Correct Option: D

Diphtheria toxin consists of a single polypeptide. Proteolysis yields two fragments (A and B) which are held together by a disulfide bond. The toxin binds to EGF-like domain of Heparin-binding EGF-like growth factor (HB-EGF) through fragment B and is internalized with HB-EGF by receptor-mediated endocytosis. Diphtheria toxin catalyzes the ADP-ribosylation of, and inactivates, the elongation factor eEF-2. In this way, it acts to inhibit translation during eukaryotic protein synthesis. Tetracyclines are antibiotics which inhibit the bacterial growth by stopping protein synthesis. Three different specific mechanisms of tetracycline resistance have been identified so far: tetracycline efflux, ribosome protection and tetracycline modification. Streptomycin is a water-soluble aminoglycoside derived from Streptomyces griseus. Streptomycin is an aminoglycoside antibiotic that is currently used largely in the therapy of active tuberculosis. Like other aminoglycosides, streptomycin is thought to act by binding to bacterial ribosomes and inhibiting protein synthesis. Nevertheless, streptomycin is considered bacteriocidal as well as bacteriostatic.