Effects of chlorination and heat disinfection on long-term starved Legionella pneumophila in warm water

AIMS: To characterize the efficacy of widely accepted heat and chlorination on culturable and non-culturable Legionella pneumophila in starved and warm water. METHODS AND RESULTS: For L. pneumophila starved for 1 day (S1), heating at 60 degrees C or more for 30 min or chlorination at 0.5-20 mg l(-1) for 60 min, a loss of 6-8 log culturability was observed, whereas only 17-47% of cells had membrane damage. Non-culturability was also observed after heating or chlorinating the cells starved for 14 days (S14). The effect of heating on membrane deterioration was reduced for S14 cells while the chlorination effect remained. Legionella pneumophila entered a non-culturable phase after being starved for 33-40 days. The disinfection effects of both heating and chlorination on non-culturable N4 and N35 cells (which were collected on the fourth and the 35th days of the non-culturability phase respectively) decreased, indicating the development of disinfection resistance among non-culturable cells that had been subjected to starvation for 1-2 months. CONCLUSIONS: Heating and chlorination significantly reduce the culturability of starved L. pneumophila, and damage cell membrane to a much less extent. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows the ability of long-term starved L. pneumophila to resist against disinfection treatments, which has implications in terms of public health.