Interaction of Vibrio cholerae non-O1/non-O139 with copepods, cladocerans and competing bacteria in the large alkaline lake Neusiedler See, Austria

Abstract

Vibrio cholerae is a human pathogen and natural inhabitant of aquatic environments. Serogroups O1/O139 have been associated with epidemic cholera, while non-O1/non-O139 serogroups usually cause human disease other than classical cholera. V. cholerae non-O1/non-O139 from the Neusiedler See, a large Central European lake, have caused ear and wound infections, including one case of fatal septicaemia. Recent investigations demonstrated rapid planktonic growth of V. cholerae non-O1/non-O139 and correlation with zooplankton biomass. The aim of this study was to elucidate the interaction of autochthonous V. cholerae with two dominant crustacean zooplankton species in the lake and investigate the influence of the natural bacterial community on this interaction. An existing data set was evaluated for statistical relationships between zooplankton species and V. cholerae and co-culture experiments were performed in the laboratory. A new fluorescence in situ hybridisation protocol was applied for quantification of V. cholerae non-O1/non-O139 cells, which significantly reduced analysis time. The experiments clearly demonstrated a significant relationship of autochthonous V. cholerae non-O1/non-O139 with cladocerans by promoting growth of V. cholerae non-O1/non-O139 in the water and on the surfaces of the cladocerans. In contrast, copepods had a negative effect on the growth of V. cholerae non-O1/non-O139 via competing bacteria from their surfaces. Thus, beside other known factors, biofilm formation by V. cholerae on crustacean zooplankton appears to be zooplankton taxon specific and may be controlled by the natural bacterial community.

Figure 1

Representative example (25°C experiment) of the development of FISH-based V. cholerae non-O1/non-O139 concentrations in 800-ml microcosms amended with 0 (control), 50 and 150 cladocerans (Clad). a sterile filtered lake water (‘without initial competition’); b 2-μm filtered lake water (‘with competition’). Small inserts: development of the natural bacterial community (counted as total bacteria less V. cholerae non-O1/non-O139 cells) during the experiment. Error bars indicate the standard error of counts derived from 20 microscopic fields and are mostly smaller than the data point

Figure 2

Representative example (15°C experiment) of the development of FISH-based V. cholerae non-O1/non-O139 concentrations in 800-ml microcosms amended with 0 (control), 50 and 150 copepods (Cop). a sterile filtered lake water (‘without initial competition’) b 2-μm filtered lake water (‘with competition’). Small inserts: development of the natural bacterial community (counted as total bacteria less V. cholerae non-O1/non-O139 cells) during the experiment. Error bars indicate the standard error of counts derived from 20 microscopic fields and are mostly smaller than the data point