Resistance To Antimicrobial Agents And Investigation Of The β-Lactamases Production And Encoded Genes In Clinical Isolates Of Acinetobacter Baumannii

Objective: To investigate the resistance to 12 common antimicrobial agents in clinical isolates of Acinetobacter baumannii, to study the frequentβ—lactamases production and encoded genes in these resistant isolates. Methods: 120 Acinetobacter baumannii strains were isolated from clinical specimens in West China Hospital from January 2005 to May 2005 and from February 2006 to June 2006. The MICs of 12 common antimicrobial agents were determined by 2-fold agar dilution method followed by NCCLS recommendations. Theβ—lactamases production was detected by the Cefinase slip method. The types ofβ—lactamases production were distinguished by a modified three-dimensional test using a big agar plates in those isolates, which showedβ—lactamases activity. Followed by the types of resistant and the results of the modified three-dimensional test, bla_OXA-23 and bla_OXA-24 in these resistant isolates were amplified by PCR and the resistant genes of ESBLs and AmpC enzyme by multiplex PCR. Results: Except IMP, the resistant rate of 120 isolates to 11 common antimicrobial agents were more than 50%.110 strains were resistant to more than 3 common antimicrobial agents and the resistant rate is 91.67%. The majority of these resistant strains were isolated from sputum, and distributed in ICUs. There were 114 strains producingβ—lactamases in 120 isolates of Acinetobacter baumannii, which were detected by the Cefinase slip method, at the proporation of 95%. The numbers were 63, in which can be typed by the modified three-dimensional test using a big agar plates. In the 63 isolates, there were 4 strains (3.51%), 15 strains (13.16%), 5 strains (4.39%), 18 strains (15.78%) showing the activity of carbapenemases, ESBLs, AmpC enzyme, IRTs, respectively, and there were 5 strains (4.39%), 9 strains (7.89%) and 7 strains (6.14%) simultaneously showing the activity of carbapenemases plus ESBLs, AmpC plus ESBLs, carbapenemases plus IRTs, respectively. Of 53 strains resistant to IMP, there were 11 stains carried blaoxA-23 in 16 stains producing non-EBL carbapenemases versus 2 stains in 37 stains without producing carbapenemases. We hadn't found the blaoxA-24 in the two groups resistant isolates. There were 29 isolates with ESBLs production among 71 strains resistant to CTX plus CAZ, including 1 strains, 1 strains, 1 strains and 2 strains carried bla_SHV, bla_CTX-M-3, bla_CTX-M-14, bla_SHV plus bla_CTX-M-14 simultaneously, respectively; and 42 stains without ESBLs production, which didn't carry the genes by the multiplex PCR of ESBLs in full. Among 109 strains resistant to FOX, 1 stains of 14 stains with ApmC production was confirmed to carry bla_CIT by cloning sequence analysis, 2 stains of 37 stains without ApmC production was confirmed to carry bla_DHA respectively. Conclusion: There were Acinetobacters baumannii, which were resistant to multiplex antimicrobial angents and produced multiplex types ofβ—lactamases in our hospital. The majority of these resistant strains producing carbapenemases were OXA-23-type carbapenemases, which linked possibly an epidemic of nosocomial infection inducing by Acinetobacters baumannii. Less ESBLs and AmpC gene were amplified by multiplex PCR, which relatived to primers design. We could detect someβ—lactamases simultaneously in Acinetobacters baumannii by the modified three-dimensional test using a big agar plates, which is effective in this study. But it need more evidence by extensive study.