The structures of Edema Factor alone and Edema Factor bound to calmodulin without substrate has been crystallized and its structure determined by x-ray crystallography. Based upon these crystal structures, a method assaying for inhibitors of infection by a bacteria is presented which comprises obtaining a potential inhibitor, obtaining a calmodulin activated adenylyl cyclase exotoxin, obtaining calmodulin, admixing the potential inhibitor, the exotoxin, and the calmodulin, and assaying to determine whether or not the potential inhibitor inhibits production of cAMP by exotoxin.