Improved and rapid detection of methicillin-resistant Staphylococcus aureus nasal carriage using selective broth and multiplex PCR.
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 micro g/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.
Schuenck
Ricardo P
RP
Departamento de Microbiologia Médica, Instituto de Microbiologia Prof Paulo de Góes, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
Lourenco
Maria Cristina S
MC
Iório
Natália L P
NL
Ferreira
Adriana Lúcia P
AL
Nouér
Simone A
SA
Santos
Kátia Regina N
KR
D001426:Bacterial Proteins / Q000235:genetics*; D002353:Carrier State / Q000382:microbiology*; D003470:Culture Media; D006801:Humans; D016106:Methicillin Resistance / Q000235:genetics*; D009666:Nose / Q000382:microbiology*; D046915:Penicillin-Binding Proteins; D016133:Polymerase Chain Reaction / Q000379:methods*; D012680:Sensitivity and Specificity; D013203:Staphylococcal Infections / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics / Q000254:growth & development / Q000302:isolation & purification*
D001426:Bacterial Proteins; D003470:Culture Media; D046915:Penicillin-Binding Proteins; C487789:mecA protein, Staphylococcus aureus