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

Abstract

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.

Antimicrobial resistance in staphylococci from animals with particular reference to bovine Staphylococcus aureus, porcine Staphylococcus hyicus, and canine Staphylococcus intermedius

“…Target modification is the most widespread resistance mechanism and refers to the dimethylation of an adenine residue in the 23S rRNA. Four rRNA methylase (erm) genes, designated erm(A), erm(B), erm(C), and erm(F), have until now been identified in staphylococci of animal origin [14,20,27,38,39,73,85,90,103,104,106].…”

“…Studies of the occurrence of the different erm genes among animal staphylococci [14,20,27] showed that erm(C) genes were frequently seen in S. hyicus and other porcine staphylococci [20,27], but also in many staphylococcal species from various animal sources [38,39,73,85,90,106] while erm(B) genes were the dominant erm genes in canine S. intermedius isolates [8,20]. Genes of the class erm(F) have so far only been detected in a few S. intermedius iso-lates from pigeons [14] and erm(A) genes have also only been identified in single animal staphylococcal isolates, mainly of avian origin [47,103] and porcine origin [27].…”

“…Genes of the class erm(F) have so far only been detected in a few S. intermedius iso-lates from pigeons [14] and erm(A) genes have also only been identified in single animal staphylococcal isolates, mainly of avian origin [47,103] and porcine origin [27]. In rare cases, two different erm genes were present in the same staphylococcal isolate [20].…”

“…The msr(A) gene has rarely been detected in animal staphylococci, but has been reported to be the second most prevalent macrolide resistance gene in staphylococci of human origin [20]. A combination of erm(C) and msr(A) has been described in a single porcine staphylococcal isolate [20].…”

“…The msr(A) gene has rarely been detected in animal staphylococci, but has been reported to be the second most prevalent macrolide resistance gene in staphylococci of human origin [20]. A combination of erm(C) and msr(A) has been described in a single porcine staphylococcal isolate [20]. The genes vga(B) coding for a streptogramin A transporter and vat(B) coding for a streptogramin A acetyltransferase have recently been identified in two S. xylosus isolates from poultry [4].…”