Distribution of genes encoding erythromycin ribosomal methylases and an erythromycin efflux pump in epidemiologically distinct groups of staphylococci

J Antimicrob Chemother. 1993 Feb;31(2):211-7. doi: 10.1093/jac/31.2.211.


Erythromycin-resistant staphylococci can be divided into two phenotypic classes based on their pattern of cross-resistance to other macrolides, lincosamides and type B streptogramins. Strains inducibly or constitutively resistant to all MLS antibiotics possess erythromycin ribosomal methylase (erm) genes, whereas strains inducibly resistant to only 14 and 15-membered ring macrolides and type B streptogramins harbour msrA, which encodes an ATP-dependent efflux pump. Dot-blot hybridization was used to study the distribution of ermA, ermB, ermC and msrA in five epidemiologically distinct groups of staphylococci. The most widely-distributed resistance determinant was ermC, which was detected in 112 (50.6%) of 221 isolates, alone in 106 isolates and in combination with a second erythromycin resistance determinant in six strains. MsrA was detected in 73 (33%) of isolates, alone in 65 and in combination with a methylase gene in eight strains. This determinant was responsible for erythromycin resistance in over one-third (36.4%) of clinical isolates of coagulase-negative staphylococci. ErmA and ermB were present in only a minority of isolates (5.9 and 7.2% of strains, respectively). The resistance determinants present in ten strains did not hybridize to any of the four probes although, in all cases, their resistance phenotype was consistent with the possession of a methylase gene. Interestingly, ermB was found exclusively in animal isolates of Staphylococcus intermedius, Staphylococcus xylosus and Staphylococcus hyicus, but not in coagulase-negative staphylococci of human origin. This determinant has previously only been found in a small number of epidemiologically related strains of Staphylococcus aureus.

MeSH terms

  • Animals
  • DNA Probes
  • Dogs
  • Drug Resistance, Microbial / genetics
  • Erythromycin / metabolism*
  • Erythromycin / pharmacology
  • Genes, Bacterial*
  • Humans
  • Methyltransferases / genetics*
  • Methyltransferases / metabolism
  • Peritoneal Dialysis, Continuous Ambulatory
  • Phenotype
  • Ribosomes / enzymology
  • Species Specificity
  • Staphylococcal Infections / microbiology
  • Staphylococcus / enzymology
  • Staphylococcus / genetics*
  • Swine


  • DNA Probes
  • Erythromycin
  • Methyltransferases