Recognition of two genetic groups in the Klebsiella oxytoca taxon on the basis of chromosomal β-lactamase and housekeeping gene sequences as well as ERIC-1R PCR typing

Whilst searching for a molecular method to identify the different species of Raoultella and Klebsiella oxytoca, it was observed that the OXY-1 and OXY-2 beta-lactamase-producing K oxytoca isolates displayed two distinguishable enterobacterial repetitive intergenic consensus (ERIC)-1 R profiles. It was hypothesized that the two groups of chromosomal beta-lactamases might correspond to two groups of strains in the K oxytoca taxon. To confirm this hypothesis, clinical isolates and reference strains of K oxytoca were studied by determination of the sequence of their bla(OXY) genes, and of a partial fragment of their 16S rRNA (387 bp) and rpoB (512 bp) genes. The sequence data were phylogenetically analysed by using the parsimony method. Four clinical isolates possessed a bla(OXY-1) gene and nine possessed a bla(OXY-2) gene. The mean percentage of rpoB and 16S rRNA gene identity was > 99% within each group of strains, whereas it was 96.56 +/- 0.24% for rpoB genes and 97.80 +/- 0.22% for 16S rRNA genes between the group of strains harbouring the bla(OXY-1) gene and the group harbouring the bla(OXY-2) gene. The phylogenetic tree resulting from combined analysis of the 16S rRNA and rpoB datasets showed that the K oxytoca isolates were monophyletic and separated into two clades; these clades included strains with either the bla(OXY-1) gene or the bla(OXY-2) gene. This result was supported with high bootstrap values of 97 and 99%, respectively. Moreover, the two groups of strains displayed distinct ERIC-1 R profiles, with bands characteristic of each profile. Thus, the chromosomal bla(OXY) gene sequence is able to delineate not only two groups of beta-lactamases in K oxytoca, but also two clades in the K. oxytoca taxon, in a manner similar to the sequence of housekeeping genes. These results suggest that K oxytoca should be divided into two genetic groups, group OXY-1 represented by K oxytoca strain SL781 (= CIP 104963) and group OXY-2 by K oxytoca strain SL911 (= CIP 106098).