Rectal inoculation of sheep with E. coli O157:H7 results in persistent infection in the absence of a protective immune response.
Escherichia coli (E. coli) O157:H7 can cause haemorrhagic colitis and the haemolytic uremic syndrome in humans. Ruminants are the main reservoir for this bacterium: they can harbour the bacteria in the gastrointestinal tract without showing clinical symptoms. The reason for this persistence is still unclear, although it has been suggested that E. coli O157:H7 can suppress the immune system. To investigate the effects on the immune system of ruminants, an infection model is needed that mimics a long-term infection as it can occur in both sheep and cattle. As the terminal rectum has recently been identified as a primary colonisation site in cattle, we developed a rectal inoculation model for sheep and used this model to study immune responses against selected virulence factors of E. coli O157:H7 (intimin, EspA and EspB). Sheep were infected and re-infected when E. coli O157:H7 excretion was no longer detectable. The animals did not develop serum or local antibody responses but showed a cellular response against EspA and intimin respectively 9 and 16 days after infection. This response was also present 5 days after re-infection, albeit lower, and did not prevent animals from being re-infected. These results demonstrate that E. coli O157:H7 can be persistently present in the large intestine of sheep without inducing a clear protective immune response.
Vande Walle
Kris
K
Laboratory of Immunology, Faculty of Veterinary Medicine, Ghent University, Salisburylaan 133, 9820 Merelbeke, Belgium. kris.vandewalle@ugent.be
Yekta
Maryam Atef
MA
Verdonck
Frank
F
De Zutter
Lieven
L
Cox
Eric
E
D000818:Animals; D000907:Antibodies, Bacterial / Q000097:blood; D049109:Cell Proliferation; D004927:Escherichia coli Infections / Q000276:immunology / Q000662:veterinary*; D019453:Escherichia coli O157 / Q000276:immunology*; D029968:Escherichia coli Proteins / Q000276:immunology; D005243:Feces / Q000382:microbiology; D005766:Gastrointestinal Contents / Q000382:microbiology; D007111:Immunity, Cellular / Q000276:immunology; D008214:Lymphocytes / Q000166:cytology; D012007:Rectum / Q000276:immunology* / Q000382:microbiology; D012756:Sheep; D012757:Sheep Diseases / Q000276:immunology* / Q000382:microbiology; D037521:Virulence Factors / Q000276:immunology
D000907:Antibodies, Bacterial; D029968:Escherichia coli Proteins; D037521:Virulence Factors