Case Commentary: The hidden side of oxacillin resistance in Staphylococcus aureus

Acquisition of PBP2a (encoded by the mec gene) is the key resistance mechanism to beta-lactams in Staphylococcus aureus. The mec gene can be easily detected by PCR assays; however, these tools will miss mec-independent oxacillin resistance. This phenotype is mediated by mutations in cell wall metabolism genes that can be acquired during persistent infections under prolonged antibiotic exposure. The complex case presented by Hess et al. (Antimicrob Agents Chemother 67:e00437-23, 2023, https://doi.org/10.1128/aac.00437-23) highlights the diagnostic and therapeutic challenges in the management of mec-independent oxacillin resistance.

Automated summary

Acquiring PBP2a is crucial for Staphylococcus aureus to develop resistance to beta-lactam antibiotics. While mec gene can be easily identified using PCR assays, these tools are not effective in detecting mec-independent oxacillin resistance. This study highlights the diagnostic and therapeutic challenges in managing mec-independent oxacillin resistance.