Investigation On The Antibacterial Activity Of Polymyxin B Against Pan-drug-resistant Pseudomonas Aeruginosa In Vitro

ObjectivePseudomonas aeruginosa is a primary pathogen in nosocomial infections.With wide use of antibiotics in the treatment of bacterial infection,pseudomonas aeruginosa has become resistant to antibiotics,even to earbapenem antibiotics like imipenem.The incidence of pan-drug-resistant pseudomonas aeruginosa was the highest in the intensive care units and followed by the department of neurosurgery.Respiratory tracts and the surgical wounds exhibited as the major infected sites.The aim of this study was to evaluate the in vitro antibacterial activity of polymyxin B and the combined effect of polymyxin B with three antibiotics(including levofloxacin,imipenem, piperacillin/tazobactam)against pan-drug-resistant pseudomonas aeruginosa strains.Methods30 isolates of pan-drug-resistant pseudomonas aeruginosa were collected from January 2006 to June 2007 in the First Affiliated Hospital of China Medical University, most of which were from ICU,neurosurgery and respiratory unit.The MICs of the antibiotics mentioned above were determined by broth dilution method,the MICs of the two antibiotics combined were determined by broth dilution test and check board method.FIC index was calculated according to MIC result of the activities of antibiotics alone and in combination against the strains. ResultsThe susceptibility rate of pan-drug-resistant pseudomonas aeruginosa to polymyxin B was 53.3%,the inter susceptibility rate was 46.7%,the resistance rate was zero.The MICs of every antimicrobial after combination were reduced significantly. 66.67%of tested bacterial after polymyxin B combined with levofloxacin revealed synergy,26.67%showed addition,6.67%exhibited indifference;46.67%of tested bacterial after polymyxin B combined with imipenem revealed synergy,40%showed addition,13.33%exhibited indifference;60%of tested bacterial after polymyxin B combined with piperacillin/tazobactam revealed synergy,33.33%showed addition, 6.67%exhibited indifference,according to the result of the FIC index assay.There was no antagonism.ConclusionPolymyxin B had good in vitro activity to pan-drug-resistant pseudomonas aeruginosa.Antibacterial activity of polymyxin B combined with other antibiotics against pan-drug-resistant pseudomonas aeruginosa was mainly synergistic and additive.I hope this study might be helpful in dealing with pan-drug-resistant pseudomonas aeruginosa.