Clostridium Questions and Answers

Answer: A

Correct answer: Type A

Clostridium perfringens is divided into types A to E by which of the four major lethal toxins each produces. All five make alpha toxin, but type A makes it most abundantly and makes essentially nothing else, which is why type A accounts for the great majority of human gas gangrene. Alpha toxin is a lecithinase, or phospholipase C, that hydrolyses the lecithin of cell membranes and so lyses red cells, platelets and muscle.

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: All of these

Tetanospasmin is a protein of about 150 kilodaltons, destroyed by heating at 65 degrees for five minutes, so it is heat-labile. It is a neurotoxin, travelling by retrograde axonal transport to the spinal cord where it blocks the release of the inhibitory transmitters glycine and GABA, producing the unopposed muscle spasm of tetanus. Treated with formalin it becomes a toxoid - immunogenic but harmless - which is the basis of the tetanus vaccine.

Answer: D

Correct answer: All of these

Seven antigenic types of botulinum toxin are recognised, A to G, but only three cause most human disease: type A, associated with home-preserved vegetables and predominant in the western United States, type B, in Europe, and type E, associated with fish and marine sediments. Types C and D affect animals and F and G are rare. This is why the therapeutic antitoxin is trivalent, covering A, B and E.

Answer: B

Correct answer: C perfringens

Nagler’s reaction demonstrates alpha toxin, the lecithinase of C. perfringens. The organism is streaked on a plate of egg yolk or human serum agar, half of which has been spread with antitoxin. Opalescence appears in the medium around the growth on the untreated half, where the lecithinase has split the lipoprotein, and is absent on the half where antitoxin has neutralised it. The specific inhibition is what makes the test identifying rather than merely suggestive.

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: D

Correct answer: All of these

C. septicum, C. perfringens and C. novyi are all saccharolytic, fermenting sugars with the production of acid and gas - and in cooked meat broth they turn the meat pink rather than digesting it. The gas is what gives gas gangrene its name and its crepitus. The proteolytic species, C. histolyticum and C. sporogenes, behave quite differently, blackening and dissolving the meat.

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: A

Correct answer: type A

Food poisoning is caused by type A strains, and specifically by those forming heat-resistant spores that survive cooking. The spores germinate as the meat dish cools slowly, the organisms multiply and are swallowed in large numbers, and they sporulate in the small intestine releasing the enterotoxin. The result is watery diarrhoea and cramps eight to twenty-four hours later, usually without vomiting or fever, and it settles in a day.

Answer: C

Correct answer: Clostridium perfringens

Robertson’s cooked meat medium separates the clostridia by what they do to the meat particles. A saccharolytic organism such as C. perfringens ferments the carbohydrate, produces acid and gas, and turns the meat pink or red without digesting it. A proteolytic organism digests the meat, turning it black and producing a foul smell. The colour change is therefore a quick guide to which group an isolate belongs to.