title: A widely used in vitro biofilm assay has questionable clinical significance for enterococcal endocarditis.
abstract: Biofilm formation may play an important role in the pathogenesis of infections caused by Enterococcus faecalis, including endocarditis. Most biofilm studies use a polystyrene dish assay to quantify biofilm biomass. However, recent studies of E. faecalis strains in tissue and animal models suggest that polystyrene dish results need to be interpreted with caution. We evaluated 158 clinical E. faecalis isolates using a polystyrene dish assay and found variation in biofilm formation, with many isolates forming little biofilm even when different types of media were used. However, all tested clinical isolates were able to form biofilms on porcine heart valve explants. Dextrose-enhanced biofilm formation in the polystyrene dish assay was found in 6/12 (50%) of clinical isolates tested and may explain some, but not all of the differences between the polystyrene dish assay and the heart valve assay. These findings suggest that in studies assessing the clinical relevance of enterococcal biofilm-forming ability, ex vivo biofilm formation on a relevant tissue surface may be warranted to validate results of in vitro assays.
authors.affiliation: Department of Medicine, University of Minnesota, Minneapolis, Minnesota, United States of America.
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Leuck
authors.affiliation: Department of Medicine, University of Minnesota, Minneapolis, Minnesota, United States of America; VA Health Care System, Minneapolis, Minnesota, United States of America.
authors.forename: James R
authors.initials: JR
authors.lastname: Johnson
authors.affiliation: Department of Microbiology, University of Minnesota, Minneapolis, Minnesota, United States of America.
authors.forename: Gary M
authors.initials: GM
authors.lastname: Dunny
mesh_terms: D000818:Animals; D018441:Biofilms / Q000187:drug effects / Q000254:growth & development*; D001681:Biological Assay / Q000379:methods*; D046508:Culture Techniques; D004696:Endocarditis / Q000382:microbiology*; D013293:Enterococcus faecalis / Q000187:drug effects / Q000502:physiology*; D005947:Glucose / Q000494:pharmacology; D006351:Heart Valves / Q000166:cytology; D011137:Polystyrenes / Q000494:pharmacology; D013045:Species Specificity; D013552:Swine
chemical_list: D011137:Polystyrenes; D005947:Glucose