Pasteurella haemolytica serotype 1 is the bacterial agent responsible for the pathophysiological events associated with bovine pneumonic pasteurellosis. Our previous studies support a role for the lipopolysaccharide (LPS) from P. haemolytica in the induction of proinflammatory cytokines. One of the pathological hallmarks of bovine pneumonic pasteurellosis is an influx of neutrophils into the al...

Infection of the bovine lung with Pasteurella haemolytica results in an acute respiratory disorder known as pneumonic pasteurellosis. One of the key virulence determinants used by this bacterium is secretion of an exotoxin that is specific for ruminant leukocytes (leukotoxin). At low concentrations, the leukotoxin can activate ruminant leukocytes, whereas at higher concentrations, it inhibits l...

OBJECTIVES To determine how resistance to macrolides is conferred in field isolates of Pasteurella multocida and Mannheimia haemolytica that lack previously identified resistance determinants for rRNA methylation, efflux and macrolide-modifying enzymes. METHODS Isolates of P. multocida and M. haemolytica identified as being highly resistant (MICs >64 mg/L) to the macrolides erythromycin, gami...

Mannheimia (Pasteurella) haemolytica A1 produces several virulence factors that play an important role in the pathogenesis of bovine pneumonic pasteurellosis. Foremost among these is a leukotoxin (LKT) that specifically kills ruminant leukocytes. Recent evidence suggests that M. haemolytica LKT binding to bovine leukocytes is mediated by the beta(2)-integrin CD11a/CD18 (lymphocyte function-asso...

Pasteurella spp. were isolated from feral goats and free-ranging bighorn sheep (Ovis canadensis canadensis) in the Hells Canyon National Recreation Area bordering Idaho, Oregon, and Washington (USA). Biovariant 1 Pasteurella haemolytica organisms were isolated from one goat and one of two bighorn sheep found in close association. Both isolates produced leukotoxin and had identical electrophoret...

The influence of the leukotoxin of Pasteurella haemolytica on the generation of arachidonic acid metabolites by bovine polymorphonuclear leukocytes (PMNs) was investigated. PMNs released 5-, 12-, and 15-hydroxyeicosatetraenoic acids (5-, 12-, and 15-HETE) and leukotriene B4 (LTB4) upon stimulation with arachidonic acid. The leukotoxin preparations dose dependently enhanced the release of the 5-...

Blood agar, prepared with Trypticase (BBL Microbiology Systems, Cockeysville, Md.) soy agar and 5% defibrinated bovine blood, is used for testing the potency of live Pasteurella multocida and Pasteurella haemolytica vaccines, but its potential for variation makes it undesirable to use in a standard assay method. Tests done with RPMI 1640 and Trypticase soy medium indicated that the benefits obt...