The Diphtheria Culture test is used to detect the presence of the bacteria called Corynebacterium diphtheria .. This test is used when a disease called diphtheria is suspected. Diphtheria is a serious, frequently fatal, bacterial infection that affects the respiratory tract. These bacteria may be found in the throat, nose, and skin. Clinical specimens for culture are taken from the nose or nasopharynx, and throat from all persons with suspected cases and their close contacts. Swabs are also taken from beneath the membrane, or a piece of the membrane is removed. Specimens for culture are obtained as soon as diphtheria is suspected.