Roles of the surface layer proteins of Campylobacter fetus subsp fetus in ovine abortion

The role of the surface (S)-layer proteins of Campylobacter fetus subsp, fe tus has been investigated using an ovine model of abortion. Wild type strai n 23D induced abortion in up to 90% of pregnant ewes challenged subcutaneou sly. Isolates recovered from both dams and fetuses expressed S-layer protei ns with variable molecular masses, The spontaneous S-layer-negative variant , strain 23B, neither colonized nor caused abortions in pregnant elves. A s eries of isogenic sapA and recA mutants, derived from 23D, also were invest igated in this model, A mutant (501 [sapA recA(+)]) caused abortion in one of five challenged animals and was recovered from the placenta of a second animal. Another mutant (502 [sapA recA]) with no S-layer protein expression caused no colonization or abortions in challenged animals but caused abort ion when administered intraplacentally, Mutants 600(2) and 600(4), both rec A, had fixed expression of 97- and 127-kDa S-layer proteins, respectively. Two of the six animals challenged with mutant 600(4) were colonized, but th ere were no abortions. As expected, all five strains recovered expressed a 127-kDa S-layer protein. In contrast, mutant 600(2) was recovered from the placentas of all five challenged animals and caused abortion in two. Unexpe ctedly. one of the 16 isolates expressed a 127-kDa rather than a 97-kDa S-l ayer protein. Thus, these studies indicate that S-layer proteins appear ess ential for colonization and/or translocation to the placenta but are not re quired to mediate fetal injury and that S-lager variation may occur in a re cA strain.