Unsaturated Fatty Acids Affect Quorum Sensing Communication System and Inhibit Motility and Biofilm Formation of Acinetobacter baumannii

The increasing threat of Acinetobacter baumannii as a nosocomial pathogen is mainly due to the occurrence of multidrug-resistant strains that are associated with the real problem of its eradication from hospital wards. The particular ability of this pathogen to form biofilms contributes to its persistence, increases antibiotic resistance, and promotes persistent/device-related infections. We previously demonstrated that virstatin, which is a small organic compound known to decrease virulence of Vibrio cholera via an inhibition of T4-pili expression, displayed very promising activity to prevent A. baumannii biofilm development. Here, we examined the antibiofilm activity of mono-unsaturated chain fatty acids, palmitoleic (PoA), and myristoleic (MoA) acids, presenting similar action on V. cholerae virulence. We demonstrated that PoA and MoA (at 0.02 mg/mL) were able to decrease A. baumannii ATCC 17978 biofilm formation up to 38% and 24%, respectively, presented a biofilm dispersing effect and drastically reduced motility. We highlighted that these fatty acids decreased the expression of the regulator abaR from the LuxIR-type quorum sensing (QS) communication system AbaIR and consequently reduced the N-acyl-homoserine lactone production (AHL). This effect can be countered by addition of exogenous AHLs. Besides, fatty acids may have additional non-targeted effects, independent from QS. Atomic force microscopy experiments probed indeed that PoA and MoA could also act on the initial adhesion process in modifying the material interface properties. Evaluation of fatty acids effect on 22 clinical isolates showed a strain-dependent antibiofilm activity, which was not correlated to hydrophobicity or pellicle formation ability of the tested strains, and suggested a real diversity in cell-to-cell communication systems involved in A. baumannii biofilm formation.

Prevention of Staphylococcus aureus biofilm formation by antibiotics in 96-Microtiter Well Plates and Drip Flow Reactors: critical factors influencing outcomes

Biofilm formation leads to the failure of antimicrobial therapy. Thus, biofilm prevention is a desirable goal of antimicrobial research. In this study, the efficacy of antibiotics (doxycycline, oxacillin and rifampicin) in preventing Staphylococcus aureus biofilms was investigated using Microtiter Well Plates (MWP) and Drip Flow Reactors (DFR), two models characterized by the absence and the presence of a continuous flow of nutrients, respectively. Planktonic culture of S. aureus was exposed to antibiotics for one hour followed by 24 hours incubation with fresh nutrients in MWP or continuous flow of nutrients in DFR. The DFR grown biofilms were significantly more tolerant to the antibiotics than those grown in MWP without the continuous flow. The differences in log reductions (LR) between the two models could not be attributed to differences in the cell density, the planktonic inoculum concentration or the surface-area-to-volume ratios. However, eliminating the flow in the DFR significantly restored the antibiotic susceptibility. These findings demonstrate the importance of considering differences between experimental conditions in different model systems, particularly the flow of nutrients, when performing anti-biofilm efficacy evaluations. Biofilm antibiotic efficacy studies should be assessed using various models and more importantly, in a model mimicking conditions of its clinical application.

Penicillin G increases the synthesis of a suicidal marker (CidC) and virulence (HlgBC) proteins in Staphylococcus aureus biofilm cells

The present study reports the effect of Penicillin G (PenG) on the proteome dynamics of the Staphylococcus aureus strain Newman during biofilm mode of growth. The viability of the 18-h-old biofilm cells challenged with PenG at the concentration of 1mgmL(-1) was first assessed by plate counting, resazurin and LIVE/DEAD fluorescence staining, which indicated that the viability was reduced by ∼35% and ∼90% at 2h and 24h, respectively, after the addition of PenG. Subsequent two-dimensional difference gel electrophoresis (2D DIGE) assay of the treated and non-treated biofilm cells at the indicated time points revealed 45 proteins showing time- and treatment-specific change (1.5-fold, p<0.01). The 2D DIGE results suggested that the PenG-induced decrease in viability was accompanied by an increased synthesis of pyruvate oxidase (CidC), a suicidal marker known to potentiate acetate-dependent cell death in S. aureus. Increased abundance was also found for the TCA cycle associated malate-quinone oxidoreductase (Mqo), the ClpC ATPase, the HlgBC toxin and phage-associated proteins, which suggests that surviving cells have induced these activities as a last effort to overcome lethal doses of PenG. Proteomic results also revealed that the surviving cells were likely to strengthen their peptidoglycan due to the increased abundance of cell-wall biogenesis associated proteins, FemA and Pbp2; a phenomenon associated with dormancy in S. aureus.

Systematic exploration of natural and synthetic flavonoids for the inhibition of Staphylococcus aureus biofilms

When single-cell (or suspended) bacteria switch into the biofilm lifestyle, they become less susceptible to antimicrobials, imposing the need for anti-biofilms research. Flavonoids are among the most extensively studied natural compounds with an unprecedented amount of bioactivity claims. Most studies focus on the antibacterial effects against suspended cells; fewer reports have researched their anti-biofilm properties. Here, a high throughput phenotypic platform was utilized to screen for the inhibitory activity of 500 flavonoids, including natural and synthetic derivatives, against Staphylococcus aureus biofilms. Since discrepancies among results from earlier antibacterial studies on flavonoids had been noted, the current study aimed to minimize sources of variations. After the first screen, flavonoids were classified as inactive (443), moderately active (47) or highly active (10). Further, exclusion criteria combining bioactivity and selectivity identified two synthetic flavans as the most promising. The body of data reported here serves three main purposes. First, it offers an improved methodological workflow for anti-biofilm screens of chemical libraries taking into account the (many times ignored) connections between anti-biofilm and antibacterial properties. This is particularly relevant for the study of flavonoids and other natural products. Second, it provides a large and freely available anti-biofilm bioactivity dataset that expands the knowledge on flavonoids and paves the way for future structure-activity relationship studies and structural optimizations. Finally, it identifies two new flavans that can successfully act on biofilms, as well as on suspended bacteria and represent more feasible antibacterial candidates.

Alpha- and β-casein components of host milk induce biofilm formation in the mastitis bacterium Streptococcus uberis

Streptococcus uberis is an environmental udder pathogen that infects cattle and can cause persistent intramammary infection (IMI), despite the fact that isolates are mainly susceptible to antibiotics. As biofilm growth can cause persistent infection, the ability of ten S. uberis isolates from clinical and subclinical IMIs to form biofilms on the polystyrene surface of a conventional 96-microplates model was examined. Biofilm formation was judged by different staining methods (crystal violet and resazurin) and by atomic force and fluorescence microscopy. These analyses revealed that two out of ten S. uberis strains tested were able to form biofilms. Upon treatment with Proteinase K, biofilms of S. uberis were completely disintegrated, which indicates that biofilm formation is protein-mediated in these strains. Addition of trace amounts of milk, the natural growth medium of S. uberis, significantly increased biofilm formation by most of the strains initially classified as non-biofilm producers. Alpha-casein and β-casein were the primary inducers of biofilm growth, and casein degradation by serine protease activity was required to achieve maximal biofilm production. These results suggest that the extracellular proteolytic activity of S. uberis contributes to an increased biofilm formation. Such a mode of growth induced by host proteins might help to explain the persistence of IMIs caused by this pathogen.