Study On AdeABC Efflux Pump Mechanisms Of Multi-drug Resistant Acinetobacter Baumannii

In the last dacade,an increasing incidence of nonfermentative gram negative bacillus emerged,especially Acinetobacter spp.(mostly Acinetobacter baumannii) and Pseudomonas aeruginosa.A.baumannii currently became one of the most important clinical pathogens,such as Pseudomonas aeruginosa.A.baumannii is emerging as a cause of numerous global outbreaks,displaying ever-increasing rates of resistance.Occurrence and outbreak of carbapenem resistant A.baumannii had become a difficult problem to the clinician and public health. AdeABC type efflux pump system was reported by Magnet S in A.baumannii in 2001, it could mediate resistance to aminoglycoside,fluquinolone,tetracycline,erythrocin, trimethoprim;also the excessive expression of the system might play an important role in resistance to carbapenems and tigecycline.We collected 700 isolates of A.baumannii from 21 hospital of 5 province in China through December 2004 to December 2005.According to the result of PFGE typing and the area distribution,total of 113 isolates,including 101 MDRAB and 12 susceptible isolates,were screened to further studied.Substance1.PFGE was used to type the relateness of MDRAB.2.MICs were determinated by agar dilution or Etest strips,including polymycin E, cefoperazone-sulbactam,pipracillin/tazobacam,tigecycline,imipenem,meropenem, minocycline,pipracillin,ciprofloxacin,amikacin,gentamycin,ceftazidime, cefotaxime.3.PCR was used to detecte the efflux genes adeA,adeB,adeC and the regulator genes adeR and adeS.Efflux pump inhibitor PAβN was used to in the EPI inhibit test.Real time RT PCR was also used to determinate the expression level of adeB gene.Result1.AdeABC efflux genes distributed widely in A.baumannii of China,both in the MDRAB and susceptible isolates,regardless of area and pulse-clone.While,the regulator genes adeS and adeR seemed to prefer MDRAB.2.Among MDRAB,the high expression of adeABC efflux pump played an important role in imipenm,and mightbe link with meropenm and tigecycline resistance. The more decrease of MICs under the EPIs indicated the higher expression of adeB gene.3.Under the 50mg/L PAβN,isolates with MICs of carbapenems decreasing more than or equal to 4 folds could be defined as efflux phenotype.50mg/L PAβN could not inhibit tigecycline to be discharged.