Seasonal changes of survival of Escherichia coli, Streptococcus faecalis, Salmonella typhimurium and Salmonella typhi dublin in lake water

Survival in an annual cycle of Escherichia coli, Streptococcus faecalis, Salmonella typhimurium and Salmonella typhi dublin were examined in non-sterilized lake water, water sterilized by heating in an autoclave (121°C/10 min.), incubated without light at 4 and 20°C, respectively. All examined bacterial strains generally survived for shorter periods in non-sterilized lake water than in sterilized lake water, and shorter at 20°C than at 4°C. Survival curves of these bacteria in non-sterilized lake water were similar to a logarythmic curve, whereas in sterilized lake water they resembled a sigmoidal curve regardless of incubation temperature. The time necessary for 90% reduction of these bacteria ranged from 1 to 32 days. It was generally shorter in non-sterilized lake water and longer for sterilized water; and it was shorter for Streptococcus faecalis and longer for Escherichia coli, Salmonella typhimurium and Salmonella typhi dublin. All four examined bacteria were more quickly reduced in summer, and slower in spring, autumn and winter.