Discordant β-Lactam Susceptibility in Clinical Staphylococcus aureus Isolates: A Molecular and Phenotypical Exploration to Detect the BORSA/MODSA Isolates in Bogotá, Colombia

Staphylococcus aureus is a human pathogen responsible for a wide range of diseases, such as skin and soft tissue infections, pneumonia, toxic shock syndrome, and urinary tract infections. Methicillin-resistant S. aureus (MRSA) is a well-known pathogen with consistently high mortality rates. Detecting the mecA resistance gene and phenotypical profile to β-lactams allows for the differentiation of MRSA from methicillin-susceptible S. aureus (MSSA) isolates. In this study, we characterized 57 S. aureus clinical isolates for β-lactam susceptibility and mecA presence. We classified 52.63% as MRSA and 45.61% as MSSA. However, some isolates evidenced different oxacillin resistance profiles, such as borderline oxacillin-resistant or modified S. aureus (BORSA/MODSA). The cefazolin inoculum effect (CzIE) was established for these samples, emphasizing the relevance of these isolates as a source of therapeutic failure. We also performed the detection of the Panton-Valentine Leucocidin virulence genes as well as the S. aureus spa-type clonality. As expected, spa-types t002 and t008 were the most prevalent clones, demonstrating the success of well-established clones. These findings emphasize the importance of establishing sensitivity profiles, especially in isolates with poor resistance mechanisms, to determine their prevalence and their impact on public health.