Distribution of genes encoding erythromycin ribosomal methylases and an erythromycin efflux pump in epidemiologically distinct groups of staphylococci.
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.
Eady
E A
EA
Department of Microbiology, University of Leeds, UK.
Ross
J I
JI
Tipper
J L
JL
Walters
C E
CE
Cove
J H
JH
Noble
W C
WC
D000818:Animals; D015342:DNA Probes; D004285:Dogs; D004352:Drug Resistance, Microbial / Q000235:genetics; D004917:Erythromycin / Q000378:metabolism* / Q000494:pharmacology; D005798:Genes, Bacterial; D006801:Humans; D008780:Methyltransferases / Q000235:genetics* / Q000378:metabolism; D010531:Peritoneal Dialysis, Continuous Ambulatory; D010641:Phenotype; D012270:Ribosomes / Q000201:enzymology; D013045:Species Specificity; D013203:Staphylococcal Infections / Q000382:microbiology; D013210:Staphylococcus / Q000201:enzymology / Q000235:genetics*; D013552:Swine
D015342:DNA Probes; D004917:Erythromycin; D008780:Methyltransferases