In vitro activity of linezolid alone and in combination with glycopeptides against methicillin-resistant Staphylococcus aureus

The emerging resistance to antibiotics and the poor pipeline of new antibacterials is creating a major health issue worldwide. Combinations of two antibiotics or antibiotics with adjuvant are emerging as a promising therapeutic approach. Staphylococcus aureus represents a major threat to a broad range of healthcare and community associated infections. It is imperative to develop novel antimicrobial strategies to enrich the currently shrinking therapeutic options against Staphylococcus aureus. In this study, we had assessed the in vitro activities of linezolid alone and in combination with vancomycin or teicoplanin against 54 methicillin-resistant Staphylococcus aureus (MRSA) strains using agar dilution method in conjunction with scanning electron microscopy. MIC50 of linezolid is 2μg/ml while those of vancomycin and teichoplanin are 8μg/ml and 16μg/ml respectively. The percentage of resistant isolates to linezolid, vancomycin and teicoplanin was 5%, 9.2% and 14.8% respectively. So this study reveals the superiority of linezolid as a single agent over vancomycin and teicoplanin against MRSA isolates. The combination of linezolid/vancomycin showed better results than linezolid/teicoplanin among all concentrations. Linezolid/vancomycin and linezolid/teicoplanin acted synergistically against 78% and 50% of the MRSA isolates respectively. There was an increase in the percentage of inhibition of the tested strains due to linezolid/glycopeptide combination compared to each drug alone. There was visible cell destruction using scanning electron microscope with either vancomycin or teicoplanin combination with linezolid compared to using a single antibiotic. Synergyism may be promising for more effective chemotherapy, particularly against MRSA strains. However, testing of the combinations in animal models or in actual clinical situations is warranted.