VANCOMYCIN PENETRATION INTO BIOFILM COVERING INFECTED PROSTHESES AND EFFECT ON BACTERIA

To evaluate the adequacy of penetration of antibiotics into biofilm, a novel in vitro model for prosthesis-related infection was developed. Sterile stainless steel orthopedic nuts were incubated with slime-prod ucing Staphylococcus epidermidis. Biofilm-covered nuts were exposed to varying concentrations of vancomycin; then biofilms were harvested. V ancomycin levels in biofilm, as measured by fluorescent polarization i mmunoassay, far exceeded the MIC and MBC of vancomycin for the organis m. Bacterial growth in biofilm was inversely related to vancomycin con centration in biofilm, but even extremely high drug concentrations did not eradicate bacteria embedded in biofilm. The MICs and MBCs for bac teria recovered from biofilm did not differ from those for incubating organisms. Thus, failure of glycopeptide antibiotics to cure prosthesi s-related infection is not due to poor penetration of drugs into biofi lm but likely due to diminished antimicrobial effect on bacteria in th e biofilm environment.