Antibiotic resistance patterns of aerobic coryneforms and furazolidone-resistant Gram-positive cocci from the skin surface of the human axilla and fourth toe cleft.

Samples of skin surface bacteria from 28 healthy subjects plated directly on to selective and non-selective media revealed that the proportion of aerobic coryneforms and furazolidone-resistant Gram-positive cocci (FURECs) resistant to erythromycin was significantly greater in the fourth toe cleft than in the axilla (P < 0.05). There were more erythromycin-resistant bacteria than tetracycline-resistant bacteria at both sites (P = 0.001 for the toe cleft; P < 0.01 for the axilla). In total, 160 distinct isolates were obtained, of which 42 were FURECs and 118 were aerobic coryneforms. Of these, 153 (96%) were resistant to erythromycin and 66 (41%) to tetracycline. All except seven of the tetracycline-resistant strains were also resistant to erythromycin. The resistant isolates belonged to a variety of species. CDC group ANF corynebacteria were most numerous and composed 31% of all isolates. The majority (76%) of FURECs were identified as Micrococcus luteus. MIC determinations on selected strains revealed that tetracycline-resistant FURECs were sensitive to doxycycline and minocycline, as were most tetracycline-resistant coryneforms. Nine coryneform isolates were cross-resistant to all three tetracyclines. Only a minority of erythromycin-resistant FURECs (21%) demonstrated a macrolide-lincosamide-streptogramin type B (MLS)-resistant phenotype with inducible or constitutive cross-resistance to clindamycin and the type B streptogramin, pristinamycin IA. Twenty-nine erythromycin-resistant FURECs had a novel phenotype distinct from MLS and macrolide-streptogramin type B resistance. In contrast, most coryneforms (79%) were MLS resistant. Among the remainder, two unusual erythromycin resistance phenotypes were apparent, both of which differed from the unusual phenotype in FURECs. This study has revealed that the non-staphylococcal aerobic flora of skin contains a considerable reservoir of tetracycline and erythromycin resistance determinants. The three unusual macrolide resistance phenotypes may be associated with novel resistance mechanisms.