The present invention is directed to bacteriophage therapy, using methods which enable the bacteriophage to delay inactivation by any and all parts of the host defense system (HDS) against foreign objects. The HDS normally reduces the number of bacteriophage in an animal, which decreases the efficiency of the bacteriophage in killing the host bacteria present during an infection. Disclosed is a method of producing bacteriophage modified for anti-HDS purposes by physico-chemical alteration of the bacteriophage surface proteins, so that the altered bacteriophage remain active in the body for longer periods of time than the unmodified bacteriophage.