Dissemination of transferable AmpC-type beta-lactamase (CMY-10) in a Korean hospital

To determine dissemination and genotype of AmpC beta-lactamases and an extended-spectrum beta-lactamase among clinical isolates of Enterobacteriaceae, we performed antibiotic susceptibility testing, pI determination, induction test, plasmid profiles, transconjugation test, enterobacterial repetitive consensus (ERIC)-PCR, and DNA sequencing. Among the 51 clinical isolates collected from a university hospital in Korea, six isolates were resistant to cephamycins. All six isolates produced a plasmid-encoded AmpC-type beta-lactamase, CMY-10. Five strains also produced one or more other beta-lactamases: SHV-12, an extended-spectrum beta-lactamase (five isolates); TEM-1, a class A beta-lactamase (two isolates); and a chromosomal AmpC beta-lactamase (one isolate, a strain of Enterobacter aerogenes, which produced all four of the beta-lactamases that were identified). One of six isolates produced only CMY-10. ERIC-PCR analysis revealed that dissemination of CMY-10 and SHV-12 was due to a clonal outbreak of a resistant strain and to the interspecies spread of resistance to cephamycins and broad-spectrum beta-lactams in Korea. CMY-10 beta-lactamase genes that are responsible for the resistance to cephamycins (cefoxitin and cefotetan), amoxicillin, cephalothin, and amoxicillin-clavulanic acid were cloned and characterized from six clinical isolates. A sequence identical to the common regions in In6, In7, and a novel integron from pSAL-1 was found upstream from blaCMY-10 gene at nucleotides 1-71. A total of 15 nucleotides (I-15) or 18 nucleotides (I-18) between position 71 and 72 were inserted into the blaCMY-10 gene. The blaCMY-10 gene might be inserted into a sul1-type complex integron by I-15 or I-18.