Screening of molecular virulence markers in Staphylococcus aureus and Pseudomonas aeruginosa strains isolated from clinical infections.

Staphylococcus (S.) aureus and Pseudomonas (Ps.) aeruginosa are two of the most frequently opportunistic pathogens isolated in nosocomial infections, responsible for severe infections in immunocompromised hosts. The frequent emergence of antibiotic-resistant S. aureus and Ps. aeruginosa strains has determined the development of new strategies in order to elucidate the different mechanisms used by these bacteria at different stages of the infectious process, providing the scientists with new procedures for preventing, or at least improving, the control of S. aureus and Ps. aeruginosa infections. The purpose of this study was to characterize the molecular markers of virulence in S. aureus and Ps. aeruginosa strains isolated from different clinical specimens. We used multiplex and uniplex PCR assays to detect the genes encoding different cell-wall associated and extracellular virulence factors, in order to evaluate potential associations between the presence of putative virulence genes and the outcome of infections caused by these bacteria. Our results demonstrate that all the studied S. aureus and Ps. aeruginosa strains synthesize the majority of the investigated virulence determinants, probably responsible for different types of infections.

The role of proteins expressed under the stress condition in virulence of some Vibrio strains.

In order to survive in changing environments, bacteria possess enormous adaptive capabilities that allow them to modulate their behavior and reprogram gene expression in response to environmental cues. Vibrios are inhabitants of estuarine and fresh waters and some species are pathogenic to humans, and marine vertebrates and invertebrates. Surface attachment is believed to be essential for colonization of all of these natural environments. Vibrio (V.) parahaemolyticus, an ubiquitous marine bacterium and human pathogen, seems to be particularly adapted to growth on surfaces or in biofilms. In response to its physical environment, V. parahaemolyticus induces the expression of a large number of genes. The purpose of the present study was to investigate the influence of different physicochemical parameters (temperature and osmolarity) on the virulence factors expression in Vibrio strains using different conditions simulating environmental stress factors. Some of the tested strains displayed a decreased adherence capacity to the inert substrate under stressful conditions, and the adherence capacity on HeLa cell was generally reduced, while the soluble enzymatic factors showed only slight changes. However, it is to be noticed that the haemolysins and Kanagawa enterotoxin were better expressed at higher temperature and osmolarity, these factors probably contributing to the bacterial adaptation and survival in the extern medium of certain Vibrio species.