Chapter Overview

Unusual groups of pathogenic bacteria include spirochetes, vibrios, obligate intracellular parasites, and cell-wall-deficient species.
Treponema are thin, flexible, spiral-shaped cells. Syphilis, an STD caused by Treponema pallidum, is a complex and chronic disease that progresses through three major phases and a latent period that may extend for many years.
Leptospira is a zoonotic pathogen spread to humans by contact with animal excrement. Borrelia spirochetes are arthropod-borne pathogens that cause two forms of relapsing fever, a recurrent febrile infection.
Lyme disease is a severe systemic syndrome caused by Borrelia burgdorferi and transmitted by tick bites. It is marked by a constellation of skin, joint, cardiac, and neurological complications.
Vibrios are curved motile rods that are widely distributed throughout aquatic environments and animals. The most prominent genus is Vibrio, which causes cholera, and several other types of food infection.
Vibrio cholerae is the agent of cholera, a toxin-induced diarrhea that greatly disrupts the fluid/salt balance of the body.
Other vibrios with wide medical impact are Campylobacter, an animal-associated gastrointestinal pathogen, and Helicobacter, a resident of the stomach involved in a variety of gastric illnesses.
Rickettsias are a large group of tiny obligate intracellular bacteria that live in the bodies of ticks and lice. The genus Rickettsia causes typhus and Rocky Mountain spotted fever, the most common rickettsial disease in North America.
Fleas, lice, and ticks are tiny arthropods that feed from humans and other animals. They serve as vectors for a number of rickettsial and borrelial diseases.
Chlamydias are obligate parasites with an unusual life cycle that varies between a sturdy infectious phase and a destructive intracellular phase.
Chlamydia trachomatis causes a prevalent STD that can damage the reproductive tract and can also infect the eyes and eye membranes. C. pneumoniae infection gives rise to a form of pneumonia, and C. psittaci causes a zoonotic infection termed ornithosis.
Mycoplasmas are the smallest infectious bacteria, known for their lack of a cell wall and their reliance on host membranes for survival. Mycoplasma pneumoniae causes a form of chronic pneumonia that lacks typical symptoms.
Dental infections are due to a mixture of normal oral bacteria that infect when host defenses or oral hygiene have been reduced. Dental infections are associated with the buildup of a complex network of bacteria that produce plaque.
Plaque buildup initiates the damage to enamel that is characteristic of dental caries; calcified plaque damages the gingiva and leads to gingivitis, periodontitis, and tooth loss.

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