The correct is Bacteria.Diphtheria is a serious infection caused by strains of bacteria called Corynebacterium diphtheriae that make a toxin (poison).Important PointsIt is the toxin that can cause people to get very sick.Diphtheria bacteria spread from person to person, usually through respiratory droplets, like from coughing or sneezing.Diphtheria is a highly contagious and potentially life-threatening bacterial disease caused by Corynebacterium diphtheriae. There are two types of diphtheria:Respiratory Cutaneous. Respiratory diphtheria involves the nose, throat and tonsils,Cutaneous diphtheria involves the skin.