C.diphtheriae can be biochemically differentiated from C.ulcerans by

Among the Corynebacterium species, all are catalase positive. All are resistant to tellurite. All Corynebacterium species are oxidase negative. C. ulcerans is differentiated from C. diphtheriae by its negative nitrate reduction and positive gelatin liquefaction. 3 species produce diphtheria toxin: C. diphtheriae, C. ulcerans, and C. pseudotuberculosis. C. ulcerans- closely related to C.diphtheriae; causes bovine mastitis; Can cause acute pharyngitis in humans; C. ulcerans has been repoed to cause a few cases of diphtheria