Abstract
Pathogenic non-O1/non-O139 Vibrio cholerae strains can cause sporadic outbreaks of cholera worldwide. In this study, multilocus sequence typing (MLST) of seven housekeeping genes was applied to 55 non-O1/non-O139 isolates from clinical and environmental sources. Data from five published O1 isolates and 17 genomes were also included, giving a total of 77 isolates available for analysis. There were 66 sequence types (STs), with the majority being unique, and only three clonal complexes. The V. cholerae strains can be divided into four subpopulations with evidence of recombination among the subpopulations. Subpopulations I and III contained predominantly clinical strains. PCR screening for virulence factors including Vibrio pathogenicity island (VPI), cholera toxin prophage (CTXΦ), type III secretion system (T3SS), and enterotoxin genes (rtxA and sto/stn) showed that combinations of these factors were present in the clinical isolates with 85.7% having rtxA, 51.4% T3SS, 31.4% VPI, 31.4% sto/stn (NAG-ST) and 11.4% CTXΦ. These factors were also present in environmental isolates but at a lower frequency. Five strains previously mis-identified as V. cholerae serogroups O114 to O117 were also analysed and formed a separate population with V. mimicus. The MLST scheme developed in this study provides a framework to identify sporadic cholera isolates by genetic identity.
Highlights
Vibrio cholerae is best known for its capacity to cause pandemic cholera and continues to be a major health threat, highlighted by a recent cholera outbreak in Haiti [1,2]
We developed a new multilocus sequence typing (MLST) scheme for V. cholerae that was based on fragments of seven housekeeping genes
An additional five V. mimicus strains, which were initially identified as V. cholerae, were included
Summary
Vibrio cholerae is best known for its capacity to cause pandemic cholera and continues to be a major health threat, highlighted by a recent cholera outbreak in Haiti [1,2]. O139 Bengal strain, which is known to be a derivative of the 7th pandemic causing epidemic cholera, all major outbreaks and pandemic cholera have been of the O1 serogoup [3,4]. Non-O1/non-O139 sporadic outbreaks have been quite common in Bangladesh and India [7,11,12,13] and have occurred in Peru [5], Thailand [14] and more recently the USA [9,10].
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