ERM GENES IN ERYTHROMYCIN-RESISTANT STAPHYLOCOCCUS-AUREUS AND COAGULASE-NEGATIVE STAPHYLOCOCCI

Erythromycin-resistant S. aureus from general practice and a dermatolo gy ward with a very high consumption of erythromycin was studied for e rmA and ermC content by Southern blot analysis. The prevalence of thes e erm genes was also studied in coagulase-negative staphylococci from the same dermatology ward and in a collection of 15 S. aureus and 18 c oagulase-negative staphylococci found in the same specimen from 15 dif ferent patients. ermA was only found as a chromosomal insert and ermC only on small plasmids. In erythromycin-resistant S. aureus from gener al practice ermC was responsible for 84% of erythromycin resistance, w hile 16% of the strains contained ermA. In 17 of 18 S. aureus strains from the dermatology ward a 2.5 kb plasmid contained ermC. Among 58 er ythromycin-resistant coagulase-negative staphylococci only 2 (3%) had ermA, whereas 44 strains (76%) had ermC. ermA or ermC genes were commo n in S. epidermidis (36/38). However, in 20 isolates of erythromycin-r esistant coagulase-negative staphylococci of other species, 10 had nei ther ermA nor ermC. ermC was the most common elm gene in both coagulas e-negative staphylococci and S. aureus. In 11 of 15 patients with eryt hromycin-resistant S. aureus the co-isolated erythromycin-resistant co agulase-negative staphylococcus had another resistance mechanism, eith er another gene or a different phenotypic expression of the same gene. Resistance to pristinamycin, a streptogramin antibiotic only used in animals, was not found in S. aureus but was found in 14% of erythromyc in-resistant coagulase-negative staphylococci.