Chromosomal cephalosporinase in Enterobacter hormaechei as an ancestor of ACT-1 plasmid-mediated AmpC β-lactamase

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Authors: Kyoung Ho Roh ; Wonkeun Song ; Hae-Sun Chung ; Yang Soon Lee ; Jong Hwa Yum ; Ha Na Yi ; Jong Sik Chun ; Dongeun Yong ; Kyungwon Lee ; Yunsop Chong

MeSH: Amino Acid Sequence ; Anti-Bacterial Agents/pharmacology ; Bacterial Proteins/genetics* ; Cefoxitin/pharmacology ; Cephalosporinase/genetics* ; Chromosomes, Bacterial/genetics* ; Enterobacter/classification ; Enterobacter/drug effects ; Enterobacter/genetics* ; Enterobacteriaceae Infections/microbiology ; Humans ; Microbial Sensitivity Tests ; Molecular Sequence Data ; Phylogeny* ; Plasmids/genetics* ; RNA, Ribosomal, 16S/genetics ; Sequence Analysis, DNA ; Species Specificity ; beta-Lactamases/genetics*

Keywords: Amino Acid Sequence ; Anti-Bacterial Agents/pharmacology ; Bacterial Proteins/genetics* ; Cefoxitin/pharmacology ; Cephalosporinase/genetics* ; Chromosomes, Bacterial/genetics* ; Enterobacter/classification ; Enterobacter/drug effects ; Enterobacter/genetics* ; Enterobacteriaceae Infections/microbiology ; Humans ; Microbial Sensitivity Tests ; Molecular Sequence Data ; Phylogeny* ; Plasmids/genetics* ; RNA, Ribosomal, 16S/genetics ; Sequence Analysis, DNA ; Species Specificity ; beta-Lactamases/genetics*

Abstract: In this study of the diversity of AmpC β-lactamase in clinical isolates of Enterobacter spp., a strain was found carrying the plasmid-mediated AmpC β-lactamase ACT-1 gene on its chromosome. The strain was identified as Enterobacter hormaechei using phylogenetic analysis of 16S rRNA and hsp60 genes. In addition, the species was confirmed by DNA-DNA hybridization. The genetic environment of the bla(ACT-1) gene was characterized, including the ampR and ampG genes, using a two-step PCR. The amino acid sequences of AmpR at serine 35, arginine 86, glycine 102, aspartic acid 135 and tyrosine 264 were conserved. Measurement of the transcription level of the bla(ACT-1) gene using real-time quantitative PCR showed that it increased 1.98-fold following cefoxitin induction. These results suggest that the plasmid-mediated bla(ACT-1) gene originated from the chromosome of E. hormaechei.