Mannheimia haemolytica serotype A1 exhibits differential pathogenicity in two related species, Ovis canadensis and Ovis aries

Acylation Enhances, but Is Not Required for, the Cytotoxic Activity of Mannheimia haemolytica Leukotoxin in Bighorn Sheep

“…Due to limited availability of BHS, we could not include control groups of animals that were inoculated with the SH1217 parental wild-type strain or RPMI medium, which could be a possible caveat in interpreting our data. Nevertheless, in our earlier studies involving serotype A1 of M. haemolytica, we demonstrated that Lkt of M. haemolytica is necessary for the induction of fatal pneumonia in BHS (6). In our animal experiments, it was also of interest to us to evaluate whether the LktC mutant SH2099 would be attenuated enough to serve as a possible vaccine candidate in BHS, although with the progression of our animal experiments, it became clearly evident that the mutant strain was unsuitable.…”

“…Serotype 2 is predominant in pneumonia in domestic sheep (37,38). However, BHS are susceptible to both serotypes 1 and 2 of M. haemolytica (6,25,(39)(40)(41). This study was conducted with serotype 1.…”

“…M. haemolytica is also an important pathogen of pneumonia in bighorn sheep (Ovis canadensis) (BHS), which is the primary disease responsible for the drastic decline of BHS populations in North America from an estimated 2 million animals in the 1800s to less than 70,000 at the present time (5). Under the experimental conditions, M. haemolytica consistently caused 100% mortality in BHS within 2 to 3 days (6)(7)(8). The bacterium possesses several virulence factors, including the capsule, outer membrane proteins, lipopolysaccharide, and leukotoxin (Lkt).…”

“…The bacterium possesses several virulence factors, including the capsule, outer membrane proteins, lipopolysaccharide, and leukotoxin (Lkt). Based on the fact that Lkt deletion mutants do not cause mortality (6) or cause reduced mortality and milder lung lesions (9,10), Lkt has been accepted as the primary virulence factor of M. haemolytica. The 104-kDa Lkt is absolutely specific for ruminant leukocytes (11).…”

Differential Expression of Interleukin-8 by Polymorphonuclear Leukocytes of Two Closely Related Species, Ovis canadensis and Ovis aries , in Response to Mannheimia haemolytica Infection

“…Leukotoxin ( Pneumonia caused by Mannheimia haemolytica is an important factor in the drastic decline of bighorn sheep (BHS; Ovis canadensis) populations in North America (3, 31). The pneumonic lesions and mortality caused by this organism in BHS are much more severe than those in the related species, domestic sheep (DS; Ovis aries), under both natural and experimental conditions (11,12,13,24). The cellular and molecular basis underlying the differential pathogenicity exhibited by M. haemolytica in BHS and DS has not been elucidated yet.…”