Adhesive ability and biofilm metabolic activity of Listeria monocytogenes strains before and after cold stress

Listeria monocytogenes is an important pathogen responsible for major outbreaks associated with food products. Adhesion to surfaces leads to significant modifications in cell physiology. In this work, the ability of L. monocytogenes to produce biofilm and its ability to adhere to abiotic surfaces under cold stress were evaluated. Metabolic activity of biofilm formed by L. monocytogenes before and after cold stress was measured in vitro using the colorimetric method based on the reduction of the tetrazolium salt 2,3-bis(2methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT). The ability to adhere to abiotic surfaces was determined by the ability of the cells to metabolically reduce bromure de 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium (MTT) to a formazan dye. Our results show that L. monocytogenes strains were able to adhere to abiotic materials with different degrees. In fact, cold stressed strains (-20°C) were more adhesive to polyethylene, glass, polyvinyl chloride and stainless style surfaces than non-stressed cells. Our observations show that the hydrophily varied with cold stress period. At freezing temperature, L. monocytogenes was strongly hydrophobic. Genetic studies of adhesive genes of L. monocytogenes will be required to fully understand the importance of this observation.Keywords: Listeria monocytogenes, slime production, cold stress, abiotic-surfaces, biofilm formatio

Modulation of drug resistance and biofilm formation of Staphylococcus aureus isolated from the oral cavity of Tunisian children

Objectives: This study aims to investigate the antimicrobial and the anti-biofilm activities of Lactobacillus plantarum extract (LPE) against a panel of oral Staphylococcus aureus (n = 9) and S. aureus ATCC 25923. The in vitro ability of LPE to modulate bacterial resistance to tetracycline, benzalchonium chloride, and chlorhexidine were tested also. Methods: The minimum inhibitory concentrations (MICs) and the minimal bactericidal concentrations of Lactobacillus plantarum extract, tetracycline, benzalchonium chloride and clohrhexidine were determined in absence and in presence of a sub-MIC doses of LPE (1/2 MIC). In addition, the LPE potential to inhibit biofilm formation was assessed by microtiter plate and atomic force microscopy assays. Statistical analysis was performed on SPSS v. 17.0 software using Friedman test and Wilcoxon signed ranks test. These tests were used to assess inter-group difference (p < 0.05). Results: Our results revealed that LPE exhibited a significant antimicrobial and anti-biofilm activities against the tested strains. A synergistic effect of LPEs and drug susceptibility was observed with a 2–8-fold reduction. Conclusion: LPE may be considered to have resistance-modifying activity. A more detailed investigation is necessary to determine the active compound responsible for therapeutic and disinfectant modulation. Keywords: Antibacterial, Staphylococcus aureus, Biofilm, Antibiotics, Synergetic, Lactobacillu

Effect of Grafted and Dyed Polyamide Nets on the Adhesion of Three Marine Bacterial Strains

Marine biofouling seriously affects the field of aquaculture. On the one hand, it causes structural fatigue of nets and on the other hand, it has harmful consequences on the health of farmed species. The aims of this study were to develop antibacterial nets using methacrylic acid and dyes. At first, polyamide 6.6 nets were grafted with methacrylic acid following two methods and dyed with 3 specific dyes. Then, modified nets were evaluated with SEM and XPS to obtain morphological and chemical information. Moreover, the antibacterial activity of nets was assessed against three bacterial strains at a laboratory scale and at a real scale by calculating the Colonies Forming Units (CFU) / gram. All treated nets showed an inhibition level higher than 65%. Besides, nets dyed with direct dye Tubantin and grafted with MA after plasma activation, showed an inhibition level higher than 95%. Also, nets modified with MA after plasma and reactive dye Bezaktiv S showed the best antifouling activity against three bacteria strains