Cholera Toxin (CTX) Genetic Element in\ud Vibrio cholerae 0139

摘要

PFGE analysis of the Notl- and Sfil-digested genome of Virbrio cholerae 0139\udstrains isolated from different epidemic regions of India showed that all the\udstrains are of clonal origin and the genome size is about 2.2 Mb. An analysis of\udthe electrophoretic profiles of the genome of 0139 strains, the RFLP of the\udcholera toxin (age)ne and Southern blot hybridization of Notidigested\udgenomes of classical, El Tor and 0139 with a Noti-linking clone of classical\udstrain 5698, suggest that these strains closely resemble V. cholerae 01 biotype\udEl Tor, but are widely different from the classical 01 vibrios. Using restriction\udenzymes which cleave a single site in either the core region or in the direct\udrepeat sequence (RS) of the CTX genetic element, it has been shown that the\udgenome of most of the 0139 strains has two copies of the ctx gene in tandem\udconnected by two RSs. The chromosomal location of the CTX genetic element\udin the 0139 strain is the same as that reported for El Tor vibrios. The\udorganization of the virulence gene cassettes in different 0139 strains shows\udgenetic heterogeneity in the population. Whilst most of the epidemic strains\udhave two copies of the CTX genetic element, in some strains the number of\udelements has been amplified and in at least one strain a single copy of the\udelement has been deleted.