Biofilm Formation Among Methicillin-resistant Staphylococcus Aureus Isolates from Patients with Urinary Tract Infection

Staphylococci have been confirmed to form biofilms on various biomaterials. The purpose of this study was to investigate biofilm formation among methicillin-resistant Staphylococcus aureus (MRSA) isolates from patients with urinary tract infection (UTI) and to assess the relationship between biofilm-forming capacities and virulence determinants/clinical background. Over a 12-year period from 1990 through 2001, a total of 109 MRSA isolates were collected from patients (one isolate per patient) with UTI at the urology ward of Okayama University Hospital. We used the in vitro microtiter plate assay to quantify biofilm formation. We then investigated the presence of several virulence determinants by polymerase chain reaction assay and found eight determinants (tst, sec, hla, hlb, fnbA, clfA, icaA, and agrII) to be predominant among these isolates. Enhanced biofilm formation was confirmed in hla-, hlb-, and fnbA-positive MRSA isolates, both individually and in combination. Upon review of the associated medical records, we concluded that the biofilm-forming capacities of MRSA isolates from catheter-related cases were significantly greater than those from catheter-unrelated cases. The percentage of hla-, hlb-, and fnbA-positive isolates was higher among MRSA isolates from catheter-related cases than those from catheter-unrelated cases. Our studies suggest that MRSA colonization and infection of the urinary tract may be promoted by hla, hlb, and fnbA gene products.