Skin carriage of antibiotic-resistant coagulase-negative staphylococci in untreated subjects

A detailed microbiological analysis was made of the antibiotic resistant coagulase-negative staphylococcal flora of facial skin of 64 untreated individuals. The flora was quantified at primary isolation using both non-selective and selective media (each containing one of seven different antibiotics). The isolates obtained were tested against 18 antibiotics for multiple resistance and biotyped to species level. The incidence of the seven primary antibiotic resistance markers among the staphylococcal flora of 64 untreated subjects was: tetracycline 87.5%, erythromycin 68.8%, fusidic acid 56.3%, trimethoprim 42.4%, chloramphenicol 25%, clindamycin 9.4% and gentamicin 4.7%. In addition, penicillin resistant staphylococci were isolated from 98% of subjects. Multiply resistant strains were carried by 62.5% of individuals, with 27.9% carrying more than 100 multiply resistant staphylococci/cm2 skin. Analysis of the frequency distributions of the size of resistant staphylococcal populations revealed considerable individual variation, with many individuals carrying greater than 10(3) resistant staphylococci/cm2 skin. Multiply resistant staphylococci usually comprised less than 10% of the total staphylococcal flora, although this often represented a large number of multiply resistant organisms. Three people carried greater than 10(4) multiply resistant staphylococci/cm2 skin. Most of the singly and multiply resistant isolates were identified as strains of Staphylococcus epidermidis, which was found to carry up to eight resistances per isolate. In contrast, S. capitis, a common resident of human facial skin, was never found to carry more than two resistances per isolate. S. aureus was rarely detected on intact facial skin and the strains were not multiply resistant. Resistance to the major antistaphylococcal antibiotics was infrequent (gentamicin, methicillin) or absent (rifampicin, vancomycin, cephalothin). It was concluded that untreated individuals carry a significant pool of singly and multiply resistant staphylococci of sufficient size to be readily disseminated by direct contact and desquamation.