Clostridium Questions and Answers

Answer: B

Correct answer: Clostridium difficile

Diarrhoea beginning after antibiotic therapy, in a hospitalised and immunosuppressed patient, is C. difficile until proved otherwise. The antibiotic suppresses the normal colonic flora, allowing the organism to overgrow and produce toxins A and B. Neutropenia and prior hospital exposure add to the risk. Salmonella and Shigella are community-acquired food and water-borne infections with no such antibiotic association, and C. perfringens causes a brief food poisoning unrelated to antibiotics.

Answer: A

Correct answer: Infant botulism is caused by ingestion of preformed toxin

This is the exception. Infant botulism is a true infection: spores - classically from honey - are swallowed, germinate in a gut whose flora is not yet established, and produce toxin in situ, giving the floppy infant. Classical food-borne botulism is the one caused by preformed toxin. The other three statements are correct: types A, B, E and F cause human disease, the toxin genes of types C and D are carried on bacteriophages, and C. baratii is among the rarer species that can produce botulinum toxin.

Answer: C

Correct answer: κ toxin

Among the minor toxins of C. perfringens, mu toxin is the hyaluronidase, which breaks down the hyaluronic acid of connective tissue ground substance and so helps the infection spread through the tissue planes. Kappa toxin is the collagenase, theta toxin the oxygen-labile haemolysin, and alpha toxin the lecithinase that is the principal lethal factor. Together they explain the speed with which gas gangrene advances.

Answer: D

Correct answer: Tetanus toxoid

Active immunisation is the only measure that reliably prevents tetanus, and countries with high immunisation coverage have all but eliminated it. Surgical toilet is important and reduces the risk of any given wound, antibiotics kill the organism but not the toxin already released, and hyperbaric oxygen has no established role in prevention. Since tetanus confers no immunity even on those who survive it, the toxoid course must still be given after recovery.

Answer: B

Correct answer: Single-dose of tetanus toxoid

The patient completed a primary course, so he needs no immunoglobulin and no fresh course - his immune memory is intact and a booster will raise protective antitoxin within days. Ten years have elapsed, which is exactly the recommended booster interval, so a single dose of toxoid is given. Human tetanus immunoglobulin is reserved for those whose immunisation is incomplete or unknown, and for tetanus-prone wounds in such patients; this wound is clean, unlacerated and only hours old.

Answer: C

Correct answer: Causes nodular lesions in the eyes and skin

Onchocerca volvulus produces subcutaneous nodules containing the adult worms, and microfilariae migrating through the skin and eye cause the dermatitis and the ocular damage that gives river blindness its name. It is transmitted by the blackfly Simulium, which breeds in fast-flowing rivers, not by a mosquito; it is a filarial nematode, not a protozoan; and it occurs across sub-Saharan Africa and in foci in Latin America and Yemen, not only in West Africa.

Answer: C

Correct answer: botulinum toxin

Botulinum toxin is the most poisonous substance known, with a lethal dose for a human estimated at around a microgram - a few hundred grams would in principle suffice for the whole world population. Tetanus toxin is second and only a little less potent. Both act at the neuromuscular junction by cleaving the SNARE proteins of vesicle fusion, botulinum blocking acetylcholine release to give flaccid paralysis and tetanus blocking inhibitory transmitters to give spastic paralysis.

Answer: B

Correct answer: enterotoxin

Clostridioides difficile produces two toxins. Toxin A is an enterotoxin, damaging the mucosa and causing fluid secretion and inflammation; toxin B is a cytotoxin, far more potent against cultured cells and the basis of the classical cell culture assay. Both glucosylate Rho GTPases, disrupting the actin cytoskeleton, and together they produce the pseudomembranes of the colitis that follows disturbance of the normal flora by antibiotics.

Answer: C

Correct answer: C perfringens

In the stormy clot or stormy fermentation reaction, C. perfringens growing in litmus milk ferments the lactose to acid, clotting the casein, and then produces so much gas that the clot is torn apart and driven up the tube against the seal. The vigour of the gas production is what makes the reaction distinctive, and it reflects the same saccharolytic activity that produces the gas in gas gangrene.

Answer: C

Correct answer: Corynebacterium minutissimum

Erythrasma is a superficial infection of the skin folds - groin, axilla and toe webs - caused by Corynebacterium minutissimum. It produces well-demarcated reddish-brown scaly patches which fluoresce coral-pink under Wood’s light because of the porphyrins the organism makes, and that fluorescence distinguishes it at once from the fungal infections it resembles. Treatment is with topical or oral erythromycin.