Chlorine and monochloramine disinfection of Legionella pneumophila colonizing copper and PVC drinking water biofilms.

Building water systems promote the regrowth and survival of opportunistic pathogens, such as Legionella pneumophila, especially within biofilms, where most drinking water microbes reside. However, compared to their planktonic form, disinfection efficacy for the biofilm-associated forms of water-based pathogens is unclear. The aim of this study was to determine the effectiveness of free chlorine and monochloramine in the inactivation of biofilm-associated L. pneumophila strain Philadelphia-1 serogroup 1 (Lp). Mature (1.5-2 y old) drinking water biofilms were developed on copper (Cu) and polyvinylchloride (PVC) slides within biofilm annular reactors, then colonized with Lp at approximately 4 log10 CFU cm-2 and exposed to 2 mg L-1 of free chlorine or monochloramine. Ct (disinfectant concentration x time, expressed as mg min L-1) inactivation values for 2-, 3-, and 4-log10 reduction of planktonic and biofilm Lp were determined. For planktonic Lp, free chlorine was more effective at inactivation compared to monochloramine treatment and for biofilm-associated Lp, monochloramine was more effective on Cu biofilms, while free chlorine was more effective on PVC biofilms. In contrast to monochloramine, free chlorine treatment of Cu and PVC biofilms, negatively impacted Lp 16S rRNA gene transcript levels, and may act synergistically with Cu surfaces to further reduce transcript levels. Moreover, Lp cells shed from biofilms into the bulk water, were more resistant to disinfection compared to prepared planktonic Lp cells. Results from this study indicate that biofilm association, disinfectant type, and substratum play an important role in the survival of Legionella pneumophila in building water systems. [ABSTRACT FROM AUTHOR]