Comparison of Xpert MRSA/SA Nasal and MRSA/SA ELITe MGB Assays for Detection of the mecA Gene with Susceptibility Testing Methods for Determination of Methicillin Resistance in Staphylococcus aureus Isolates

ABSTRACT In a series of 82 Staphylococcus strains isolated from culture, 100% were identified as Staphylococcus aureus by matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS); 99.9% (77/82) of them were resistant to benzylpenicillin, oxacillin, and cefoxitin, and 6.1% (5/82) were susceptible to methicillin. Xpert MRSA/SA assay results were concordant with the phenotypic results in 76.8% (63/82) of cases and discordant in 23.2% (19/82) of cases. The MRSA/SA ELITe MGB kit results were concordant with phenotypic results in 100% of the cases. When comparing the Xpert MRSA/SA assay results with the MRSA/SA ELITe MGB kit results, 78% (64/82) of the cases were concordant, while 22% (18/82) of the cases were discordant. No statistically significant differences were observed between the two techniques. The PCR protocol that was used to validate the results of these two methods gave the following results: 49 were conventional methicillin-resistant S. aureus (MRSA) isolates ( mecA positive and mecA LGA251 negative), and 25 were phenotypic MRSA isolates ( mecA negative and mecA LGA251 positive).