Summary auto-generated
This study investigated whether Shiga-toxigenic Escherichia coli O157:H7 (STEC O157:H7) can produce attaching-effacing (AE) lesions in the intestines of 6-month-old sheep using ligated colon loop techniques. Two sheep underwent surgical procedures to create ligated loops in the spiral colon, which were then inoculated with various bacterial strains including STEC O157:H7, non-toxigenic O157:H7, and O26:K60:H11 strains. Tissue samples were collected after 6 hours and examined using light microscopy, immunohistochemistry, and electron microscopy. All inoculated strains produced AE lesions characterized by intimate bacterial adherence to enterocytes. However, the lesions were sparse and small, typically involving only one or a few adjacent cells. No clear correlation was found between lesion formation and bacterial cell density, pre-inoculation growth conditions, or specific strain characteristics. The research demonstrates that STEC O157:H7 can induce AE lesions in older sheep when high bacterial concentrations are introduced directly into intestinal loops, contrasting with previous findings that showed no lesion formation following oral inoculation of older animals. This finding is significant for understanding the mechanisms of persistent bacterial colonization in ruminant reservoirs.
Key findings
- All tested E. coli strains (STEC O157:H7, non-toxigenic O157:H7, and O26:K60:H11) produced attaching-effacing lesions within 6 hours in ligated colon loops of 6-month-old sheep
- AE lesions were sparse and small, typically involving single or few adjacent enterocytes, with no correlation to bacterial cell density or pre-inoculation growth conditions
- Immunohistochemistry proved more sensitive than standard staining for detecting some lesions, revealing AE lesions in loops where H&E staining alone did not detect them
- Lamina proprial colonization by O157 bacteria was observed in some sheep, suggesting tissue-level invasion capacity independent of AE lesion formation
- The sparse nature of lesions in ligated loops resembles those found in experimentally inoculated neonatal lambs, suggesting current detection techniques may underestimate lesions in naturally infected animals
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Abstract
Shiga-toxigenic Escherichia coli O157:H7 (STEC O157:H7) is associated with potentially fatal human disease, and a persistent reservoir of the organism is present in some farm animal species, especially cattle and sheep. The mechanisms of persistent colonisation of the ruminant intestine by STEC O157:H7 are poorly understood but may be associated with intimate adherence to eukaryotic cells. Intimate adherence, as evidenced by induction of attaching-effacing (AE) lesions by STEC O157, has been observed in 6-day-old conventional lambs after deliberate oral infection but not in older animals. Thus, the present study used a ligated intestinal loop technique to investigate whether STEC O157:H7 and other attaching-effacing E. coli may adhere intimately to the sheep large intestinal mucosa. To do this, four STEC O157:H7 strains, one STEC O26:K60:H11 and one Shiga toxin-negative E. coli O157:H7 strain, suspended in either phosphate-buffered saline or Dulbecco's modified Eagle's medium, were inoculated into ligated spiral colon loops of each of two lambs. The loops were removed 6 h after inoculation, fixed and examined by light and electron microscopy. AE lesions on the intestinal mucosa were produced by all the inoculated strains. However, the lesions were sparse and small, typically comprising bacterial cells intimately adhered to a single enterocyte, or a few adjacent enterocytes. There was little correlation between the extent of intimate adherence in this model and the bacterial cell density, pre-inoculation growth conditions of the bacteria or the strain tested.