Occurrence and distribution of plankton-associated and free-living toxigenic Vibrio cholerae in a tropical estuary of a cholera endemic zone

NEOGI, S.B.; ISLAM, S.M.; NAIR, G.B.; LARA, R.J.

WETLANDS ECOLOGY AND MANAGEMENT

SPRINGER

Lugar: Berlin; Año: 2012 vol. 20 p. 271 - 285

0923-4861

Abstract Cholera epidemics are thought to beinfluenced by changes in populations of estuarineVibrio cholerae. We investigated the abundanceand distribution of this bacterium, as ??free-living??( lm fraction) and associated with microphytoplankton([20 lm) or zooplankton ([60 lm), in theKarnaphuli estuary of Bangladesh during pre- andpost-monsoon seasons. Cultivable Vibrio populationswere *102?104 colony forming units (CFU) ml-1 inthe high saline zone (19?23 practical salinity unit,PSU) and declined in freshwater (A CFU ml-1).Culture independent detection of toxigenic V. choleraeO1 and O139 serogroups revealed a higherabundance of ??free-living?? (104?105 cells l-1) thanthose attached to plankton (101?103 cells l-1). However,??free-living?? O1 and O139 cells were sometimesabsent in the medium saline and freshwater areas(0.0?11 practical salinity unit [PSU]). In contrast,plankton samples always harbored these serogroupsdespite changes in salinity and other physico-chemicalproperties. Microphytoplankton and zooplanktonwere dominated by diatoms and blue-green algae,and copepods and rotifers, respectively. Toxigenic V.cholerae abundance did not correlate with planktonabundance or species but had a positive correlationwith chitin in the lm fraction, where suspendedparticulate matter (SPM), V. cholerae and chitinconcentrations were highest. C:N ratios indicated thatorganic matter in SPM originated predominantly fromplankton. The differential occurrence of ??free-living??and attached V. cholerae suggests a pivotal function ofplankton in V. cholerae spreading into freshwaterareas. The probable association of this pathogen withorganisms and particles in the nanoplankton ( lm)fraction requires validation of the concept of the ??freeliving?? state of V. cholerae in aquatic habitats