Detection of mecA, mecR1 and mecI genes among clinical isolates of methicillin-resistant staphylococci by combined polymerase chain reactions.

The distribution of the mec genes mecA, mecR1 and mecI that regulate the expression of methicillin resistance was investigated by PCR in 145 staphylococci of hospital origin. Determination of alterations and deletions in parts of the genes was achieved using 11 sets of primers in combined reactions. Methicillin-resistant Staphylococcus epidermidis strains appeared relatively stable, with 57.9% of isolates containing the whole regulatory region. Alterations within the mecA gene were detected more often in other coagulase-negative staphylococci, which also had a higher percentage with deletions of regulatory genes. Among methicillin-resistant S. aureus, a genetically heterogeneous population was identified, with several alterations and deletions of mec genes.