title: 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.
abstract: 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.
  
  
  RESULTS
  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
  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.
authors.affiliation: Thailand-Japan Research Collaboration Center on Emerging and Re-emerging Infections (RCC-ERI), Nonthaburi, Thailand; Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan.
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Okada
authors.affiliation: Thailand-Japan Research Collaboration Center on Emerging and Re-emerging Infections (RCC-ERI), Nonthaburi, Thailand.
authors.forename: Mathukorn
authors.initials: M
authors.lastname: Na-Ubol
authors.affiliation: Thailand-Japan Research Collaboration Center on Emerging and Re-emerging Infections (RCC-ERI), Nonthaburi, Thailand.
authors.forename: Wirongrong
authors.initials: W
authors.lastname: Natakuathung
authors.affiliation: Thailand-Japan Research Collaboration Center on Emerging and Re-emerging Infections (RCC-ERI), Nonthaburi, Thailand.
authors.forename: Amonrattana
authors.initials: A
authors.lastname: Roobthaisong
authors.affiliation: Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Fumito
authors.initials: F
authors.lastname: Maruyama
authors.affiliation: Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, Tokyo, Japan.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Nakagawa
authors.affiliation: National Institute of Health, Department of Medical Sciences (DMSc), Ministry of Public Health, Nonthaburi, Thailand.
authors.forename: Siriporn
authors.initials: S
authors.lastname: Chantaroj
authors.affiliation: Thailand-Japan Research Collaboration Center on Emerging and Re-emerging Infections (RCC-ERI), Nonthaburi, Thailand; Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan.
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Hamada
mesh_terms: D002875:Chromosomes / Q000235:genetics; D002999:Clone Cells; D017124:Conserved Sequence / Q000235:genetics; D019143:Evolution, Molecular; D016679:Genome, Viral / Q000235:genetics; D006801:Humans; D016013:Likelihood Functions; D008969:Molecular Sequence Data; D016366:Open Reading Frames / Q000235:genetics; D010802:Phylogeny; D012015:Reference Standards; D026801:Synteny / Q000235:genetics; D013785:Thailand; D014481:United States; D041241:Vibrio cholerae O1 / Q000235:genetics* / Q000302:isolation & purification*