Objective: Bloodstream infections are important causes of morbidity and mortality in hospitalized patients. The objective of this investigation was to evaluate the in vitro susceptibilities of ceftaroline, linezolid and vancomycin, against methicillin-resistant Staphylococcus aureus (MRSA) and coagulasenegative staphylococci (MRCoNS) strains grown in blood cultures.

Method: A total of 50 MRSA and 50 MRCoNS strains isolated from blood cultures between January 2015-February 2018, were included in this study. Only one isolate from each patient was included in the study. Bacterial identification was performed by conventional methods (Gram staining, catalase, coagulase testing) and the resistance of the isolates to methicillin was determined using cefoxitin (30 μg) Kirby-Bauer disk diffusion method according to EUCAST susceptibility criteria. The minimum inhibitory concentration (MIC) values for vancomycin and linezolid were determined according to the gradient strip diffusion method. Susceptibility testing of ceftaroline was performed by using the broth microdilution method as recommended by CLSI.

Results: All isolates tested were found to be susceptible to linezolid (MIC<1 μg/ml) and vancomycin (MIC<2 μg/ml). Ceftaroline was detected to be susceptible in 45/50 (90%) of the MRSA isolates. MIC50 and MIC90 values of ceftaroline for MRSA were found as 0.5 μg/ml and 1 μg/ml, respectively, with a MIC range of 0.125-2 μg/ml. MIC50 and MIC90 values of ceftaroline for MRCoNS were found as 0.25 μg/ml and 0.5 μg/ml, respectively, with a MIC range of 0.125-2 μg/ml.

Conclusion: The fifth generation cephalosporin, ceftaroline that has not been in use in our country yet, showed a similar in vitro activity as vancomycin and linezolid against MRSA and MRCoNS isolates. These findings suggest that ceftaroline could be a good therapeutic option for the treatment of infections caused by MRSA and MRCoNS.