Actinomycetes and Non Sporing Anaerobes Questions and Answers

Answer: D

Correct answer: Inhibits protein synthesis

The anthrax toxin does not inhibit protein synthesis - that is the mechanism of diphtheria toxin and of Pseudomonas exotoxin A, both of which act on elongation factor 2. The other three statements are true: the toxin has three components (protective antigen, oedema factor and lethal factor); oedema factor is an adenylate cyclase and raises intracellular cyclic AMP, producing the characteristic oedema; and the genes for all three lie on the plasmid pXO1.

Answer: A

Correct answer: Veillonella

Veillonella are the only anaerobic Gram-negative cocci of medical note, occurring as small diplococci in the mouth, intestine and vagina and appearing in mixed anaerobic infections. Peptococcus and Peptostreptococcus are the anaerobic Gram-positive cocci, and Sporosarcina is a spore-forming Gram-positive coccus. The Gram reaction is the whole of the answer here, and Veillonella is the name to attach to it.

Answer: C

Correct answer: Organism cannot be cultured

Actinomyces israelii can certainly be cultured, though it demands anaerobic or microaerophilic conditions and patience - the molar tooth colonies may take a week or more to appear on brain heart infusion or thioglycollate medium. The other three statements are all true of actinomycosis: sulphur granules are found in the pus, crushing them shows branching filaments, and A. israelii is the usual agent. Failure to grow the organism usually reflects prior antibiotics or inadequate anaerobiosis, not any inherent unculturability.

Answer: B

Correct answer: Prolonged high-dose penicillin, often for several months

Actinomyces is fully sensitive to penicillin, but the lesion is a dense fibrotic mass with poor blood supply through which the drug penetrates badly, so treatment must be given in high dose and continued for weeks to months - conventionally intravenous penicillin followed by several months of oral therapy - with surgical drainage of any collection. A short course relapses. Metronidazole is inactive against Actinomyces, and amphotericin B is irrelevant, since the organism is a bacterium and not a fungus despite its fungus-like growth.

Answer: B

Correct answer: adult vagina

Lactobacilli - Doderlein’s bacilli - colonise the vagina only when oestrogen causes the epithelium to lay down glycogen, which the organism ferments to lactic acid. That happens from puberty to the menopause, so the adult vagina is dominated by them and its pH is held around 4 to 4.5. Before puberty and after the menopause there is no glycogen, the lactobacilli are scanty, and the pH is near neutral, which is one reason the flora of those two age groups resembles each other more than either resembles the adult.

Answer: A

Correct answer: They are Gram-negative bacilli

Streptococci are Gram-positive cocci arranged in chains, so this statement is the exception. The other three are true: they are lactic acid bacteria, fermenting sugars to lactic acid as their principal end product; Streptococcus mutans adheres to the enamel pellicle through the glucans it makes from sucrose, which is the first step in dental caries; and they are catalase negative, which is the standard bench test separating them from the catalase-positive staphylococci.

Answer: D

Correct answer: All of these

The family Bacteroidaceae as classically defined embraces the non-sporing, anaerobic, Gram-negative bacilli, and Bacteroides, Fusobacterium and Leptotrichia are all members. Bacteroides species are pleomorphic rods of the gut, Fusobacterium are spindle-shaped organisms of the mouth, and Leptotrichia buccalis is a large filamentous rod of dental plaque. Modern taxonomy has since redistributed several of these genera into separate families, but they remain grouped together clinically as the non-sporing Gram-negative anaerobes.

Answer: D

Correct answer: Nocardia asteroides

Nocardia is a strict aerobe of the soil, acquired by inhalation or inoculation, and it grows readily on ordinary media in air. Actinomyces israelii is an anaerobe or microaerophile of the mouth, Bacteroides fragilis is an obligate anaerobe of the gut, and Veillonella parvula is an anaerobic Gram-negative coccus. The aerobic-anaerobic split, together with partial acid-fastness, is the standard way of separating Nocardia from Actinomyces, which they otherwise closely resemble.

Answer: A

Correct answer: Prevotella

When the old genus Bacteroides was dismembered, the pigmented species were divided by their ability to ferment sugars. The saccharolytic ones, chiefly the old B. melaninogenicus, became Prevotella, while the asaccharolytic ones, chiefly B. gingivalis and B. asaccharolyticus, became Porphyromonas. Only the B. fragilis group retained the name Bacteroides. The distinction is worth holding by its root: saccharo- for sugar-fermenting Prevotella, porphyro- for the porphyrin pigment of the asaccharolytic group.

Answer: A

Correct answer: Lemierre’s syndrome, a septic jugular thrombophlebitis following pharyngitis

Fusobacterium necrophorum is a spindle-shaped Gram-negative anaerobe of the throat. In a young adult it may follow an ordinary sore throat by invading the parapharyngeal space, thrombosing the internal jugular vein and showering septic emboli to the lungs - the postanginal sepsis described by Lemierre. Cavitating lung lesions with a recent history of pharyngitis in a previously well adolescent should raise it at once. Madura foot and bacterial vaginosis have other causes, and rat-bite fever is due to Streptobacillus or Spirillum.