Molecular Analysis of Non-O1, Non-O139 Vibrio cholerae Associated with an Unusual Upsurge in the Incidence of Cholera-Like Disease in Calcutta, India

Abstract

There was an inexplicable upsurge in the incidence of non-O1, non-O139 Vibrio cholerae among hospitalized patients admitted to the Infectious Diseases Hospital, Calcutta, India, between February and March 1996. Of the 18 strains of V. cholerae isolated during this period, 15 belonged to the non-O1, non-O139 serogroups (4 belonged to O144, 3 belonged to O11, 1 each belonged to O6, O8, O12, O19, O39, and O58, and 2 strains could not be typed), 2 belonged to the O139 serogroup, and 1 belonged to the O1 serogroup. Cell-free culture supernatants of 13 representative non-O1, non-O139 V. cholerae strains evoked a distinct cytotoxic effect on CHO and HeLa cells, and the strains examined produced the nonmembrane-damaging cytotoxin. By several PCR assays, it was determined that none of the non-O1, non-O139 strains were positive for the ctxA, zot, ace, andtcpA genes and for the genes representing the heat-labile toxin, heat-stable toxin, and verotoxin of Escherichia coli and the various variants of these genes. Studies on the clonality of non-O1, non-O139 V. cholerae strains by restriction fragment length polymorphism (RFLP) analysis of rRNA genes and of other genes (hlyA, hlyU,hlx, toxR, and attRS1) and by pulsed-field gel electrophoresis (PFGE) collectively indicate that the upsurge which occurred in February and March 1996 was caused by strains belonging to different clones. Overall, there was an excellent correlation between the results of ribotyping, RFLP analysis of various genes, and PFGE, with strains belonging to a particular serogroup showing nearly identical restriction patterns and PFGE profiles. It is clear from this study that some serogroups of V. cholerae can cause diarrhea by a mechanism quite different from that of toxigenic V. cholerae O1 and O139, and we have proposed the nomenclature of enteropathogenic V. cholerae to include these serogroups.

Gene Analysis of Vibrio cholerae NAGV14 Pilus and Its Distribution

“…V. cholerae non-Ol, non-0139 strains, on the other hand, rarely express TCP or contain the tcpA gene (9). Interestingly, Sharma et al described as enteropathogenic V. cholerae (EPVC), serogroups of non-O 1, non-0139 V. cholerae that do not possess the CTX genetic element but that can cause diarrhea in humans by an unknown mechanism (32).…”

Characterization of non-membrane-damaging cytotoxin of non-toxigenic Vibrio cholerae O1 and its relevance to disease

“…Our previous studies have shown that the amount of NMDCY produced by strains of V. cholerae vary widely [15]. Therefore, it appears that strains of V. cholerae which produce NMDCY above a certain amount are capable of inducing diarrhea which might explain why certain strains of V. cholerae non-O1 non-O139 devoid of CT are associated with sporadic diarrhea [12,34]. One means to assess the contribution of NMDCY to the secretory response induced by bacterial cells would be to compare a mutant devoid of NMDCY and such a mutant is currently being constructed.…”

Septaplex PCR assay for rapid identification ofVibrio choleraeincluding detection of virulence andintSXT genes

“…Vibrio cholerae O1 or O139 can be detected rapidly using probes or primers that use the rfb region responsible for O-antigen biosynthesis (Albert et al, 1997;Hoshino et al, 1998). This might not be the case for non-O1, non-O139 strains diagnosed as the causative agent of diarrhea cases in the Indian subcontinent and elsewhere (Bagachi et al, 1993;Dalsgaard et al, 1995;Rudra et al, 1996;Sharma et al, 1998). From a diagnostic point of view, toxigenicpathogenic and nontoxigenic-nonpathogenic strains of V. cholerae can be differentiated by the presence of CT and the toxin coregulated pilus genes.…”