Biofilm composition and threshold concentration for growth of Legionella pneumophila on surfaces exposed to flowing warm tap water without disinfectant

Dick van der Kooij*, Geo L. Bakker, Ronald Italiaander, Harm R. Veenendaal, Bart A. Wullings

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

22 Citations (Scopus)

Abstract

Legionella pneumophila in potable water installations poses a potential health risk, but quantitative information about its replication in biofilms in relation to water quality is scarce. Therefore, biofilm formation on the surfaces of glass and chlorinated polyvinyl chloride (CPVC) in contact with tap water at 34 to 39°C was investigated under controlled hydraulic conditions in a model system inoculated with biofilm-grown L. pneumophila. The biofilm on glass (average steady-state concentration, 23 ± 9 pg ATP cm -2 ) exposed to treated aerobic groundwater (0.3 mg C liter -1 ; 1 μg assimilable organic carbon [AOC] liter -1 ) did not support growth of the organism, which also disappeared from the biofilm on CPVC (49 ± 9 pg ATP cm -2 ) after initial growth. L. pneumophila attained a level of 4.3 log CFU cm -2 in the biofilms on glass (1,055 ± 225 pg ATP cm -2 ) and CPVC (2,755± 460 pg ATP cm -2 ) exposed to treated anaerobic groundwater (7.9 mg C liter -1 ; 10 μg AOC liter -1 ). An elevated biofilm concentration and growth of L. pneumophila were also observed with tap water from the laboratory. The Betaproteobacteria Piscinibacter and Methyloversatilis and amoeba-resisting Alphaproteobacteria predominated in the clones and isolates retrieved from the biofilms. In the biofilms, the Legionella colony count correlated significantly with the total cell count (TCC), heterotrophic plate count, ATP concentration, and presence of Vermamoeba vermiformis. This amoeba was rarely detected at biofilm concentrations of <100 pg ATP cm -2 . A threshold concentration of approximately 50 pg ATP cm -2 (TCC = 1 × 106 to 2 × 106 cells cm -2 ) was derived for growth of L. pneumophila in biofilms.

Original languageEnglish
Article numbere02737-16
JournalApplied and Environmental Microbiology
Volume83
Issue number5
DOIs
Publication statusPublished - 15 Feb 2017
Externally publishedYes

Keywords

  • Legionella pneumophila
  • Predominating biofilm bacteria
  • Threshold biofilm concentration
  • Warm tap water

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