cholerae O1/O139 cluster that are absent in non-toxigenic V. cholerae O1 isolates. Previous studies have shown the presence of non-toxigenic V. cholerae O1 strains in the environment and in humans [6, 18, 21, 27]. Serotyping is therefore not a reliable method for the identification of toxigenic and epidemic V. cholerae O1/O139 strains. Furthermore,

V. cholerae non-O1/O139 isolates have been described that are able to produce the cholera toxin but are not considered epidemic because only strains of serogroup O1/O139 and O37 are able to cause large outbreaks [6, 21, 27]. Thus, the presence of the ctxAB and tcpA genes is not the only prerequisite for epidemic potential. We have found that OmpU from epidemic V. cholerae has a unique and conserved amino acid sequence, which not only can be used in the presented BMN 673 MALDI-TOF selleck products MS assay, but also in a targeted PCR method. The difference in OmpU sequences between epidemic and non-epidemic isolates as well as the sequence variation among

non-epidemic strains raises the question of whether this variation is due to genetic drift or specific adaptation to different niches. From a DNA alignment of a 5,000 bp region surrounding the ompU gene of seven epidemic O1 and five non-toxigenic strains (Additional file 2: Figure S2), it became clear that the ompU gene has undergone a higher mutation rate compared to the surrounding genes and intergenic regions. This suggests that OmpU has been subject to selective pressure, possibly as a result of adaptation

to particular niches. A role for OmpU in host colonization has been proposed, potentially in enhancing attachment to epithelia in the gut or conferring resistance to bile, ionic detergents and organic acids [28–31]. Based on a three-dimensional model of V. cholerae OmpU, most of the variable regions are located in regions exposed to the outside of the cell (not shown), which supports a host-dependent variation science hypothesis. Conclusions Each year more than half a million people develop cholera. To reduce the burden of this devastating disease, new strategies must be developed. By minimizing the spread of the pathogen, the disease incidence can be reduced. To control a cholera outbreak, quick identification at the start of a potential outbreak and rapid discrimination between epidemic V. cholerae and other V. cholerae isolates could be helpful in introducing effective hygienic measurements [32, 33]. To this point, discrimination between the toxigenic and epidemic V. cholerae strains and the non-pathogenic or less pathogenic strains has required multiple tests. The deviation in amino acid sequences of OmpU homologs of non-epidemic strains from those of the OmpU protein of strain N16961, which is conserved among almost all epidemic strains, makes OmpU an important biomarker to discriminate between epidemic V. cholerae O1/O139 and other V. cholerae isolates.