Evaluation of a 23S rDNA polymerase chain reaction assay for identification of Serpulina intermedia, and strain typing using pulsed-field gel electrophoresis

A polymerase chain reaction assay, amplifying a 1027 base pair portion of t he 23S rDNA gene, was evaluated for identification of the intestinal spiroc haete Serpulina intermedia. A total of 34 strains of S. intermedia isolated from pigs and chickens and 195 strains of other related species were teste d. The optimised assay correctly identified all the S. intermedia strains, but generated 11 false positive reactions, giving a test sensitivity of 100 % and a test specificity of 94.3%. The false positive reactions were genera ted from strains of four different species of intestinal spirochaetes, and the product was of the original predicted size. This suggests that the prim er sites selected on the 23S rRNA gene were not completely specific for S. intermedia. Pulsed-field gel electrophoresis was then developed to investig ate diversity amongst the S. intermedin strains. All strains rested had dis tinct DNA banding patterns using Mlu1, although three isolates from chicken s on the same farm appeared closely related. The collection exhibited consi derable genetic diversity, and strains from pigs and chickens were distribu ted in clusters throughout the dendrogram produced. The most closely relate d porcine and avian strains shared only 62% similarity. (C) 2000 Elsevier S cience B.V. All rights reserved.