Molecular epidemiology of macrolide resistance in beta-haemolytic streptococci of Lancefield groups A, B, C and G and evidence for a new mef element in group G streptococci that carries allelic variants of mef and msr(D).
OBJECTIVE
To study the molecular mechanisms of erythromycin resistance in beta-haemolytic streptococci of Lancefield groups A, B, C and G.


METHODS
Erythromycin-resistant clinical isolates from North East Scotland were collected over 2 years. Resistance phenotypes were determined by disc diffusion and MICs by Etest. Resistance genes mef, msr(D), erm(B) and erm(TR) were identified by PCR and mef and msr(D) were sequenced.


RESULTS
Erythromycin resistance prevalence was 1.9% in group A streptococci (31 of 1625), 4.3% in group B (53 of 1233), 3.8% in group C (18 of 479) and 6.2% in group G (64 of 1034). The numbers of resistant isolates available were 26, 42, 9 and 52 in each group respectively. The majority of resistant isolates in groups A (57.7%, 15 of 26), B (88.1%, 37 of 42) and G (90.4%, 47 of 52) were MLS(B). The contribution of M phenotype was significant in groups C (77.8%, 7 of 9) and A (42.3%, 11 of 26). Group A isolates carried mef(A) and group B carried mef(E) exclusively. A mef sequence distinct from mef(A) and mef(E) was identified in group G and was associated with a new msr(D) sequence. These sequence variants appear to be part of a new genetic element that is inserted in the comEC gene. A bimodal distribution of erythromycin MICs was noted in erm(TR) isolates.


CONCLUSIONS
The results demonstrate significant differences in the mechanisms of macrolide resistance amongst different Lancefield groups in the same geographical area. New sequences show that resistance mechanisms are still evolving.
Amezaga
Maria Rosario
MR
Department of Medical Microbiology, University of Aberdeen School of Medicine, Polwarth Buildings, Foresterhill, Aberdeen AB25 2ZD, UK.
McKenzie
Hamish
H
D000483:Alleles; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D004917:Erythromycin / Q000494:pharmacology; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D018942:Macrolides / Q000494:pharmacology*; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D017720:Molecular Epidemiology; D010641:Phenotype; D013045:Species Specificity; D013290:Streptococcal Infections / Q000453:epidemiology / Q000382:microbiology; D013291:Streptococcus / Q000145:classification / Q000187:drug effects* / Q000235:genetics*
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D018942:Macrolides; C117866:MefA protein, Streptococcus; D008565:Membrane Proteins; D004917:Erythromycin