The prevalence of genotypes that determine resistance to macrolides, lincosamides,and streptogramins B compared with spiramycin susceptibility among erythromycin-resistant Staphylococcus epidermidis

Coagulase-negative staphylococci, particularly Staphylococcusepidermidis, can be regarded as potential reservoirs of resistance genesfor pathogenic strains, e.g., Staphylococcus aureus. The aim of thisstudy was to assess the prevalence of different resistance phenotypes to macrolide,lincosamide, and streptogramins B (MLSB) antibiotics among erythromycin-resistantS. epidermidis, together with the evaluation of genes promotingthe following different types of MLSB resistance:ermA,ermB, ermC,msrA,mphC, and linA/A’. Susceptibility to spiramycinwas also examined. Among 75 erythromycin-resistantS. epidermidisisolates, the most frequent phenotypes were macrolides and streptogramins B (MSB) andconstitutive MLSB (cMLSB). Moreover, all strains with the cMLSB phenotype and themajority of inducible MLSB (iMLSB) isolates were resistant to spiramycin, whereasstrains with the MSB phenotype were sensitive to this antibiotic. The D-shape zone ofinhibition around the clindamycin disc near the spiramycin disc was found for somespiramycin-resistant strains with the iMLSB phenotype, suggesting an induction ofresistance to clindamycin by this 16-membered macrolide. The most frequently isolatedgene was ermC, irrespective of the MLSB resistance phenotype,whereas the most often noted gene combination wasermC,mphC, linA/A’. The results obtained showed thatthe genes responsible for different mechanisms of MLSB resistance in S.epidermidis generally coexist, often without the phenotypic expression ofeach of them.