Molecular-genetic Method for Fast Direct Detection of Staphylococcus Aureus and Methicillin Resistance in Blood...

Invasive infections caused by methicillin resistant Staphylococcus aureus and coagulase-negative staphylococci (MRSA/MRSCoN) require fast, adequate treatment.

of this study was to develop a faster protocol for direct detection of MRSA/MRSCoN in blood cultures and in abscess punctures based on mecA and species specific identification of S. aureus by polymerase-chain reaction (PCR).

We examined 77 growth-positive BACTEC blood cultures and 50 abscess punctures by routine microbiological assay and simultaneous PCR detection of MRSA/MRSCoN. The specificity of the PCR was evaluated by using DNA from another 15 microbial species for negative controls. We determined the minimum inhibitory concentration (MIC) of oxacillin, vancomycin, tigecycline, linezolid, levofloxacin, clindamycin, and erythromycin against the S. aureus isolates using the E-test.

In the blood cultures, the two methods detected 39.3% of MRSA, and 93.9% of MRCoNS. In the punctures, the PCR assay identified 20.9% of MRSA and 79.2% of MSSA. In the puncture cases, there were three PCR MRSA positive and culture negative samples. Screening for susceptibility to 14 antimicrobial agents demonstrated significantly higher (p<0.05) methicillin resistance in blood culture isolates than in the puncture ones (39.3% and 20.0%, respectively).

The new PCR protocol was very fast and specific. It was more sensitive in detecting MRSA from abscess punctures than the routine microbiological techniques. This protocol will speed up the right choice of empirical therapy, which is extremely important for saving patients’ lives.