Abstract
Vibrio metoecus is a recently described aquatic bacterium and opportunistic pathogen, closely related to and often coexisting with Vibrio cholerae. To study the relative abundance and population dynamics of both species in aquatic environments of cholera-endemic and cholera-free regions, we developed a multiplex qPCR assay allowing simultaneous quantification of total V. metoecus and V. cholerae (including toxigenic and O1 serogroup) cells. The presence of V. metoecus was restricted to samples from regions that are not endemic for cholera, where it was found at 20% of the abundance of V. cholerae. In this environment, non-toxigenic O1 serogroup V. cholerae represents almost one-fifth of the total V. cholerae population. In contrast, toxigenic O1 serogroup V. cholerae was also present in low abundance on the coast of cholera-endemic regions, but sustained in relatively high proportions throughout the year in inland waters. The majority of cells from both Vibrio species were recovered from particles rather than free-living, indicating a potential preference for attached versus planktonic lifestyles. This research further elucidates the population dynamics underpinning V. cholerae and its closest relative in cholera-endemic and non-endemic regions through culture-independent quantification from environmental samples.
Highlights
Vibrio cholerae is an autochthonous aquatic bacterium [1] which shows variable physiologies, from non-pathogenic to extremely virulent strains capable of causing a life-threatening diarrheal infection: cholera [2]
V. metoecus, as well as toxigenic and O1 serogroup V. cholerae, all sampled from their natural aquatic environments (Figure 1)
The viuB and mcp markers are specific to V. cholerae and V. metoecus and present in single copies, facilitating quantification of the absolute abundance of these two species
Summary
Vibrio cholerae is an autochthonous aquatic bacterium [1] which shows variable physiologies, from non-pathogenic to extremely virulent strains capable of causing a life-threatening diarrheal infection: cholera [2]. According to the World Health Organization (2016), every year, 1.4 to 4 million people are infected with cholera, and 21,000 to 143,000 people die from this disease [3]. This species comprises over 200 serogroups [4], but strains of the O1 and O139 serogroups are distinguished as the most virulent, having caused some of the most devastating pandemics in human history [5,6,7,8]. During 2005, the O139 serogroup was isolated sporadically from both clinical and environmental samples in Bangladesh but there was no reported large-scale outbreak of cholera caused by this serogroup. V. cholerae O1 has been prevalent in the Ganges Delta for several hundred years; this remains the only place in the world where cholera has been continually endemic since the first modern pandemic in 1817 [14,15]
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