Primary-colonizing betaproteobacteriales play a key role in growth of legionella pneumophila in biofilms on surfaces exposed to drinking water treated by slow sand filtration

“Slow sand filtration with extensive pre-treatment reduces the microbial growth potential of drinking water to a minimum level at four surface water supplies in The Netherlands. The potential of these slow sand filtrates (SSFs) to promote microbial growth in warm tap water installations was assessed by measuring biofilm formation and growth of Legionella on surfaces of glass and chlorinated polyvinylchloride (CPVC) exposed to SSF of 37 ± 2°C in a model system for up to six months. The steady-state biofilm concentration on glass ranged from 230 to 3980 pg ATP cm−2 and 1.4 (± 0.3) times higher levels on CPVC. These concentrations correlated significantly with the assimilable organic carbon (AOC) concentration of the warm water (8 to 24 µg acetate C equivalents liter−1) that was raised about two times by mixing of cold and heated (70°C) SSF. All biofilms supported growth of L. pneumophila to a maximum level ranging from 2×103 to 1.5×105 CFU cm−2 on glass. Biofilms after ≤ 50 days of exposure were predominated by the Betaproteobacteriales, mainly Piscinibacter, Caldimonas, Methyloversatilis and an uncultured Rhodocyclaceae bacterium. These rapidly growing primary colonizers most likely served as prey for the host amoebae of L. pneumophila. The Alphaproteobacteria, mostly Xanthobacteraceae, e.g. Bradyrhizobium, Pseudorhodoplanes and other amoeba-resistant bacteria, accounted for 37.5% of the retrieved clones. A conceptual model based on a quadratic relationship between the L. pneumophila colony count and the biofilm concentration under steady-state conditions is used to explain the varying Legionella CFU pg−1 ATP ratio in the biofilms.”

Copyright © 2018 American Society for Microbiology.

(Citaat: van der Kooij, D., Veenendaal, H.R., Italiaander, R., van der Mark, E.J., Dignum, M. – Primary-colonizing betaproteobacteriales play a key role in growth of legionella pneumophila in biofilms on surfaces exposed to drinking water treated by slow sand filtration – Applied and Environmetal Microbiology (2018) DOI: 10.1128/AEM.01732-18 – (Open Access))