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 (10**4-10**5 cells l-1) thanthose attached to plankton (10**1-10**3 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-livingand 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 fraction requires validation of the concept of the freeliving  state of V. cholerae in aquatic habitats