Survival of biofilm-associated Legionella pneumophila exposed to various stressors.

Biofilm is crucial for the multiplication and survival of Legionella pneumophila. The survival after different stressors of biofilm-associated L. pneumophila was evaluated during 150 days in this study. Mixed biofilms were allowed to develop on coupons in a biofilm reactor, which was experimentally infected with L. pneumophila. A dose of 2 ppm of monochloramine was found ineffective to kill younger (60 days) biofilm-associated L. pneumophila, whereas shock treatment (500 and 1000 ppm) was found to be significantly successful, as expected. Also, short exposure to 60 °C was insufficient to kill all young L. pneumophila within biofilms. A significant amount of young L. pneumophila bacteria also resisted pH 11 and 3 molar salt solution. No significant change was observed after exposure to 4 °C, ultra pure water and pH 5. Interestingly, L. pneumophila bacteria in biofilm became more sensitive after 90 days.