Lactococcus lactis AbiD1 abortive infection efficiency is drastically increased by a phage protein

Three genetically defined Actinobacillus pleuropneumoniae serotype 7 mutants with deletions in the small (tbpB), the large (tbpA), and both transferrin binding protein genes were constructed and examined in an aerosol infection model. Neither mutant caused clinical disease or could be reisolated, and no immune response could be detected 21 days after infection. This result clearly implies that each transferrin binding protein on its own is a virulence factor of A. pleuropneumoniae serotype 7.