| Summary: | Maria Stańkowska,1 Katarzyna Garbacz,1 Lidia Piechowicz,2 Marek Bronk3 1Department of Oral Microbiology, Faculty of Medicine, Medical University of Gdansk, Gdansk, Poland; 2Department of Medical Microbiology, Faculty of Medicine, Medical University of Gdansk, Gdansk, Poland; 3Laboratory of Clinical Microbiology, University Clinical Center, Gdansk, PolandCorrespondence: Katarzyna GarbaczDepartment of Oral Microbiology, Medical University of Gdansk, 25 Dębowa St, Gdansk 80-204, PolandTel +48 58 349 1900Fax +48 58 349 1668Email katarzyna.garbacz@gumed.edu.plBackground: In a recent decade, the occurrence of S. aureus isolates with low-level oxacillin resistance, have been reported increasingly. The aim of this study was to estimate the prevalence of S. aureus with low-level of oxacillin resistance and to determine their molecular characteristics, including spa types, SCCmec types and presence of toxin genes.Methods: A total of 249 S. aureus strains were analyzed. Antimicrobial susceptibility was preliminarily tested by the disk diffusion method, and further was verified with the E-test and agar dilution methods. All borderline oxacillin-resistant strains (BORSA) were screened for the mecA gene and virulence factors, including Panton-Valentine leukocidin (PVL). Staphylococcal cassette chromosome mec (SCCmec) typing and spa typing were also carried out.Results: Twelve (4.8%) borderline oxacillin-resistant strains with MIC ≤4 μg/mL were identified. Almost all strains (11/12) were oxacillin-susceptible methicillin resistant S. aureus carrying mecA gene (OS-MRSA). Among the 12 bordeline strains, five spa types (t437, t037, t015, t216, t267) and two SCCmec types (III, IV) were identified, with the most prevalent being t437-SCCmecIV pvl-positive. The second most frequent spa type, t037-SCCmecIII, was sea-positive and did not produce coagulase. The majority of borderline strains originated from skin infections and diabetic foot ulcers and were multidrug-resistant (macrolides, lincosamides and chloramphenicol).Conclusion: This study demonstrated that S. aureus with borderline resistance to oxacillin represented primarily SCCmecIV spa type t437 and coagulase-negative SCCmecIII spa type t037 and were isolated from skin infections and diabetic foot ulcers.Keywords: Staphylococcus aureus, MRSA, OS-MRSA, borderline oxacillin-resistant S. aureus, low-level oxacillin resistance
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