Improved and rapid detection of methicillin-resistant Staphylococcus aureus nasal carriage using selective broth and multiplex PCR

• Published in: Research in microbiology 2006-12, Vol.157 (10), p.971-975
• Main Authors: Schuenck, Ricardo P., Lourenco, Maria Cristina S., Iório, Natália L.P., Ferreira, Adriana Lúcia P., Nouér, Simone A., Santos, Kátia Regina N.
• Format: Article
• Language: English
• Subjects: Bacterial Proteins - genetics; Bacteriology; Biological and medical sciences; Carrier State - microbiology; Culture Media; Fundamental and applied biological sciences. Psychology; Humans; Methicillin resistance; Methicillin Resistance - genetics; Microbiology; Miscellaneous; Multiplex PCR; Nasal carrier; Nose - microbiology; Penicillin-Binding Proteins; Polymerase Chain Reaction - methods; Selective broth; Sensitivity and Specificity; Staphylococcal Infections - microbiology; Staphylococcus aureus; Staphylococcus aureus - drug effects; Staphylococcus aureus - genetics; Staphylococcus aureus - growth & development; Staphylococcus aureus - isolation & purification
• ISSN: 0923-2508; 1769-7123
• DOI: 10.1016/j.resmic.2006.08.004

To improve efficiency in detecting nasal methicillin-resistant Staphylococcus aureus (MRSA), we evaluated a multiplex PCR using pre-enrichment of the specimen in selective broths, and compared it with detection performed by routine tests in hospital laboratories. Nasal swab specimens from 311 patients were inoculated onto mannitol–salt agar (MSA) at the hospital laboratories and in two Mueller–Hinton broths with 7% NaCl containing oxacillin at concentrations of 2 and 4 μg/ml. Isolates on MSA were identified as MRSA by classical laboratory tests (coagulase and oxacillin disk diffusion tests). Oxacillin broth cultures were subcultured on blood agar and MRSA isolates were identified by coagulase and susceptibility tests, including agar dilution and the oxacillin-screening method (gold standard method). Simultaneously, multiplex-PCR was performed from the selective broths to detect S. aureus species-specific and mecA gene segments (OxMPCR method). Thirty-two S. aureus isolates were recovered: 29 (90.6%) were MRSA strains and 3 (9.4%) were oxacillin-susceptible isolates. Twenty-eight (96.5%) MRSA isolates were detected by OxMPCR, while 17 (58.6%) were identified by routine tests ( P = 0.002 ). This new method for detection of MRSA nasal carriers showed higher sensitivity and led to faster reporting—i.e., within 24 h—of results.