Mannheimia spp

From Cow
Mannheimia spp bacterial infection in a cow, resulting in fibrinous bronchopneumonia. The ventral regions of cranial, middle, and caudal lobes are markedly dark purple, consolidated, regionally collapsed, and sharply demarcated.

Mannheimia haemolytica (formerly Pasteurella haemolytica), together with Pasteurella multocida are a leading cause of respiratory disease, enzootic pneumonia in cattle worldwide[1].

Lechiguana disease is also reportedly associated with this bacterium.

M. haemolytica is an opportunistic bacterium which normally inhabits the nasopharynx and tonsils of cattle. Although the exact mechanisms are not known, stress or concurrent viral infections result in microenvironmental change that favors increased multiplication and colonization of the M. haemolytica S1 serotype within in the microvilli of the upper respiratory tract[2]. M. haemolytica serotype S1 is considered the major cause of the most severe form of pneumonia.

M. haemolytica results in fibrinous and necrotizing lobar pneumonia and pleuropneumonia of cattle.

Various virulence factors allow M haemolytica to colonize the lungs and establish infection. These virulence factors include leukotoxin (LKT), lipopolysaccharide, adhesins, capsule, outer membrane proteins, and various proteases[3].


  1. McClary DG et al (2011) Relationship of in vitro minimum inhibitory concentrations of tilmicosin against Mannheimia haemolytica and Pasteurella multocida and in vivo tilmicosin treatment outcome among calves with signs of bovine respiratory disease. J Am Vet Med Assoc 239(1):129-135
  2. Briggs RE & Frank GH (1992) Increased elastase activity in nasal mucus associated with nasal colonization by Pasteurella haemolytica in infectious bovine rhinotracheitis virus-infected calves. Am J Vet Res 53:631–635
  3. Singh, K et al (2011) Mannheimia haemolytica: Bacterial–Host Interactions in Bovine Pneumonia. Veterinary Pathology 48(2):338-348