Enterohemorrhagic Escherichia coli serotype O157:H7 is a pathotype of diarrheagenic E. coli that produces one or more Shiga toxins, forms a characteristic histopathology described as attaching and effacing lesions, and possesses the large virulence plasmid pO157. The bacterium is recognized worldwide, especially in developed countries, as an emerging food-borne bacterial pathogen, which causes disease in humans and in some animals. Healthy cattle are the principal and natural reservoir of E. coli O157:H7, and most disease outbreaks are, therefore, due to consumption of fecally contaminated bovine foods or dairy products. In this review, we provide a general overview of E. coli O157:H7 infection, especially focusing on the bacterial characteristics rather than on the host responses during infection.
Animals ; Cattle ; Cattle Diseases/blood/epidemiology ; Developing Countries ; *Enterohemorrhagic Escherichia coli ; Escherichia coli Infections/blood/*epidemiology/veterinary ; *Escherichia coli O157/genetics/pathogenicity ; Feces/microbiology ; Hemolytic-Uremic Syndrome/blood/epidemiology/veterinary ; Operon ; Shiga Toxins/analysis ; Shigella dysenteriae ; Virulence

Healthy ruminants carry intestinal Shiga toxin (Stx)-producing Escherichia coli (STEC). Stx has antiviral activities in vitro and STEC numbers correlate with reduced early viremia in sheep experimentally infected with bovine leukemia virus (BLV). This study assessed the impact of intestinal STEC on BLV-induced disease for one year post-BLV-challenge. High STEC scores (CFU/g feces x frequency of STEC-positive samples) correlated with good health, whereas poor weight gain, distress, and tumor development occurred only among animals with low STEC scores. STEC carriage was associated with increased percentages of B cells in peripheral blood.
Animals ; Deltaretrovirus Infections/microbiology/*veterinary ; Intestines/*microbiology ; Leukemia Virus, Bovine/*physiology ; Male ; Sheep ; Sheep Diseases/*microbiology ; Shiga-Toxigenic Escherichia coli/*physiology