Genetic and phenotypic characterization of intestinal spirochetes colonizing chickens and allocation of known pathogenic isolates to three distinct genetic groups.

Abstract

Infection with intestinal spirochetes has recently been recognized as a cause of lost production in the poultry industry. Little is known about these organisms, so a collection of 56 isolates originating from chickens in commercial flocks in Australia, the United States, The Netherlands, and the United Kingdom was examined. Strength of beta-hemolysis on blood agar, indole production, API ZYM enzyme profiles, and cellular morphology were determined, and multilocus enzyme electrophoresis was used to analyze the extent of genetic diversity among the isolates. The results were compared with those previously obtained for well-characterized porcine intestinal spirochetes. The chicken isolates were genetically heterogeneous. They were divided into 40 electrophoretic types distributed among six diverse genetic groups (groups b to g), with a mean genetic diversity of 0.587. Strains in two groups (groups d and e) may represent new species of Serpulina, and the groups contained only strains isolated from chickens. Three genetic groups contained isolates previously shown to be pathogenic for chickens. These corresponded to the proposed species "Serpulina intermedius," to an unnamed group (group e), and to Serpulina pilosicoli. Two of the chicken isolates (one "S. intermedius" and one S. pilosicoli isolate) were strongly beta-hemolytic, two (both "S. intermedius") had an intermediate level of beta-hemolysis, and the rest were weakly beta-hemolytic. Fourteen isolates of "S. intermedius" produced indole, as did one isolate from group d. Isolates identified as S. pilosicoli resembled porcine isolates of this species, having four to six periplasmic flagella inserted subterminally in a single row at each end of the cell, and had tapered cell ends. All other spirochetes were morphologically similar, having seven or more periplasmic flagella and blunt cell ends. The identification of three genetic groups containing pathogenic isolates provides an opportunity for more detailed epidemiologic studies with these pathogens and for the development of improved diagnostic tests.