Prevalence of macrolide-resistance genes in Staphylococcus aureus and Enterococcus faecium isolates from 24 European university hospitals

The polymerase chain reaction (PCR) was used to study the prevalence of the macrolide resistance genes ermA, ermB, ermC, msrA/msrB, ereA and ereB, in 851 clinical isolates of Staphylococcus aureus and 75 clinical isolates of Enterococcus faecium that were erythromycin resistant. The isolates were fr om 24 European university hospitals. In S. aureus, the ermA gene was more c ommon in methicillin-resistant S. aureus (MRSA) isolates (88%) than in meth icillin-susceptible S. aureus (MSSA) isolates (38%), and occurred mainly in strains with constitutive MLSB expression. In contrast, ermC was more comm on in MSSA (47%) than in MRSA (5%), occurring mainly in strains with induci ble expression. The ereB gene was only found in MRSA isolates expressing a constitutive MLSB phenotype (1%). The ereA gene was not detected. Macrolide resistance by efflux due to the msrA/msrB gene was only detected in MSSA i solates (13%). In contrast to S. aureus, erythromycin resistance in E. faec ium was almost exclusively due to the presence of the ermB gene (93%).