Application of three different methods to determine the prevalence, the abundance and the environmental drivers of culturable Vibrio cholerae in fresh and brackish bathing waters

Abstract

Aims: Three cultivation methods were used to study the prevalence and abundance of Vibrio cholerae in Eastern Austrian bathing waters and to elucidate the main factors controlling their distribution.

Methods and results: Vibrio cholerae abundance was monitored at 36 inland bathing sites with membrane filtration (MF), a standard most probable number (MPN) approach and direct plating (DP). Membrane filtration yielded the most reliable and sensitive results and allowed V. cholerae detection at 22 sites with concentrations up to 39 000 CFU per 100 ml, all belonging to serogroups other than O1 and O139 and not coding for cholera toxin and toxin coregulated pilus. Direct plating turned out as an easy method for environments with high V. cholerae abundances, conductivity was the only significant predictor of V. cholerae abundance in the bathing waters at warm water temperatures.

Conclusions: Vibrio cholerae nonO1/nonO139 are widely prevalent in Eastern Austrian bathing waters. Instead of the standard MPN approach, MF and DP are recommended for V. cholerae monitoring. Conductivity can be used as a first easy-to-measure parameter to identify potential bathing waters at risk.

Significance and impact of the study: Vibrio cholerae nonO1/nonO139 infections associated with bathing activities are an increasing public health issue in many countries of the northern hemisphere. However, there are only limited data available on the prevalence and abundance of V. cholerae in coastal and inland bathing waters. For monitoring V. cholerae prevalence and abundance, reliable and simple quantification methods are needed. Moreover, prediction of V. cholerae abundance from environmental parameters would be a helpful tool for risk assessment. This study identified the best culture-based quantification methods and a first quick surrogate parameter to attain these aims.

Keywords: Vibrio cholerae nonO1/nonO139; conductivity; cultivation; direct plating; infection; membrane filtration; most probable number.