Résumé
OBJECTIVE To evaluate the antibiotic susceptibility on coagulase negative staphylococci(CNS) in Xiangya Hospital and to investigate the role of slime in the resistance mechanism of biofilms.METHODS To isolate and identify CNS from clinical(specimens).The susceptibility of 15 antibiotics was tested by the disc diffusion method.The quantity of slime(produced) by CNS was measured by the colorimetric method.Slime was isolated from selected strains of CNS and analyzed by SDS-PAGE.The MICs to vancomycin,gentamicin and rifampin were determined with and(without) the addition of extracted slime by a standard microtiter method.RESULTS Of all these 15 antibiotics,the highest resistance to CNS was penicillin,followed by erythromycin and trimethoprim-sulfamethoxazole.CNS was more susceptible to ampicillin/sulbactam and rifampin.None was resistant to vancomycin.All of 158 CNS,except one strain,could produce slime.There was a statistical difference between the quantities of slime produced by CNS that produced high and low quantity slime.However,there was a non-statistical difference of resistance to these 15 antibiotics of above CNS. There was an increase in the MICs to vancomycin and gentamicin,but no in the MIC to rifampin,in the absence of 20mg/ml extracted slime.The extracted slime seemed to be similar to the glycosaminoglycans(GAG);it had mobility similar to that of chondroitin sulfate.CONCLUSIONS CNS can(produce slime) on some condition,universally,then to form biofilms.However,in vitro susceptibility testing(employed) cannot really reflect the susceptibility of bacteria in biofilms in vivo.Slime can increase the MICs to vancomycin and gentamicin because of interference with either the antimicrobial action of these drugs or the(perfusion) of these drugs through the medium to increase the resistance of biofilms.It does not affect the MIC to rifampin.