Project Leader:

Dr. Jose Perez-Casal

Background:
Mycoplasma bacteria cause a range of illnesses – pneumonia, arthritis, mastitis – in cattle of all ages and are difficult to eradicate. M. bovis is one of the more serious pathogens, yet it may be overlooked as a causative agent of these conditions because of the presence of other, more familiar bacteria. Difficult to treat, M. bovis is suspected of being a main predisposing factor in disease development, particularly with respect to respiratory disease.

First seen in the U.S. in 1961, M. bovis is now thought to be circulating worldwide. In the U.S., the impact of this pathogen on weight gain and carcass value as part of the bovine respiratory disease complex was estimated at $32 million per year (1999). Over the past decade, M. bovis has been responsible for a chronic pneumonia-polyarthritis syndrome plaguing the beef industries of Canada and the United States. It can also cause abortion and sterility.

Pathogenic mycoplasmas attach to mucosal surfaces, so they can infect the respiratory and urogenital tracts, the mammary glands, and the serosal membranes (pericardial, pleural and peritoneal). Due to antigenic variability, treatment of M. bovis infections with antibiotics is difficult. Once established in the herd, the infection is difficult to control.

The inability of chemotherapy to control M. bovis has focused attention on vaccination. This research is based upon our identification of a unique group of surface-localized enzymes involved in glucose metabolism (glycolytic enzymes), including GAPDH, that show remarkable antigenic conservation within species and are effective protective antigens against bacterial, mycotic and parasitic infections. We have demonstrated that these proteins are promising vaccine targets to control bovine mastitis. A protein with homology to GAPDH has been identified in Mycoplasma genitalium and we believe that a similar protein is expressed on the cell surface of M. bovis.

Objectives:

1. Develop a reliable Mycoplasma bovis infection model
2. Isolate the gene encoding the M. bovis GAPDH protein and characterize the protein product
3. Construct a GAPDH/Vsp chimeric protein
4. Test different vaccine formulations and immunization routes
5. Carry out vaccination trials

Progress:
To date, we have successfully developed a challenge model and determined optimal challenge doses of M. bovis. We have cloned the gene encoding the M. bovis GAPDH protein and successfully expressed and purified the protein. We have also constructed a Vsp-GAPDH protein chimera and were able to express and purify it on a large scale for use in the vaccine trials. In addition, we tested different vaccine formulations and conducted trials to determine the optimum immunization route.

Recent publication: Detection of antibodies against the Mycoplasma bovis glyceraldehyde-3-phosphate dehydrogenase protein in beef cattle.

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