SPECIFIC DETECTION OF METHICILLIN-RESISTANT STAPHYLOCOCCUS SPECIES BYMULTIPLEX PCR

In Staphylococcus aureus, mecA and femA are the genetic determinants o f methicillin resistance. By using a multiplex PCR strategy, 310- and 686-bp regions of the mecA and femA genes, respectively, were coamplif ied to identify susceptible (lacking mecA) and resistant (mecA(+)) sta phylococci and to differentiate S. aureus (femA(+)) from coagulase-neg ative staphylococci (lacking femA). A third staphylococcal genomic seq uence, corresponding to IS431 and spanning 444 bp, was used as a PCR c ontrol, One hundred sixty-five staphylococcal strains were tested. All 72 methicillin-resistant strains were found to he mecA(+), and 92 of the 93 susceptible isolates lacked mecA. Only one coagulase-negative S taphylococcus isolate carrying the mecA gene was highly susceptible to oxacillin, The femA determinant was a unique feature of S. aureus; it was found in 100% of the S. aureus strains tested but was undetectabl e in all of the coagulase-negative staphylococci tested, The possibili ty of directly detecting the mecA and femA genes in blood samples was also investigated. After two amplification steps, a sensitivity of 50 microorganisms per mi of freshly collected spiked blood was achieved, In conclusion, coamplification of mecA and femA determinants proved to be very reliable both for rapid detection of methicillin resistance a nd differential diagnosis between S. aureus and other staphylococci, T his technique, which can be successfully performed with blood samples, could be a useful tool in the diagnosis and treatment monitoring of s taphylococcal infections.