SPECIFIC DETECTION OF SERPULINA-HYODYSENTERIAE AND POTENTIALLY PATHOGENIC WEAKLY BETA-HEMOLYTIC PORCINE INTESTINAL SPIROCHETES BY POLYMERASE CHAIN-REACTION TARGETING 23S RDNA

A 2470-bp section of the 23S ribosomal DNA from Serpulina hyodysenteri ae and five biochemical ly different groups of weakly beta-haemolytic porcine intestinal Serpulina strains was sequenced. The similarity bet ween the sequenced strains was high (96.85% to 99.84%). A phylogenetic tree was estimated by the maximum likelihood method. The sequenced st rains formed three groups. Serpulina hyodysenteriae and biochemical gr oup II ('S. intermedius') formed a cluster, but 20 nucleotide position s were different between the two, suggesting that biochemical group II is a separate species. Another cluster consisted of the closely relat ed biochemical group IIIa ('S. murdochii') and IIIb/c (S. innocens) (9 9.84% similarity), while biochemical group IV (S. pilosicoli) constitu ted a separate group with a relatively low similarity (96.85% to 9701% ) to the other groups. Three primer pairs were designed for specific P CR detection of the clinically important S. hyodysenteriae and biochem ical group II and IV. PCR amplification was accomplished with DNA extr acted from bacterial colonies by a simple boiling procedure, and with DNA extracted directly from porcine stool samples using a bead beating extraction procedure. The level of detection for the direct extractio n and amplification method was 5 x 10(5) cells added g(-1) normal faec es. (C) 1997 Academic Press Limited.