Isolation, Identification and Whole Genome Sequence Analysis of a Goat-derived Type 2 Mannheimia haemolytica

PurposeTo isolate and identify pathogenic a bacteria that caused serious respiratory diseases and deaths in goats in a large-scale sheep farm in Sichuan Province, and to analyze their pathogenic and drug resistance mechanisms.

MethodBiochemical tests, pathogenicity tests in mice, drug susceptibility tests, 16S rRNA analysis, capsule serotyping and genome-wide sequencing were went through after isolation and purification of pathogens. Through the sequence, the species typing were analysed and gene function annotations of the isolated strains were carried out.

ResultThe same bacteria was isolated from the nasal fluid, trachea, lung and liver of dead goat. It was identified as Mannheimia haemolytica capsulatum type 2 and named MHLB002. The LD₅₀ values of the bacteria in mice was 4.4×10⁷ CFU/mL. The drug susceptibility test showed that the M. haemolytica was sensitive to cephalosporins, β-lactamides, sulfonamides and quinolones, and resistant to some macrolides and aminoglycosides. Whole-genome sequence analysis showed that the bacterial genome was 2 580 488 bp in size and the sequence type was ST-43. It had the closest homology with the MH1475 strain, and the average nucleotide identity (ANI) value of the two strains reached 98.60%. There were 19 ORFs in the whole genome encoding MHLB002 genes related to pathogenicity, and 9 ORFs encoding drug-resistant genes.

ConclusionThe M. haemolytica capsulatum type 2 isolated in this experiment is the pathogenic bacteria that caused serious respiratory diseases and deaths in goats in this farm. It also provides a theoretical basis for the prevention and treatment of goat M. haemolytica.