Phylogenetic and Epidemiologic Relationships among Pasteurellaceae from Colorado Bighorn Sheep Herds

Abstract

We used 16S rRNA sequencing and leukotoxin gene (lktA) screening via PCR assay to clarify phylogenetic and epidemiologic relationships among Pasteurellaceae isolated from bighorn sheep (Ovis canadensis). Only six of 21 bighorn isolates identified as "Mannheimia haemolytica" in original laboratory reports appeared to be isolates of M. haemolytica sensu stricto based on 16S rRNA sequence comparisons; the remainder grouped with M. glucosida (n=8) or M. ruminalis (n=7). Similarly, 16S rRNA sequence comparisons grouped only 16 of 25 trehalose-fermenting bighorn isolates with reference strains of Bibersteinia trehalosi; nine other trehalose-fermenting bighorn isolates formed a clade divergent from B. trehalosi reference strains and may belong to another species. Of the 16 bighorn isolates identified as B. trehalosi by 16S rRNA sequences, only nine carried detectable lktA and thus seemed likely pathogens; none of the Bibersteinia clade isolates yielded detectable lktA despite reportedly showing β hemolysis in culture. Our findings suggest that traditional metabolism-based methods for identifying Pasteurellaceae isolates lack sufficient accuracy and resolution for reliably discerning bacterial causes of respiratory disease in bighorn sheep. Consequently, these traditional methods should minimally be augmented by molecular techniques to improve epidemiologic relevance. Streamlined surveillance approaches focused primarily on detecting pathogenic Pasteurellaceae (e.g., M. haemolytica sensu stricto and lktA-positive B. trehalosi) and other select pathogens may be most informative for investigating and managing bighorn respiratory disease.

Pneumonia in bighorn sheep: Risk and resilience

“…to leukotoxin positive Pasteurellaceae, to a multi‐factorial respiratory disease complex (Besser et al ). Much attention has focused on virulent Pasteurellaceae bacteria where problems with accurate detection and classification have also complicated efforts to establish an association with pneumonia outbreaks in wild sheep (Angen et al , Walsh et al , Miller et al , Shanthalingam et al , Walsh et al ).…”

Assessing respiratory pathogen communities in bighorn sheep populations: Sampling realities, challenges, and improvements

“…It should be noted, however, that presence of the lktA gene indicates potential virulence of an organism, but does not necessarily indicate that leukotoxin is being actively produced by the organism [21]. Diagnostic tests do not consistently distinguish among some species in the Mannheimia genus [22]. For this analysis Mannheimia glucosida was included within the M .…”

Potential disease agents in domestic goats and relevance to bighorn sheep (Ovis canadensis) management

“…The cause of pneumonia in BHS is likely multifactorial [8, 10] with pathogen introduction from domestic livestock that occurred in the past. [11, 12]. However introduction of new pathogens with direct contact with domestic livestock, including goats, is also possible.…”