Dissemination of Vibrio cholerae O1 isolated from Odisha, India

Spectrum of ctxB genotypes, antibiogram profiles and virulence genes of Vibrio cholerae serogroups isolated from environmental water sources from Odisha, India

BACKGROUND

The present study reports on the comprehensive analysis of Vibrio cholerae O1 and non-O1/non-O139 serogroups isolated from environmental water sources during cholera outbreaks, epidemics and surveillance studies between years 2007 to 2019 from different districts of Odisha, India.

METHODS

A total of 85 stocked cultures of V. cholerae O1 and non-O1/non-O139 strains were analyzed for different ctxB genotypes, toxic genes, antibiogram profiles through PCR assays and pulsotyped by pulsed-field gel electrophoresis (PFGE).

RESULTS

From all V. cholerae strains tested, 51 isolates were O1 Ogawa and the rest 34 strains were non-O1/non-O139. All the V. cholerae O1 strains were altered El Tor variants carrying ctxB1, ctxB3 and ctxB7 genotypes. However, only ctxB1 genotypes were present in V. cholerae non-O1/non-O139. Though non-O1/non-O139 strains were negative by O1 antisera, 20% strains were positive for rfbO1 gene by PCR assay. All the V. cholerae isolates possessed a variety of virulence genes including ace, ctxAB, toxR, zot, hlyA which were in higher percentage in the case of V. cholerae O1. The Vibrio cholerae O1 and non-O1-/non-O139 strains showed multiple antibiotic resistances in 2007 and 2012. The PCR detection of four resistance associated genes (strB, dfrA1, sulll, SXT) confirmed higher prevalence in V. cholerae non-O1/non-O139 strains. The PFGE analysis revealed 3 pulsotypes having 93% similarity among V. cholerae O1 strains.

CONCLUSION

This study indicates the changing epidemiology, antibiogram patterns and continuous genetic variation in environmental V. cholerae strains of Odisha over the years. So continuous surveillance is necessary to understand the changing patterns of V. cholerae different serogroups isolated from stool and water samples from Odisha.

Origin and Dissemination of Altered El Tor Vibrio cholerae O1 Causing Cholera in Odisha, India: Two and Half Decade's View

The origin, spread and molecular epidemiology of altered El Tor Vibrio cholerae O1 strains isolated from cholera outbreaks/surveillance studies between 1995 and 2019 from different district of Odisha were analyzed. The stock cultures of V. cholerae O1 strains from 1995 to 2019 were analyzed through molecular analysis using different PCR assays and pulse field gel electrophoresis (PFGE) analysis. The spread map (month, year and place) was constructed to locate the dissemination of altered El Tor variants of V. cholerae O1 in this region. A total of 13 cholera outbreaks were caused by V. cholerae O1 Ogawa biotype El Tor carrying ctxB1 and ctxB7 genotypes. The ctxB1 alleles of V. cholerae O1 mostly confined to the coastal areas, whereas the ctxB7 genotypes, though originating in the coastal region of Odisha, concentrated more in the tribal areas. The positive correlation between virulence-associated genes (VAGs) was found through Pearson’s correlation model, indicative of a stronger association between the VAGs. The clonal relationship through PFGE between ctxB1 and ctxB7 genotypes of V. cholerae O1 strains exhibited 80% similarity indicating single- or multi-clonal evolution. It is evident from this study that the spread of multidrug-resistant V. cholerae O1-altered El Tor was dominant over the prototype El Tor strains in this region. The origin of altered El Tor variants of V. cholerae O1 occurred in the East Coast of Odisha established that the origin of cholera happened in the Gangetic belts of Bay of Bengal where all new variants of V. cholerae O1 might have originated from the Asian countries.