Study Of Anti-MRSA Activity Of Linezolid Combined With Other Antibiotics In Vitro

PurposeStaphylococcus aureus (Staphylococcus aureus,SA) is an important cause of suppurative disease pathogens,and is the most virulent pyogenic bacteria.Has now been confirmed with the same MRSA and other staphylococal virulence and pathogenicity.At present,methicillin-resistant Staphylococcus aureus nosocomial infection has become one of the important pathogens.MRSA in health care organizations around the world to spread. Glycopeptide antibiotics is the main drug treatment of MRSA. Because MRSA infections increasing year by year and the clinical use of vancomycin increased,SA resistance to vancomycin has become increasingly serious. Developed in recent years, many of the multi-drug resistant gram-positive bacteria (including MRSA, VISA) has a good antibacterial drugs, in our current listing only linezolid. In the treatment of infections caused by MRSA, clinical cure rate, whether or bacterial clearance rate, linezolid superior to vancomycin, linezolid alternative to vancomycin in treatment of MRSA. However, with the large-scale public use of the drug in clinical work, continuing linezolid-resistant strains were reported. Some scholars abroad reported linezolid and other antibiotics in vitro combined treatment of MRSA, the result is MRSA strains have synergistic or additive effect, enhances the antibacterial activity of linezolid. In this study, linezolid and three kinds of commonly used antibiotic (rifampicin, levofloxacin, gentamicin factor) were combined, against clinical isolates of MRSA in vitro antibacterial activity, as clinically effective in the treatment of MRSA infections and provide experimental evidence.MethodMethod of bacteria isolated from conventional methods to obtain pure cultured microorganism with the VITEK automatic analyzer to identify Staphylococcus aureus, and then according to CLSI (2006) standard, with the broth method with the determination of oxacillin MIC values, MIC value determined result≥4μg/ml for the MRSA strain. Susceptibility test methods using broth dilution method. Determination of four kinds of antimicrobial drugs first tested the MIC values alone. The combined sensitivity test method designed by the board to determine linezolid in conjunction with the other three kinds of antibiotics used for MIC. Inhibition index calculated part of the FIC (fractional inhibitory concentration index). FIC index=MIC A drug combined with/MIC A drug alone + MIC B drugs combination/MIC drug B alone. Interpretation of standards:FIC index≤0.5, synergy;> 0.5-1.0. Additive effect;> 1.0-2.0, no relevant effect;> 2.0, antagonism.ResultLinezolid MIC against 30 strains of MRSA in the range of 0.5-4 ug/ml, MIC90 was 4 ug/ml, levofloxacin against 30 strains of MRSA in the MIC range of 16-256 ug /ml, MIC90 for the 256 ug/ml, rifampicin level of the 30 MRSA the MIC range of 8-256 ug/ml, MIC90 for the 256 ug/ml, and gentamicin against 30 strains of MRSA in the MIC range of 128-1024 ug/ml, MIC90 was 1024 ug/ml.Linezolid combined with levofloxacin MIC90 reduced to 2 ug/ml, linezolid and rifampicin combined with MIC90 reduced to 1 ug/ml, linezolid combined with gentamicin MIC90 reduced to 2 ug/ml.ConclusionLinezolid has high sensitivity of the MRSA, linezolid and rifampicin in combination with synergistic based, linezolid and levofloxacin, gentamicin in combination with synergistic and additive effect dominated, both of no antagonism.