Clostridium Questions and Answers

Answer: A

Correct answer: All of these

Gas gangrene is a clostridial myonecrosis, and several species can cause it. C. perfringens is much the commonest, accounting for some 60 to 80 per cent, followed by C. novyi and C. septicum, with C. histolyticum and others contributing to mixed infections. Since more than one is usually present in a given wound, the diagnosis and the treatment address the group rather than a single species.

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: Cl. Perfringens

Nagler’s reaction demonstrates the lecithinase activity of alpha toxin. C. perfringens is grown on egg yolk agar half of which carries antitoxin: opalescence appears around the growth on the untreated half where the lecithin has been split, and is absent where antitoxin has neutralised the enzyme. It is the specific inhibition by antitoxin that makes the test conclusive.

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: C

Correct answer: Most common toxin is hyaluronidase

This is the exception. The principal toxin of C. perfringens is the alpha toxin, a lecithinase that lyses cell membranes and is the main lethal and necrotising factor. Hyaluronidase is the mu toxin, one of the minor spreading factors. The other three statements are true: C. perfringens is the commonest cause of gas gangrene, it is Nagler positive, and its food poisoning strains form heat-resistant spores.

Answer: B

Correct answer: Predominantly seen in dry and winter season

This is the false statement: tetanus is commoner in the warm, moist months, when soil contamination of wounds and agricultural injury are both more frequent. The other three are true - soil, dust and the intestines of humans and animals are the reservoirs, transmission is through contaminated wounds including trivial ones and the umbilical stump, and there is no herd immunity, since the disease is not transmitted person to person and every individual must be immunised in their own right.

Answer: D

Correct answer: Most common organism implicated is Cl. perfringens

C. perfringens accounts for the large majority of gas gangrene. The other statements belong to tetanus or contradict the disease: the overlying skin and muscle are grossly abnormal, with oedema, discoloration, crepitus and frank necrosis; the toxin is alpha toxin, not tetanospasmin; and muscle rigidity and spasm are the picture of tetanus, whereas gas gangrene destroys muscle rather than making it contract.

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: B

Correct answer: Injection of human antiserum

The boy has had a complete primary course and a booster at school entry, so he is immune and needs only a booster dose of toxoid for this contaminated wound; passive immunisation adds nothing and carries the risks of a serum product. The other three are all appropriate: tetanus toxoid, antibiotics, and above all thorough debridement and cleaning, which removes the devitalised tissue in which clostridia would otherwise grow.

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.