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Methicillin-resistant Staphylococcus aureus: A challenge for infection control

Objective The aim of this study was to evaluate a method for rapid and direct detection of methicillin-resistant Staphylococcus aureus (MRSA), allowing clinicians to make prompt decisions for the management of patients with staphylococcal bacteremia. Background The prevalence of methicillin resistance in nosocomial staphylococci has increased in the past decade. There has also been a recent increase in community-acquired MRSA infections in patients without apparent recognized risk factors. Patients and Methods In this work, blood culture was performed for all cases for isolation of the causative organisms. Staphylococcal isolates were then identified by standard methods including Gram stain, catalase, and bacitracin susceptibility tests. This was followed by testing the staphylococcal isolates with oxacillin using the disc diffusion method. All positive blood cultures were subjected to a multiplex PCR assay targeting 16S rRNA, nuc, and mecA genes. Results Our results showed that blood cultures were positive for 85% of the patients. Staphylococci accounted for 58.8% of the positive cases. In total, 52% of the isolated staphylococci were S. aureus and 48% were coagulase-negative staphylococci (CoNS). 76.9% of S. aureus isolates were MRSA; 23.1% were methicillin-sensitive S. aureus. 91.7% of CoNS isolates were methicillin-resistant CoNS and 8.3% were methicillin-sensitive CoNS. The sensitivity and specificity of the oxacillin disk diffusion method in relation to mecA PCR were 95.2% and 87.5%. The total time required to perform the multiplex PCR assay directly from positive blood cultures was 3 h. Conclusion Current standard laboratory methods for detection of oxacillin resistance require at least 48–72 h for isolation, identification, and susceptibility testing. The multiplex PCR assay is a rapid, sensitive, and specific method for the detection of MRSA colonies and MRSA-positive blood culture bottles.