spa-deletion MRSA

Microbiological testing identified the organism as methicillin-resistant Staphylococcus aureus, but the MRSA rapid gene cartridge yielded a false-negative result. Matrix-assisted laser desorption ionisation-time of flight mass spectrometry identified the organism as S. aureus, but genetic testing was negative for S. aureus. There was no discrepancy between the antimicrobial susceptibility test and genetic testing. The false-negative result for S. aureus was attributed to the absence of the spa gene.