Impact of Different Parameters upon the Production of Virulence Factors in Escherichia coli Strains Isolated from Marine Water

Abstract

This study aimed to look into the expression of 10 virulence factors (VF) in 100 Escherichia coli strains harvested from the Black Sea Coast. E. coli strains were grown under different conditions, simulating various environmental stressors. The VF production [esculinase, amylase, pore-forming enzymes (hemolysin - spot and CAMP-like hemolysis; lipase; lecithinase)], lysine-decarboxylase, proteases (caseinase, gelatinase) and DNase was investigated at variable temperatures (4°C, 22°C, 37°C, 44°C and 56°C), NaCl (from 0 to 10%) and glucose concentrations (1.5% and 3%), different pH values (5.0, 7.2 and 9.6) and also in aerobic or anaerobic incubation conditions. The investigation of E. coli strains unraveled their ability to grow at 22°C, 37°C, 44°C, regardless of the salinity, pH, and glucose concentration, both in aerobic and anaerobic incubation conditions. The VF were better expressed at 37°C, followed by 22°C, especially siderophores, amylase, and caseinase production. The expression of different VF was variable at a certain salinity, i.e., at 0% NaCl, only amylase and siderophores production was observed. At 2% and 3%, the amylase was better expressed. The best expression of siderophores and caseinase was at 6% NaCl. At higher salinity, the expression of VF started to decrease. The amylase and caseinase were better expressed at pH 9.6 and siderophores at pH 7.2. Higher glucose concentrations (3%) proved to have an inhibitory effect on amylase expression and caseinase. The aerobic/anaerobic incubation conditions exhibited no significant differences in the VF expression. In conclusion, these outcomes reveal the ability of enterobacterial aquatic strains to survive in the presence of different stressors and maintain the expression of potential VF expression even in extreme environmental conditions.