Characterization of Pasteurella multocida mutants of low virulence

Ten temperature-sensitive mutants of the Clemson University (CU) vaccine strain of Pasteurella multocida have been developed and were characterized by phenotypic attributes such as carbohydrate fermentation, antibiotic resistance, and membrane protein profiles. Some mutants were found to have lost the ability to utilize some substrates, notably xylose and gluconate, whereas others were able to ferment additional carbohydrates such as arabinose and rhamnose. CU was found to be resistant to sulfisoxazole, of intermediate resistance to bacitracin, and sensitive to rifampin; the sensitivity to these three antibiotics varied among the mutant strains, but 60% were resistant to rifampin. Membrane protein profiles demonstrated some changes in major bands, and there was variation in 50% of the mutants in proteins in the 31 kilodalton range. All strains were assayed for the presence of several virulence factors, and many were found to produce siderophore and to exhibit some degree of complement resistance.