Modelling enteric bacteria survival in aquatic systems

Abstract

Enteric bacteria in natural and drinking waters present an important health risk. Adequate modelling of the survival of enteric bacteria in such systems can provide a valuable tool in assessing water quality. Herein, the survival curves of two enteric bacteria, Escherichia coli and Enterococcus faecalis, in fresh and marine waters were studied. Both, colony-forming units (CFU) and total number of enteric bacteria were analyzed. Log-linear (LL) and other nonlinear (ONL) (Gompertz and Logistic) models were compared; with the premise that the best-fitting model of predicted survival should deviate least from the experimental data. In 68% of cases ONL models gave statistically lower deviations than LL models; LL models never fitted the experimental data significantly better than ONL models. Data obtained under different experimental conditions, such as different enteric bacterial species, different ecosystems, decay of CFU number, or decay of total number of enteric bacteria, were analyzed separately and together. Separately analyzed data were in general agreement with the overall data set. Significant correlations were observed between the parameters estimated from the studied models. The commonly used parameter, T90, correlated with both the lag phase and the decay rate of the survival curves. ONL models, as well as fitting significantly better (P<0.05) to experimental data, provided information about the lag phase (time needed for a significant decrease in enteric bacterial number), the decay rate and the asymptote (final enteric bacterial concentration) of the survival curves. Furthermore, ONL models allow comparisons between different experiments, bacterial strains or species, and aquatic systems.