Lack of a Role of Cytotoxic Necrotizing Factor 1 Toxin fromEscherichia coliin Bacterial Pathogenicity and Host Cytokine Response in Infected Germfree Piglets

Abstract

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⌬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.

Interleukin‐8 Secretion by Epithelial Cells Infected with Diffusely Adherent Escherichia coli Possessing Afa Adhesin‐Coding Genes

“…2, Tables 2 and 3). Fournout et al also reported that intestinal colonization by nonpathogenic E. coli did not cause an inflammatory reaction in piglets (12). Although Bétis et al (4) showed that nonmotile E. coli laboratory strain HB101 acquired an ability to induce IL-8 after transformation with plasmid carrying a kind of Afa gene (daa), it was not shown whether the level of IL-8 was similar to those caused by the well-established enteropathogenic strains.…”

Detection of cytotoxic necrotizing factor types 1 and 2 among fecal Escherichia coli isolates from brazilian children with and without diarrhea

“…Recently, Van Bost et al (2001b) reported that CNF2-producing strains were able to colonize the intestines, cause long-lasting diarrhea, and invade the blood stream of newborn colostrum-restricted calves after experimental inoculation through the oral route. A previous report on the experimental infection of germfree colostrum-deprived newborn piglets showed no evidence for a pathogenic role of CNF1 in the development of diarrhea (Fournout et al 2000). To date, there is no report on a comprehensively case-control epidemiological study of the association of CNF-producing E. coli strains with human diarrheal diseases.…”

Characteristics of necrotoxigenic Escherichia coli isolated from septicemic and diarrheic calves between 1958 and 1970

“…On the other hand, most of the NTEC1 isolates harbour sequences typical of the P®mbrial adhesin family and either one S-®mbrial (Sfa or F1C) (Fournout et al, 2000) or the AfaVIII-a®mbrial adhesins (Mainil et al, 1997(Mainil et al, , 1999Lalioui et al, 1999;Ge Ârardin et al, 2000), which are all located on the chromosome. The pap/prs gene clusters coding for P®mbriae and the cnf1 gene are actually associated with a hly operon coding for the ahemolysin, forming the so-called pathogenicity island 5 or Pai 5 (Blum et al, 1995;De Rycke et al, 1999;Dozois and Curtiss III, 1999).…”