A method of using selective binding properties of killed and live isolates of Mycobacterium avium subspecies paratuberculosis (Map) to gastrointestinal tract mucosa is described which permits: selecting as a killed Map test candidate for oral administration a strain of Map which will have greater organismal attachment; and selecting as a live Map test candidate for oral administration a live strain of Map whose virulence had been significantly reduced and which exhibits a diminished ability to bind to gastrointestinal mucosa The method also includes preservation of binding ability of Map isolates after inhibition of organism replication or virulence reduction.