Investigating the virulence some Vibrio cholerae strains isolated in Vietnam by evaluating the production of several extracellular enzymes and the presence of CTX genes.

Abstract

Vibrio cholerae, causative agent of severe watery diarrhea re-emerged in 2007 in Vietnam and since then caused several large cholera outbreaks threatening public health. Clinical data indicated a change in the virulence of V. choleraee strains associated with the outbreaks, however evidence is still lacking. To fulfill this gap, a representative collection of five V. cholerae strains isolated from diarrheal patients in southern Vietnam between 2010 and 2012 was investigated. They were examined for the production of extracellular protease, hemolysin and lipase enzyme activities and presence of cholera toxin gene by using PCR method. The enzymatic activities were tested on solid media supplemented with the corresponding substrates. The protease activity and hemolysis activity of V. cholerae strains in 2010 and 2012 were not significantly different. Proteolytic ring ranged from 2.67±0.57 mm (104-2012) to 3.67±1.15 mm (242-2012) and hemolytic ring was from 2mm (242-2012) to 3 mm (104-2012). Lipase activity was absent in strain 42-2010 and present in 4 remaining strains (41-2010, 242-2012, VCTC-2012 and 104-2012), ranging from 2mm (104-2012) to 3.5±0.71mm (41-2010 and VCTC-2012). In addition, the PCR result of ctx genes showed that, among these 5 clinical strains, 3 isolates had ctxA and ctxB genes (VCTC-2012, 41-2010, and 242-2012), 1 isolate just contained ctxA but not ctxB (42-2010) and impressively, 1 isolate did not contain any ctx genes (104-2012). These results indicated that the virulence of V. cholerae may not only depend on their cholera toxin but also on other factors which should be further investigated. Key words: Vibrio cholerae, protease, hemolysin, lipase, cholera toxin, virulence factors