Impact of different parameters upon the expression of certain virulence factors of nonhalophilic and halophilic Vibrio strains

The purpose of the present study was to investigate the expression of 13 virulence factors (VF) in nonhalophilic and halophilic vibrios isolated from clinical cases and external medium, in different cultivation conditions simulating environmental stress factors. Some of these strains displayed positive slime and indole reaction at 4 C, demonstrating the bacterial ability to survive in stress conditions by biofilm development and preservation of certain active enzymes. Haemolysins, lecithinase and aesculinase were better expressed at 28C than at 37C, demonstrating the dual role of these enzymes in microbial surviving and adaptation to external medium as well as to homeotermic hosts. The ability of surviving and synthesis of different VF was present both in non-halophilic and halophlic strains in the presence of certain limits of NaCl concentrations. Kanagawa toxin was present not only in V. parahaemolyticus but also in V. metschnikovii, V. alginolyticus, V. vulnificus, V. fischeri and V. anguillarum. The halophilic vibrios proved higher resistance to broad range of pH (1.0-9.2), than nonhalophilic strains, the most resistant proving to be V. vulnificus, followed by V. fischeri and V. anguillarum, expressing 4 VF (mucinase, lecithinase, gelatinase, aesculinase), whereas non-halophilic vibrios cultivated starting only from pH 6.0-6.5 (7 active enzymes), reaching the highest number of 12 VF at pH.7.2 decreasing thereafter to pH 9.2 at 7 VF. The different glucose concentrations (1.5-3.0%) in the culture media proved to have more evident and variable effects on halophilic than upon non-halophilic strains, with an evident increasing effect especially on V. vulnificus sp. on one side, as well as on caseinase expression in different species, on the other side. In conclusion, the present results demonstrated the higher resistance of halophilic vibrios in different environmental stress conditions as well as their particular high virulence and resistance to acid pH, during the gastric infection in humans (similar to Campylobacter pylori).