Susceptibility of different Serpulina species in pigs to antimicrobial agents

Five reference Serpulina strains, 36 Serpulina hyodysenteriae field strains and 17 field strains identified as Serpulina innocens, S. murdochii, Serpulina pilosicoli and Serpulina intermedia were tested for sensitivity to seven antibacterial agents. Lowered susceptibility to tiamulin was seen in some S. hyodysenteriae strains from farms in which insufficient therapeutic results were obtained with this antibiotic. The susceptibility levels of carbadox, gentamicin, dimetridazole and salinomycin were distributed normally. S. intermedia strains tended to be more susceptible to dimetridazole than the S. hyodysenteriae strains. The susceptibility levels of the other species did not differ from those of S. hyodysenteriae. Nearly all strains showed acquired resistance to tylosin and to a lesser degree also to lincomycin. Only two field strains and three of the five reference strains were an exception to this.