Properties

Pathogenesis

Clinical findings

Laboratory diagnosis

Treatment & Prevention

Gram-positive rods

Club-shaped

Stain metachromatically

Transmission:

- humans are only natural hosts.

- infect upper respiratory tract – throat, nasal mucosa, larynx or trachea.

- air-borne droplets

Diphtheria toxin:

- 2 domains: one for binding, one with enzymatic activity.

- inhibits protein synthesis by ADP ribosylation of elongation factor 2.

Thick, gray, adherent membrane over tonsils & throat.

Extension of membrane into larynx & trachea, causing airway obstruction.

Fever, sore throat, cervical adenopathy.

Myocarditis accompanied by arrhythmias & circulatory collapse.

Nerve damage results in weakness or paralysis of various muscle groups.

Recurrent laryngeal nerve palsy

Throat swabs are plated onto special selective media which suppress normal throat flora.

Suspect colonies are confirmed as C.diphtheriae by performing sugar fermentation reactions.

Elek plate used to confirm a stain is toxigenic.

Loffler’s medium: gray-black color of tellurium in colony.

Stained with Gram’s stain & methylene blue: tapered, pleomorphi gram-positive rods.

Treatment:

- antitoxin neutralize toxin before it can bind to & damage cells.

- erythromycin or penicillin.

Prevention:

- immunization with diphtheria toxoid.

- prepared by treating exotoxin with formaldehyde.

Immunization of 3 doses at:

- 2, 4, 6 months of age.

- booster at 1 & 6 years of age.