Survival and biofilm formation of Listeria monocytogenes in simulated vaginal fluid: influence of pH and strain origin.

Listeria monocytogenes, the agent responsible for listeriosis, can be transmitted from mother to fetus/neonates by vertical transmission, transplacentally or during passage through the birth canal. The purpose of this study was to investigate the survival and biofilm formation of L. monocytogenes (isolated from clinical cases or from food) in simulated vaginal fluid at different pH values (4.2, 5.5 and 6.5). The results demonstrated that this pathogen is inhibited by the normal vaginal pH, but may proliferate when it increases. Clinical strains were significantly more resistant to pH 4.2 than food isolates. Listeria monocytogenes survived and even grew at the higher pHs investigated, suggesting that fetus/neonates from women having increased vaginal pH values during pregnancy may be at a higher risk of listeriosis. All isolates tested were producers of biofilm at different pH values; however, L. monocytogenes produced higher quantities of biofilm in a nutrient-rich medium. No significant differences in biofilm production were detected between food and clinical isolates. As L. monocytogenes are biofilm producers, this increases the probability of occurrence of neonatal infection.

Application of an Impedimetric Technique for the Detection of Lytic Infection of Salmonella spp. by Specific Phages.

This study was performed to evaluate the adaption of the impedimetric method to detect the lytic infection by Salmonella-specific bacteriophages and to provide a higher selectivity to this rapid method in detecting Salmonella spp. by using specific agents. Three bacteriophages and twelve strains of Salmonella spp. were tested. Each of the twelve strains was used separately to inoculate TSB together with each one of the phages. The inoculum concentration was between 10(6) and 10(7) cfu/mL, at a cell: phage ratio of 1 : 100. From the sample analysis, based on conductance (G) measurements (37 degrees C), the infection could be detected, by observation of both detection-time delay and distinct curve trends. The main conclusions were that kinetic detection by impedance microbiology with phage typing constitutes a method of determining whether a test microorganism is sensitive to the bacteriophage and a method to evaluate whether a lytic bacteriophage is present in a sample, by affecting bacterial growth rate/metabolic change.