Clostridium Questions and Answers

Answer: B

Correct answer: False

Botulism is treated with trivalent antitoxin covering types A, B and E, since these are the three types responsible for almost all human cases and the type cannot be known when treatment must begin. Antitoxin neutralises only toxin still circulating and cannot reverse what is already bound to nerve endings, so it must be given as early as possible - with ventilatory support, which is what actually keeps the patient alive.

Answer: A

Correct answer: Clostridium sporogenes

The clostridia are classified by the shape and position of the spore. C. sporogenes has an oval subterminal spore, as do C. perfringens, C. septicum, C. novyi and C. histolyticum. C. sordellii and C. tertium carry oval terminal spores, and C. tetani a spherical terminal one that swells the rod into the drumstick. Spore position is one of the first things looked at on a Gram film and narrows the identification considerably.

Answer: D

Correct answer: Man-to-man transmission is seen

This is the false statement. Tetanus is acquired from the environment, not from other people: spores enter through a wound, and a patient with tetanus is not infectious. It is precisely for this reason that there is no herd immunity and every individual must be immunised. The other three are true - heat-resistant spores, an incubation period usually of six to eleven days, and three primary doses for full protection.

Answer: C

Correct answer: E

Type E strains are characteristically found in the sediments of lakes and coastal waters, including the Great Lakes, and are associated with outbreaks following fish and marine products, particularly uncooked or fermented preparations. The type distribution is geographical and ecological: type A predominates in the soils of the western United States and type B in Europe, so the food history often suggests which type is involved.

Answer: D

Correct answer: C. sporogenes

C. sporogenes is a strongly proteolytic saprophyte, common in soil and in the gut and often isolated from wounds, but it is not itself a cause of gangrene - it grows alongside the pathogenic species without invading healthy tissue. C. perfringens, C. histolyticum and C. novyi are all established agents of clostridial myonecrosis, C. perfringens by a wide margin the commonest.

Answer: A

Correct answer: Increased acetylcholine release

Botulinum toxin does exactly the opposite: its light chain is a zinc protease that cleaves the SNARE proteins of vesicle fusion, so acetylcholine cannot be released at the neuromuscular junction and flaccid paralysis follows. That is why it treats blepharospasm, dystonia and wrinkles, and why the option describing an irreversible decrease in acetylcholine is true. The block persists until new nerve terminals sprout, which is why the therapeutic effect lasts some three to four months.

Answer: B

Correct answer: Cl. Perfringens

Enteritis necroticans - pigbel - is caused by the beta toxin of C. perfringens type C. It appeared in Papua New Guinea after pig feasts, where a diet rich in sweet potato supplied trypsin inhibitors that protected the beta toxin from digestion, allowing it to destroy the jejunal mucosa. The result is a severe segmental necrotising enteritis with a high mortality, quite unlike the mild type A food poisoning.

Answer: C

Correct answer: Both (a) and (b)

The clostridia divide by what they attack. C. sporogenes and C. histolyticum are proteolytic: they digest protein, blacken and disintegrate the meat in cooked meat broth, and produce the foul putrefactive smell of a spreading anaerobic infection. C. perfringens and C. septicum are saccharolytic, fermenting sugars and turning the meat pink without digesting it. C. histolyticum is the most strongly proteolytic of all, dissolving meat particles completely.

Answer: D

Correct answer: Clostridium botulinum

Botulinum toxin is the most poisonous substance known, effective in microgram quantities, stable, and capable of being disseminated in food or as an aerosol, which is why it heads the list of potential biological weapons and is a Category A agent. Plague and smallpox are also Category A and are serious threats, but neither approaches the toxicity of botulinum toxin per unit mass; tuberculosis spreads too slowly to serve the purpose at all.

Answer: A

Correct answer: The bacteria can be found in lesions of primary syphilis

Treponemes are abundant in the chancre and are demonstrated by dark-ground microscopy of the exudate, which is the classical bedside diagnosis of primary syphilis. The organism has never been cultivated on ordinary laboratory media - it is maintained only by animal passage, which is why serology dominates the diagnosis. VDRL is a non-treponemal test using a cardiolipin antigen and gives biological false positives, so it is not specific; TPHA or FTA-ABS is required to confirm.