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.

Kazuhisa Okada,Ichiro Nakagawa,Wirongrong Natakuathung,Amonrattana Roobthaisong,Shigeyuki Hamada,Fumito Maruyama,Mathukorn Na-Ubol,Siriporn Chantaroj,Bas E Dutilh

doi:10.1371/journal.pone.0098120

Abstract

BackgroundThe 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 FindingsThe 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/SignificancePhylogenetic 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.

Highlights

Vibrio cholerae, which is present in aquatic environments worldwide, is a facultatively anaerobic, asporogenous, motile, curved, or straight gram-negative rod
Growth Conditions, and DNA Isolation V. cholerae O1 El Tor serotype Ogawa strain MS6 was isolated from a Myanmanese inpatient suffering from diarrhea who was treated at a hospital located in a Thai–Myanmar border city [12]
We compared the genome sequences of MS6 with those of the prototype seventh pandemic El Tor, N16961 [22], seventh pandemic atypical El Tor, 2010EL-1786 [23], and the pre-seventh pandemic El Tor, M66-2 [24] strains deposited in the EMBL/ GenBank/DDBJ databases

Summary

Introduction

Vibrio cholerae, which is present in aquatic environments worldwide, is a facultatively anaerobic, asporogenous, motile, curved, or straight gram-negative rod. The sixth cholera pandemic (1899–1923) was caused by the classical biotype, and the ongoing seventh cholera pandemic is caused by El Tor. Several other outbreaks of cholera occurred between the sixth and seventh pandemics, and some El Tor strains were isolated and are designated pre-seventh pandemic El Tor. During the past two decades, atypical V. cholerae O1 El Tor was isolated more frequently and was spread widely [2,3,4,5,6]. During the past two decades, atypical V. cholerae O1 El Tor was isolated more frequently and was spread widely [2,3,4,5,6] These isolates produce a cholera toxin that is distinct from that expressed by El Tor. 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. Gulf Coast clone with the exception of two novel housekeeping genes

Methods

Results

Conclusion