Originally named bipolare multocidum in 1885, the bacteria now called Mannheimia haemolytica, was renamed Pasteurella haemolytica in 1932. Based on the ability to ferment either arabinose or trehalose, isolates were classified into biotypes A and T. In 1990, the T biotypes were reclassified and named Pasteurella trehalosi. Nine years later, all of the A biotypes, with the exception of A11, were renamed Mannheimia haemolytica. A11 was given the name Mannheimia glucosida. Recently, P. trehalosi was once again reclassified and given the name Bibersteinia trehalosi, in honor of Ernst Biberstein, who did much of the characterization work on the organism.

Bibersteinia trehalosi is most commonly known for causing severe pneumonia and death in bighorn sheep. However, isolations from cases of bovine pneumonia have made this organism a more frequent topic of interest during discussions of vaccines for pasteurellosis. A recent paper¹ describes the interaction between B. trehalosi and M. haemolytica. The authors point out that although B. trehalosi is commonly isolated from cases of pneumonia in big horn sheep, M. haemolytica is the only pathogen that has consistently been shown to cause bronchopneumonia and death under experimental conditions.

In addition, other studies show that only leukotoxin producing strains of B. trehalosi can cause pneumonia, and only about 15% of the B. trehalosi strains produce leukotoxin. As a result, there is some question as to whether or not B. trehalosi is likely to be the major cause of pneumonia in big horn sheep. Research by the authors shows that B. trehalosi replicates at almost twice the rate of M. haemolytica and is able to inhibit and overgrow M. haemolytica. This data would lead to speculation that, in many cases, M. haemolytica might be the initial cause of pneumonia but is then overgrown by B. trehalosi, which is the organism subsequently isolated.

So what are the implications of all this for prevention by the use of commercially available vaccines? Since B. trehalosi and M. haemolytica are closely related on the family tree, there may be some shared whole cell antigens which could aid in cross protection. However, the primary virulence factor for both is leukotoxin, which is identical for both organisms. Thus, a vaccine that does a good job of stimulating antibodies to leukotoxin, should provide similar protection for both M. haemolytica as well as the strains of B. trehalosi that produce leukotoxin.

1.  Rohana P. Dassanayake,  Douglas R. Call,  Ashish A. Sawant,  N. Carol Casavant,  Glen C. Weiser,  Donald P. Knowles,  and Subramaniam Srikumaran  (2010). Bibersteinia trehalosi  Inhibits the Growth of  Mannheimia haemolytica  by a Proximity-Dependent Mechanism. Applied and Environmental Microbiology, February 2010, p. 1008-1013, Vol. 76, No. 4