The Epidemic Characterics Of Multidrug Resistant Acinetobacter Baumannii And The Resistant Mechanism To Intergon In Acinetobacter Baumannii

ObjectiveAcinetobacter baumannii is a common pathogen of nosocomial infection, which has been multidrug resistant, extensively drug-resistant,and even pan-resistant strains because of the antibiotic abuse. Once patients are infected especially those with severe infection, they wouldn’t be cured. The outbreak of nosocomial infection has become an important public health issue, which caused by multidrug-resistant Acinetobacter baumannii(MDRAB).Most studies have shown that the prevalence of MDRAB would be different due to the diversity of the antibiotic use and the measures about infection control.Therefore we studied the epidemic characteristics and resistance mechanisms of MDRAB in our region to effectively prevent and control the outbreaks by the bacteria.Methods1. By a case-control study, the data of cases infected by MDRAB from January2011 to June 2012 were analyzed in a general hospital.The cases infected by common Acinetobacter baumannii were selected randomly at the same time as control.Univariate analysis(t-test and chi-square test) and multivariate logistic regression were used for statistics analysis.2. A total of 286 strains of Acinetobacter baumannii were randomly collected from various clinical specimens from 2009 to 2012.The isolates were identified by VITEK260. The susceptibility tests were performed with the Kirby-Bauer agar diffusion method.The analysis of homology was performed with pulsed-field gel electrophoresis(PFGE).3. Results of susceptibility tests were analyzed by WHONET 5.6. The chi-square test was used for the statistical analysis of the diversity on drug-resistant rates.4. The susceptibility of MDRAB to three common disinfectants(alcohol,chlorine and iodophor) was evaluated by determination of minimum bactericidal concentration(MBC) and minimum inhibitory concentrati on(MIC),compared with the sensitive strains of Acinetobacter baumannii and Pseudomonas.And the correlation analysis was conducted between the susceptibility of MDRAB to the disinfectants and antibiotics. The gene of qac E △ 1 was analyzed using Polymerase Chain Reaction(PCR).5. MDRAB isolates were identified by PCR, agar dilution method for drug susceptibility testing, PFGE for homology analysis and screened about the type of integron and gene cassettes by PCR. The fragments of gene cassettes were sequenced.Results1. In a general hospital, 58.76% patients with MDRAB belonged to nosocomial infection, 85.05% found in the respiratory tract. Compared with patients infected by sensitive strains, those infected by MDRAB were higher in the length of hospital stay(the average growth of 13.39 days),the total cost of treatment(the average growth of￥ 95,171.58) and the sum rate of mortality and automatic discharge rate(the average growth of 31.96%).Multivariate logistic regression analysis revealed that the number of underlying disease(OR: 3.012,95% CI :1.153 to 7.868), ever staying at ICU(OR:2.935,95% CI: 1.093 to 7.885), disease severity(OR:6.481, 95% CI: 2.524 to 16.644),carbapenem drug use(OR:7.988,95% CI:2.961 to 21.547) and deep venous catheter(OR:2.875,95% CI:1.049 to 7.880) were significantly related to the infected risk.The difference of resistance rates between case group and control group had statistics significance.The resistance rates in case group were severe, which for 9 kinds of 14 drugs were 100%.2. A total of 43 gene groups were detected according to 90% identity for 286 strains of MDRAB. G23 and G25 were dominant groups and all detected from 2009 to2012, which were mainly prevalent in the surgical departments, especially general Intensive Care Unit(ICU).Moreover the same gene groups were detected from the ICU enviroment. The drug-resistant rate of Ab was higher than 65%, except Cefoperazone /sulbactam and minocycline(<40%). The drug-resistant rate of G23 group was highest.The statistical analysis was obviously significant about the Carbapenems-resistant rate between G23 and G25.3. The results of sensitive tests to three common disinfectant revealed that the value of MBC and MIC on MDRAB representative strains was higher than that of the sensitive strain and standard strain about iodophor, and there were little different between them about alcohol and chlorine disinfectant. But the routine concentration of them exceeded the MIC and MBC values. There was no correlation between antimicrobial drug resistance and disinfectant resistantance. The detection rate of the qac E△1 gene was 57.97%.4. The homology analysis revealed that 5 major clones of 425 strains of MDRAB were prevalent in 13 hospitals of 10 districts from southeastern China, Beijing and Yantai.Among them, C25 and C33 were the main clone,which C25 clone was epidemic in Hangzhou, Wenzhou and Yantai including Fujian Province and C33 clone was endemic in Fujian Province,including Fuzhou, Nanping and Quanzhou. The total drug resistance of 425 MDRAB was higher than 70%, except minocycline. The detective rate of carbapenem-resistant Acinetobacter baumannii(CRAB)was 78%.The detection of class ? integrase was 69.6%,wheras classⅡand Ⅲintegrase weren’t detected.The drug resistance of the positive strains about class ? integrase was higher than the negative.The homology analysis revealed that there were four major clones in the positive.The dominant clone P4 was endemic, where the extensively drug- resistant strains were in majority. The gene cassettes of class ? integron was aac A4-cat B8-aad A1 and dfr Ⅻ-orf F-aad A2, which was first reported in Fujian Province.Conclusions1. Because the drug-resistant status of MDRAB was severe and the prognosis of patients infected by MDRAB was poor, those patients should be supervised, especially those staying at ICU with severe diseases.To avoid the outbreak of MDRAB, and we should take effective measures and emphasize the rational use of antimicrobial agents,especially the carbapenems.2. The dominant clones should be monitored to control the epidemic strains of MDRAB. We should strengthen at disinfection and hand hygiene of the staff in the epidemic departments and timely isolate infected patients who should be reduced unnecessary transfer.3.When an outbreak of MDRAB happens,we can use the disinfectants to successfully deal with the contaminant according to the manual.Since the qac E△1 gene expresses the efflux pumps of the quaternary ammonium and biguanide disinfectant, we should reduce to use the quaternary ammonium disinfectant at disposing the contaminant of MDRAB and advocate using the compound disinfectants containing alcohol for hand hygiene instead of using the pure biguanide disinfectant.4. The dominant clones of MDRAB were epidemic in southeastern China.The popular model of MDRAB was the co-existence of the endemic strains and epidemic strains in Fujian Province.The drug-resistant status of MDRAB was servere in the region, which the detective rate of CRAB was high and even pan drug-resistant isolates were found.5. The kind of integron for MDRAB isolates of southeastern China was Class ?integron, which can increase the drug resistance of MDRAB. They had the dominant clones.The propotion of extensively drug-resistant strains about the dominant clones was higher in Fujian Province than those in southeastern China.The kinds of gene cassettes were both global and local type.So the measures for preventing the epidemic strains to widely spread should be taken of the rational antibiotics use and strengthening surveillance on epidemic strains according to regional differences.