Survey of pathogenic bacteria of biofilms in a metropolitan drinking water distribution system.

: Bacteria, especially pathogenic bacteria, were detected in order to estimate the safety of drinking water distribution systems (DWDS). 16 biofilms and 12 water samples (6 retained and 6 flowing) were collected from a city DWDS in Eastern China. Biofilms were observed using scanning electron microscopy. Cultivable bacteria of biofilms were counted by heterotrophic plate counts, ranging from 3.61 × 101 to 1.67 × 106 CFU·cm-2. Coliforms, Salmonella, Shigella, Vibrio, and Legionella were separated by EMB agar, Salmonella chromogenic medium, Shigella chromogenic medium, TCBS agar, BCYE agar, and 13/16, 8/16, 7/16, 6/16, 0/16 biofilm samples were found positive respectively. Retained and flowing water samples were collected to estimate the influence of hydrodynamic conditions on biofilm detachment. All 6 retained water samples were positive for bacteria, count ranged from 1.2 × 103 to 2.8 × 104 CFU·mL-1 and 2/6, 3/6, 2/6, 0/6, 0/6 samples were positive for coliforms, Salmonella, Shigella, Legionella, and Vibrio, respectively. While only 3 of 6 flowing water samples were bacteria positive, counts ranged from 102 to 103 CFU·mL-1, 2/6 were coliforms positive, no pathogens under testing were detected. The results show that there are pathogens in DWDS biofilms, which can cause health related problems if detached from their surface.