Virulence genes of clinical Vibrio cholerae O1 isolates in Thailand and their ribotypes

Genotypic and PFGE/MLVA analyses of Vibrio cholerae O1: geographical spread and temporal changes during the 2007-2010 cholera outbreaks in Thailand

BACKGROUND

Vibrio cholerae O1 El Tor dominated the seventh cholera pandemic which occurred in the 1960s. For two decades, variants of V. cholerae O1 El Tor that produce classical cholera toxin have emerged and spread globally, replacing the prototypic El Tor biotype. This study aims to characterize V. cholerae O1 isolates from outbreaks in Thailand with special reference to genotypic variations over time.

METHODS/FINDINGS

A total of 343 isolates of V. cholerae O1 from cholera outbreaks from 2007 to 2010 were investigated, and 99.4% were found to carry the classical cholera toxin B subunit (ctxB) and El Tor rstR genes. Pulsed-field gel electrophoresis (PFGE) differentiated the isolates into 10 distinct pulsotypes, clustered into two major groups, A and B, with an overall similarity of 88%. Ribotyping, multiple-locus variable-number tandem-repeat analysis (MLVA), and PCR to detect Vibrio seventh pandemic island II (VSP-II) related genes of randomly selected isolates from each pulsotype corresponded to the results obtained by PFGE. Epidemiological investigations revealed that MLVA type 2 was strongly associated with a cholera outbreak in northeastern Thailand in 2007, while MLVA type 7 dominated the outbreaks of the southern Gulf areas in 2009 and MLVA type 4 dominated the outbreaks of the central Gulf areas during 2009-2010. Only MLVA type 16 isolates were found in a Thai-Myanmar border area in 2010, whereas those of MLVA types 26, 39, and 41 predominated this border area in 2008. Type 39 then disappeared 1-2 years later as MLVA type 41 became prevalent. Type 41 was also found to infect an outbreak area.

CONCLUSIONS

MLVA provided a high-throughput genetic typing tool for understanding the in-depth epidemiology of cholera outbreaks. Our epidemiological surveys suggest that some clones of V. cholerae O1 with similar but distinctive genetic traits circulate in outbreak sites, while others disappear over time.

A cholera outbreak of the Vibrio cholerae O1 El Tor variant carrying classical CtxB in northeastern Thailand in 2007

Cholera outbreaks occurred in Thailand in 2007. Isolates from the northeastern regions were analyzed. Interestingly, the outbreak strain was identified as biotype El Tor; serotype Ogawa with cholera toxin B subunit gene (ctxB) of the classical type and CTX prophage repressor gene of the El Tor type. The clone was genetically closely related to pulsotype H, which is predominantly found in India. It was probably introduced into Thailand recently.

Application of PCR-Based DNA Fingerprinting Techniques for the Genetic Differentiation of Vibrio cholerae Non-01/Non-0139 Isolates from Kuching, Sarawak

Fifty-four Vibrio cholerae non-01/non-0139 isolates were evaluated for their genetic diversity via randomly amplified polymorphic DNA-PCR (RAPD-PCR), enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR) and BOX-PCR assays. Based on the various PCR fingerprints, the V. cholerae isolates were successfully differentiated into 39 types by RAPD-PCR, 43 types by ERIC-PCR, and 38 types by the BOX PCR, with the overall average polymorphic distances observed to be at 0.593, 0.527 and 0.504, respectively. The Simpson’s index of diversity of the isolates based on the fingerprinting analyses indicated that these DNA fingerprinting methods have high discriminatory power 0.986 (RAPD-PCR), 0.992 (ERIC-PCR) and 0.983 (BOX-PCR), and could be used independently or as supplements to other methods for the epidemiological investigation of the V. cholerae from water and seafood sources. The dendrograms constructed also showed that the V. cholerae isolates were clustered into several main clusters and sub-clusters, suggesting that different strains were circulating in the water environment and in the seafood sources. We conclude that molecular genotyping of V. cholerae isolates from surface water and seafood samples in Kuching, Sarawak (Malaysia) enabled high level observation of clonal diversity within V. cholerae isolates, and is directly applicable for the molecular epidemiological studies of the V. cholerae isolates.