Production and characterization of anti-bifidobacteria monoclonal antibodies and their application in the development of an immuno-culture detection method.

An immuno-culture method has been developed by combination of specific monoclonal antibodies and plate culture to allow detection of viable bifidobacteria. Cell wall proteins were selected as surface antigen to produce antibodies against bifidobacteria. The cell wall proteins were extracted and purified from six ATCC strains of bifidobacteria grown in MRS broth using an anaerobic system. To compare the profile of the protein extracts, all the protein solutions obtained were analyzed by SDS-PAGE. Similar bands corresponding to the major proteins of each species of bifidobacteria were observed. The proteins were tested for their immunogenicity in Balb/c mice after immunization and subsequent analysis using ELISA procedures. High immune responses were generated in mice immunized by proteins from Bifidobacterium bifidum and Bifidobacterium longum. Monoclonal antibodies were produced against B. longum and tested for their specificity, sensitivity and cross reactivity with other bifidobacteria species. All the hybridoma cells selected produced anti-B. longum antibodies cross-reacting with native and purified proteins from five other bifidobacteria species. An epitope supported by a cross-reacting protein of 58 kDa shared by bifidobacteria was revealed by western blot. This was confirmed by immune-transmission electron microscopy observations which showed the specific interaction of these antibodies with bifidobacterial cell wall proteins. Also, the antibody obtained was found to be specific for the genus Bifidobacterium and sensitive, allowing the detection of at least 10(5) target cells/ml. An immuno-culture detection approach was then developed using the selected anti-B. longum antibodies. This method was shown to be very efficient for the detection of viable cells of bifidobacteria suggesting the possibility of its use to quantify these bacteria in various food matrices.