The porcine intestinal spirochaetes: identification of new genetic groups

Abstract

Ninety porcine isolates of weakly beta-haemolytic intestinal spirochaetes that resembled Serpulina (Treponema) innocens were examined using multilocus enzyme electrophoresis (MEE). Results were compared with those previously obtained for 98 isolates of Serpulina (Treponema) hyodysenteriae (Lee et al, 1992). The weakly beta-haemolytic isolates were divided into 56 electrophoretic types (ETs), contained in three distinct genetic groups (A, B and C). Group A corresponded to the genus Serpulina, and could be divided into three divisions. It contained 17 weakly haemolytic isolates in divisions b and c, as well as all 98 isolates of S. hyodysenteriae, located in division a. All seven weakly beta-haemolytic isolates that produced indole and had alpha-glucosidase but not alpha-galactosidase activity fell into division b. These spirochaetes may represent a distinct species. The other ten weakly beta-haemolytic spirochaetes, in division c, fitted the original description of S. innocens. Group B contained 17 of the weakly beta-haemolytic isolates (18.9%) in ten ETs. Isolates in this group differed from typical S. innocens in that they lacked alpha-galactosidase activity. Group B represented a distinct group of weekly beta-haemolytic spirochaetes, which may constitute a new genus. Group C contained 56 of the weakly beta-haemolytic isolates (62.2%) located in 29 ETs. The original isolate from “spirochaetal diarrhoea” (P43/6/78—Taylor et al., 1980) was located in this group, together with Australian isolates from a similar condition. Spirochaetes in group C were morphologically distinct from those in groups A and B in that they possessed only four, five, or occasionally six, subterminal axial filaments, were more slender, and had more pointed ends to their cells. We consider that group C represents a new genus of spirochaetes, members of which may be associated with spirochaetal diarrhoea.