Role of biofilms in the survival of Legionella pneumophila in a model potable-water system

Epidemiology and Laboratory Branch, Division of Healthcare Quality Promotion 1 , and Respiratory Disease Branch, Division of Bacterial and Mycotic Diseases 2 , National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333, USA Author for correspondence: Ricardo Murga. Tel: +1 404 639 2321. Fax: +1 404 639 3822. e-mail: rmurga{at}cdc.gov Legionellae can infect and multiply intracellularly in both human phagocytic cells and protozoa. Growth of legionellae in the absence of protozoa has been documented only on complex laboratory media. The hypothesis upon which this study was based was that biofilm matrices, known to provide a habitat and a gradient of nutrients, might allow the survival and multiplication of legionellae outside a host cell. This study determined whether Legionella pneumophila can colonize and grow in biofilms with and without an association with Hartmannella vermiformis . The laboratory model used a rotating disc reactor at a retention time of 6·7 h to grow biofilms on stainless steel coupons. The biofilm was composed of Pseudomonas aeruginosa , Klebsiella pneumoniae and a Flavobacterium sp. The levels of L. pneumophila cells present in the biofilm were monitored for 15 d, with and without the presence of H. vermiformis , and it was found that, although unable to replicate in the absence of H. vermiformis , L. pneumophila was able to persist. Keywords: Hartmannella vermiformis , protozoa, growth, ecology Abbreviations: GFP, green fluorescent protein