Escherichia coli O157:H7 is only occasionally isolated from healthy swine, but some experimentally infected animals will shed the organism in their feces for at least 2 months. Potential explanations for the paucity of naturally occurring infections in swine, as compared to cattle, include a lack of animal-to-animal transmission so that the organism cannot be maintained within a herd, a high infectious dose, or herd management practices that prevent the maintenance of the organism in the gastrointestinal tract. We hypothesized that donor pigs infected with E. coli O157:H7 would transmit the organism to naïve pigs. We also determined the infectious dose and whether housing pigs individually on grated floors would decrease the magnitude or duration of fecal shedding. Infected donor pigs shedding <10 4 CFU of E. coli O157:H7 per g transmitted the organism to 6 of 12 naïve pigs exposed to them. The infectious dose of E. coli O157:H7 for 3-month-old pigs was approximately 6 ؋ 10 3 CFU. There was no difference in the magnitude and duration of fecal shedding by pigs housed individually on grates compared to those housed two per pen on cement floors. These results suggest that swine do not have an innate resistance to colonization by E. coli O157:H7 and that they could serve as a reservoir host under suitable conditions.

We assessed the ability of a kanamycin-marked Stx phage to move into a commensal, ovine Escherichia coli strain in the ruminant gastrointestinal tract. Transduction was detected in 19/24 sheep tested, resulting in the recovery of 47 transductants. Subtherapeutic doses of the quinolone antibiotic enrofloxacin did not increase the rate of transduction.

Edema disease is a systemic disease of weaned pigs caused by host-adapted strains of Escherichia coli, most commonly belonging to serogroup O138, O139, or O141. In the late 1990s, E. coli O147 strains containing the virulence genes f18, sta, stb, and stx 2 were recovered from outbreaks of edema disease in the United States. Pulsed-field gel electrophoresis (PFGE) was used to determine that the majority of these strains (34/43) were closely related to one another. Subsequent analysis by multilocus restriction typing confirmed the PFGE results and indicated that the cluster of edema disease strains were only distantly related to other E. coli O147 strains. Serogrouping of edema disease isolates from the Iowa State University Veterinary Diagnostic laboratory recovered between 1996 and 2000 indicated that 42% belonged to serogroup O147. Our data suggest that these strains may be a common serotype of edema disease-causing E. coli in the United States.

Isogenic strains of Escherichia coli O157:H7, missing either stx 2 or the entire Stx2-encoding phage, were compared with the parent strain for their abilities to colonize sheep. The absence of the phage or of the Shiga toxin did not significantly impact the magnitude or duration of shedding of E. coli O157:H7.The major reservoirs for Shiga toxin-producing Escherichia coli (STEC) are cattle and other ruminants. These bacteria are carried in the gastrointestinal tract and do not cause disease in mature ruminants even when administered at very high doses (2). It is not known why the majority of ruminants are colonized by STEC in contrast to other animal species. One of the major virulence factors of STEC is Shiga toxin (Stx), an A 1 B 5 toxin which is encoded by lysogenic bacteriophages. The preferred receptor for the toxin is globotriaosylceramide (Gb 3 ). It has been shown that cattle lack Gb 3 receptors in their vascular endothelium, and it is thought that this may protect them from the systemic effects of Stx (9, 14). It has also been proposed that Stx may reduce the severities of viral infections such as bovine leukemia virus (4, 5) or modulate intestinal inflammation (12) in cattle.The objective of this study was to determine whether the Stx2-encoding bacteriophage or the Shiga toxin itself contributed to the magnitude or duration of colonization by E. coli O157:H7 in ruminants.(A preliminary report of this work was presented at the symposium Beyond Antimicrobials, the Future of Gut Microbiology, Aberdeen, Scotland, 2002.) The inoculum stains used in this study are listed in Table 1. Spontaneous nalidixic acid-, novobiocin-, and/or streptomycinresistant mutants were selected from parent strain 86-24 and its isogenic derivatives. Strain 86-24 ⌬933 was made as previously described by site-directed mutagenesis to delete stx 2 (15). Some mutants not only lost the stx 2 operon but suffered deletions in the region flanking the deleted stx 2 operon, suggesting that these mutants may have lost the entire 933 phage. Loss of the phage was confirmed by a PCR assay that utilized several sets of primers (designed based on the published nucleotide sequence for 933 [13]) to amplify approximately 1-kb portions from different regions of the 933 genome. The loss of 933 in strain 86-24 ⌬933 was also verified by challenging exponentially growing broth cultures of this strain and a 933-positive E. coli O157:H7 strain with subinhibitory amounts of norfloxacin (11). Inoculum strains were grown overnight in Trypticase soy broth and frozen in glycerol at Ϫ80°C until use.All experiments complied with the Iowa State University Animal Care and Use guidelines. Young adult sheep (4 to 12 months old, 80 to 120 lb) were purchased from a local source, housed two per pen under biosafety level 2 conditions, and acclimated to a diet of commercial sheep feed concentrate (1 lb/animal/day) and alfalfa/grass hay ad libitum for 2 weeks prior to inoculation as described previously (1). Sheep were randomly divided into three groups and inoculated wi...

BackgroundHemolytic uremic syndrome (HUS) is a systemic and potentially fatal complication of gastroenteritis secondary to Shiga toxin-producing enterohemorrhagic Escherichia coli (EHEC) infection characterized by microangiopathic hemolytic anemia, thrombocytopenia, and acute renal damage. Shiga toxin (Stx), the toxin principle in HUS, is produced locally within the gut following EHEC colonization and is disseminated via the vasculature. Clinical development of HUS currently has no effective treatment and is a leading cause of renal failure in children. Novel post-exposure therapies are currently needed for HUS; therefore, the purpose of this study was to investigate the efficacy of a Stx receptor mimic probiotic in a porcine model of HUS. Edema disease, an infection of swine caused by host adapted Shiga toxin-producing Escherichia coli (STEC) and mediated by Shiga toxin 2e (Stx2e), shares many pathogenic similarities to HUS. In this study, three-week old piglets were inoculated with STEC and 24 hours later treated twice daily with a probiotic expressing an oligosaccharide receptor mimic for Stx2e to determine if the probiotic could reduce intestinal toxin levels.MethodsPiglets were orally inoculated with 1010 CFU of STEC strain S1191 eight days after weaning. Beginning day 1 post-inoculation, piglets were treated orally twice daily with 5 × 1011 CFU of either the receptor mimic probiotic or a sham probiotic for 10 days. Intestinal Stx2e levels were assessed daily via Vero cell assay. The efficacy of the probiotic at reducing intestinal Stx2e, vascular lesions, and clinical disease was evaluated with repeated measures ANOVA and Fisher’s exact test as appropriate.ResultsThe probiotic significantly reduced intestinal Stx2e, as reflected by decreased fecal toxin titers on days 3–8 post-inoculation (p < 0.01). Despite this reduction in intestinal toxin levels, however, the probiotic failed to reduce the incidence of vascular necrosis in target organs and had no effect on clinical disease.ConclusionsThe data suggest that post-exposure treatment with a Stx-binding probiotic is effective in reducing intestinal toxin burden. Future studies could target this approach for possible development of post-exposure interventions.