Resistance & Immunity to C. diphtheria

Resistance & Immunity to C. diphtheria
Since diphtheria is principally the result of the action of the toxin formed by the organism rather than invasion by the organism, resistance to the disease depends largely on the availability of specific neutralizing antitoxin in the bloodstream and tissues. Assessment of immunity to diphtheria toxin for individual patients can best be made by review of documented diphtheria toxoid immunizations and primary or booster immunization if needed.
Treatment
The treatment of diphtheria rests largely on rapid suppression of toxin-producing bacteria by antimicrobial drugs and the early administration of specific antitoxin against the toxin formed by the organisms at their site of entry and multiplication. Diphtheria antitoxin is produced in various animals (horses, sheep, goats, and rabbits) by the repeated injection of purified and concentrated toxoid. Antimicrobial drugs (penicillin, erythromycin) inhibit the growth of diphtheria bacilli. Although these drugs have virtually no effect on the disease process, they arrest toxin production.
Epidemiology, Prevention, & Control
Active immunization in childhood with diphtheria toxoid yields antitoxin levels that are generally adequate until adulthood. Young adults should be given boosters of toxoid, because toxigenic diphtheria bacilli are not sufficiently prevalent in the population of many developed countries to provide the stimulus of subclinical infection with stimulation of resistance. Levels of antitoxin decline with time, and many older persons have insufficient amounts of circulating antitoxin to protect them against diphtheria.
A filtrate of broth culture of a toxigenic strain is treated with 0.3% formalin and incubated at 37 °C until toxicity has disappeared. This fluid toxoid is purified and standardized in flocculating units (Lf doses). Fluid toxoids prepared as above are adsorbed onto aluminum hydroxide or aluminum phosphate. This material remains longer in a depot after injection and is a better antigen. Such toxoids are commonly combined with tetanus toxoid (Td) and sometimes with pertussis vaccine (DPT or DaPT) as a single injection to be used in initial immunization of children. For booster injection of adults, only Td toxoids are used; these combine a full dose of tetanus toxoid with a tenfold smaller dose of diphtheria toxoid in order to diminish the likelihood of adverse reactions.

Other Coryneform Bacteria
Many other Corynebacterium and Propionibacterium species have been associated with disease in humans. The coryneform bacteria are classified as nonlipophilic or lipophilic depending upon enhancement of growth by addition of lipid to the growth medium. The lipophilic corynebacteria grow slowly on sheep blood agar, producing colonies < 0.5 mm in diameter after 24 hours of incubation. Additional key reactions for the classification of the coryneform bacteria include but are not limited to the following tests: fermentative or oxidative metabolism, catalase production, motility, nitrate reduction, urease production, and esculin hydrolysis. Corynebacterium species are typically nonmotile and catalase-positive. The coryneform bacteria are normal inhabitants of the mucous membranes of the skin, respiratory tract, urinary tract, and conjunctiva.
Anaerobic Corynebacteria
Anaerobic corynebacteria (eg, Propionibacterium species) reside in normal skin. Propionibacterium acnes, however, is aerotolerant and grows aerobically. It participates in the pathogenesis of acne by producing lipases that split free fatty acids off from skin lipids. These fatty acids can produce tissue inflammation and contribute to acne. Because P acnes is part of the normal skin flora, it occasionally appears in blood cultures and must be differentiated as a culture contaminant or a true cause of disease. P acnes occasionally causes infection of prosthetic heart valves and cerebrospinal fluid shunts.
Actinomyces pyogenes, Actinomyces neuii, and other Actinomyces species are occasionally associated with clinically significant infections. Actinomyces viscosis grows readily under aerobic conditions.