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So Asthma Mark would sit on the corner And he would play his Diphtheria Blues
—Frank Zappa
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This chapter includes a variety of highly pathogenic Gram-positive rods that are not currently common causes of human disease. Their medical importance lies in the lessons learned when they were more common, and the continued threat their existence poses. Corynebacterium diphtheriae, the cause of diphtheria, is a prototype for toxigenic disease. Listeria monocytogenes is a sporadic cause of meningitis and other infections in the fetus, newborn, and immunocompromised host. Occurrences in 2001 have served as a painful reminder that Bacillus anthracis, the cause of anthrax, is still the agent with the most potential for use in bioterrorism. The characteristics of these bacilli are presented in Table 26–1.
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Corynebacteria (from the Greek koryne, club) are small and pleomorphic. The genus Corynebacterium includes many species of aerobic and facultative Gram-positive rods. The cells tend to have clubbed ends and often remain attached after division, forming “Chinese letter” or palisade arrangements. Spores are not formed. Growth is generally best under aerobic conditions on media enriched with blood or other animal products, but many strains grow anaerobically. Colonies on blood agar are typically small (1-2 mm), and most are nonhemolytic. Catalase is produced, and many strains form acid (usually lactic acid) through carbohydrate fermentation. Surface and cell wall structure is similar to other Gram-positive bacteria.
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Pleomorphic club-shaped rods
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Corynebacterium diphtheriae
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Corynebacterium diphtheriae produces a powerful exotoxin that is responsible for diphtheria. Other corynebacteria are nonpathogenic commensal inhabitants of the pharynx, nasopharynx, distal urethra, and skin; they are collectively referred to as “diphtheroids.” The species that have disease associations are included in Table 26–2.
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