Construction of a Nanobodies Phage Display Library From an Escherichia coli Immunized Dromedary

Diarrhea caused by Escherichia coli is a major cause of morbidity and mortality in young animals. Few treatment options are available, mainly antibiotic therapy increasingly limited by resistance to commonly used drugs. The aim of this work was to develop immunotherapy based on the use of camel VHH antibody fragments, or nanobodies, to target pathogenic E. coli surface antigens. We immunized a camel with a killed strain we had previously isolated from a diarrheic camel calf and identified as expressing the F17 fimbriae antigen. The immunized animal developed an anti-E.coli immune response including heavy-chain antibodies. Lymphocytes from this animal were purified and RNA isolated to create a VHH library by phage display with a size of about 109 individual transformants. Panning on live E. coli cells resulted in the isolation of VHH fragments specific to the cell surface antigens. The identification of these antigens can lead to the development of new diagnostic and therapeutic tools against diarrhea.