![]() Only flagellated organisms, such as Escherichia and Salmonella, have H antigens, whereas the nonmotile ones, such as Klebsiella and Shigella, do not. (2) The H antigen is on the flagellar protein. The number of different O antigens is very large (e.g., there are approximately 1500 types of Salmonella and 150 types of E. The O antigen, which is composed of repeating oligosaccharides consisting of three or four sugars repeated 15 or 20 times, is the basis for the serologic typing of many enteric rods. (1) The cell wall antigen (also known as the somatic, or O, antigen) is the outer polysaccharide portion of the lipopolysaccharide (see Figure 2–6). The three surface antigens are as follows: The antigens of several members of the Enterobacteriaceae, especially Salmonella and Shigella, are important they are used for identification purposes both in the clinical laboratory and in epidemiologic investigations. coli and Vibrio cholerae secrete exotoxins, called enterotoxins, that activate adenylate cyclase within the cells of the small intestine, causing diarrhea) (see Chapter 7). ![]() In addition, several exotoxins are produced (e.g., E. In contrast to the Enterobacteriaceae, it is a strict aerobe and derives its energy from oxidation, not fermentation.Īll members of the Enterobacteriaceae, being gram-negative, contain endotoxin in their cell walls. aeruginosa, a significant cause of urinary tract infection and sepsis in hospitalized patients, does not ferment glucose or reduce nitrates and is oxidase-positive. These four reactions can be used to distinguish the Enterobacteriaceae from another medically significant group of organisms-the nonfermenting gram-negative rods, the most important of which is Pseudomonas aeruginosa. TABLE 18–5 Diseases Caused by Members of the Enterobacteriaceaeįeatures common to all members of this heterogeneous family are their anatomic location and the following four metabolic processes: (1) they are all facultative anaerobes (2) they all ferment glucose (fermentation of other sugars varies) (3) none have cytochrome oxidase (i.e., they are oxidase-negative) and (4) they reduce nitrates to nitrites as part of their energy-generating processes. 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
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