Identification and phylogenetic relationship of Mannheimia varigena using the 16S rRNA subunit and the rpoB gene

The objective of this work was to identify Mannheimia varigena strains in samples of bovine nasal exudates and bovine pneumonic lung using the API 20E bacterial identification system, 16S rRNA gene sequencing, and rpoB gene sequencing, as well as the establishment of the phylogenetic relationship with the Pasteurellaceae family. The API 20E identification system determined the strains correspond to the genus Mannheimia spp. Sequencing of the 16S rRNA gene showed 100 % homology with Mannheimia varigena and sequencing of the rpoB gene showed 99 % homology with M. varigena; phylogenetic analysis confirmed the isolates belong to M. varigena by locating the isolates in a separate and independent clade. In contrast to sequences from bovine pneumonic lung, the amino acid sequence of the rpoB gene from bovine nasal exudates showed two different mutations, the changing of aspartate for asparagine at position 158 and alanine for aspartate at position 160. These mutations are non-synonymous changes that have not been reported in the Mannheimia complex or related species.