Emergence of Plasmid-Mediated AmpC beta-Lactamases in ESBL-Producing Enterobacterias in Buenos Aires, Argentina.

M. RADICE; R. CITTADINI; M. STORTZ; M. RUGGIERO; G. GUTKIND; C. VAY

Chicago, Illinois

Congreso; 47th Interscience Conference on Antimicrobial Agents and Chemotherapy; 2007

Background: Despite the increasing recognition of plasmid-mediated AmpC beta-lactamases worldwide, this enzymes were not reported in Argentina, except FOX-1 producing K. pneumoniae, in 1989 and more recently, CMY-type-producing Shigella flexneri, in 2006. In fact, co-production of plasmid AmpC beta-lactamases and ESBLs has not been described in our country. We describe two clinical isolated, one K.pneumoniae and one Citrobacter koseri, co-producing CMY-2 and CTX-M-2 enzymes, recovered at the same center in Buenos Aires. Methods: Susceptibility was determined by diffusion methods according to CLSI. Screening for ESBLs was performed by clavulanic acid synergy tests using ceftazidime, cefotaxime and cefepime. Presence of class C beta-lactamases was investigated using boronic acid containing disks. Bacterial conjugation and transformation of plasmid DNA were conduced by conventional assay. bla genes were detected by PCR amplification on plasmid DNA extracted from the clinical strains and transformants. For sequencing ampC genes, plasmids were digested with SphI and ligated in a kanamycin resistant pK19 vector. Recombinant plasmids were transformed in Escherichia coli Top10. Results: Both isolates were resistant to all beta-lactams except imipenem. PCR amplification for ESBL encoding genes and amplicon sequencing confirmed the presence of ctx-m-2. Inhibition with boronic acid suggested the presence of an AmpC beta-lactamase in both strains. DNA sequencing confirmed the presence of cmy-2. Both resistance markers were co-transferred in the same mobile element. Conclusion: The occurrence of this unusual pattern constitutes en emerging resistance mechanism in our country, and merits further study to define best options for is detection and dissemination control.