title: Factors influencing persistence of Legionella pneumophila serogroup 1 in laboratory cocultures.
abstract: BACKGROUND
  Risk for infections from Legionella pneumophila for immunocompromised individuals increases greatly when this species is present within the biofilm of the water distribution systems of hospitals or other health facilities. Multiplication and persistence of Legionella may dependent also upon planktonic growth in alternative to sessile growth. Here we compared the persistence of L. pneumophila serogroup 1 in experimental planktonic co-cultures subsided with iron, Pseudomonas aeruginosa and other non Legionella bacteria (quantified as Heterotrophic Plate Count, HPC at 37°C), isolated from drinking water sources of a large hospital.
  
  
  RESULTS
  Concentrations of L. pneumophila showed a decreasing pattern with incubation time in all co-cultures, the degree of reduction depending on the experimental treatment. In co-cultures with added P. aeruginosa, no L. pneumophila was detectable already after 4 days of incubation. In contrast in co-cultures without P. aeruginosa, HPC but not iron were significant factors in explaining the pattern of L. pneumophila, although the HPC effect was different according to the incubation time (HPC x time interaction, p < 0.01).
  
  
  CONCLUSIONS
  Our results highlight the need of controlling for both HPC and metal constituents of the water systems of buildings used by individuals at particular risk to the effects of Legionella exposure.
authors.affiliation: Department of Public Health and Infectious Diseases, Sapienza University of Rome, Piazza A, Moro 5, Rome, 00185, Italy. angelo.solimini@uniroma1.it.
authors.forename: Angelo G
authors.initials: AG
authors.lastname: Solimini
authors.forename: Alessia
authors.initials: A
authors.lastname: Cottarelli
authors.forename: Lucia
authors.initials: L
authors.lastname: Marinelli
authors.forename: Maria
authors.initials: M
authors.lastname: De Giusti
mesh_terms: D006801:Humans; D007501:Iron / Q000378:metabolism; D016952:Legionella pneumophila / Q000145:classification / Q000254:growth & development* / Q000302:isolation & purification; D056265:Microbial Interactions; D050296:Microbial Viability; D011550:Pseudomonas aeruginosa / Q000254:growth & development* / Q000302:isolation & purification; D065288:Serogroup; D013696:Temperature; D014871:Water Microbiology
chemical_list: D007501:Iron