Changing resistance to antimicrobial drugs, and resistance typing in clinically significant strains of Staphylococcus epidermidis.

Resistance to 11 antimicrobial drugs was assessed in 532 clinically significant strains of Staphylococcus epidermidis received in the years 1978, 1979 and 1980 and compared with that of strains collected in 1976 and 1977 for an international study. Only 14% of strains were sensitive to all the drugs tested. Resistance to gentamicin increased significantly from 7% to 33% during the study period. The degree of association between pairs of drugs was assessed. There was strong association between resistance to methicillin, aminoglycosides and macrolide antibiotics and only weak association between resistance to novobiocin, tetracycline, chloramphenicol and penicillin. Patterns of resistance were complex and may be useful as an accessory typing system.