Characterization Of Biofilm Formation By Clinical Heterogeneous Vancomycin-intermediate Methicillin-resistant Staphylococcus Aureus Exposed To Vancomycin

Objective: the precise mechanism of vancomycin involvement in biofilm formation by heterogeneous vancomycin-intermediate Staphylococcus aureus(h VISA),especially by clinical isolates,remains unclarified.The present study aimed to investigate the effect of vancomycin on the major components of biofilm formation by clinical h VISA,and its association with the high frequency of failure in vancomycin treatment failure of h VISA.Methods:(1)Clinical h VISA were defined by the population analysis profile(PAP)with an area under the curve(AUC)ratio(PAP / AUC).(2)A clinical strain of h VISA(05307)and the Mu3 strain(ATCC 700698,used as h VISA reference)were exposed to different concentrations(1/4×MIC,1/2×MIC,1×MIC)of vancomycin.The broth alone and the bacterial suspension without antibiotics were served as negative and positive controls,respectively.(3)The biofilm biomass of h VISA was measured using the crystal violet(CV)staining and(4)visualized under the Confocal laser scanning microscopy(CLSM).(5)Protein components,polysaccharide intracellular adhesin(PIA)and extracellular DNA(e DNA)in the extracellular matrices(ECM)were quantified directly and indirectly,respectively.Results:(1)One fold minimal inhibitory concentration(MIC)vancomycin enhanced the biofilm formation by h VISA,however no effects of this concentration was noted on the biofilm formation in the two strains when the bacteria were exposed to sub-MICs vancomycin compared with the positive controls.(2)Additionally,no significant increase of PIA and protein components production were observed.(3)Vancomycin-enhanced biofilm formation was remarkably suppressed to a level similar to vancomycin-untreated cells following DNase ? administration.Conclusions: The 1× MIC vancomycin induced release of e DNAs is an essential factor for vancomycin-enhanced biofilm formation of h VISA,which may help account for the failure of vancomycin treatment in h VISA infections.