Corynebacterium diphtheriae is isolated from a patient with pharyngitis. What is the best predictor that the strain is pathogenic?

Question

Quizplus · Accepted Answer

Only toxin-producing strains of Corynebacterium diphtheriae cause diphtheria. The genes directing the production of the toxin are located on molecules of $corynebacteriophage-\beta$ DNA, which may infect and lysogenize C. diphtheriae, causing production of the toxin. Neither plasmids nor the chromosome contain the genes to direct the synthesis of the toxin. Repressor molecules for the tox+ gene are on the chromosome, however. Both toxigenic and nontoxigenic strains of C. diphtheriae will be gray to black on tellurite medium.

Corynebacterium Diphtheriae Is Isolated from a Patient with Pharyngitis corynebacteriophage−βcorynebacteriophage-\betacorynebacteriophage−β

Corynebacterium Diphtheriae Is Isolated from a Patient with Pharyngitis $corynebacteriophage-\beta$