Clostridium Questions and Answers

Answer: A

Correct answer: Diphtheria

The Schick test detects susceptibility to diphtheria. A small dose of diphtheria toxin is injected intradermally: in a person without circulating antitoxin the toxin produces local redness and induration - a positive test, meaning susceptible - while in an immune person the antitoxin neutralises it and no reaction appears. A control of heated toxin in the other arm distinguishes a true reaction from hypersensitivity to the protein.

Answer: C

Correct answer: It is due to the production of phospholipase A

This is the exception. Pseudomembranous colitis is caused by toxins A and B of Clostridioides difficile, which glucosylate Rho GTPases and disrupt the actin cytoskeleton of the colonic epithelium; phospholipase A is not involved. The other three are correct: the organism is carried asymptomatically in the gut of a proportion of healthy people, the disease follows antibiotic disturbance of the flora, and oral vancomycin is a standard treatment.

Answer: D

Correct answer: Gas gangrene producing strains of C. perfringens produce heat resistant spores

This is the exception. It is the food poisoning strains of type A whose spores are heat resistant, surviving cooking to germinate as the food cools; the gas gangrene strains produce heat-sensitive spores. The other three statements are true: C. perfringens is much the commonest cause of gas gangrene, it is a normal inhabitant of the human intestine, and its principal toxin is the alpha toxin, a lecithinase.

Answer: D

Correct answer: Gas is invariably present in the muscle compartments

Gas in the muscle compartments, detectable as crepitus or on radiograph, is the defining feature that names the disease and is produced by the saccharolytic fermentation of the clostridia. The other statements are all wrong: gas gangrene is caused by C. perfringens and other clostridia, not C. botulinum; clostridia are Gram-positive spore formers; and the clinical features are due to exotoxins, chiefly alpha toxin, endotoxin being a feature of Gram-negative organisms.

Answer: A

Correct answer: 109 to 116 degree F

C. perfringens grows fastest at about 43 to 47 degrees Celsius, that is 109 to 116 degrees Fahrenheit, and at that temperature its generation time can be under ten minutes - among the shortest of any pathogen. This is why a cooked meat dish left to cool slowly, passing through that range, is such a classic vehicle for its food poisoning, and why rapid cooling is the standard control measure.

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: Diphthin

Diphthin is an IgA protease produced by Corynebacterium diphtheriae; by cleaving secretory IgA it disables the principal antibody defence of the respiratory mucosa and helps the organism establish itself there. Cord factor is a mycobacterial glycolipid responsible for serpentine growth and granuloma formation, neuraminidase promotes spread through mucus, and K antigens are capsular antigens that resist phagocytosis - none of them acting on IgA.

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.

Answer: A

Correct answer: It is a Gram positive bacilli with terminal spore

C. tetani is a Gram-positive bacillus whose spherical terminal spore swells the rod into the classic drumstick appearance. The other statements are false: it is a strict anaerobe and will not grow in air; the symptoms are produced by tetanospasmin, an exotoxin, endotoxin being a Gram-negative cell wall component; and gas gangrene is caused by C. perfringens and its relatives, not by C. tetani, which remains localised in the wound and invades nothing.

Answer: B

Correct answer: preformed toxin

Classical botulism is an intoxication and not an infection: the organism grows in improperly preserved food, produces its toxin there, and the toxin is swallowed ready-made. The organism itself need not colonise the gut at all, and there is no fever and no diarrhoea. That is why the incubation is short, 12 to 36 hours, and why boiling the food before eating - the toxin being heat-labile - prevents the disease. Infant botulism and wound botulism are the two exceptions, in which the organism does grow in the host.