Chapter Overview

Gram-positive bacilli account for a number of significant infectious diseases. General separation into groups can be done according to presence of spores, acid fastness, and cell morphology.
The major genera of endospore-forming bacilli are Bacillus and Clostridium.
Members of the genus Bacillus are primarily aerobic soil inhabitants that are noninfectious. The most important pathogen is B. anthracis, the cause of anthrax, a zoonotic disease of livestock.
Members of the genus Clostridium are anaerobic inhabitants of soil, vegetation, and occasionally normal flora. Their pathogenesis is due to resistant spores and powerful exotoxins and enzymes.
Clostridial diseases arising from wounds include tetanus, a neuromuscular disease, and gas gangrene, a soft-tissue infection that damages muscles.
Clostridia are also implicated in food-borne illness, notably botulism, a food intoxication.
Listeria monocytogenes and Erysipelothrix rhusiopathiae are non-spore-forming rods that can infect humans.
Listeria is widespread throughout natural habitats and may be ingested in contaminated food. It causes a systemic infection, listeriosis, which can be very serious in babies and the elderly.
Erysipelothrix causes a zoonosis in pigs and erysipeloid, a skin infection in humans.
Corynebacterium species are gram-positive pleomorphic rods with palisades arrangement.
The primary pathogen in the group is Corynebacterium diphtheriae, the agent of diphtheria, a toxin-induced disease of the throat, heart, and nervous system.
Members of Mycobacterium are acid-fast bacilli with complex lipids in their cell walls.
The most prominent pathogen worldwide is Mycobacterium tuberculosis, the cause of tuberculosis, a disease spread by respiratory droplets.
Tuberculosis begins with a lung infection but can progress chronically to other organs. It is diagnosed by skin testing, X ray, and acid-fast staining.
Mycobacterium leprae is an obligate parasite of humans that is weakly communicable through very close contact.
The disease leprosy is a slow, progressive infection of skin and nerves that leads to nerve damage, deformities, and thickened nodules in the skin of the face and extremities.
The gram-positive bacillary diseases for which there is effective vaccination are anthrax, tetanus, diphtheria, and tuberculosis.

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