Actinomycetes and Non Sporing Anaerobes Questions and Answers

Answer: A

Correct answer: Yellow

The granules of Actinomyces israelii are the sulphur granules, and they are named for their colour: yellow, sometimes deepening to yellowish-brown. Among the other actinomycetes, Nocardia and Actinomadura madurae give white to yellowish granules and Actinomadura pelletieri red ones. Black granules are produced only by the true fungi, chiefly Madurella mycetomatis, so a black granule points away from an actinomycete altogether and towards a eumycetoma.

Answer: C

Correct answer: Polypeptide

The capsule of Bacillus anthracis is a polymer of D-glutamic acid, and it is almost unique among bacterial capsules in being a polypeptide rather than a polysaccharide. Because it is made of the D-isomer it is poorly immunogenic and resists digestion by host proteases, and it protects the organism from phagocytosis. Its genes lie on the plasmid pXO2, separate from the toxin genes on pXO1; a strain losing pXO2 loses its capsule and much of its virulence, which is the basis of the Sterne vaccine strain.

Answer: C

Correct answer: An anaerobic infection

The foul, putrid smell of an anaerobic infection comes from the short-chain fatty acids and amines - butyric acid, cadaverine, putrescine - produced by the fermentative metabolism of these organisms, and it is one of the few bedside findings that points to a bacteriological group before any culture. Other pointers are gas in the tissues, necrotic tissue, an abscess, and a proximity to a mucosal surface. Pseudomonas has its own sweetish, grape-like odour, and Streptococcus pyogenes produces no characteristic smell.

Answer: B

Correct answer: A skin commensal introduced during venepuncture

Propionibacterium acnes is an anaerobic diphtheroid of the sebaceous follicles and one of the commonest contaminants of blood cultures, especially when only one bottle of a set grows it after several days. It can cause genuine disease - prosthetic joint infection, shunt infection, and endocarditis on a prosthetic valve - but the diagnosis then rests on repeated isolates from separate sets, not on a single bottle. It is an anaerobe, not an aerobe, and it has no connection with actinomycosis.

Answer: B

Correct answer: The tonsillar crypts and dental plaque of healthy people

Actinomyces israelii is an endogenous organism: it is a normal inhabitant of the mouth, particularly the tonsillar crypts, gingival margin and carious teeth, and it causes disease only when trauma, extraction or aspiration carries it into deeper tissue where the oxygen tension is low enough for it to grow. Because the source is the patient’s own flora, actinomycosis is never transmitted from person to person, and it has no soil or animal reservoir - a point that distinguishes it sharply from Nocardia.

Answer: C

Correct answer: Fusobacterium together with Borrelia vincentii

Vincent’s angina, or acute ulcerative gingivostomatitis, is a synergistic infection of two organisms already present in the mouth: the fusiform bacillus Fusobacterium and the spirochaete Borrelia vincentii. A Gram or dilute carbol fuchsin film of the ulcer showing both together is diagnostic, and the condition responds to penicillin or metronidazole. It appears where oral hygiene is poor or resistance is lowered, and neither organism produces the lesion alone - hence the term fusospirochaetal.

Answer: C

Correct answer: A. israelii

Actinomyces israelii causes the great majority of human actinomycosis in all its forms, and the cervicofacial form - lumpy jaw - is the commonest presentation, typically following dental extraction or trauma that carries the organism from the mouth into the tissues. A. naeslundii, A. viscosus and A. meyeri are all recognised human pathogens but are recovered far less often. The lesion is a chronic indurated swelling with multiple discharging sinuses exuding sulphur granules.

Answer: D

Correct answer: Bacillus anthracis

McFadyean’s reaction is the demonstration of the anthrax capsule in a blood film from an infected animal stained with polychrome methylene blue: the bacilli stain blue and the capsule appears as an amorphous pink-purple halo around them. It is a rapid presumptive test used on peripheral blood or splenic pulp. The clostridia and Bacillus cereus do not give it, B. cereus being uncapsulated, which is one of the features separating it from anthrax.

Answer: B

Correct answer: Binary fission

Bacteria multiply by binary fission: the chromosome replicates, a septum forms across the middle of the cell, and one cell becomes two genetically identical daughters, which under favourable conditions can happen every twenty minutes. Budding is the usual mode in yeasts and occurs only exceptionally in bacteria. Sporulation is a survival response producing one spore from one cell, so it is not multiplication at all, and bacteria are of course not manufactured by host cells.

Answer: C

Correct answer: Actinomyces israelii

On prolonged anaerobic incubation, Actinomyces israelii forms rough, heaped, nodular colonies whose irregular surface is likened to a molar tooth; younger colonies show the delicate branching filaments described as spider or breadcrumb colonies. The Nocardia species are aerobes and produce chalky, folded colonies that are often pigmented, and Actinomadura madurae gives a waxy, adherent growth. The molar tooth appearance is a useful bedside clue in a suspected cervicofacial lesion.