Assessment of particle associated bacteria in unchlorined drinking water from three treatment plants by cultivationindependent methods

Particle associated bacteria (PAB) in drinking water are of potential health significance due to their resistance to disinfection. In the current study, PAB from unchlorined drinking water of three treatment plants in the Netherlands were studied by cultivation-independent methods: Adenosine triphosphate (ATP) and total cell counts (TCC) with flow cytometry were used to quantify PAB, and high-throughput pyrosequencing was used to identify PAB. Scanning microscopy study confirmed the presence of multiple cells associated with single particle. The coupled energy dispersive spectroscopy found the particles were mainly consisted of Carbon, Oxygen, Silicon, Sodium, Calcium, Iron, Manganese. The number and activity of PAB ranged between 1.0-3.5×10³ cells ml^-1and 0.04-0.154 ng l ^-1 ATP and represented less than 2% of bacterial numbers (0.45-1.65 ×10⁵ cells ml^-1) and activity (1- 6 ng l ^-1 ATP) in water samples. These results indicate that a relatively low, but sufficient amount of PAB is present in drinking water. Furthermore, ATP per cell in PAB is higher than in planktonic bacteria indicating higher metabolic activity in PAB.