Penetration of antibiotics through Staphylococcus aureus and Staphylococcus epidermidis biofilms

This study was carried out to elucidate the role of reduced antibiotic penetration in the resistance of Staphylococcus aureus and Staphylococcus epidermidis biofilms to different antibiotics. The biofilms of S. aureus ATCC 29213 and S. epidermidis ATCC 35984 were grown on black, polycarbonate membranes (diameter, 13 mm; pore size, 0.4 mu m) placed on tryptic soy agar plates at 37 degrees C for 48 h. The penetration of oxacillin, cefotaxime, amikacin, ciprofloxacin and vancomycin through the biofilms was determined by measuring the diameter of zones of growth inhibition (of S. aureus ATCC 25923, a quality control strain) on Mueller-Hinton agar plates following diffusion of each antibiotic from an overlying antibiotic disc through the biofilm to the agar medium versus the respective control assemblies. The penetration of oxacillin and cefotaxime (beta-lactams) and vancomycin (a glycopeptide) was significantly reduced through S. aureus and S. epidermidis biofilms whereas that of amikacin (an aminoglycoside) and ciprofloxacin (a fluoroquinolone) was unaffected. The results of this study indicate that the role of reduced antibiotic penetration in the drug resistance of S. aureus and S. epidermidis biofilms may vary with the antibiotic being used.