Emended descriptions of indole negative and indole positive isolates of Brachyspira (Serpulina) hyodysenteriae

Two type/reference strains of Brachyspira (B.) hyodysenteriae, 14 Belgian a nd German indole negative, and 14 Belgian, German and Swedish indole positi ve field isolates of strongly beta-haemolytic intestinal spirochaetes were compared by pulsed-field gel electrophoresis (PFGE) patterns, biochemical r eaction patterns, 16S rDNA sequences and MIC determinations of six antibact erial substances. Three tests for indole production, including a spot indol e test, were compared with congruent results. All field isolates were class ified as B. hyodysenteriae due to a high genetic and phenotypic similarity with the type strains. The Belgian and German indole negative isolates had identical and unique PFGE patterns for the tested restriction enzymes MluI and SalI, as well as identical 16S rDNA sequences, and they could not be di fferentiated by any of the methods used. Seven unique PFGE patterns were ac hieved from the 14 indole positive field isolates. The patterns were identi cal and unique for epidemiologically related isolates. Type/reference strai ns and isolates without known relation to other tested isolates showed uniq ue banding patterns. The MICs of tylosin, tiamulin, erythromycin, clindamyc in, carbadox and virginiamycin were determined in broth for all isolates. I n contrast to Belgian and German isolates, the majority of the Swedish fiel d isolates were susceptible to tylosin, erythromycin and clindamycin. Proba ble pathways of infection for some of the Swedish isolates were determined. The PFGE patterns of epidemic clones of B. hyodysenteriae remained stable for a period of up to 8 years. In vivo development of resistance to macroli de and lincosamide antibiotics due to use of tylosin was clearly indicated for two epidemic clones, (C) 1999 Elsevier Science B.V. All rights reserved .