Vibrio cholerae Classical Biotype Strains Reveal Distinct Signatures in Mexico

Abstract

f Vibrio cholerae O1 classical (CL) biotype caused the fifth and sixth pandemics, and probably the earlier cholera pandemics, before the El Tor (ET) biotype initiated the seventh pandemic in Asia in the 1970s by completely displacing the CL biotype. Although the CL biotype was thought to be extinct in Asia and although it had never been reported from Latin America, V. cholerae CL and ET biotypes, including a hybrid ET, were found associated with areas of cholera endemicity in Mexico between 1991 and 1997. In this study, CL biotype strains isolated from areas of cholera endemicity in Mexico between 1983 and 1997 were characterized in terms of major phenotypic and genetic traits and compared with CL biotype strains isolated in Bangladesh between 1962 and 1989. According to sero-and biotyping data, all V. cholerae strains tested had the major phenotypic and genotypic characteristics specific for the CL biotype. Antibiograms revealed the majority of the Bangladeshi strains to be resistant to trimethoprim-sulfamethoxazole, furazolidone, ampicillin, and gentamicin, while the Mexican strains were sensitive to all of these drugs, as well as to ciprofloxacin, erythromycin, and tetracycline. Pulsed-field gel electrophoresis (PFGE) of NotI-digested genomic DNA revealed characteristic banding patterns for all of the CL biotype strains although the Mexican strains differed from the Bangladeshi strains in 1 to 2 DNA bands. The difference was subtle but consistent, as confirmed by the subclustering patterns in the PFGE-based dendrogram, and can serve as a regional signature, suggesting the pre-1991 existence and evolution of the CL biotype strains in the Americas, independent from Asia.

Occurrence in Mexico, 1998–2008, of Vibrio cholerae CTX + El Tor carrying an additional truncated CTX prophage

“…In Mexico, both V. cholerae CL and ET biotype progenitors were isolated during cholera outbreaks, together with altered ET, dominant between 1991 and 1997 (7). The consistent association of V. cholerae CL, ET, and altered ET with local cholera outbreaks in the Americas between 1991 and 1997 and their occurrence in the natural aquatic environment, together with non-O1 phenotypically and genetically O1 CL, suggest that the emergence of altered V. cholerae ET has occurred locally in Mexico (7,17) and is not clonal expansion from endemic regions of Asia (14), as has been proposed for Africa (5). According to our data, V. cholerae altered ET was not isolated in Mexico after 2000 nor was the CL biotype reported in Mexico until 1997 (7).…”

The Seventh Pandemic Vibrio cholerae O1 El Tor Isolate in China Has Undergone Genetic Shifts

“…Another study (6) reported a hybrid CTX⌽ isolate carrying El Tor rstR and classical ctxB that has completely replaced the El Tor biotype in Kolkata, India, since 1995. Other atypical El Tor isolates have been reported in other countries in Asia (7,8) and Africa (9,10), as well as in Mexico (11). Previously, we identified three novel El Tor variants from China in which the ctxB genotype was different from known genotypes (12).…”

Outbreak of Cholera Caused by <i>Vibrio cholerae</i> O1 El Tor Variant Strain in Bihar, India

“…Background subtraction and gel normalization were performed; the fingerprint patterns were then subjected to typing on the basis of banding similarity and dissimilarity, using the Dice similarity coefficient and cluster analysis based on the unweighted-pair-group method using average linkages (UPGMA), as recommended by the software manufacturer (17). The results were graphically represented as dendrograms.…”