Diarrheogenic Escherichia coli (DEC) are responsible for several cases of acute diarrhea, especially among children in developing countries, with important public health effect. Among the pathotypes of DEC, can be highlighted enterotoxigenic E. coli (ETEC) producer of heat-labile toxin (LT) and heat-stable toxin (ST), one of the most frequent pathotypes of diarrheagenic E. coli. Indeed, the diagnosis is essential in order to prevent possible outbreaks and determine the best method of treatment. Immunological tests has several advantages compared to other detection methods, such as high specificity, sensibility, easy sample preparation and to perform, besides the rapid achievement of results. Antibodies generated from the natural immune response or through immunization (polyclonal) are presented as a molecules mixture with different affinities and specificities, being produced in limited quantities. In the other hand, monoclonal antibodies compared to polyclonal antibodies, exhibit homogeneity, high specificity and are produced indefinitely, however, require a specialized cell culture and extensive involvement of time and effort. Genetic engineering has been used to obtain recombinant antibodies, in order to maintain homogeneity and specificity of monoclonal antibodies, with large-scale production, low cost and the construction development that maintains or improve the functional properties of an antibody. Currently it is possible to produce recombinant proteins, like antibody fragments, using different expression systems. One of the methodologies used is the cloning of variable domains of light chains (VL) and heavy chains (VH) fused to an immunoglobulin by flexible linker, allowing the correct interaction between the domains and the preservation of the antigen binding site called ScFv ( Single Chain Variable Fragment). Because the limiting polyclonal antibodies production and the extensive time and labor involved in the monoclonal antibodies production emerged the aim of this work, which is the optimization of the expression and purification of the construction of ScFv pMST3-LT for it use as tool in the immunodiagnosis of ETEC strains.
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