BackgroundIn 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.MethodsA 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.ResultsTwelve (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).ConclusionThis 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.

Diabetic foot ulcer (DFU) is one of the most common chronic complications of diabetes. This study aimed to assess the factors with an impact on the infection of diabetic foot ulcers by methicillin-resistant S. aureus and to evaluate the influence of methicillin resistance on the frequency of osteitis (based on classic X-ray images). A total of 863 patients suffering from DFU were analyzed during the study period. Out of 201 isolated S. aureus cases, 31 (15.4%) were methicillin-resistant (MRSA). MRSA infections were associated with a higher incidence of osteitis compared to MSSA infections (p << 0.0001), both the occurrence of smaller (<50%)) and greater (>50%) inflammatory bone changes (p << 0.0001). Furthermore, MRSA occurred significantly more frequently in men than in women (p < 0.01) and more often among patients with type 2 diabetes than among patients with type 1 diabetes (p < 0.05). MRSA were isolated statistically less often in overweight patients than in patients with normal BMI (p < 0.05). DFUs infected with MRSA were significantly more frequently associated with the presence of Pseudomonas sp. and other non-fermenting bacilli than those infected with MSSA (p < 0.05). To conclude, osteitis incidence is related to MRSA infection in patients with diabetic foot ulcers; thus, patients infected by S. aureus should be closely monitored in the course of using antibiotics and treated with narrow-spectrum antibiotics.