The invention provides isolated, purified, recombinant receptor binding proteins Gp-6, Gp-10 and Gp-31 from mycobacterium phage L5, and methods for producing these recombinant receptor binding proteins. The invention also provides the use of recombinant receptor binding proteins, including Gp-6, Gp-10 and Gp-31, as probes for the identification and diagnosis of mycobacterium infections and conditions caused by mycobacterium. Further provided by the invention are methods of targeting mycobacteria using recombinant receptor binding proteins, including Gp-6, Gp-10 and Gp-31. Other methods provided by the invention include the use of recombinant receptor binding proteins, such as Gp-10, in diagnostic assays for diseases, such as Johne's disease, in animals, including ruminants.