Described herein are methods for detecting a bacteria in a subject and methods for detecting, imaging or diagnosing a site, disease, disorder or condition in a subject using bacteria. The methods can be used in conjunction with methods for treating a disease, disorder or condition. Such sites, diseases and disorders include sites of cellular proliferation, such as tumors, tumor tissues, metastases, areas of inflammation, immunoprivileged sites or tissues, wounds and infections. Further described are bacteria for use in the methods and compositions, combinations and kits, including diagnostic and pharmaceutical compositions, containing a bacterium. Bacteria described herein include those that bind, sequester or accumulate radiolabeled compounds by expression of an endogenous gene product that binds to the radiolabeled compound. Additional imaging and therapeutic agents and methods also are described.