Clostridium Questions and Answers

Answer: D

Correct answer: all of these

A drumstick appearance means a spherical spore at the very end of the bacillus, swelling it to a diameter greater than the rod. Three clostridia show it: C. tetani, C. tetanomorphum and C. sphenoides. Since morphology alone therefore cannot identify C. tetani, the diagnosis rests on culture characteristics, the swarming growth on blood agar, and toxin demonstration.

Answer: C

Correct answer: Persistent presence of HBsAg increases the risk of chronic liver disease

Surface antigen persisting beyond six months defines chronic infection and carries the risk of cirrhosis and hepatocellular carcinoma. The other statements are all false: hepatitis B is a DNA virus, of the hepadnavirus family; the vaccine is a recombinant surface antigen subunit, not a live attenuated virus; and the incubation period averages 75 to 90 days rather than 30, which is nearer that of hepatitis A.

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: 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: Botulism

The combination is characteristic: an acute descending paralysis beginning with the cranial nerves, blurred vision from failure of accommodation, and fixed non-reactive pupils from the block of parasympathetic cholinergic transmission. Poliomyelitis gives an asymmetrical flaccid paralysis with intact pupils and usually a febrile prodrome, and Guillain-Barré ascends rather than descends. Pupillary involvement in a descending paralysis points to botulism.

Answer: A

Correct answer: C histolyticum

C. histolyticum is the most strongly proteolytic of the clostridia, and in cooked meat broth it digests the meat particles, turning them black and eventually dissolving them, with a foul putrefactive odour. C. sporogenes does the same. The saccharolytic species, chiefly C. perfringens, redden the meat instead without digesting it, so the two reactions divide the genus at a glance.

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: 3

Hyperbaric oxygen for gas gangrene is given at about three atmospheres absolute, in sessions of an hour or two. The raised oxygen tension is directly toxic to the obligately anaerobic clostridia, halts further alpha toxin production, and improves the oxygenation of the marginal tissue at the edge of the lesion. It is an adjunct rather than a substitute: surgical debridement of the dead muscle and penicillin remain the essentials.

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: C

Correct answer: Mycobacterium bovis

M. bovis causes tuberculosis in cattle and, through unpasteurised milk, in humans, where it classically produces intestinal and cervical lymph node disease as well as pulmonary tuberculosis indistinguishable from that caused by M. tuberculosis. It is a member of the M. tuberculosis complex, and the BCG vaccine is an attenuated strain of it. M. leprae causes leprosy, M. ulcerans the Buruli ulcer, and M. kansasii an opportunistic lung disease resembling but distinct from tuberculosis.