Clinical implications of biofilm formation by Enterococcus faecalis in the urinary tract

The potential relationships between biofilm formation and pathogenicity of Enterococcus faecalis in urinary tract infections (UTI) were investigated. Over a 12-year period from 1991 through 2002, a total of 352 E. faecalis isolates were collected from patients with complicated UTI (one isolate per patient) at the urology ward of Okayama University Hospital. We analyzed the prevalence and transferability of genes encoding virulence factors (asal, esp, cylA, gefE/sprE) and antimicrobial resistance (aac(6')/aph(2")). The production of biofilm, hemolysin and gelatinase by these isolates was also examined and the associated medical records of patients were retrospectively reviewed. Of 352 E. faecalis isolates, 315 possessed asa1 and/or esp genes. Of the 63 hemolysin- and 167 gelatinase-producing isolates, 59 and 94 isolates, respectively, possessed both asal and esp genes. E. faecalis isolates with both asal and esp genes formed biofilms at significantly higher rates than those with neither gene (P = 0.038). The genes encoding asa1, cylA and aac(6')/aph(2") were transferable and appeared to have accumulated in these isolates. The E. faecalis isolates possessing asal and/or esp genes were found from both catheter -related or -unrelated UTI. Our study indicates that E. faecalis isolates that have accumulated virulence genes are apt to form persistent biofilms in the urinary tract.