Fatal sepsis caused by mecA-positive oxacillin-susceptible Staphylococcus aureus: First report in a tertiary hospital of southern Brazil.

mecA-positive oxacillin phenotypically susceptible Staphylococcus aureus (OS-MRSA) is increasingly reported worldwide. This bacterium poses a therapeutic threat, as it can be misidentified as an oxacillin-susceptible organism by phenotypic methods that are routinely used in the majority of clinical microbiology laboratories. Herein, we report the first case of fatal sepsis in a 43-year-old female patient caused by an OS-MRSA SCCmec type IVa/ST1/CC1 in a tertiary hospital in southern Brazil, which highlights the difficulties involved in diagnosing this bacterium. Blood cultures and phenotypic susceptibility tests on admission yielded a penicillin-resistant S. aureus. Although vancomycin therapy was initiated, this antibacterial was replaced by oxacillin, based on the susceptibility result. However, the clinical conditions of the patient deteriorated rapidly evolving to fatal septic shock. Clinical microbiology laboratories should consider the use of additional tests to accurately distinguish between various antimicrobial phenotypes of S. aureus.