Survival of Shigella flexneri in artificial aquatic environment: effects of different physicochemical stress factors

Survival of bacteria in aquatic environment is influenced by the prevailing physicochemical characteristics of water. A study was carried out to assess the effects of temperature, pH, and salinity of water on the survival of Shigella flexneri in laboratory microcosms. Survival of S. flexneri was assessed by viable counts of Shigella on MacConkey agar plates. At pH 7.0 and temperature of 4 degrees C, S. flexneri survived longer in 0.5% salinity than in salt-free distilled water, while at pH 7.0 and at higher temperatures (25 degrees C and 37 degrees C), the bacteria survived longer in distilled water than in 0.5% salinity. It was also observed that 2.0% NaCl solution was detrimental to bacterial survival at pH 8.0 and temperature of 37 degrees C. Survival times of the viable cells increased with reduction of temperatures and salinity. These findings demonstrated that survival of S. flexneri in the aquatic environment is greatly influenced by physicochemical factors.