A Comparison of the Minimum Inhibitory Concentration of Antibiotics in Staphylococcus Species Isolated From Orthopedic and Respiratory Medicine Infections.

Introduction: Antibiotic susceptibility is very important for the successful treatment of orthopedic infections, particularly for implant-related infections. While the minimum inhibitory concentrations (MICs) of species were well investigated for the isolates from the respiratory tract, investigations for orthopedic pathogens are very limited. We investigated the antibiotic MIC values of species isolated from orthopedic infections and compared them with those of respiratory medicine isolates used as a control.

Methods: The MICs of vancomycin (VCM), arbekacin (ABK), teicoplanin (TEIC), linezolid (LZD), and rifampicin (RFP) of a total of consecutive 259 (89 orthopedic and 170 respiratory) speciesisolated in our laboratory from January 2013 to July 2016 were retrospectively reviewed. Differences between the MICs of each antibiotic in orthopedic and respiratory samples were determined.

Results: The number of methicillin-sensitive (MSSA) with a VCM MIC of <0.5 μg/mL among respiratory isolates was significantly higher than that among orthopedic isolates, while those with a MIC of 2 μg/mL were significantly lower (P = 0.0078). The proportion of methicillin-resistant coagulase-negative staphylococci (MRCNS) isolates with a VCM MIC of 2 μg/mL was significantly higher in orthopedic samples than that of methicillin-resistant (MRSA) (P < 0.001) in respiratory isolates. The proportion of MRCNS orthopedic isolates with an RFP MIC of >2 μg/mL was significantly higher (P = 0.0058) than that of other orthopedic staphylococci.

Conclusions: The VCM MICs of species from orthopedic infections were higher than those of respiratory samples, particularly MRCNS from implant-related samples.