Survival of enteric bacteria and viruses in Lake Kinneret, Israel

The survival of indicator bacteria (Escherichia coli and enterococci) and polio viruses in Lake Kinneret were studied at different seasons, under various light and oxygen-sulfide regimes. Survival of the bacteria was dependent on environmental conditions, whereas numbers of polioviruses (pfu) were high for all the seasons studied. A large discrepancy was often noted between the methods to determine bacterial numbers (plate counts on selected media and direct counts). Under certain conditions, bacterial plate counts dropped, even though the direct counts remained the same or increased. These “inactive” or non-culturable cells were still viable, since glucose uptake activity was not impaired in such bacteria. Inactivation of E. coli appears to be initiated by light, although sulfide also renders the cells non-culturable. Survival patterns of E. coli and polioviruses in the lake were similar, suggesting that for the Kinneret, at least, E. coli is a better indicator of fecal pollution than the enterococci.