Comparative Genomic Characterization of a Thailand-Myanmar Isolate, MS6, of Vibrio Cholerae O1 El Tor, Which Is Phylogenetically Related to a "US Gulf Coast" Clone

PLoS One. 2014 Jun 2;9(6):e98120. doi: 10.1371/journal.pone.0098120. eCollection 2014.


Background: The cholera outbreaks in Thailand during 2007-2010 were exclusively caused by the Vibrio cholerae O1 El Tor variant carrying the cholera toxin gene of the classical biotype. We previously isolated a V. cholerae O1 El Tor strain from a patient with diarrhea and designated it MS6. Multilocus sequence-typing analysis revealed that MS6 is most closely related to the U. S. Gulf Coast clone with the exception of two novel housekeeping genes.

Methodology/principal findings: The nucleotide sequence of the genome of MS6 was determined and compared with those of 26 V. cholerae strains isolated from clinical and environmental sources worldwide. We show here that the MS6 isolate is distantly related to the ongoing seventh pandemic V. cholerae O1 El Tor strains. These strains differ with respect to polymorphisms in housekeeping genes, seventh pandemic group-specific markers, CTX phages, two genes encoding predicted transmembrane proteins, the presence of metY (MS6_A0927) or hchA/luxR in a highly conserved region of the V. cholerae O1 serogroup, and a superintegron (SI). We found that V. cholerae species carry either hchA/luxR or metY and that the V. cholerae O1 clade commonly possesses hchA/luxR, except for MS6 and U. S. Gulf Coast strains. These findings illuminate the evolutionary relationships among V. cholerae O1 strains. Moreover, the MS6 SI carries a quinolone-resistance gene cassette, which was closely related with those present in plasmid-borne integrons of other gram-negative bacteria.

Conclusions/significance: Phylogenetic analysis reveals that MS6 is most closely related to a U. S. Gulf Coast clone, indicating their divergence before that of the El Tor biotype strains from a common V. cholerae O1 ancestor. We propose that MS6 serves as an environmental aquatic reservoir of V. cholerae O1.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Chromosomes / genetics
  • Clone Cells
  • Conserved Sequence / genetics
  • Evolution, Molecular
  • Genome, Viral / genetics
  • Humans
  • Likelihood Functions
  • Molecular Sequence Data
  • Open Reading Frames / genetics
  • Phylogeny*
  • Reference Standards
  • Synteny / genetics
  • Thailand
  • United States
  • Vibrio cholerae O1 / genetics*
  • Vibrio cholerae O1 / isolation & purification*

Associated data

  • GENBANK/AP014524
  • GENBANK/AP014525

Grant support

This work was supported by the program of Japan Initiative for Global Research Network on Infectious Diseases by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) of Japan, by Grant-in-Aid for Young Scientists (B) (No. 22710252) from the MEXT of Japan, by the Oyama Health foundation, and by the Department of Medical Sciences, the Ministry of Public Health, Thailand. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.