Genomic diversity ofmecregulator genes in methicillin-resistantStaphylococcus aureusandStaphylococcus epidermidis

Abstract

Summary: Low-affinity penicillin-binding protein PBP-2a encoded bymecAis closely related to methicillin resistance in staphylococci, and expression of PBP-2a is controlled by regulator elements encoded bymecRlandmecIwhich are located adjacent tomecAon the chromosome. Deletion or mutation which occurred inmecregulator gene is considered to be associated with constitutive production of PBP-2a. The distribution of themecregulator genes in 176 strains ofStaphylococcus aureusand 33 strains ofS. epidermidisisolated from a single hospital was studied by polymerase chain reaction amplification. Most clinical isolates of methicillin-resistantS. aureus(MRSA) (94.3 %) andS. epidermidis(MRSE) (83.9 %) possessed bothmecIandmecR1genes (type I), whereas nomecregulator genes were detected inmecA-negative isolates. In contrast, 7 MRSA and 5 MRSE isolates were found to have incomplete regulator genes, and they were classified into three groups; strains which lacked onlymecIgene (type II), strains which lackedmecIand 3'-end ofmecR1gene (type III), and strains which lacked both regulator genes (type IV). Analysis ofmecIgene from all the strains havingmecIby restriction fragment length polymorphism afterMseI digestion indicated that three MRSA strains possessed one of the known point mutations identified previously. These findings indicated the predominance of a single type of MRSA possessing bothmecIandmecR1in the study period and also suggested a high genomic diversity inmecregulator region of staphylococci.