Division of Microbiology, National Institute of Cholera and Enteric Diseases, P33 CIT Road, Scheme XM, Beliaghata, Kolkata-700010, India.
Abstracts of the papers presented at the International Conference of Indian Virological Society on “Emerging and Re-emerging viral Diseases of the Tropics and Subtropics” at Indian Agricultural Research Institute, New Delhi, India, December 11–14, 2007.
Cholera toxin (CT) is primarily responsible for massive outpouring of water and electrolytes in the form of diarrhoea among cholera patients. The genes ctxAB encode CT and are located on a mobile genetic element known as CTX genetic element. Neither the ctxAB nor the genetic element are integral part of Vibrio cholerae genome, instead acquired by lysogenic conversion of the filamentous phage CTXf. Significant variation was observed in copy numbers as well as localization of the CTX prophage among toxigenic V. cholerae strains. Organization of multiple prophage copies in either of the two or both chromosomes of V. cholerae have proven to be an important tool for understanding of the epidemiology of V. cholerae. In addition to the copy number and the localization analysis, genotyping of the CTX prophage have been widely used to demonstrate appearance and disappearance of multiple clones of epidemic causing V. cholerae O1 and O139 strains over the period of time. Genomic analysis on constituting genes of ∼7.2 kb CTX prophage revealed conserved existence of biotype specific prophages in V. cholerae O1. Analysis on the nucleotide sequences of repressor rstR and the receptor orfU of the prophages present in the clinical and the environmental toxigenic V. cholerae non-O1, non-O139 strains revealed that these CTX prophages were of different lineages to that of their epidemic counterpart.
