[Long-term study of the persistence of E. coli in waters of different composition].

The survival of E. coli ATCC 11229 at different initial concentrations was determined in water of standardized hardness, in tap water from Kiel and in groundwater from the Segeberger forest with pH-values of 4.5, 6.9 and 8.5. In groundwater at pH 4.5 the bacteria died relatively soon, whereas otherwise in relation to the test conditions long persistence times have been determined. The persistence of E. coli in tap water from Kiel and in water of standardized hardness differed from that in groundwater with comparable pH-values of pH 6.9 and pH 8.5. In groundwater the colony forming units generally decreased slightly, whereas in tap water and in water of standardized hardness high initial bacterial concentrations resulted in growth, low ones on the other hand in a decrease of the colony forming units. In the area of middle initial bacterial concentrations a significant growth of E. coli (frequently not before 50 days) as well as a die-off could be observed in parallel samples. The influence of the water volume of the sample and the conditioning of the bacteria (unwashed - washed) were of secondary importance.