Study The Activity Of Fusidic Acid Combined With Fosfomycin Against MRSA Bacterial Biofilm

【Objective】To investigate the in vitro effects of fusidic acid combined with fosfomycin against 196 MRSA isolated from clinical. To evaluate fusidic acid combined with fosfomycin against MRSA biofilm in vitro and in vivo, and study fusidic acid combined with fosfomycin against MRSA biofilm in hypo-immunity rats radiationed by 60Co.【METHOD】(1)A checkerboard method that adhered to the recommendations of the National Committee for Clinical Laboratory Standards was applied to assess the synergism effect between fusidic acid and fosfomycin,the FIC Index was calculated according to the results.Observe the morphology of the MRSA by SEM and AFM.(2)The modified plate culture method was used to establish MRSA biofilm model in vitro and the morphology of biofilms were observed by silver staining. To evaluate the effect of "Time-lag therapy" of the fusidic acid combined with fosfomycin on MRSA biofilm by viable count method and SEM.(3) To establish a rat model of burned and MRSA BBF infection. Observe the vital sign, blood test, colony count of the infected tissuse. Evaluate the effects of a combination of fusidic acid combined and fosfomycin on the model through viable count method and SEM.(4) To establish a 60Co radiation, burned and MRSA BBF infection rat model. Evaluate the effects of a combination of fusidic acid and fosfomycin on the model through observing the vital sign, blood test, colony count of the infected tissues, IL-6, CRP, pathology of skin and marrow.【RESULT】(1) The combination of fusidic acid and fosfomycin demonstrated the following interactions:87.76%(172/196) synergism; 12.24%(24/196) indifference; and no antagonism was seen. (2) Silver staining of MRSA morphological results show that cluster Spherical surrounded by dense black stained film-like substance. The Single and combination drugs all can affect the MRSA biofilm (1 day model and 7 day model) in vitro by viable count method. The efficacy of the combination(FA/FOM 16/256μg/ml) was greater than the single drugs (FA16μg/ml,FOM256μg/ml) on 1 day and 7day MRSA BBF model(p<0.05) because the detectable colony count decrease >2 log10, synergism were defined as a decrease>2 log10. The SEM observed the complicated fibrous structures, cells and colonies of bacteria are shown from the model group. The SEM results of the combination FA and FOM showed marked change in the appearance of the biofilm, with a considerable reduction in the density of adherent bacteria and biofilm structures.(3) The WBC,Monocyt, neutrophilic granulocyte of the model rat serum is far higher than the normal. The WBC, Monocyte, Neutrophilic granulocyte of the FOM rats and FA/FOM rats decreased significantly than the model rats normal. The efficacy of the combination FA/FOM was greater than the single drugs because the detectable colony count decrease >2 loglO.The SEM observed the complicated fibrous structures, cells and colonies of bacteria are shown from the model group. The scanning electron micrograph from the combination FA and FOM showed marked change in the appearance of the biofilm, with a considerable reduction in the density of adherent bacteria than FOM single dose and several MRSA structures is changed.(4) The WBC of the model rat decreased to the minimum in the third days after injury, The WBC still lower on the 7th day after injury. After 7 days administration the CRP, IL-6 of the model rat is higher than the normal; IL-6 of the FOM group are higher than the normal. CRP and IL-6 of the FA combined with FOM group is normal. The detectable colony count decreases >2 log10. Some blood in the marrow cavity, blood-producing function is damaged in the model rats. There were a large number of bacterial colonies, neutrophils in the model, suggesting a severe inflammatory response associated with the infection. Nothing found in the FA/FOM group. These histological findings indicated that the inflammatory reaction associated with MRSA BBF infection was also suppressed by the combined treatment with FA and FOM. 【CONCLUSION】In vitro the combination of FA and FOM presented synergistic on MRSA. MRSA biofilm infection was also suppressed by the combined treatment with FA and FOM in vitro and in vivo. FA combined with FOM can also against MRSA biofilm in hypoimmunity rats radiationed by 60Co.