Dissemination of SHV-12 and Characterization of New AmpC-Type Beta-Lactamase Genes among Clinical Isolates of Enterobacter Species in Korea

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Abstract
To determine the prevalence and genotype of an extended-spectrum beta-lactamase and new chromosomal AmpC beta-lactamases among clinical isolates of Enterobacter species, we performed antibiotic susceptibility testing, pI determination, induction tests, transconjugation, enterobacterial repetitive consensus (ERIC) PCR, sequencing, and phylogenetic analysis. Among the 51 clinical isolates collected from a university hospital in Korea, 6 isolates have been shown to produce SHV-12 and inducible AmpC beta-lactamases. These also included three isolates producing TEM-1b and one strain carrying TEM-1b and CMY-type beta-lactamases with a pI of 8.0. The results from ERIC PCR revealed that six isolates were genetically unrelated, suggesting that dissemination of SHV-12 was responsible for the spread of resistance to extended-spectrum beta-lactams in Korea. Six genes of inducible AmpC beta-lactamases that are responsible for the resistance to cephamycins (cefoxitin and cefotetan), amoxicillin, cephalothin, and amoxicillin-clavulanic acid were cloned and characterized. A 1,165-bp DNA fragment containing the ampC genes was sequenced and found to have an open reading frame coding for a 381-amino-acid beta-lactamase. The nucleotide sequence of four ampC genes ( bla EcloK992004.1 , bla EcloK995120.1 , bla EcloK99230 , and bla EareK9911729 ) shared considerable homology with that of AmpC-type class C beta-lactamase genes of gram-negative bacteria, especially that of the chromosomal ampC gene ( bla EcloMHN1 ) of Enterobacter cloacae MHN1 (99.9, 99.7, 99.6, and 99.6% identity, respectively). The sequences of two ampC genes ( bla EcloK9973 and bla EcloK9914325 ) showed close similarity to the chromosomal ampC gene ( bla EcloQ908R ) of E. cloacae Q908R (99.7% identity). The results from phylogenetic analysis suggested that six ampC genes could originate from bla EcloMHN1 or bla EcloQ908R .