Actinomycetes and Non Sporing Anaerobes Questions and Answers

Answer: C

Correct answer: Mycetoma

Granules discharged through chronic sinuses are the hallmark of mycetoma, whether caused by a filamentous bacterium (actinomycetoma) or a true fungus (eumycetoma), and the granules are colonies of the organism growing within the pus. Actinomycosis produces the same picture at cervicofacial, thoracic and abdominal sites. Staphylococcal sinuses and chancroid discharge pus without granules, and sporotrichosis produces a chain of nodules along the lymphatics rather than granule-bearing sinuses.

Answer: B

Correct answer: Epithelial cells studded with adherent coccobacilli

A clue cell is a vaginal squamous epithelial cell whose border is obscured by a dense coating of adherent Gram-variable coccobacilli, chiefly Gram-negative organisms, giving it a granular, stippled edge. It is one of Amsel’s criteria for bacterial vaginosis, alongside a thin homogeneous discharge, a pH above 4.5, and a fishy odour on adding potassium hydroxide. Intracellular diplococci in polymorphs indicate gonorrhoea, and yeasts with pseudohyphae indicate candidiasis.

Answer: B

Correct answer: Filamentous organism

The question asks what distinguishes Actinomyces from ordinary bacteria in appearance. It grows as fine branching filaments about 1 micrometre wide that fragment into bacillary and coccoid forms, a mycelial habit that led to its long misclassification as a fungus. The other three options are all shared with many ordinary bacteria and so distinguish nothing. Actinomyces is in fact a true bacterium: its filaments are a tenth the width of a fungal hypha, it has a bacterial cell wall, and it is sensitive to penicillin.

Answer: D

Correct answer: Anthrax

On nutrient agar, Bacillus anthracis forms large, flat, dull, greyish-white colonies with an irregular edge made up of long parallel chains of bacilli curling outward, giving under low power the appearance of a lock of matted hair - the medusa head. In gelatin stab culture the same growth pattern gives the inverted fir tree appearance. Pneumococcus gives draughtsman colonies, and Legionella and Brucella will not grow on plain nutrient agar at all.

Answer: B

Correct answer: Pulmonary nocardiosis, which may disseminate to the brain

Nocardia is an aerobic soil organism acquired by inhalation, and in a patient with impaired cell-mediated immunity - a transplant recipient, someone on long-term steroids, or a patient with lymphoma - it produces a subacute pneumonia with cavitation that resembles tuberculosis. Haematogenous spread to the brain, giving single or multiple abscesses, occurs in up to a third of cases and is what makes the diagnosis urgent. Cervicofacial actinomycosis is a disease of Actinomyces, not Nocardia, and the other two options belong to quite different organisms.

Answer: D

Correct answer: Pseudomonas aeruginosa

Every feature points to Pseudomonas aeruginosa: it is an oxidase-positive Gram-negative rod, in contrast with the oxidase-negative Enterobacteriaceae; it produces pyocyanin and pyoverdin, giving the blue-green pigment and the characteristic sweetish odour; it is a leading cause of burn wound infection; and its resistance to most agents with sensitivity confined to the antipseudomonal aminoglycosides and penicillins is entirely typical. Escherichia coli, Klebsiella pneumoniae and Proteus mirabilis are all oxidase negative and none produces this pigment.

Answer: C

Correct answer: Non-motile

Bacillus anthracis is the only non-motile member of its genus, and this is one of the standard tests distinguishing it from the anthracoid bacilli - the saprophytic Bacillus species that resemble it on culture. It is also capsulated, which they are not, and non-haemolytic on blood agar, whereas they are usually haemolytic. Both anthrax and the anthracoids are aerobic or facultatively anaerobic, so that is not a distinguishing feature, and the remaining options state the reverse of the truth.

Answer: D

Correct answer: Treponema pallidum

Syphilis is caused by the spirochaete Treponema pallidum subspecies pallidum, a thin regularly coiled organism too slender to be seen on Gram film and demonstrated instead by dark-ground microscopy of a chancre exudate. Borrelia burgdorferi causes Lyme disease, Chlamydia trachomatis causes trachoma and non-gonococcal urethritis, and Leptospira interrogans causes leptospirosis. All four are spirochaetes or intracellular organisms with quite different clinical pictures.

Answer: A

Correct answer: Bifidobacterium

Human milk contains oligosaccharides that Bifidobacterium can ferment and most other gut organisms cannot, so the breast-fed infant develops a flora in which bifidobacteria predominate overwhelmingly. The acids they produce lower the colonic pH and suppress enteric pathogens, which is part of the protection breast feeding confers. On weaning, and in the formula-fed infant much earlier, the flora shifts towards the adult pattern dominated by Bacteroides.

Answer: C

Correct answer: Cutaneous type is rare nowadays

Cutaneous anthrax is not rare - it is by far the commonest form, making up more than 95 per cent of naturally occurring cases, so this statement is the exception and the required answer. The other three are true: the organism enters through abraded skin, particularly in those handling hides, wool and bone meal; biting flies can transfer it mechanically; and inhalation of spores produces the woolsorter’s disease form, which is far less common but far more lethal.