Experimental Model of Enterococcus Faecalis Surveillance in Recreational Waters of the Southern Coast of the Caspian Sea: a Case Study in a Microcosm

摘要

This study was conducted to survey the presence and survival of Enterococcus faecalis as a microbial index in the recreational waters of the southern Caspian Sea using a microcosm as an experimental model. The salinity of about 1% and the self-cleansing properties of the Caspian Sea make it feasible to use this microorganism as a measure of water quality in the region. Efforts were directed at maintaining the physicochemical characteristics of the sampled water in the microcosm close to the natural readings. The median of these values during fall for example were as follows: DO 9.6, pH 7.8, temperature 11 °C and turbidity of 4.43. The number of E. faecalis cells from sampled water was estimated using membrane filtration method and MFESA, an enterococcus selective medium which contains triphenyl tetrazolium chloride. Results from monthly sampling in spring and summer as well as single sampling during fall and winter on site indicate the persistence of the bacteria in water. Subsequently, the survival period of Enterococcus faecalis in a microcosm resembling an aquarium was studied under conditions (such as pH, temperature, soluble oxygen and sunlight intensity) which mimicked the natural sea environment during fall. In a fourteen day period, the concentration of the Enterococcus faecalis cells dropped from 35000 CFU/100 ml to nearly 0. However, the observed 10 fold reduction in the bacterial count during a 4 day period accompanied fluctuations. These results showed the rate of self-cleansing in the coastal recreational waters of the Caspian Sea. Nevertheless, the persistence of this bacterium in these recreational waters all year round is an indication of high microbial pollution.