, determining the most prevalent pathotypes in food and environmental sources may help provide better guidance to various stakeholders in ensuring food safety and public health and advancing understanding of the epidemiology of enteric disease. We characterized 205 E. coli strains previously isolated from producer distributor bulk milk (PDBM)(118), irrigation water (48), irrigated lettuce (29) and street vendor coleslaw (10) in South Africa. Enteropathogenic E. coli (EPEC), enterotoxigenic E. coli (ETEC), enteroaggregative E. coli (EAEC) and diffusely adherent E. coli (DAEC) were sought. We used PCR and partial gene sequencing for all 205 strains while 46 out of 205 that showed poor resolution were subsequently characterized using cell adherence (HeLa cells). PCR and partial gene sequencing of aatA and/or aaiC genes confirmed EAEC (2%, 5 out of 205) as the only pathotype. Phylogenetic analysis of sequenced EAEC strains with E. coli strains in GenBank showing ≥80% nucleotide sequence similarity based on possession of aaiC and aatA generated distinct clusters of strains separated predominantly based on their source of isolation (food source or human stool) suggesting a potential role of virulence genes in source tracking. EAEC 24%, 11 out of 46 strains (PDBM = 15%, irrigation water = 7%, irrigated lettuce = 2%) was similarly the predominant pathotype followed by strains showing invasiveness to HeLa cells, 4%, 2 out of 46 (PDBM = 2%, irrigated lettuce = 2%), among stains characterized using cell adherence. Therefore, EAEC may be the leading cause of DEC associated food and water-borne enteric infection in South Africa. Additionally, solely using molecular based methods targeting virulence gene determinants may underestimate prevalence, especially among heterogeneous pathogens such as EAEC.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.ijfoodmicro.2018.04.018DOI Listing
August 2018

Quantitative Risk Assessment of Hemolytic Uremic Syndrome Associated with Consumption of Bulk Milk Sold Directly from Producer to Consumer in South Africa.

J Food Prot 2018 Feb 23:472-481. Epub 2018 Feb 23.

1 Department of Food Science, University of Pretoria, Private Bag X20, Hatfield, Pretoria 0028, South Africa (ORCID: http://orcid.org/0000-0002-1392-9797 [V.N.]).

This study was conducted to estimate the hemolytic uremic syndrome (HUS) risk associated with consumption of producer-distributor bulk milk (PDBM) contaminated with Shiga toxin-producing Escherichia coli (STEC) in South Africa. Data were obtained from recently completed studies in South Africa taking into account prior collected prevalence data of STEC in raw and pasteurized PDBM and survey information from producer-distributor outlets and households. Inputs for the models were complemented with data from published and unpublished literature. A probabilistic exposure model was developed with Monte Carlo simulation in Excel add-in software using @Risk software. Hazard characterization was based on an exponential dose-response model to calculate the probability of illness from STEC infection in individuals 5 years and younger and individuals older than 5 years. The estimated mean STEC level was 0.12 CFU/mL (95% confidence interval [CI]: 0 to 1.2; σ = 0.34) for raw PDBM and 0.08 CFU/mL (95% CI: 0 to 1; σ = 0.27) for pasteurized PDBM. A higher risk of HUS cases per year was recorded in raw than in pasteurized PDBM and also in individuals younger than 5 years of age. For every 100,000 servings consumed, the expected median numbers of HUS cases per year from raw PDBM were 52 for 5 years and younger and 3.2 for older than 5 years. The median numbers of cases per year for pasteurized PDBM were 47 for 5 years and younger and 2.9 for older than 5 years. Sensitivity analysis revealed that serving volume and time taken to sell PDBM at producer-distributor outlets were the factors with the greatest impact on probability of illness. The models developed in this study are an example of risk assessments for milk produced and marketed from similar scenarios across the globe.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.4315/0362-028X.JFP-17-199DOI Listing
February 2018

Resuscitation and growth kinetics of sub-lethally injured Listeria monocytogenes strains following fluorescence activated cell sorting (FACS).

Food Res Int 2017 10 14;100(Pt 2):150-158. Epub 2017 Aug 14.

Department of Food Science, Institute for Food, Nutrition and Well-Being, University of Pretoria, Private Bag X20, Hatfield, 0028, South Africa. Electronic address:

This study investigated the effect of acid (pH4.2), osmotic (10% NaCl) and heat (55°C for 30min) stress induced injury on Listeria monocytogenes strains ATCC19115, 69, 159/10 and 243 using differential plating and flow cytometry coupled with membrane integrity indicators, thiazole orange (TO) and propidium iodide (PI) staining. Growth kinetics of injured cells sorted by fluorescence activated cell sorting (FACS) were studied at 4, 25 and 37°C. The percentage of cell injury detectable by both flow cytometry and differential plating varied significantly among strains and stress treatments (p<0.0001). Based on flow cytometry and TO/PI staining, acid stress caused the highest level of injury followed by heat and osmotic stress. Following cell sorting, acid and osmotic stress injured cells were capable of resuscitation and re-growth while heat injured cells (except for strain 69) were incapable of re-growth despite having a high level of membrane intact cells. The lag phase duration (λ) of sorted stress injured cells resuscitated in brain heart infusion (BHI) broth was significantly influenced by strain variations (p<0.0001), stress treatments (p=0.007) and temperature of resuscitation (p≤0.001). Following repair, the maximum specific growth rate (μ) of resuscitated cells was not different from untreated control cells regardless of strain differences and stress treatments. Only temperature had a significant effect (p<0.0001) on growth rate. Sorted cells were also capable of growth at 4°C, with the time to detectable growth (≥1.40LogCFUml) ranging from 3 to 15days. Overall, re-growth potential of sorted cells showed that while membrane integrity was a good indicator of cell injury and viability loss for acid and osmotic stress, it was not a sufficient indicator of heat stress injury. Once injured cells repair the cellular damage, their growth rate is not different from non-injured cells regardless of form of stress and strain differences. Thus highlighting the potential food safety risks of stress injured L. monocytogenes cells.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.foodres.2017.08.020DOI Listing
October 2017

Mechanism of cassava tuber cell wall weakening by dilute sodium hydroxide steeping.

Food Chem 2017 Aug 3;228:338-347. Epub 2017 Feb 3.

Institute for Food, Nutrition and Well-being and Department of Food Science, University of Pretoria, Private Bag X 20, Hatfield 0028, South Africa. Electronic address:

Steeping of cassava root pieces in 0.75% NaOH in combination with wet milling was investigated to determine whether and how dilute NaOH modifies cassava cell walls. Gas chromatography data of cell wall constituent sugar composition and Fourier transform infrared (FTIR) data showed that NaOH steeping reduced the level of pectin in cassava cell walls. FTIR and wide-angle X-ray scattering spectroscopy also indicated that NaOH steeping combined with fine milling slightly reduced cellulose crystallinity. Scanning electron microscopy showed that NaOH steeping produced micropores in the cell walls and light microscopy revealed that NaOH steeping increased disaggregation of parenchyma cells. Steeping of ground cassava in NaOH resulted in a 12% decrease in large residue particles and approx. 4% greater starch yield with wet milling. Therefore dilute NaOH steeping can improve the effectiveness of wet milling in disintegrating cell walls through solubilisation of pectin, thereby reduced cell wall strength.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.foodchem.2017.02.006DOI Listing
August 2017

Potency and selectivity indices of acetone leaf extracts of nine selected South African trees against six opportunistic Enterobacteriaceae isolates from commercial chicken eggs.

BMC Complement Altern Med 2017 Feb 2;17(1):90. Epub 2017 Feb 2.

Phytomedicine Programme, Department of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort, 0110, Pretoria, South Africa.

Background: The rise in antimicrobial resistance in a plethora of nosocomial and opportunistic bacterial pathogens often isolated from commercial eggs, poses a serious public health concern. The existence of these contaminants may also serve as a drawback in the current efforts of improving the well-being of immunocompromised patients. The aim of this study was to determine the efficacy of plant extracts that had good activity on Escherichia coli in previous word on pathogens isolated from eggs for possible use in combating pathogens from eggs.

Methods: Acetone leaf extracts of nine trees with good activities against Escherichia coli were tested for their in vitro antibacterial activity against six opportunistic bacterial isolates from commercial eggs (Stenotrophomonas maltophilia, Klebsiella pneumoniae, Salmonella serotype Typhimurium, Proteus mirabilis, Enterobacter cloacae and Escherichia coli) using a serial microdilution method with tetrazolium violet as indicator of growth. Cytotoxicity was determined using a tetrazolium-based colorimetric assay against Vero kidney cells, and selectivity index calculated.

Results: The MIC values range of the different extracts against Stenotrophomonas maltophilia was 0.08-0.31 mg/ml, Klebsiella pneumonia 0.08-0.63 mg/ml, Salmonella ser. Typhimurium 0.08-0.63 mg/ml, Proteus mirabilis 0.02-1.25 mg/ml, Enterobacter cloacae 0.08-0.31 mg/ml and Escherichia coli 0.08-0.16 mg/ml respectively. Escherichia coli was the most sensitive while Proteus mirabilis was most resistant pathogen to the different test extracts, with mean MIC values of 0.08 mg/ml and 0.46 mg/ml respectively. Cremaspora triflora extracts had good activity against all the pathogenic egg isolates, with the exception of Proteus mirabilis. Maesa lanceolata and Elaeodendron croceum had the best total antibacterial activity (TAA), while generally the selectivity index of the extract was low (SI < 1).

Conclusion: The exceptional activity of C. triflora extracts suggests that the plant has potential as a therapeutic agent against some members of the Enterobacteriaceae. Further pharmacological investigations may be interesting in the search for new antimicrobial leads.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1186/s12906-017-1597-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5289020PMC
February 2017

Characterization of bacterial pathogens in rural and urban irrigation water.

J Water Health 2015 Mar;13(1):103-17

Department of Food Science, University of Pretoria, Lynwood Road, Pretoria 0002, South Africa E-mail:

The study aimed to compare the bacteriological quality of an urban and rural irrigation water source. Bacterial counts, characterization, identification and diversity of aerobic bacteria were determined. Escherichia coli isolated from both sites was subjected to antibiotic susceptibility testing, virulence gene (Stx1/Stx2 and eae) determination and (GTG)5 Rep-PCR fingerprinting. Low mean monthly counts for aerobic spore formers, anaerobic spore formers and Staphylococcus aureus were noted although occasional spikes were observed. The most prevalent bacterial species at both sites were Bacillus spp., E. coli and Enterobacter spp. In addition, E. coli and Bacillus spp. were most prevalent in winter and summer respectively. Resistance to at least one antibiotic was 84% (rural) and 83% (urban). Highest resistance at both sites was to cephalothin and ampicillin. Prevalence of E. coli possessing at least one virulence gene (Stx1/Stx2 and eae) was 15% (rural) and 42% (urban). All (rural) and 80% (urban) of E. coli possessing virulence genes showed antibiotic resistance. Complete genetic relatedness (100%) was shown by 47% of rural and 67% of urban E. coli isolates. Results from this study show that surface irrigation water sources regardless of geographical location and surrounding land-use practices can be reservoirs of similar bacterial pathogens.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.2166/wh.2014.228DOI Listing
March 2015

Pathogenic and commensal Escherichia coli from irrigation water show potential in transmission of extended spectrum and AmpC β-lactamases determinants to isolates from lettuce.

Microb Biotechnol 2015 May 9;8(3):462-73. Epub 2014 Dec 9.

Department of Food Science, University of Pretoria, Lynwood Road, Pretoria, 0002, South Africa.

There are few studies on the presence of extended-spectrum β-lactamases and AmpC β-lactamases (ESBL/AmpC) in bacteria that contaminate vegetables. The role of the production environment in ESBL/AmpC gene transmission is poorly understood. The occurrence of ESBL/AmpC in Escherichia coli (n = 46) from lettuce and irrigation water and the role of irrigation water in the transmission of resistant E. coli were studied. The presence of ESBL/AmpC, genetic similarity and phylogeny were typed using genotypic and phenotypic techniques. The frequency of β-lactamase gene transfer was studied in vitro. ESBLs/AmpC were detected in 35 isolates (76%). Fourteen isolates (30%) produced both ESBLs/AmpC. Prevalence was highest in E. coli from lettuce (90%). Twenty-two isolates (48%) were multi-resistant with between two and five ESBL/AmpC genes. The major ESBL determinant was the CTX-M type (34 isolates). DHA (33% of isolates) were the dominant AmpC β lactamases. There was a high conjugation efficiency among the isolates, ranging from 3.5 × 10(-2) to 1 × 10(-2)  ± 1.4 × 10(-1) transconjugants per recipient. Water isolates showed a significantly higher conjugation frequency than those from lettuce. A high degree of genetic relatedness between E. coli from irrigation water and lettuce indicated possible common ancestry and pathway of transmission.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1111/1751-7915.12234DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4408178PMC
May 2015

Effect of sorghum type and malting on production of free amino nitrogen in conjunction with exogenous protease enzymes.

J Sci Food Agric 2015 Jan 9;95(2):417-22. Epub 2014 Jun 9.

Department of Food Science, University of Pretoria, Hatfield, South Africa.

Background: Sorghum types suitable for brewing and bioethanol production are required. The effect of sorghum type (white non-tannin versus white type II tannin) on free amino nitrogen (FAN) production from sorghum grain and malt using exogenous protease enzymes was investigated over extended incubation at moderate temperature (45 °C).

Results: With grain in the absence of exogenous proteases, white non-tannin sorghum produced substantially higher levels of FAN than white type II tannin sorghum, due to the tannins in the latter. Incubating sorghum grain with neutral proteinase and amino-peptidase in combination improved FAN production. The two sorghum types produced similar FAN levels when malted and incubated in the absence of the exogenous proteases. When both sorghums were malted and incubated with neutral proteinase alone substantially more FAN yield (124-126 mg 100 g(-1)) occurred than with grains (61-84 mg 100 g(-1)). The combination of amino-peptidase and proteinase did not improve FAN further. Neither, did malting influence wort free amino acid profile. Group B amino acids constituted the highest percentage (42-47%).

Conclusion: With grain, white non-tannin sorghum plus proteinase and amino-peptidase yields the highest FAN, with malt both white non-tannin and white type II tannin sorghums plus proteinase yield the highest FAN.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jsfa.6739DOI Listing
January 2015

Undesirable sulphur and carbonyl flavor compounds in UHT milk: a review.

Crit Rev Food Sci Nutr 2012 ;52(1):21-30

Department of Food Science, University of Pretoria, South Africa.

Ultra High Temperature (UHT) processing leads to the formation of "cooked" and "flat" flavors in milk. These undesirable notes occur due to the volatile formation of a variety of sulphur containing compounds, methyl ketones and aliphatic aldehydes, derived from the constituents of the milk's matrix during thermal processing and storage. The "cooked" flavor of UHT milk is associated with the presence of a variety of sulphur containing compounds while the "stale" flavor is characterized by the dissipation of these sulphur volatiles and an increase of the formation and presence of both methyl ketones and aliphatic aldehydes over time. The extent to which the individual volatiles contribute to the overall flavor of UHT milk is not clear. The proposed formation of these volatiles, that is, the methods to control the intensity of "cooked" and "stale" flavors associated with UHT milk and extraction techniques for the isolation of these volatiles from milk, have been reviewed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1080/10408398.2010.487166DOI Listing
January 2012

Relative gene expression in acid-adapted Escherichia coli O157:H7 during lactoperoxidase and lactic acid challenge in Tryptone Soy Broth.

Microbiol Res 2010 Sep 14;165(7):546-56. Epub 2009 Dec 14.

Department of Food Science, University of Pretoria, Lynwood Road, Pretoria 0002, South Africa.

Cross-protection of acid-adapted Escherichia coli O157:H7 against inimical stresses is mediated by the glucose-repressed sigma factor RpoS. However, many food systems in which E. coli O157:H7 occurs are complex and contain glucose. This study was aimed at investigating the contribution of acid and lactoperoxidase (LP)-inducible genes to cross-protection of E. coli O157:H7 against LP system and lactic acid (LA) in Tryptone Soy Broth (TSB). Acid-adapted and non-adapted E. coli O157:H7 were challenged to activated LP and LA at pH 4.0 and 5.0 in TSB for 6h at 25°C followed by expression of acid and LP-inducible genes. Acid-adapted E. coli showed cross-protection against activated LP and LA. All the acid-inducible genes tested were repressed at pH 4.0 with or without activated LP system. At pH 7.4, gadA, ompC and ompF were induced in acid-adapted cells. Induction of corA occurred in non-adapted cells but was repressed in acid-adapted cells. Although acid-inducible genes were repressed at pH 4.0, high resistance of acid-adapted cells indicates that expression of acid-inducible genes occurred during acid adaptation and not the actual challenge. Repression of rpoS indicates that RpoS-independent systems contribute to cross-protection in acid-adapted E. coli O157:H7.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.micres.2009.11.003DOI Listing
September 2010

Adaptation of Escherichia coli O157:H7 to acid in traditional and commercial goat milk amasi.

Food Microbiol 2009 Feb 22;26(1):58-64. Epub 2008 Aug 22.

Department of Food Science, University of Pretoria, Lynnwood Road, Pretoria 0002, South Africa.

Acid resistance of Escherichia coli O157:H7 strains UT 10 and UT 15 were determined in traditional Amasi fermented for 3 days at ambient temperature (ca 30 degrees C) and commercial Amasi fermented at 30 degrees C for 24h and stored at 7 degrees C for 2 days. Escherichia coli O157:H7 counts in commercial Amasi were detected at 2.7 log(10)cfu/ml after 3 days while those in traditional Amasi could not be detected after the same period. There was no significant difference (p< or =0.05) in the survival of acid adapted (AA) and non-adapted (NA) E. coli O157:H7 in traditional Amasi, while in commercial Amasi, the NA strain survived significantly (p< or =0.05) better than its AA counterpart. Regardless of prior adaptation to acid, E. coli O157:H7 can survive during fermentation and storage of fermented goat milk Amasi. Also, the fermentation time, pH and storage temperature affects the survival of E. coli O157:H7 in the fermented milk.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.fm.2008.07.007DOI Listing
February 2009

Use of γ-irradiation to reduce Clostridium perfringens on ready-to-eat bovine tripe.

Meat Sci 2008 Mar 30;78(3):194-201. Epub 2007 Jun 30.

Department of Food Science, University of Pretoria, 0002, South Africa.

The aim of this study was to determine the effect of gamma irradiation at a target dose of 9kGy and storage at 5 and 15°C on the safety of ready-to-eat (RTE) tripe with respect to Clostridium perfringens count (CC) and aerobic plate count (APC), and to determine the effect of boiling (1h) and irradiation (9kGy) on Cl. perfringens ATCC 13124 spore structure. Irradiation significantly reduced APC stored at 5 and 15°C for 7 days. However, 0kGy control samples increased in their APC to >7log(10) cfu/g throughout 7 days of storage. Irradiation eliminated the inoculated Cl. perfringens ATCC 13124 spores on RTE tripe throughout storage at 5 and 15°C. Transmission electron microscopy of Cl. perfringens ATCC 13124 spores showed that boiling caused a reduction in spore material, irradiation caused elongation of the Cl. perfringens ATCC 13124 spores, and boiling in combination with gamma irradiation caused loss of spore material. Therefore, irradiation at 9kGy, together with storage at 5°C, can assure the microbiological safety of RTE bovine tripe, with respect to Cl. perfringens spores for at least 7 days at 5 and 15°C.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1016/j.meatsci.2007.06.010DOI Listing
March 2008