The most common mechanism of the resistance to MLS-B antibiotics among staphylococci depends on the presence of one of the methylase genes: ermA or ermC, expressed inductively or constitutively.
Rare S. aureus strains synthesize other methylases; ErmGM, ErmB or ErmF.
Resistance to M14S-B depends on active efflux and is determined by the MsrA or MsrB proteins.
Other rare mechanisms include MefA, Cfr and synthesis of enzymes that inactivate several antibiotics of the group: esterases EreA and EreB, nucleotidylotransferases LinA, LinA1, LinA', and lyases VgbA and VgbB.
The purpose of the work was to estimate the frequency of the specific mechanisms determining the resistance to MLS-B antibiotics among hospital-acquired MRSA strains.
The recent isolates of MRSA were examined to the resistance to MLS-B. Strains resistant to at least one of MLS-B were investigated for the presence of ermA, ermB, ermC, msrA/B and linA / linA' genes by using PCR.
Gene ermA was found in 43 from 50 investigated strains (86%). Twenty of them demonstrated inducible whereas 23 constitutive type of expression. The gene ermC was present in 15 of examined MRSA strains (30%). The expression of the gene was inducible in the case of 9 and constitutive in the case of 6 of the strains. The msrA/B gene was present in the case of 5 strains. Three strains possessed the linA/linA' gene.
The most common appeared the ermA gene. In the cases of simultaneous occurrence of two different genes, detection of the determinants with phenotype methods frequently was impossible.