The influence of temperature, disinfection and water softening of drinking water on the multiplication of Legionella pneumophila

Abstract

The influence of temperature, disinfectant and water softener for drinking water preparation on the bacterial growth of Legionella pneumophila was examined.The optimal temperature for bacterial growth was 36 °C. At the incubation temperature of 15 °C the multiplying of bacteria slowed down, as confirmed by the bacteriostatic effect of this temperature. The number of bacteria was after the first 24 h of incubation at 55 °C reduced by more than 6 log in comparison to the culture at 36 °C. After 10 minutes of exposure to the disinfectant dichloroisocyanuric acid, the number of bacteria in the culture decreased for 1.4 log CFU mL-1, followed by an intensive growth immediately after the disinfectant degradation. The number of bacteria was up to 72 hours incubation even higher than in the control sample without a disinfectant, and then the number in both samples equalled at approximately 7.3 log CFU mL-1. Sodium polyphosphate used as a water softener stimulated the bacterial growth. The largest difference in growth was observed after 72 h of incubation, which was 1.9 log CFU mL-1 higher in samples with sodium polyphosphate in comparison to those without the softener