Detection of methicillin-resistant Staphylococcus aureus directly by loop-mediated isothermal amplification and direct cefoxitin disk diffusion tests

ABSTRACT

We evaluated the utility of 2 methods for detection of methicillin-resistant Staphylococcus aureus [MRSA] directly from signal-positive blood culture bottles loop-mediated isothermal amplification [LAMP] assay, and direct cefoxitin disk diffusion [DCDD] test using a 30 microg cefoxitin disk. In parallel, standard microbiological identification and oxacillin susceptibility testing with MecA PCR was performed. Of 60 blood cultures positive for Gram-positive cocci in clusters, LAMP [via detection of the FemA and MecA genes] showed 100% sensitivity and specificity for identification of MRSA/MSSA. When coagulase-negative staphylococci were tested, sensitivity for detection of methicillin resistance was 91.7% and specificity was 100%. DCDD along with direct tube coagulase assay detected only 80.6% of MRSA/MSSA. LAMP showed higher diagnostic accuracy although DCDD was more cost-effective and did not require additional reagents or supplies