Research On Molecular Homology And Virulence Genes Of Acinetobacter Baumannii From Bloodstream Infections

Objective To study the sensitivity of Acinetobacter baumannii isolates from bloodstream infections from the patients in 17 Hospitals on various kinds of antibiotics,so as to provide a basic for effective control and rational use of antimicrobial drugs;The molecular homology of multidrug-resistant Acinetobacter baumannii(MDRAB)were investigated,Which provides the strategies of controlling the prevalence of MDRAB;By testing the virulence phenotype and detecting virulence genes of Acinetobacter baumannii,To analysis the correlation of virulence factors and the drug resistance;At the same time,The resistance,virulence and homologous characteristics were analyzed of seven mucoid isolates.Methods A total of 90 isolates from 17 hospitals were collected from the patients with bloodstream infections during July 2013 and July 2014,Which contains 75 MDRAB isolates and 15 non-MDRAB isolates.The repeated strains isolated from the same patient and the same part are removed.The bacteria identification and antimicrobial susceptibility tests were carried out by using Vitek-2 compact system and the susceptibility of cefoperazone/Sulbactam is tested by disk diffusion method(K-B).The clinical characteristics of patients,including age,gender and department were collected and analysed.To analyze the molecular homology of 90 MDRAB isolates by Pulsed Field Gel Electrophoresis(PFGE).Four virulence phenotype tests were detected: Twitching motility by motorial plate,Hemagglutination test and hemagglutination inhibition test were conduct by serially diluted micro-hemagglutination test,Biofilm formation ability were performed by crystal violet staining,Serum bactericidal assay by adding 20% normal human serum to the bacterial suspension.PCR was used to detect D carbapenemase-encoding genes(blaOXA-23、24、51、58)and virulence genes(aba I、cus E、bap、bfm S、omp A).Results(1)Antimicrobial susceptibility results of the 75 MDRAB isolates,65.3%(n=54)of the patients were from ICU.MDRAB showed higher sensitivity to cefoperazone-sulbactam,amikacin and tigecycline with the sensitive rate 69.3%,77.3% and 100.0%,respectively.While for other drugs the sensitive rate were under 30%.(2)PFGE analysis showed 21 different clone types,designated A to U.Amongthem,75 MDRAB isolates belonged to eight clone types(A to H),with the A(n=51)and B(n=14)clone being the dominant PFGE clone types.while non-MDRAB isolates were seen in I to U clone type.There are no identical clone types between them.Different clone isolates spread in different hospitals.However,most of the hospitals were given priority to with clone A.(3)There only one strain showed twitching motility positive;No isolates found were agglutinated to human group O erythrocytes and only one strain was agglutinated to human group AB erythrocytes;Biofilm formation activity was detected in 57 isolates.While the biofilm formation ability of 7 mucoid isolates was negative;The serum killing ability was test positive in 71 isolates.Clone A presents stronger biofilm than clone B.(4)There were 83 non-mucoid isolates.All virulence genes were positive in 54 strains of 69 MDRAB isolates.The MDRAB isolates’ detection rates of aba I,bap and bfms genes was higher than non-MDRAB isolates.All virulence genes were detected in 82.4%(n = 42)of A clone strains.(5)There are 7 mucoid stains,which all belong to MDRAB and clone B.All virulence genes were positive in the 7 mucoid strains.5 of them that their phenotype and genotype are exactly the same are from JL hospital.The other two strains showed different antimicrobial drugs phenotype are from NJ hospital and TJ hospital respectively.Conclusion This study showed that MDRAB isolates from bloodstream infections in our country have a lower resistance rate to cefoperazone-sulbactam,amikacin and tigecycline.The dominant clone type of MDRAB is clone A,Which indicates that multiple drug-resistant isolates might spread between the different regions,resulting in MDRAB separation rate is rising in our country.Clone A presents stronger biofilm ability witch make it easily to live in the hospital environment,causing strains spread in popularity.The detection rates of virulence genes from MDRAB was higher than non-MDRAB isolates,Which prompts clinical should not only focus on multiple drug resistant strains,also should pay attention to strains of pathogenic ability.Mucus phenotypic strains may have stronger virulence and easy to spread.