Colonization, Persistence, and Tissue Tropism ofEscherichia coliO26 in Conventionally Reared Weaned Lambs

Abstract

Escherichia coli O26 is recognized as an emerging pathogen associated with disease in both ruminants and humans. Compared to those of E. coli O157:H7, the shedding pattern and location of E. coli O26 in the gastrointestinal tract (GIT) of ruminants are poorly understood. In the studies reported here, an stx-negative E. coli O26 strain of ovine origin was inoculated orally into 6-week-old lambs and the shedding pattern of the O26 strain was monitored by serial bacteriological examination of feces. The location of colonization in the GIT was examined at necropsy at two time points. The numbers of O26 organisms excreted in feces declined from approximately 10 7 to 10 4 CFU per gram of feces by day 7 and continued at this level for a further 3 weeks. Beyond day 30, excretion was from few animals, intermittent, and just above the detection limit. By day 38, all fecal samples were negative, but at necropsy, O26 organisms were recovered from the upper GIT, specifically the ileum. However, no attaching-effacing (AE) lesions were observed. To identify the location of E. coli O26 within the GIT early after inoculation, two lambs were examined postmortem, 4 days postinoculation. High numbers of O26 organisms were recovered from all GIT sites examined, and ϳ10 9 CFU were recovered from 1 gram of ileal tissue from one animal. Despite high numbers of O26 organisms, AE lesions were identified on the mucosa of the ascending colon of only one animal. These data indicate that E. coli O26 readily colonizes 6-week-old lambs, but the sparseness of AE lesions suggests that O26 is well adapted to this host, and mechanisms other than those dependent upon intimin may play a role in persistence.Attaching-effacing Escherichia coli (AEEC) strains associated with human gastrointestinal disease are classified as either enteropathogenic E. coli (EPEC) or enterohemorrhagic E. coli (EHEC), depending on their abilities to produce Shiga toxins (41). Although E. coli O157:H7 is the most prevalent EHEC serotype associated with serious disease in humans, non-O157:H7 EHEC strains represent an emerging threat to public health and, unlike O157 strains, to animal health also (24). Indeed, non-O157 EHEC may be more prevalent than serogroup O157 in some countries (3).E. coli O26 is a well-recognized EPEC serogroup associated with disease in humans, notably infantile diarrhea (36). Significantly, Shiga toxin-elaborating E. coli (STEC) O26 bacteria are also associated with serious human infections, including severe diarrhea with sequelae similar to those of EHEC infections. Such infections have been recorded in Italy (55), Ireland (38), Japan (28, 29), Scotland (51), and elsewhere. The World Health Organization (WHO) has identified O26 STEC as the second most important serogroup of E. coli (65).EHEC and EPEC belong to the AEEC pathotype whose bacteria attach intimately to the microvillus brush border of enterocytes of animals and humans, forming attaching-effacing (AE) lesions (47, 57). The genes encoding the classical AE histopathology are located on a pat...

Clearance of Escherichia coli O157:H7 Infection in Calves by Rectal Administration of Bovine Lactoferrin

“…In calves, the terminal rectal mucosa, which is rich in lymphoid follicles, has been identified as the major site of E. coli O157:H7 colonization (13,24). In sheep, the bacteria seem to colonize the entire intestinal tract (16,20,25), even though slightly higher numbers could be seen in the ileum and large intestine (26) or at the recto-anal junction (6,27). It is likely that the antimicrobial activity of orally administered lactoferrin decreases from cranial to caudal in the gut so that an effect can be seen on O157:H7 colonization in the orally inoculated sheep, with a more equal colonization throughout the gut, compared to calves, in which the bacterium has a predilection for the recto-anal junction.…”

Comparison of recto-anal mucosal swab and faecal culture for the detection ofEscherichia coliO157 and identification of super-shedding in a mob of Merino sheep

“…Using ovine intestinal in vitro organ culture techniques, a number of studies have demonstrated an association between E. coli O157 and the rectal mucosa of neonatal lambs: following oral inoculation of 30 neonatal lambs, Best et al [16] observed small, diffuse E. coli O157 colonies at numerous locations in the gastrointestinal tract, while large, densely packed colonies were only observed at the terminal rectum. Using a similar method, Aktan et al [17] did not observe preferential colonization of any single location in the gastrointestinal tract. Studies of naturally infected lambs have also been inconclusive [18], with characteristic attaching-and-effacing lesions observed at various locations along the gastrointestinal tract.…”

“…Using a similar method, Aktan et al . [17] did not observe preferential colonization of any single location in the gastrointestinal tract. Studies of naturally infected lambs have also been inconclusive [18], with characteristic attaching-and-effacing lesions observed at various locations along the gastrointestinal tract.…”

Escherichia coliO157:H7 colonization in small domestic ruminants

“…La Ragione et al (2004) reported on the interactions between E. coli O26:K60 and E. coli O157:H7 in tissue culture adherence assays, which showed that preincubation of tissue culture cells with either strain reduced significantly the extent of adherence of the strain that was applied second. Aktan et al (2007) reported that atypical EPEC O26:K60 colonized 6‐week‐old conventionally reared lambs after oral inoculation, with persistent shedding for well over a month and with the induction of AE lesions that were small and sparse in the distal gastrointestinal tract. In the field, more than one group has shown E. coli serogroup O26 to be prevalent in ruminant animals at slaughter when the prevalence of E. coli O157:H7 in the same study animals was very low (Aktan et al , 2004; Fukushima & Seki, 2004).…”

“…Oral inoculation studies with a nontoxigenic ovine‐derived E. coli O26:K60 strain (Aktan et al , 2007) showed that the challenge organism could be recovered from all sites in the gastrointestinal tract during the high excretion phase, but from just the distal small intestine during long‐term persistence, 38 days after inoculation. This illustrates that tissue tropisms probably vary among differing persistent AEEC, including those in common EHEC and EPEC serogroups.…”