Mannheimia kashgarensis sp. nov., isolated from the nasopharynx of sheep with ovine respiratory disease

Two Gram-stain-negative, facultative anaerobic, pleomorphic rod-shaped strains, designated E16BA^T and E15BD, were isolated from the nasopharynx of two different sheep exhibiting clinical signs of ovine respiratory disease at a commercial farm in Kashgar, Xinjiang, China. Their taxonomic identities were determined using a polyphasic approach, integrating morphological, physiological, biochemical, genotypic and chemotaxonomic analyses. The strains exhibited optimal growth at 37 °C, pH 9 and in 2% (w/v) NaCl and shared identical 16S rRNA, <i>recN</i> and <i>rpoB</i> gene sequences. Based on the 16S rRNA gene sequence phylogeny, the strains clustered within the genus <i>Mannheimia</i>, exhibiting the highest sequence similarity (97.3%) to <i>Mannheimia caviae</i>. Whole-genome comparisons revealed average nucleotide identity values below 87.1% and digital DNA-DNA hybridization values below 32.9% with other <i>Mannheimia</i> species, confirming their status as a novel species. Furthermore, 2-9 biochemical characteristics helped differentiate the new strains from other <i>Mannheimia</i> species and supported the identification of the novel species. Chemotaxonomic features, including major fatty acids (C_{14 : 0}, C_{16 : 0}, summed feature 3 and summed feature 2), major polar lipids (phosphatidylethanolamine, phosphatidylglycerol and phosphatidylinositol) and respiratory quinones (coenzyme Q7 and coenzyme Q8), further supported species differentiation. Genomic analysis revealed the presence of putative virulence-associated genes, suggesting potential involvement in ovine respiratory disease. Based on these data, strains E16BA^T and E15BD represent a novel species of the genus <i>Mannheimia</i>, for which the name <i>Mannheimia kashgarensis</i> sp. nov. is proposed. The type strain is E16BA^T (=CCTCC AB 2023215^T=KCTC 8480^T).