|Cray Jr, William|
Submitted to: Infection and Immunity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/1996
Publication Date: N/A
Interpretive Summary: Escherichia coli O157:H7 are bacteria which can cause disease in humans. Most of the reported outbreaks of E. coli O157:H7 disease are linked to the consumption of undercooked meat, which at some point was probably contaminated with feces. E. coli O157:H7 can be found in the intestines of approximately 1% of cattle; the animals remain healthy while infected. Because the immune response of cattle to E. coli O157:H7 infection is unknown, we experimentally infected calves and adult cattle with E. coli O157:H7 and then measured their antibodies to a component of the bacterial cell surface. After infection, all animals had a long-lasting increase in antibodies to the bacterial cell surface. However, these antibodies did not result in rapid elimination of the E. coli O157:H7, nor did they protect cattle from reinfection by E. coli O157:H7. These findings suggest that novel approaches are required to develop vaccines to protect cattle from E. coli O157:H7 infection. This is important information for scientists trying to develop vaccines to prevent E. coli O157:H7 infection in cattle.
Technical Abstract: Sera from 4 preweaned calves and 9 adult cattle inoculated orally with 10**10 CFU of Escherichia coli O157:H7 producing Verotoxin (VT) 1 and VT2 were tested by an enzyme-linked immunosorbent assay (ELISA) for antibodies to E. coli O157:H7 lipopolysaccharide (LPS), and by neutralization tests for VT antibodies. All animals had antibodies reactive in the O157 LPS ELISA before inoculation, at higher titers in adults than calves. By 3 weeks postinoculation, titers of the O157 LPS antibodies had increased several-fold in inoculated animals, but not in uninoculated calves, and remained elevated for at least 19 weeks. None of the animals developed VT2 neutralizing antibodies. VT1 neutralizing antibody titers increased rapidly 7/9 inoculated adults, but more gradually in 2/4 inoculated calves. Persistence of infection in 4/4 calves and 2/9 adults for 7 or more weeks indicated that the induced immune response was not highly effective in eliminating infection. Also, the immune response did not prevent re-infection of the calves on challenge with the same dose of the homologous strain several weeks after they had ceased shedding the organism. We conclude that the immune response of cattle following oral inoculation with 10**10 CFU of E. coli O157:H7 is accompanied by strong and sustained serum antibody responses to O157 LPS antigens, but does not result in effective elimination of infection, or protection against re-infection with the homologous strain.