Clostridium Questions and Answers

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: 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: A

Correct answer: True

Immunity following tetanus toxoid wanes with time, so a booster is recommended every ten years to keep the antitoxin level above the protective threshold. The same interval governs wound management: a clean minor wound in someone immunised within ten years needs no further dose, while a longer gap or a contaminated wound calls for a booster, and human tetanus immunoglobulin as well if the primary course was never completed.

Answer: A

Correct answer: Immediate suturing

Closing a contaminated wound immediately is precisely what must not be done: it seals in devitalised tissue and creates the anaerobic environment in which clostridia flourish. Such wounds are debrided, cleaned and left open, with delayed primary closure later. The other three are all part of management - radical surgical debridement of the dead muscle above all, penicillin in high dose, and, in some protocols, antitoxin, though its value is now regarded as doubtful.

Answer: A

Correct answer: It is caused by an acid fast bacteria

Mycobacterium leprae is an acid-fast bacillus, demonstrated in slit-skin smears by a modified Ziehl-Neelsen stain and never yet cultivated on artificial media. The other statements are false: leprosy is spread by prolonged close contact through nasal secretions, not by an insect vector; tuberculoid leprosy occurs in patients with good cell-mediated immunity, which is why it is paucibacillary and localised; and it is tuberculoid, not lepromatous, leprosy that gives a strongly positive lepromin test, the lepromatous form being anergic.

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: D

Correct answer: All of these

The entire genus Clostridium is anaerobic, lacking catalase and superoxide dismutase and therefore unable to deal with the toxic products of oxygen metabolism. C. septicum, C. novyi and C. tetani are all obligate anaerobes, C. novyi being among the most oxygen-sensitive of all and requiring particular care in culture. This is why anaerobic jars and reduced media are essential and why a negative culture never excludes a clostridial infection.

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: Clostridium tetani

Tetanospasmin is the neurotoxin of C. tetani and is responsible for the whole clinical picture of tetanus; the organism itself remains localised in the wound and is barely invasive. Bacillus anthracis produces a three-component toxin acting through adenylate cyclase and a protease, Streptococcus pneumoniae produces pneumolysin, a cytolysin, and Staphylococcus aureus produces a range of toxins including enterotoxins and toxic shock syndrome toxin - none of them a neurotoxin.

Answer: C

Correct answer: C tetani

Among the four listed, only C. tetani carries a terminal spherical spore that swells the rod into the classic drumstick. C. perfringens is famous for rarely showing spores at all in clinical material, C. botulinum has subterminal oval spores, and C. histolyticum likewise. The appearance is suggestive rather than diagnostic, since C. tetanomorphum and C. sphenoides share it, but among these four it points unambiguously to C. tetani.