Dissemination Of t437-SCCIV And Coagulase-Negative t037-SCCIII Types Among Borderline Oxacillin-Resistant Isolated From Skin Infections And Diabetic Foot Ulcers.

Background: In a recent decade, the occurrence of isolates with low-level oxacillin resistance, have been reported increasingly. The aim of this study was to estimate the prevalence of with low-level of oxacillin resistance and to determine their molecular characteristics, including types, SCC types and presence of toxin genes.

Methods: A total of 249 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 A gene and virulence factors, including Panton-Valentine leukocidin (PVL). Staphylococcal cassette chromosome (SCC) typing and 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 carrying gene (OS-MRSA). Among the 12 bordeline strains, five types (t437, t037, t015, t216, t267) and two SCC types (III, IV) were identified, with the most prevalent being t437-SCCIV -positive. The second most frequent type, t037-SCCIII, was -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 with borderline resistance to oxacillin represented primarily SCCIV type t437 and coagulase-negative SCCIII type t037 and were isolated from skin infections and diabetic foot ulcers.