In Vitro Activity of Linezolid in Combination with Vancomycin, Teicoplanin, Fusidic Acid, and Ciprofloxacin Against Gram-Positive Pathogens

Objective: In this study, it was aimed to investigate in vitro activities of linezolid combined with vancomycin, teicoplanin, fusidic acid, and ciprofloxacin against Gram-positive pathogens. Material and Methods: This study was conducted at Ego University, Faculty of Pharmacy, Department of Pharmaceutical Microbiology. Clinical isolates used in this study were obtained retrospectively from the collection of Ege University Medical Faculty, Department of Microbiology and Clinical Microbiology, Bacteriology Laboratory. Minimal inhibitor concentrations (MICs) of test strains_methicillin-susceptible Staphylococcus aureus (MSSA), methicillin-resistant S. aureus (M RSA), vancomycin intermediate S. aureus (VISA), Mu50 (vancomycin intermediate S. aureus strain), methicillin-susceptible Staphylococcus epidermidis (MSSE), methicillin-resistant S. epidermidis (MRSE), vancomycin-susceptible Enterococcus faecalis (VSE) and vancomycin-resistant E. faecalis (VRE)) were determined by microdilution method. Time-kill studies were performed over 24 busing an inoculum of 5 x 10(6) and 1 x 10(7) CFU/mL. Antibiotics were tested at concentrations 1x and 4 x MIC (minimum inhibitory concentration). Results: Synergy was detected between linezolid plus teicoplanin and fusidic acid at 1 x MIC concentrations in MSSA strain. In MRSE strain, linezolid showed the same effect with fusidic acid at 1x MIC. Antagonistic effect was found linezolid plus vancomycin and teicoplanin (4 x MIC) in VSE and linezolid plus ciprofloxacin (4 x MIC) in MRSE strain. Conclusion: In this study, linezolid plus fusidic acid appeared to be the most active combination against Gram-positive pathogens.