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Infection and Immunity, February 2000, p. 839-847, Vol. 68, No. 2
Laboratoire de Pharmacologie
Toxicologie1 and Laboratoire de
Microbiologie Moléculaire
Associé,3 Institut National de
Recherche Agronomique, Toulouse, France, and GREMIP,
Faculté de Médecine Vétérinaire,
Saint-Hyacinthe, Québec, Canada2
Received 22 June 1999/Returned for modification 25 August
1999/Accepted 26 October 1999
Some Escherichia coli strains isolated from intestinal
or extraintestinal infections in pigs produce cytotoxic necrotizing factor 1 (CNF1). In order to analyze the role of CNF1 in the
pathogenesis of porcine colibacillosis, newborn colostrum-deprived
germfree piglets were orally inoculated with a wild-type CNF1-producing strain (M623) or with an isogenic cnf1 mutant
(M623
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Lack of a Role of Cytotoxic Necrotizing Factor 1 Toxin from Escherichia coli in Bacterial Pathogenicity and
Host Cytokine Response in Infected Germfree Piglets


CNF1). The two isogenic strains induced a high mortality with
similar lung and serosal inflammatory lesions, indicating that both
strains were pathogenic in these piglets. Bacterial counts in various organs of inoculated piglets revealed an intestinal predisposition of
M623 and M623
CNF1 strains for the cecum and colon. Extraintestinal organs (lungs, liver, spleen, and kidney) were also colonized by both
strains. Similar colonization of intestinal and extraintestinal tissues
in animals inoculated with either strain was observed, except in the
ileum, where M623 showed a higher colonization than M623
CNF1.
Intestinal (ileum and colon), extraintestinal (lung and kidney), and
immune (mesenteric lymph nodes and spleen) tissues were sampled at 1 day postinoculation and analyzed for cytokine expression by a reverse
transcriptase PCR technique. Inoculation with E. coli M623
induced an enhanced expression of inflammatory cytokines
(interleukin-1
[IL-1
], tumor necrosis factor
, and IL-12p40)
in the intestinal organs compared to uninoculated piglets or piglets
inoculated with nonpathogenic intestinal E. coli 862B, which is also able to colonize the intestinal tract. There was little
difference in cytokine transcript levels in the intestinal and
extraintestinal organs in piglets inoculated with E. coli strains M623 or M623
CNF1, except in the ileum, where IL-1
and IL-8 mRNA levels correlated with bacterial colonization. Expression of
regulatory cytokines (gamma interferon and IL-4) was weak in immune
tissues from piglets inoculated with M623 or M623
CNF1. Taken
together, our data indicate that the CNF1-producing strain, M623, is
pathogenic and induces inflammatory cytokine expression in germfree,
colostrum-deprived piglets. Nevertheless, in this model, the CNF1 toxin
does not appear to be a major factor for pathogenicity or cytokine
response, as demonstrated by the use of an isogenic cnf1 mutant.
*
Corresponding author. Mailing address: Laboratoire de
Pharmacologie Toxicologie, INRA, 180 Chemin de Tournefeuille, 31931 Toulouse Cedex 9, France. Phone: 33 (0) 561285480. Fax: 33 (0) 561285310. E-mail: ioswald{at}toulouse.inra.fr.
Present address: Department of Biology, Washington University,
Saint Louis, MO 63130.
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