Molecular comparison of toxigenic clinical & non-toxigenic environmental strains of Vibrio cholerae O1 Ogawa isolated during an outbreak of cholera in South India

Background and Objectives: While investigating a cholera outbreak in south India, toxigenic and nontoxigenic strains of Vibrio cholerae O1 were isolated from patients and from the environment, respectively. This study was performed to compare the genetic relatedness of the patient and environmental strains to determine clonal relationships among these strains and thereby determine the source of the cholera outbreak. Methods: The 16 strains of V. cholerae isolated from hospitalized patients and 8 environmental V. cholerae strains isolated from the environment were phenotypically and genotypically characterized using a variety of standard techniques. Results: Sixteen toxigenic clinical strains and 2 nontoxigenic environmental strains belonged to O1 serogroup, Ogawa serotype and El Tor biotype. The remaining 6 nontoxigenic environmental strains were classified as non-O1, non-O139 V. cholerae. The drug resistance pattern of the clinical and environmental strains of V. cholerae showed marked differences with the patient strains being resistant to more number of drugs as compared to the environmental strains. DNA fingerprinting of the strains showed considerable diversity between toxigenic clinical and nontoxigenic environmental O1 Ogawa isolates and between the O1 and non-O1, non-O139 isolates. Interpretation and Conclusions: In this outbreak of cholera, the O1 strains of V. cholerae from clinical and environmental sources belonged to two different clones and the environmental strains could perhaps be the future cholera outbreak causing clones