title: Are clinical isolates of Pseudomonas aeruginosa more virulent than hospital environmental isolates in amebal co-culture test?
abstract: OBJECTIVE
  Pseudomonas aeruginosa is an important opportunistic pathogen in hospital-acquired infections. As an environmental bacterium, it colonizes soil and water as well as hospital water supply and shares its natural habitat with free-living amebae. It has been shown previously that an ameba host system can be used to analyze the virulence of P. aeruginosa strains. In this study we have developed a simple amebal co-culture test with Acanthamoeba polyphaga to compare the virulence of P. aeruginosa between human and environmental isolates.
  
  
  METHODS
  Experimental study.
  
  
  METHODS
  The four state hospitals Intensive of Marseille.
  
  
  METHODS
  Eighty-one environmental strains isolated from the hospital water and 69 clinical isolates of P. aeruginosa (52 from blood cultures and 17 from bronchoalveolar lavage) were tested in the amebal co-culture test.
  
  
  RESULTS
  The results show that compared with environmental isolates, the isolates of P. aeruginosa from blood cultures were significantly more virulent in the ameba assay (37% vs. 62%, p=.006).
  
  
  CONCLUSIONS
  These data suggest that clinical infections due to Pseudomonas aeruginosa are due, at least in part, to bacterial virulence. Furthermore, even within the constraints of small sample size, virulence of respiratory isolates is significantly correlated with the occurrence of P. aeruginosa bacteremia. Our results, as those published previously, suggest that at the strain level, acquisition of antimicrobial resistance is correlated with the diminution of virulence. However, at the population level, clinical isolates are more virulent as well as more frequently resistant to antibiotics, presumably due to acquisition of strains mostly through cross-contaminations.
authors.affiliation: Unité des Rickettsies, Service de réanimation médicale, Hôpital Sainte Marguerite, Faculté de Médecine de Marseille, Université de la Méditerranée, France.
authors.forename: Lukas
authors.initials: L
authors.lastname: Fenner
authors.forename: Hervé
authors.initials: H
authors.lastname: Richet
authors.forename: Didier
authors.initials: D
authors.lastname: Raoult
authors.forename: Laurent
authors.initials: L
authors.lastname: Papazian
authors.forename: Claude
authors.initials: C
authors.lastname: Martin
authors.forename: Bernard
authors.initials: B
authors.lastname: La Scola
mesh_terms: D000048:Acanthamoeba; D000818:Animals; D002478:Cells, Cultured; D018920:Coculture Techniques; D003428:Cross Infection / Q000453:epidemiology / Q000382:microbiology*; D024881:Drug Resistance, Bacterial; D004783:Environmental Microbiology; D005602:France / Q000453:epidemiology; D006801:Humans; D008826:Microbial Sensitivity Tests; D011552:Pseudomonas Infections / Q000453:epidemiology / Q000382:microbiology*; D011550:Pseudomonas aeruginosa / Q000472:pathogenicity*; D014774:Virulence