Six Groups of the OXY β-Lactamase Evolved over Millions of Years in Klebsiella oxytoca

Abstract

ABSTRACT The diversity and evolution of the class A OXY β-lactamase from Klebsiella oxytoca were investigated and compared to housekeeping gene diversity. The entire bla OXY coding region was sequenced in 18 clinical isolates representative of the four K. oxytoca β-lactamase gene groups bla OXY-1 to bla OXY-4 and of two new groups identified here, bla OXY-5 (with four isolates with pI 7.2 and one with pI 7.7) and bla OXY-6 (with four isolates with pI 7.75 and three with pI 8.1). Genes bla OXY-5 and bla OXY-6 showed 99.8% within-group nucleotide similarity but differed from each other by 4.2% and from bla OXY-1 , their closest relative, by 2.5% and 2.9%, respectively. Antimicrobial susceptibility to β-lactams was similar among OXY groups. Nucleotide sequence diversity of the 16S rRNA (1,454 bp), rpoB (940 bp), gyrA (383 bp), and gapDH (573 bp) genes was in agreement with the β-lactamase gene phylogeny. Strains with bla OXY-1 , bla OXY-2 , bla OXY-3 , bla OXY-4 , and bla OXY-6 genes formed five phylogenetic groups, named KoI, KoII, KoIII, KoIV, and KoVI, respectively. Isolates harboring bla OXY-5 appeared to represent an emerging lineage within KoI. We estimated that the bla OXY gene has been evolving within K. oxytoca for approximately 100 million years, using as calibration the 140-million-year estimation of the Escherichia coli - Salmonella enterica split. These results show that the bla OXY gene has diversified along K. oxytoca phylogenetic lines over long periods of time without concomitant evolution of the antimicrobial resistance phenotype.