Virstatin inhibits biofilm formation and motility of Acinetobacter baumannii.

BACKGROUND: Acinetobacter baumannii has emerged as an opportunistic nosocomial pathogen causing infections worldwide. One reason for this emergence is due to its natural ability to survive in the hospital environment, which may be explained by its capacity to form biofilms. Cell surface appendages are important determinants of the A. baumannii biofilm formation and as such constitute interesting targets to prevent the development of biofilm-related infections. A chemical agent called virstatin was recently described to impair the virulence of Vibrio cholerae by preventing the expression of its virulence factor, the toxin coregulated pilus (type IV pilus). The objective of this work was to investigate the potential effect of virstatin on A. baumannii biofilms. RESULTS: After a dose-response experiment, we determined that 100 µM virstatin led to an important decrease (38%) of biofilms formed by A. baumannii ATCC17978 grown under static mode. We demonstrated that the production of biofilms grown under dynamic mode was also delayed and reduced. The biofilm susceptibility to virstatin was then tested for 40 clinical and reference A. baumannii strains. 70% of the strains were susceptible to virstatin (with a decrease of 10 to 65%) when biofilms grew in static mode, whereas 60% of strains respond to the treatment when their biofilms grew in dynamic mode. As expected, motility and atomic force microscopy experiments showed that virstatin acts on the A. baumannii pili biogenesis. CONCLUSIONS: By its action on pili biogenesis, virstatin demonstrated a very promising antibiofilm activity affecting more than 70% of the A. baumannii clinical isolates.

Overview of multi-species biofilms in different ecosystems: Wastewater treatment, soil and oral cavity.

In various natural ecosystems, bacteria most often live in a sessile state enchased in a self-produced extracellular matrix forming biofilms. Due to their either negative or positive impact on different aspects of our daily life, the number of studies devoted to biofilms is increasing. Most research is based on biofilms formed by a single bacterial species. These simple models allowed the understanding of the mechanisms involved in biofilms formation and regulation. This likewise helped the development of several means to control the biofilms formation. However, these models do not closely mimic the natural biofilms known as biochemically and microbiologically heterogeneous and dynamic structures. For this reason, current studies focus more on multispecies biofilms using complex models to best approximate the natural environment. In this review, we addressed on available examples of multispecies biofilms in different domains to illustrate the complexity and organization of life within a consortium. Finally, we review the most used analytical techniques to study multispecies biofilms highlighting the need of multi-scale strategies to better decipher this complex lifestyle.

Genome sequence data of Bacillus amyloliquefaciens L-17.

Bacillus amyloliquefaciens L-17 strain was isolated from a sample of chicken feathers. Here, we report complete genome sequence data of B. amyloliquefaciens L-17. The size of the genome is 3,933,788 bp which harbours 4001 coding Sequences. The BioProject has been deposited at NCBI GenBank. The GenBank accession numbers are PRJNA727793 for the BioProject, CP074391.1 for the chromosome, GCA_018363035.1 for GenBank assembly accession and SAMN19035411 for the BioSample.

Architecture and physico-chemical properties of Bacillus amyloliquefaciens L-17 pellicle formed at the air-liquid interface.

Bacillus amyloliquefaciens is a ubiquitous soil and plant-associated bacterial species which shows structural and adaptative responses to the environment. This present paper explores the ability of the strain L-17 to form subaerial biofilms on a liquid surface. Hydrophobic and non-wetting properties were observed for the rough top biofilm layer in contact with the air, which are quite different to the hydrophilic properties which were observed for the smooth biofilm layer in contact with the liquid. Both pellicle interfaces were visualized by scanning electron microscopy revealing a complex three-dimensional architecture composed of exopolymers organized in stacked fibrous network or sheet-like structures in the vicinity of the subaerial surface. Disruption of the extracellular matrix by combining physical and chemical treatments indicated that both loosely and tightly bound polysaccharides were found as major components of this complex pellicle. Proteins were also involved in the aggregation and cohesion of the matrix as multi extraction steps were needed to recover some tightly bounded proteins. This was confirmed by applying protease treatment which was able to significantly disrupt the pellicle. Overall results underline the ability of B. amyloliquefaciens L-17 to survive on air-liquid interfaces. This feature offers an interesting strategy to escape aquatic environments and develop aerial biofilm in response to environmental changes involving wet-dry cycles.

Characterisation of pellicles formed by Acinetobacter baumannii at the air-liquid interface.

The clinical importance of Acinetobacter baumannii is partly due to its natural ability to survive in the hospital environment. This persistence may be explained by its capacity to form biofilms and, interestingly, A. baumannii can form pellicles at the air-liquid interface more readily than other less pathogenic Acinetobacter species. Pellicles from twenty-six strains were morphologically classified into three groups: I) egg-shaped (27%); II) ball-shaped (50%); and III) irregular pellicles (23%). One strain representative of each group was further analysed by Brewster's Angle Microscopy to follow pellicle development, demonstrating that their formation did not require anchoring to a solid surface. Total carbohydrate analysis of the matrix showed three main components: Glucose, GlcNAc and Kdo. Dispersin B, an enzyme that hydrolyzes poly-N-acetylglucosamine (PNAG) polysaccharide, inhibited A. baumannii pellicle formation, suggesting that this exopolysaccharide contributes to pellicle formation. Also associated with the pellicle matrix were three subunits of pili assembled by chaperon-usher systems: the major CsuA/B, A1S_1510 (presented 45% of identity with the main pilin F17-A from enterotoxigenic Escherichia coli pili) and A1S_2091. The presence of both PNAG polysaccharide and pili systems in matrix of pellicles might contribute to the virulence of this emerging pathogen.

Growth of Acinetobacter baumannii in pellicle enhanced the expression of potential virulence factors.

BACKGROUND: Interestingly, Acinetobacter baumannii presents an enhanced capacity to form biofilms (also named pellicles) at the air-liquid interface as compared to the other Acinetobacter species. This characteristic questions the contribution of this phenotype to an increased risk of clinical infections by this pathogen. METHODOLOGY/PRINCIPAL FINDINGS: By a proteomic approach using 2-D gel electrophoresis-LC-MS/MS mass spectrometry, we compared the membrane protein patterns of A. baumannii 77, a pellicle-forming clinical isolate, grown in planktonic and in sessile modes. We identified 52 proteins with a differential expression, including 32 up-regulated and 20 down-regulated in the pellicle state. Several proteins, differentially expressed during pellicle development, were of particular interest. We determined the over-expression of four siderophore iron uptake systems including the acinetobactin and enterobactin receptors and confirmed that the development of this type of biofilm is promoted by ferric ions. Two over-expressed proteins, CarO and an OprD-homologue, putative carbapenem-resistance associated porins, would be involved in the transport of specific compounds, like ornithine, a biosynthesis precursor of a siderophore from the hydroxamate family. We evidenced the overexpression of a lipase and a transporter of LCFA that may be involved in the recycling of lipids inside the pellicle matrix. Finally, we demonstrated both by proteomic and by AFM studies that this particular type of biofilm required multiple pili systems to maintain this cohesive structure at the air-liquid interface; two of these systems have never been described in A. baumannii. CONCLUSIONS/SIGNIFICANCE: Our study demonstrated that several proteins, overexpressed at a late state of pellicle development, could be potentially involved in virulence processes. Therefore, regarding the number of potential virulence factors that are over-expressed in this growth mode, the pellicle-forming clinical isolates should be kept under survey.