A MICROCOSM STUDY OF THE SURVIVAL OF ESCHERICHIA-COLI AND SALMONELLA-TYPHIMURIUM IN BRACKISH-WATER

The study of the survival of Escherichia coli and Salmonella typhimuri um in sewage treated by stabilization ponds, and then mixed more or le ss rapidly with coastal marine water, has been experimentally tested i n microcosms (membrane diffusion chambers). The results obtained show that under the same experiment conditions (slow saline, marine and rap id saline stress) the survival time of the two bacteria varies conside rably. In sewage treated by stabilization ponds, Salmonella typhimuriu m and Escherichia coli exhibit the similar survival rates. T-90 evalua ted for Escherichia coli and Salmonella typhimurium in the winter peri od was, respectively, 125 and 132 h. In brackish water the survival ra te of Salmonella typhimurium was generally higher than that of Escheri chia coli. When these two bacteria were suspended in stabilization pon ds effluent and rapidly mixed with brackish water, survival time was p articularly short, whereas it was prolonged when the bacteria were sub mitted to a gradual increase in salinity. Biological factors, and in p articular predation, can play an important role in eliminating enteric bacteria during pond system treatment, but their efficiency is suppos ed to diminish significantly when there is an environmental change suc h as the discharge of pond system effluent into brackish water. This c an explain the increase of enteric bacteria survival.