Study On Major β-lactamases And Relateness Of Multi-drug Resistant Acinetobacter Baumannii

Acinetobacter baumannii is an important pathogen which caused the nosocomial infection. With the use of a broad range of antimicrobial agents, the proportion of the multi-drug resistant Acinetobacter baumannii strains is rising, and happened outbreak in many intensive care unit around the world. According to monitoring data of National nosocomial infection surveillance (NNIS) and nosocomial infection surveillance in Chinese, Acinetobacter spp. was the 4 most frequently isolated pathogens causing nosocomial infection. Since 1991 ,the first carbapenem- resistant Acinetobacter (CRA) has been reported in the United States , such strains have emerged one after another around the world. Recently, CRA has become one of the hot topics in the international community. Once imipenem-resistant clone was found, it means that those resistant to all classes of antimicrobial agents available ,that is, the pandrug-resistant Acinetobacter (PDRA). Infection caused by PDRA usually cannot use any classes of antimicrobial agents available, and the fatality rate was high.Acinetobacter have complex resistance mechanisms, including generating of inactivated enzyme to inactivate of antimicrobial agents; changing the target site to escape the role of antimicrobial agents; changing the outer membrane pore protein structure and quantity to reduce permeability of the bacterial outer membrane; activating the efflux pump systems to decrease the bacterial intracellular concentration of antibiotics. In recent years, the isolation rate and resistance rates of Acinetobacter baumannii increases gradually in the second hospital of Shanxi Medical University rising. This study screened multi-drug resistant Acinetobacter strains from July 2007 to May 2008 , analyzing their resistance, homology and the majorβ-lactamase genotype.1. The screen of multi-drug resistant A. baumannii and Minimal Inhibitory Concentrations determinationStrain Source: collect the multi-drug resistant A. baumannii which were isolated from July 2007 to May 2008 from the second hospital of Shanxi Medical University. All strains were identified by VITEK-2.Methods: Muti-resistant A. baumannii were screened by using K-B method. The MICs of 12 antimicrobials to muti-resistant A. baumannii were detected by agar dilution.Results: The resistant rates to imipenem and meropenem were 45.2% and 33.9%, and Cefoperzone/sulbactam and piperacillin/sulbactam were 33.9% and 59.0%, respectively. The strains were resistant to minocycline and polymyxin E of 16.1 and 9.7%, respectively. The resistant rates to other antimicrobial agents were more than 70%.2. The relateness of multi-drug resistant A. baumanniiStrain Source: The multi-drug resistant A. baumannii which were isolated from July 2007 to May 2008 from the second hospital of Shanxi Medical University.Methods: Pulse field gel electrophoresis (PFGE) was performed to analyze the relateness of 60 isolates of multi-drug resistant A. baumannii.Results:Total of 60 strains belonged to the popular 5 clones. Clone A had 28 strains, Clone B had 9 strains. Clone C, Clone D and Clone E had 4 strains,3 strains and 2 strains respectively. We found that clones A and B were the dominant isolates and had spread widely among wards in the hospitals.3.Investigation of majorβ-lactamase genotype in multi-drug resistant A. baumannii Strain Source: Collect the multi-drug resistant A. which were isolated from July 2007 to May 2008 from the second hospital of Shanxi Medical University.Methods: Crudeβ-lactamase preparations were extracted and three-dimensional tests were performed to detectedβ-lactamase. Metallo-β-lactamaseproducing isolates were screened by the double-disk.β-lactamase genotype were analyzed by PCR. Conjugation test, plasmid extraction and electrotransformation were performed to locate theβ-lactamase gene.Results: Metallo-β-lactamase were not detected by the double-disk. Three-dimensional tests were positive, suggesting that the strains can produceβ-lactamases.42 multi-drug resistant A. baumannii contained blaTEM-1, blaPER has 20 positive. 2 strains and 1 strains carried blaSHV-2 and CTX-M-1 respectively. blaOXA-23 gene-positive was detect in 15 strains. And the 15 strains were CARB.The conjugation test of producing CTX-M-3-type ESBLs strains were performed successfully. There is no reports which we investigated on A. baumannii C in China. Although the strains blaSHV-1 extracted the plasmid , the conjugation test failed. Plasmid extraction, conjugation test, electrotransformation, and Sourthern blot were not successful in other strains.The above sresults shows:1. Multi-drug resistance was more and more serious. Colinstin remained good susceptibility against A. baumannii. The resistance rates to cefoperazone/sulbactam were low relatively.2. The isolate rates of multi-drug resistant Acinetobacter baumannii increased.Total of 60 strains belonged to the popular 5 clones and clones A and B were the dominant isolates.It suggested that there ia a small outbreak of multi-drug resistant Acinetobacter baumannii in our hospital.3. Metallo-β-lactamase were not detected by the double-disk. Three-dimensional tests were positive, suggesting that the strains can produceβ-lactamases.4. In our multi-drug resistant A. baumannii, blaTEM and blaPER are the main ESBL genotype. blaOXA-23 was main carbapenemases genotype,and the strains were CARB.It show that there was a diversity in the distribution of lactamase genotype between our hospital and other regions.5. There are strains producing the more than twoβ-lactamase genotypes. It suggested that we should choose the antibacterial agent reasonably to this situation.6.The conjugation test of producing CTX-M-3-type ESBLs strains were performed successfully. The plasmid-mediated resistance of A. baumannii can be transfered widely in different species, leading to disseminating resistance. It resulted in the prevalence of nosocomial infection .