Evaluation of an inactivated whole-cell vaccine-adjuvant preparation for reducing fecal shedding of Escherichia coli O157:H7 in cattle

Authors: Sharma, Vijay

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/14/2017
Publication Date: 5/30/2017
Citation: Sharma, V.K. 2017. Evaluation of an inactivated whole-cell vaccine-adjuvant preparation for reducing fecal shedding of Escherichia coli O157:H7 in cattle [abstract]. Microbe, American Society of Microbiology, June 1-5, 2017, New Orleans, Louisiana. Page No. 669.

Interpretive Summary:

Technical Abstract: Cattle are the primary reservoir for Escherichia coli O157:H7 (O157). O157 can cause from a mild diarrheal illness in healthy adults to hemorrhagic colitis and hemolytic uremic syndrome in young children and elderly patients. O157-colonized cattle remain asymptomatic but shed these bacteria in feces intermittently. Most O157 disease outbreaks in humans are linked to the consumption of bovine food products, water, and vegetables contaminated with cattle feces. Vaccination of cattle is proposed as a viable intervention for reducing fecal shedding of O157 in these animals. In this study, we evaluated the efficacy of a formalin-inactivated whole-cell vaccine-adjuvant preparation in reducing fecal shedding of O157 in cattle. The vaccine consisted of a hha deletion mutant of O157 strain 86-24, linked to the foodborne outbreak in 1986. The hha deletion enhances the expression and secretion of proteins encoded by the locus of enterocyte effacement (LEE). The LEE-encoded proteins are essential for O157 colonization in cattle. Two ml of the vaccine formulation (0.8 ml of the buffered saline containing approximately 1.0E plus 09 inactivated bacterial cells emulsified with 1.2 ml of the mineral oil based adjuvant) was used for the intramuscular (neck region) vaccination of weaned calves (n equals 6), followed three weeks later with a booster vaccination with the same formulation. One group of calves served as the unvaccinated control group (n equals 5). Animals in all groups were orally inoculated three weeks post second vaccination with 1.0E+10 live O157 bacterial cells, and fecal samples were collected for about 4 weeks. Blood was collected from the jugular vein pre-vaccination, 3-weeks post first and second vaccinations, and at the end of the study. Fecal samples were plated on selective medium for enumerating inoculated O157-specific bacterial colonies, which were confirmed by an agglutination assay. Fecal shedding of the inoculated O157 strain was 2 -3 log lower in the vaccinated animals compared to the unvaccinated group. The blood serum ELISA revealed significantly higher antibody titers in the vaccinated animals for the LEE-encoded protein EspA, which is present on the bacterial cell surface as a hollow tubular element of the type-III secretion system. In conclusion, the results of this pilot animal study show that two doses of the whole cell vaccine-adjuvant formulation is capable of inducing O157-specific immune response that in turn reduces the fecal shedding of O157 in cattle.