A-037. Plasmid Analysis of AmpC β-Lactamase-Bearing Plasmids from Escherichia coli in Canadian Intensive Care Units (ICUs)

P. J. Baudry1, K. Nichol2, M. DeCorby1, L. Mataseje1, P. Lagace-Wiens1,2, J. A. Karlowsky2, D. J. Hoban1,2, G. G. Zhanel1, M. R. Mulvey1,3;
1Univ. of Manitoba, Winnipeg, MB, CANADA, 2Hlth. Sci. Ctr., Winnipeg, MB, CANADA, 3Natl. Microbiology Lab., Winnipeg, MB, CANADA.

Background: Plasmid-mediated AmpC β-lactamases have been increasing in prevalence and diversity worldwide. The purpose of this study was to investigate the AmpC-bearing plasmids isolated from E. coli in Canadian ICUs. Methods: 27 E. coli (5.0 % of all 536 E. coli tested) identified as AmpC β-lactamase producers by elevated MICs to ceftriaxone, a negative extended-spectrum β-lactamase double disk test and multiplex PCR for acquired AmpC genes were investigated from the Canadian Intensive Care Unit Surveillance Study (CAN-ICU). Strains were sub-typed using pulsed-field gel electrophoresis (PFGE). Plasmids were extracted and transformed by electroporation into E. coli DH10B. AmpC-bearing plasmids were selected for on LB plates containing ampicillin and cefoxitin. Plasmid incompatibility groups were determined by replicon PCR and were sub-typed using restriction fragment length polymorphism (RFLP). Results: PFGE revealed both genetically related (>80% homology) and unrelated groups of AmpC producing E. coli. Transformants were obtained for all 26 blaCMY-2-bearing plasmids but not for the blaACT-1-bearing plasmid. Replicon typing revealed that the CMY-2-bearing plasmids were distributed among 3 replicon types: repI1 (40.7%), repK/B (37.0%) and repA/C (25.9%). Two plasmids were identified as both repI1 and repK/B. The RFLP patterns of plasmid transformant DNA consisted of 3 clusters corresponding to prevalent replicon types. The repI1 cluster consisted of 9 plasmids (33.3%) that were both genetically related and unrelated varying in size from ~70-105 Kb. The repA/C cluster consisted of 7 (25.9%) plasmids that were predominantly related and ranged in size from ~68-87 Kb. The repK/B cluster consisted of 10 (37.0%) plasmids that were highly genetically related and were ~84 Kb in size. Conclusions: Both genetically related (>80% homology) and unrelated groups of AmpC producing E. coli were observed. The CMY-2-bearing plasmids were divided into 3 clusters based on RFLP patterns corresponding to the prevalent replicon types: repI1, repK/B and repA/C.