Correct Option: B

Diphtheria is an upper respiratory tract illness caused by Corynebacterium diphtheriae, a facultative anaerobic, Gram-positive bacterium. Diphtheria is a contagious disease spread by direct physical contact or breathing the aerosolized secretions of infected individuals. Diphtheria toxin is produced by C. diphtheriae only when infected with a bacteriophage that integrates the toxin-encoding genetic elements into the bacteria.