A patient presents with rapid onset severe respiratory symptoms. Chest radiographs show a hemorrhagic lymphadenitis. The isolation of chains of fairly large, aerobic Gram-positive rods, some of which have started to sporulate from a patient with this resentation, should raise a major concern of which organism? (You should be able to answer this question from the genus alone, although a question might also mention that it was nonmotile.)

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Bacillus is the correct genus. There are two Gram-positive spore-forming rods. Bacillus is aerobic with one species (Bacillus anthracis), causing hemorrhagic lymphadenitis and pulmonary edema. The other genus with bacterial endospores, the Clostridia, do not grow aerobically. The other Gram-positive organism listed, Actinomyces, often described as a branching bacterium, is also anaerobic. Campylobacter and Haemophilus are both Gram-negative.

A Patient Presents with Rapid Onset Severe Respiratory Symptoms