Increased resistance of bacteria after adherence to polymethyl methacrylate. An in vitro study.

The pathobiology of total joint prosthesis infection was investigated in vitro. Discs of polymethylmethacrylate (PMMA) were exposed to a suspension containing cells of 10(8) per mL Staphylococcus epidermidis E-46. After 12 hours, exposed discs were rinsed with phosphate-buffered saline and placed in brain heart infusion broth containing antibiotics (2.5 mg per mL of Cephaloridine). After gentle shaking for 24 hours at 37 degrees C, the bacteria on the PMMA surface were detached and washed with phosphate-buffered saline to remove the antibiotics. Compared with the free bacteria which were detached from the PMMA by sonication immediately after exposure to the antibiotic solution, those allowed to remain adhered to the PMMA surface were more resistant to antibiotics. Scanning electron microscopy showed accumulation of bacteria surrounded by slime on PMMA discs exposed for 12 hours. Our results indicate that resistance of bacteria to antibiotics is increased after adherence to the biomaterial and formation of a slime layer.