Shiga Toxin-Producing E. coli in Animals: Detection, Characterization, and Virulence Assessment

Cross-sectional study: prevalence of oedema disease Escherichia coli (EDEC) in weaned piglets in Germany at pen and farm levels

BACKGROUND

Escherichia coli bacteria capable of producing the toxin Stx2e and possessing F18-fimbriae (edema disease E. coli, EDEC) are considered causative agents of porcine oedema disease. This disease, which usually occurs in piglets shortly after weaning, has a high lethality in affected animals and can lead to high economic losses in piglet rearing. The aim of this cross-sectional field study was to determine the prevalence of EDEC in weaned piglets in Germany at pen and farm levels.

RESULTS

Ninety-nine farms with unknown history of infections with shigatoxin-producing E. coli (STEC) and oedema disease were sampled. On each farm, up to five pens were selected for sampling (n = 481). The piglets in these pens were at an age 1-3 weeks after weaning. Single faecal samples (n = 2405) and boot swabs (n = 479) were collected from the floor. On 50 farms, cotton ropes were additionally used to collect oral fluid samples (n = 185) and rope wash out samples (n = 231) from the selected pens. All samples were analyzed by bacterial culture combined with a duplex PCR for the presence of the corresponding genes stx2e and fedA (major subunit protein of F18 fimbriae). In addition, whole DNA specimens extracted from boot swabs, oral fluid samples, and rope wash out samples were directly examined by duplex PCR for DNA of stx2e and fedA. A pen was classified as positive if at least one of the samples, regardless of the technique, yielded a positive result in the PCR, and farms were considered positive if at least one pen was classified as positive. Overall, genes stx2e and fedA were found simultaneously in 24.9% (95% CI 22.1-29.1%) of sampled pens and in 37.4% (95% CI 27.9-47.7%) of sampled farms. Regardless of the presence of F18-fimbriae, Escherichia coli encoding for Stx2e (STEC-2e) were found in 35.1% (95% CI 31.0-39.1%) of the pens and 53.5% (95% CI 44.4-63.6%) of the farms sampled.

CONCLUSIONS

Escherichia coli strains considered capable to cause oedema disease in swine (EDEC) are highly prevalent in the surveyed pig producing farms in Germany. Due to intermittent shedding of EDEC and a potentially low within-farm prevalence, we recommend a combination of different sampling techniques for EDEC monitoring at pen and farm levels. Further studies are needed to understand which STEC-2e strains really pose the risk of causing severe porcine disease.

Enterohemorrhagic Escherichia coli and a Fresh View on Shiga Toxin-Binding Glycosphingolipids of Primary Human Kidney and Colon Epithelial Cells and Their Toxin Susceptibility

Enterohemorrhagic Escherichia coli (EHEC) are the human pathogenic subset of Shiga toxin (Stx)-producing E. coli (STEC). EHEC are responsible for severe colon infections associated with life-threatening extraintestinal complications such as the hemolytic-uremic syndrome (HUS) and neurological disturbances. Endothelial cells in various human organs are renowned targets of Stx, whereas the role of epithelial cells of colon and kidneys in the infection process has been and is still a matter of debate. This review shortly addresses the clinical impact of EHEC infections, novel aspects of vesicular package of Stx in the intestine and the blood stream as well as Stx-mediated extraintestinal complications and therapeutic options. Here follows a compilation of the Stx-binding glycosphingolipids (GSLs), globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer) and their various lipoforms present in primary human kidney and colon epithelial cells and their distribution in lipid raft-analog membrane preparations. The last issues are the high and extremely low susceptibility of primary renal and colonic epithelial cells, respectively, suggesting a large resilience of the intestinal epithelium against the human-pathogenic Stx1a- and Stx2a-subtypes due to the low content of the high-affinity Stx-receptor Gb3Cer in colon epithelial cells. The review closes with a brief outlook on future challenges of Stx research.

Primary Human Renal Proximal Tubular Epithelial Cells (pHRPTEpiCs): Shiga Toxin (Stx) Glycosphingolipid Receptors, Stx Susceptibility, and Interaction with Membrane Microdomains

Tubular epithelial cells of the human kidney are considered as targets of Shiga toxins (Stxs) in the Stx-mediated pathogenesis of hemolytic–uremic syndrome (HUS) caused by Stx-releasing enterohemorrhagic Escherichia coli (EHEC). Analysis of Stx-binding glycosphingolipids (GSLs) of primary human renal proximal tubular epithelial cells (pHRPTEpiCs) yielded globotriaosylceramide (Gb3Cer) and globotetraosylceramide (Gb4Cer) with Cer (d18:1, C16:0), Cer (d18:1, C22:0), and Cer (d18:1, C24:1/C24:0) as the dominant lipoforms. Investigation of detergent-resistant membranes (DRMs) and nonDRMs, serving as equivalents for the liquid-ordered and liquid-disordered membrane phase, respectively, revealed the prevalence of Gb3Cer and Gb4Cer together with cholesterol and sphingomyelin in DRMs, suggesting lipid raft association. Stx1a and Stx2a exerted strong cellular damage with half-maximal cytotoxic doses (CD₅₀) of 1.31 × 10² pg/mL and 1.66 × 10³ pg/mL, respectively, indicating one order of magnitude higher cellular cytotoxicity of Stx1a. Surface acoustic wave (SAW) real-time interaction analysis using biosensor surfaces coated with DRM or nonDRM fractions gave stronger binding capability of Stx1a versus Stx2a that correlated with the lower cytotoxicity of Stx2a. Our study underlines the substantial role of proximal tubular epithelial cells of the human kidney being associated with the development of Stx-mediated HUS at least for Stx1a, while the impact of Stx2a remains somewhat ambiguous.