Molecular study of Vibrio cholerae O1 serotype Ogawa and non-O1/139 isolated from the environment in Tunisia

Objective: Vibrio cholerae represents an enormous public health burden, especially in developing countries. In this study we report for the first time the incidence of V. cholerae isolated in Tunisia during a 6-year period (2007-2012). Methods: Forty-six V. cholerae isolates were isolated from wastewater, patients and aquatic environment. The isolates were identified as O1 Ogawa (n=16) and non-O1/non-O139 (n=30) and were investigated by determining the antibiotic susceptibility, virulence genes, plasmid content, and genetic relationship by PFGE. Results: 84.7 % of isolates were susceptible to all antibiotics, 8.7 % and 6.5% were resistant to 2 and 3 antibiotics, respectively.  Fifteen non-O1/139 isolates harbored plasmids and a common ca-7kb plasmid was observed. The PCR for virulence-associated genes within the CTX element and the VPI gene cluster showed that ctxA , zot , and tcpA genes were detected each in 75 % of isolates; the ace gene in 50% of isolates. In non-O1/139 isolates, ace gene was amplified in 43.3% of isolates and ctxA , tcpA , and zot genes were found each in 6.6% of isolates. The clinical non-O1 isolates were negative for tested genes. For V. cholerae O1 isolates, three virulence-genes combination were detected: ace-ctxA - tcpA - zot (7 isolates), ctxA - tcpA-zot (5 isolates), and ace-ctxA (one isolate). PFGE owed five pulsotypes, among which the majority of isolates clustered in the pulsotype A. Conclusions: The occurrence of toxigenic V. cholerae isolates in treated wastewater and aquatic environment is worrisome and warrant for a risk of possible biodiversity and human infection in the future.