Porth's Essentials of Pathophysiology, 4e

301

Mechanisms of Infectious Disease

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FIGURE 14-4. Microscopic morphology of bacteria demonstrating their variability in size and shape: (A) colorized scanning electron micrograph (SEM) of the spherical gram-positive β -hemolytic group C Streptococcus sp.; (B) colorized SEM of the rod-shaped gram-negative Escherichia coli of the strain O157:H7; and (C) corkscrew-shaped spirochete Borrelia burgdorferi (responsible for causing Lyme disease) shown using darkfield microscopy technique (magnified ×400). (From the Centers for Disease Control and Prevention Public Images Library. Nos. 10591, 10586, 10068, 6631. A and B courtesy of Janice Haney Carr.)

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visible colony composed of millions of bacteria within a few hours. In nature, however, bacteria rarely exist as single cells floating in an aqueous environment. Rather, bac- teria prefer to stick to and colonize environmental sur- faces, producing structured communities called biofilms (Fig. 14-6). The organization and structure of biofilms permit access to available nutrients and elimination of metabolic waste. Within the biofilm, individual organ-

isms use chemical signaling as a form of primitive inter- cellular communication to represent the state of the environment. These signals inform members of the com- munity when sufficient nutrients are available for pro- liferation or when environmental conditions warrant dormancy or evacuation. Examples of biofilms abound in nature and are found on the surfaces of aquatic environments, in the human oral cavity, on indwelling medical devices, and on human cells. One has only to

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FIGURE 14-5. The manner in which microorganisms divide (arrows) can assist in their identification. Photomicrographs of gram- positive (A) Staphylococcus aureus, which divide in clusters; (B) Streptococcus spp. bacteria, which divide in chains; and (C) urethral exudate, which is diagnostic of gonococcal urethritis revealing intracellular (within polymorphonuclear leukocytes) and extracellular Gonococci, which divide in pairs. (From the Centers for Disease Control and Prevention Public Health Images Library. Nos. 2296, 2170, 4086. A courtesy of Richard Facklam; C courtesy of Norman Jacobs.)

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