Publications by authors named "A Viljoen"

320 Publications

AFM force-clamp spectroscopy captures the nanomechanics of the Tad pilus retraction.

Nanoscale Horiz 2021 May 13. Epub 2021 May 13.

Louvain Institute of Biomolecular Science and Technology, UCLouvain, Croix du Sud, 4-5, bte, L7.07.07, Louvain-la-Neuve B-1348, Belgium.

Motorization of bacterial pili is key to generate traction forces to achieve cellular function. The Tad (or Type IVc) pilus from Caulobacter crescentus is a widespread motorized nanomachine crucial for bacterial survival, evolution and virulence. An unusual bifunctional ATPase motor drives Tad pilus retraction, which helps the bacteria to land on target surfaces. Here, we use a novel platform combining a fluorescence-based screening of piliated bacteria and atomic force microscopy (AFM) force-clamp spectroscopy, to monitor over time (30 s) the nanomechanics and dynamics of the Tad nanofilament retraction under a high constant tension (300 pN). We observe striking transient variations of force and height originating from two phenomena: active pilus retraction and passive hydrophobic interactions between the pilus and the hydrophobic substrate. That the Tad pilus is able to retract under high tensile loading - at a velocity of ∼150 nm s-1 - indicates that this nanomachine is stronger than previously anticipated. Our findings show that pilus retraction and hydrophobic interactions work together to mediate bacterial cell landing and surface adhesion. The motorized pilus retraction actively triggers the cell to approach the substrate. At short distances, passive hydrophobic interactions accelerate the approach phenomenon and promote strong cell-substrate adhesion. This mechanism could provide a strategy to save ATP-based energy by the retraction ATPase. Our force-clamp AFM methodology offers promise to decipher the physics of bacterial nanomotors with high sensitivity and temporal resolution.
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http://dx.doi.org/10.1039/d1nh00158bDOI Listing
May 2021

Staphylococcus aureus vWF-binding protein triggers a strong interaction between clumping factor A and host vWF.

Commun Biol 2021 Apr 12;4(1):453. Epub 2021 Apr 12.

Louvain Institute of Biomolecular Science and Technology, UCLouvain, Louvain-la-Neuve, Belgium.

The Staphylococcus aureus cell wall-anchored adhesin ClfA binds to the very large blood circulating protein, von Willebrand factor (vWF) via vWF-binding protein (vWbp), a secreted protein that does not bind the cell wall covalently. Here we perform force spectroscopy studies on living bacteria to unravel the molecular mechanism of this interaction. We discover that the presence of all three binding partners leads to very high binding forces (2000 pN), largely outperforming other known ternary complexes involving adhesins. Strikingly, our experiments indicate that a direct interaction involving features of the dock, lock and latch mechanism must occur between ClfA and vWF to sustain the extreme tensile strength of the ternary complex. Our results support a previously undescribed mechanism whereby vWbp activates a direct, ultra-strong interaction between ClfA and vWF. This intriguing interaction represents a potential target for therapeutic interventions, including synthetic peptides inhibiting the ultra-strong interactions between ClfA and its ligands.
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http://dx.doi.org/10.1038/s42003-021-01986-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8041789PMC
April 2021

Efficacy of a novel topical combination of esafoxolaner, eprinomectin and praziquantel against Rhipicephalus sanguineus in cats.

Parasite 2021 2;28:24. Epub 2021 Apr 2.

Clinvet International (Pty) Ltd., P.O. Box 11186, Universitas, Bloemfontein 9321, Republic of South Africa.

Esafoxolaner is a purified enantiomer of afoxolaner with insecticidal and acaricidal properties. It is combined with eprinomectin and praziquantel in a novel topical endectoparasiticide formulation for cats. The efficacy of this novel formulation was assessed in an experimental study against induced infestation of Rhipicephalus sanguineus ticks. Twenty cats were randomly allocated to either a placebo control group or a treated group in a 1:1 ratio. Infested cats were treated topically once at the minimum recommended dose. The study was designed to assess curative efficacy 48 h after treatment and to test preventive efficacy 48 h after weekly infestations for 2 months. At each weekly infestation, all cats were infested with 25 male and 25 unfed female R. sanguineus ticks. At each tick count, at least 6 in 10 control cats had a retention of 13 (26%) or more live ticks, demonstrating adequate infestation throughout the study. Curative efficacy on existing tick infestation was 90%; preventive efficacy over the following 6 weeks was at least 96%.
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http://dx.doi.org/10.1051/parasite/2021020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8019555PMC
April 2021

Efficacy of a novel topical combination of esafoxolaner, eprinomectin and praziquantel against adult cat flea Ctenocephalides felis and flea egg production in cats.

Parasite 2021 2;28:21. Epub 2021 Apr 2.

Boehringer-Ingelheim Animal Health, Missouri Research Center, 6498 Jade Rd., Fulton, MO 65251, USA.

Esafoxolaner, a purified enantiomer of afoxolaner with insecticidal and acaricidal properties, is combined with eprinomectin and praziquantel in NexGard Combo, a novel topical endectoparasiticide formulation for cats. The efficacy of this novel formulation against adult and immature stages of Ctenocephalides felis fleas was tested in four experimental studies. Two studies were designed to test adulticide efficacy, one to test inhibition of immature stages, and one to test both adulticide efficacy and inhibition of immature stages. In each study, cats were randomly allocated to a placebo control group or to a novel formulation group treated once at the minimum recommended dose. Cats were experimentally infested weekly for one to two months with unfed C. felis originating from North America or Europe. For adulticide efficacy evaluations, live fleas were counted 24 h after treatment and after subsequent weekly infestations. For immature stages, flea eggs were collected and counted weekly for evaluation of egg production inhibition and incubated for larval hatching evaluation. In the three studies testing adult fleas, curative efficacies, 24 h after treatment, were 92.1%, 98.3% and 99.7%; preventive weekly efficacies, 24 h after weekly infestations, remained higher than 95.5% for at least one month. In the two studies testing immature stages, egg production and larval hatching was significantly reduced for at least one month. These studies provide robust evidence of efficacy of the novel formulation against experimental adult flea infestations and for the prevention of environmental contamination by immature flea stages, for at least one month.
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http://dx.doi.org/10.1051/parasite/2021017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8019553PMC
April 2021

AFM Unravels the Unique Adhesion Properties of the Type IVc Pilus Nanomachine.

Nano Lett 2021 Apr 23;21(7):3075-3082. Epub 2021 Mar 23.

Louvain Institute of Biomolecular Science and Technology, UCLouvain, Croix du Sud, 4-5, bte, L7.07.07., B-1348 Louvain-la-Neuve, Belgium.

Bacterial pili are proteinaceous motorized nanomachines that play various functional roles including surface adherence, bacterial motion, and virulence. The surface-contact sensor type IVc (or Tad) pilus is widely distributed in both Gram-positive and Gram-negative bacteria. In , this nanofilament, though crucial for surface colonization, has never been thoroughly investigated at the molecular level. As assembles several surface appendages at specific stages of the cell cycle, we designed a fluorescence-based screen to selectively study single piliated cells and combined it with atomic force microscopy and genetic manipulation to quantify the nanoscale adhesion of the type IVc pilus to hydrophobic substrates. We demonstrate that this nanofilament exhibits high stickiness compared to the canonical type IVa/b pili, resulting mostly from multiple hydrophobic interactions along the fiber length, and that it features nanospring mechanical properties. Our findings may be helpful to better understand the structure-function relationship of bacterial pilus nanomachines.
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http://dx.doi.org/10.1021/acs.nanolett.1c00215DOI Listing
April 2021