REDUCED VIRULENCE OF SERPULINA-HYODYSENTERIAE HEMOLYSIN-NEGATIVE MUTANTS IN PIGS AND THEIR POTENTIAL TO PROTECT PIGS AGAINST CHALLENGE WITHA VIRULENT-STRAIN

The role of the Serpulina hyodysenteriae hemolysin encoded by the tlyA gene in the pathogenesis of swine dysentery (SD) was studied. tlyA mu tants of two S. hyodysenteriae strains (B204 and C5) were tested for v irulence in pigs. None of the animals developed SD. Hoc-ever, after in fection with wild-type strain B204 or C5, the incidence of SD was 100 or 60%, respectively. Thus, the tlyA-encoded hemolysin of S. hyodysent eriae is an important virulence factor in SD. The potential of these m utants to protect pigs against challenge with a virulent S. hyodysente riae strain was also studied. After challenge with wild-type strain B2 04, 50% of pigs previously inoculated with the B204 tlyA mutant were p rotected, whereas all control pigs contracted SD. None of the pigs pre viously inoculated,vith the C5 tlyA mutant developed SD upon challenge with wild-type strain B204, whereas 40% of the control pigs developed SD in this experiment. Thus, previous colonization with S. hyodysente riae tlyA mutants in pigs provides partial protection against challeng e with a virulent S. hyodysenteriae strain.