Genes encoding ten newly designated OXA-63 group class D β-lactamases identified in strains of the pathogenic intestinal spirochaete Brachyspira pilosicoli.

Abstract

The anaerobic spirochaete Brachyspira pilosicoli colonizes the large intestine of birds and mammals, including human beings, and may induce colitis and diarrhoea. B. pilosicoli has a recombinant population structure, and strains show extensive genomic rearrangements and different genome sizes. The resident chromosomal gene blaOXA-63 in B. pilosicoli encodes OXA-63, a narrow-spectrum group IV class D β-lactamase. Genes encoding four OXA-63 variants have been described in B. pilosicoli, and the current study was designed to investigate the distribution and diversity of such genes and proteins in strains of B. pilosicoli. PCRs were used to amplify blaOXA-63 group genes from 118 B. pilosicoli strains from different host species and geographical origins. One primer set was targeted externally to the gene and two sets were designed to amplify internal components. A total of 16 strains (13.6%) showed no evidence of possessing blaOXA-63 group genes, 44 (37.3%) had a full gene, 27 (22.9%) apparently had a gene but it failed to amplify with external primers, and 29 (24.6%) had only one or other of the two internal components amplified. Based on translation of the nucleotide sequences, ten new variants of the β-lactamase, designated OXA-470 through OXA-479, were identified amongst the 44 strains that had the full gene amplified. The 16 strains lacking blaOXA-63 group genes had a region of 1674 bp missing around where the gene was expected to reside. Despite apparent genomic rearrangements occurring in B. pilosicoli, positive selection pressures for conservation of blaOXA-63 group genes and OXA proteins appear to have been exerted.