Shiga toxin-producing Escherichia coli as a possible etiological agent of chronic diarrhea

Effect of lactoferrin on release and bioactivity of Shiga toxins from different Escherichia coli O157:H7 strains

Prevention of enterohemorrhagic Escherichia coli (EHEC) O157:H7 infections and of their severe clinical sequelae in humans remain to be a current challenge. Administration of bovine lactoferrin (bLF) proved to be effective in clearing EHEC from the bovine intestine, an important EHEC reservoir, suggesting that bLF may also be beneficial in human application against EHEC infections. To estimate the biological safety of this approach, we analyzed the effects of bLF on the main EHEC virulence factor, Shiga toxin (Stx). We quantified the release of Stx 1 and 2 from two O157:H7 EHEC strains (Stx1⁺Stx2⁺ and Stx2⁺ producing, respectively) cultured in the presence of bLF using ELISA assays and assessed cytotoxic effects of bLF and co-cultured EHEC on Vero cells. Effects of bLF on the stability of Stx2 were investigated using western blotting. ELISA results indicate a bLF concentration-dependent decrease of active, cell-free Stx2, but not Stx1 in EHEC cultures. High concentrations (100 and 50mg/ml) of bLF resulted in significantly reduced (p<0.05) metabolic activity rates of Vero cells, whereas a concentration of 10mg/ml bLF was considered non-toxic for Vero cells. At concentrations of 1 or 0.1mg/ml, bLF mitigated the verocytotoxicity of EHEC strains in a co-culture model up to 48h after inoculation. When only colonizing bacteria were taken into account, cytotoxicity could be significantly reduced by 10 and 1mg/ml bLF during 48h. This effect of bLF at least partly results from degradation of the Stx2 receptor-binding B-subunit.

Characterization of Shiga toxin - producing Escherichia coli infections in beef feeder calves and the effectiveness of a prebiotic in alleviating Shiga toxin - producing Escherichia coli infections

Background

In the less-sensitive mouse model, Shiga toxin-producing Escherichia coli (STEC) challenges result in shedding that reflect the amount of infection and the expression of virulence factors such as Shiga toxins (Stx). The purpose of this study was to characterize the contribution of STEC diversity and Stx expression to shedding in beef feeder calves and to evaluate the effectiveness of a prebiotic, Celmanax®, to alleviate STEC shedding. Fecal samples were collected from calves at entry and after 35 days in the feedlot in spring and summer. STECs were evaluated using selective media, biochemical profile, serotyping and Stx detection. Statistical analysis was performed using repeated measures ANOVA and logistic regression.

Results

At entry, non-O157 STEC were dominant in shedding calves. In spring, 21%, 14% and 14% of calves acquired O157, non-O157 and mixed STEC infections, respectively. In contrast, 45%, 48% and 46% of calves in summer acquired O157, non-O157 and mixed STEC infections, respectively. Treatment with a prebiotic, Celmanax®, in spring significantly reduced 50% of the O157 STEC infections, 50% of the non-O157 STEC infections and 36% of the STEC co-infections (P = 0.037). In summer, there was no significant effect of the prebiotic on STEC infections. The amount of shedding at entry was significantly related to the number and type of STECs present and Stx expression (r² = 0.82). The same relationship was found for shedding at day 35 (r² = 0.85), but it was also related to the number and type of STECs present at entry. Stx - producing STEC infections resulted in 100 to 1000 × higher shedding in calves compared with Stx-negative STECs.

Conclusions

STEC infections in beef feeder calves reflect the number and type of STECs involved in the infection and STEC expression of Stx. Application of Celmanax® reduced O157 and non-O157 STEC shedding by calves but further research is required to determine appropriate dosages to manage STEC infections.

A Bayesian approach to acute infectious diarrhea in adults

Acute infectious diarrhea is a yearly occurrence for most Americans, and is associated with 1 million hospitalizations and about 6000 deaths in the United States annually. Up to 80% of acute infectious diarrhea is caused by noroviruses, which produce a clinically mild illness with a predictable short course and good outcome that make laboratory testing and antimicrobial treatment unnecessary. Most diarrhea-causing bacteria and protozoa can cause a clinical illness "like norovirus"; when they do so in healthy adults neither specialized testing nor antimicrobials is required. The presence or absence of epidemiologic evidence (such as travel, hospitalization, antibiotic use, other exposures)and clinical evidence (such as diarrhea frequency and duration, severity of abdominal pain and fever, character of stool, presence of chronic illness or immune deficiency) can change the probability of "not norovirus" from as low as 8% to as high as 100%. Such probabilities guide the use of laboratory testing and antimicrobial therapy in patients who have acute infectious diarrhea.

Isolation of Escherichia coli O5 :H-, possessing genes for Shiga toxin 1, intimin-beta and enterohaemolysin, from an intestinal biopsy from an adult case of bloody diarrhoea: evidence for two distinct O5 :H- pathotypes

Two typical coliforms from an intestinal biopsy from an adult case of bloody diarrhoea carried genes encoding intimin-beta, stx(1) and ehxA, and produced verocytotoxin 1 and enterohaemolysin in culture. Both were biochemically typical Escherichia coli O5 :H(-), apart from producing urease. Such O5 isolates represent a human pathogenic E. coli lineage.