The organisms and some of the diseases they cause are listed in Table 18–5. Although the members of the Enterobacteriaceae are classified together taxonomically, they cause a variety of diseases with different pathogenetic mechanisms. These organisms are the major facultative anaerobes in the large intestine but are present in relatively small numbers compared with anaerobes such as Bacteroides. The Enterobacteriaceae is a large family of gram-negative rods found primarily in the colon of humans and other animals, many as part of the normal flora. In addition, infection with Campylobacter jejuni predisposes to Guillain-Barré syndrome.īefore describing the specific organisms, it is appropriate to describe the family Enterobacteriaceae, to which many of these gram-negative rods belong. Patients infected with such enteric pathogens as Shigella, Salmonella, Campylobacter, and Yersinia have a high incidence of certain autoimmune diseases such as Reiter’s syndrome (see Chapter 66). TABLE 18–4 Gram-Negative Rods Causing Urinary Tract Infection 1 or Sepsis 2 TABLE 18–3 Gram-Negative Rods Causing Diarrhea TABLE 18–2 Frequency of Diseases Caused in the United States by Gram-Negative Rods Related to the Enteric Tract The medically important gram-negative rods that cause urinary tract infections are described in Table 18–4. coli the other organisms occur less commonly. Urinary tract infections are caused primarily by E. The medically important gram-negative rods that cause diarrhea are described in Table 18–3. Enterotoxigenic strains of Escherichia coli are a common cause of diarrhea in developing countries but are less common in the United States. Salmonella, Shigella, and Campylobacter are frequent pathogens in the gastrointestinal tract, whereas Escherichia, Vibrio, and Yersinia are less so. The frequency with which the organisms related to the enteric tract cause disease in the United States is shown in Table 18–2. TABLE 18–1 Categories of Gram-Negative Rods These genera have therefore been divided into three groups depending on the major anatomic location of disease, namely, (1) pathogens both within and outside the enteric tract, (2) pathogens primarily within the enteric tract, and (3) pathogens outside the enteric tract ( Table 18–1). Gram-negative rods related to the enteric tract include a large number of genera. (Figure courtesy of Public Health Image Library, Centers for Disease Control and Prevention.) Arrowhead points to a flagellum at one end of a curved gram-negative rod. Long arrow points to a curved gram-negative rod. (Used with permission from Professor Shirley Lowe, University of California, San Francisco School of Medicine.)įIGURE 18–2 Vibrio cholerae-Gram stain. Although this approach leads to some overlap, it should be helpful because it allows general concepts to be emphasized.įIGURE 18–1 Escherichia coli-Gram stain. In this book, these bacteria are subdivided into three clinically relevant categories, each in a separate chapter, according to whether the organism is related primarily to the enteric or the respiratory tract or to animal sources ( Table 18–1). Gram-negative rods are a large group of diverse organisms (see Figures 18–1, 18–2, and 19–1).
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