Study On The Resistance, The Class B And D Of Carbapenemases In Acinetobacter Baumannii

Background Soon after introducing the clinical use of carbapenems, such as imipenem, meropenem and so on, carbapenem-resistant Acinetobacter were firstly isolated from Acinetobacter baumannii in the United States of America in 1991. Then, Emergence of Acinetobacter baumannii with resistance or reduced susceptibility to carbapenems has been reported worldwide. Acinetobacter baumannii is an emerging nosocomial pathogen that is in part due to the capacity of acquiring resistance to multiple antimicrobial agents. Infection caused by carbapenemases producers increased year by year, and has been reported to cause epidemic outbreak in some hospitals. Resistance of carbapenemases was the most important problem of hospital-acquired drug resistance in the world. Acinetobacter may develop resistance to carbapenems through various mechanisms, including decreased permeability, efflux pump overexpression, and production of carbapenema. Mostly, carbapenemase included the class B(metallo-beta-lactamases) and the class D carbapenem-hydrolyzing oxacillinases. Carbapenem-hydrolyzing OXA enzymes are the most important cause of carbapenem resistance in A. baumannii worldwide.Oxacillinases are enzymes belonging to the molecular class Dβ- lactamases and are included in group 2d of the classificationof Bush et al. They can hydrolyze carbopenems, penicillins, cephalosporin and aztreonam, and so on.MBLs are class B beta-lactamases that are able to hydrolyze carbapenems as well as every other betalactams with the exception of aztreonam, this results in carbapenems and other antibiotics resistance. In view of lacking wide-ranging investigation about the prevalence of carbapenemases in Anhui, we studied the resistance in 141 Acinetobacter baumannii isolates in the part hospital of Anhui Province in 2005.Objective To investigate the resistance in 141 clinical isolates of Acinetobacter baumannii to 15 kinds of antimicrobial agents for the rational application of antimicrobial agents.Methods 141 isolates of Acinetobacter baumannii were tested for minimus inhibitory concentration (MIC) to 15 kinds of antimicrobial agents using agar dilution method;The antimicrobial agents included meropenem, imipenem, piperacillin, and so on.Results The lowest resistance rate of Acinetobacter baumannii to the antimicrobial agents was imipenem (6.4%), then was meropenem and cefoperazone/sulbactam(20.5%, 29.7%). The highest resistance rate was tetracycline (81.5%). The resistance rate to other antimicrobial agents was about or more than 50%.Conclusions Most of Acinetobacter baumannii isolates are susceptible to meropenem, imipenem, and cefoperazone/sulbactam and resistant to other antimicrobial agents, it is especially significant multidrug resistance in imipenem-resistant and/or meropenem-resistant Acinetobacter baumannii isolates, therefore, we should enhance to detect and survey those isolates. Background By now, there have been many types of carbapenemase, including OXA, IMP, VIM and so on. These began to be described over a decade ago( in1993) with the description of ARI-1( later renamed OXA-23) in an imipenem-resistant Acinetobacter baumannii strain from a patient in the Edinburgh Royal Infirmary. Since then, carbapenem-resistant isolates of A. baumannii carrying oxacillinases have been reported worldwide. Four of the eight carbapenemase-hydrolyzing oxacillinase (OXA) clusters have been identified in A. Baumannii, including the OXA-23, OXA-24, OXA-51, and OXA-58enzymes and their variants. IMP MBLs were first described in a strain of P. Aeruginosa found in Japan in 1988. Although MBLs are not the predominant carbapenemases in A. baumannii, several have been described: IMP-1, IMP-2, IMP-4, IMP-5, IMP-6, and IMP-11. The broad-spectrum VIM MBLs possesses 30- 40%identity with IMP MBLs, VIM-1 was first identified in Italy in 1997 in a P.aeruginosa isolate; A. baumannii harboring VIM-2 has been reported only in Korea. The main type of carbapenemase was different in countries and areas. Infection caused by carbapenemase producers increased year by year, and has been reported to cause epidemic outbreak in some hospitals. Carbapenemase producing Acinetobacter baumannii was the most important problem in clinic. OXA, IMP, VIM carbapenemase have been reported all around the world, including UK, Spain, Belgium, and Singapore. Owning to different favorite drug, the spreading type of carbapenemases was then different in countries and areas. So, understanding drug resistance profile and type distribution of carbapenemase producing strains can help us preventing regional spreading and guiding clinical therapy. In view of carbopenems was widely used in our country, so it caused the spreading of carbapenemase. To understand the genotype distribution of carbapenemase and drug resistance profile in Anhui province, we perform a series of molecular biology study on A. baumannii isolates collected from imipenem and/or meropenem-resistant Acinetobacter baumannii isolates.Objective To investigate the genetype of carbapenemase produced by imipenem- resistant and/or meropenem-resistant Acinetobacter baumannii, the molecular epidemiology was screened by ERIC-PCR.Methods A total of 29 strains of imipenem-resistant and/or meropenem-resistant Acinetobacter baumannii were screened by PCR with primer pairs designed to detect genes encoding OXA-23, 24, 51, 58 and VIM, IMP enzymes, respectively. The study of molecular epidemiology was carried by ERIC-PCR.Results In 29 carbapenemase producers, OXA-24 and IMP were at most (including other carbapenemases producing simultaneously), were 51.7% respectively(15/29). the positive strains of OXA-24+IMP, OXA-24+OXA-51+IMP, VIM, OXA-24+OXA-58+IMP, OXA-23+OXA-24+IMP, OXA-23+IMP, OXA-51+OXA-24, OXA-24, IMP, were 5, 4, 4, 2, 2, 1, 1, 1, 1, respectively. The ERIC-PCR pattern was same in 2 isolates producing OXA-24+IMP, which were same in 2 isolates producing OXA-24+OXA-51+IMP and OXA-23+OXA-24+IMP, respectively.Conclusions OXA-24 and IMP are the main genotype of carbapenemase in imipenem-resistant and/or meropenem-resistant Acinetobacter baumannii , in the part of which produced two or more carbapenemases and the clone spread is found in a few of them.