Dissemination Of t437-SCC mecIV And Coagulase-Negative t037-SCC mecIII Types Among Borderline Oxacillin-Resistant Staphylococcus aureus Isolated From Skin Infections And Diabetic Foot Ulcers

Abstract

Background

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, SCC mec 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 (SCC mec) 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 SCC mec types (III, IV) were identified, with the most prevalent being t437-SCC mecIV pvl-positive. The second most frequent spa type, t037-SCC mecIII, 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 SCC mecIV spa type t437 and coagulase-negative SCC mecIII spa type t037 and were isolated from skin infections and diabetic foot ulcers.