Early events in the pathogenesis of avian salmonellosis

Abstract

Salmonellae are gastrointestinal pathogens of man and animals. However, strains that are host-specific avian pathogens are often avirulent in mammals, and those which are nonspecific are commensal in poultry. The objective of this study was to determine whether host specificity was exhibited by bacterial abilities to invade epithelial cells or resist leukocyte killing. In this study, leukocytes isolated from humans and chickens were used to kill Salmonella in vitro. Both Salmonella pullorum, an avian-specific serotype, and Salmonella typhimurium, a broad-host-range serotype, were sensitive to killing by polymorphonuclear leukocytes isolated from both species. Both serotypes replicated in cells of the MQ-NCSU avian-macrophage cell line. In contrast, S. pullorum was noninvasive for cultured epithelial Henle 407, chick kidney, chick ovary, and budgerigar abdominal tumor cells. In the bird challenge, however, S. typhimurium rapidly caused inflammation of the intestinal mucosa, but S. pullorum preferentially targeted the bursa of Fabricius prior to eliciting intestinal inflammation. Salmonella serotypes which cause typhoid fever in mice have been shown to target the gut-associated lymphoid tissue. Observations from this study show that S. pullorum initiated a route of infection in chicks comparable to the route it takes in cases of enteric fever.

FIG. 1

Histopathologic changes and immunohistochemical staining from S. typhimurium-challenged chicks, 2 days postchallenge. (A) Section taken from cecum shows marked infiltration of heterophils into the lamina propria and migration through the mucosal epithelium (arrows). Multiple crypt abscesses are identified by arrowheads. (B) Immunohistochemical staining of S. typhimurium in cecum from the same bird as in A. Bacteria are identified within a vacuole by brown staining (arrow). (C) Bursa contains mild infiltrates of heterophils (arrow) in the connective tissue between follicles, but not within the bursal follicles. (D) Immunohistochemical staining of S. typhimurium (arrow) within a vacuole in bursal follicles from the same bird as in C.

FIG. 2

Histopathologic changes and immunohistochemical staining from S. pullorum-challenged chicks, 2 days postchallenge. (A) Section taken from cecum shows infiltration of heterophils into the lamina propria and migration into the mucosal epithelium (arrow). (B) Immunohistochemical staining of S. pullorum in cecum from the same bird as in A. Bacteria were found very infrequently and are not present in this section. (C) Bursa contains marked infiltrates of heterophils that have disrupted normal architecture. (D) Immunohistochemical staining of S. pullorum (arrow) within multiple vacuoles in bursal follicles from the same bird as in C.