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GENERAL FEATURES AND PRINCIPLES

The post-antibiotic era has begun. For most people, this is the first time in their lives that an effective treatment for a bacterial infection may not exist. The Enterobacteriaceae are at the forefront of this evolving public health crisis. For example, the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) have designated carbapenem-resistant Enterobacteriaceae (CRE) as representing a threat level of “urgent” and “priority one, critical.” Enterobacteriaceae are responsible for a significant proportion of the deaths attributed to antimicrobial-resistant bacteria, of which an estimated 23,000 and 25,000 occur annually in the United States and the European Union, respectively, and three to five times as many (per capita) in low- and middle-income countries (e.g., Thailand). These pathogens cause a wide variety of infections involving diverse anatomic sites in both healthy and compromised hosts. Therefore, a thorough knowledge of clinical presentations and appropriate therapeutic choices is necessary for optimal outcomes. Escherichia coli, Klebsiella, Proteus, Enterobacter, Serratia, Citrobacter, Morganella, Providencia, Cronobacter, and Edwardsiella are enteric gram-negative bacilli (GNB) within the family Enterobacteriaceae that commonly cause extraintestinal infections. Salmonella, Shigella, and Yersinia, which also are in the family Enterobacteriaceae but more commonly cause gastrointestinal infections, are discussed in Chaps. 165, 166, and 171, respectively.

EPIDEMIOLOGY

E. coli, Klebsiella, Proteus, Enterobacter, Serratia, Citrobacter, Morganella, Providencia, Cronobacter, and Edwardsiella are components of the normal animal and human colonic microbiota and/or the microbiota in various environmental habitats, including long-term-care facilities (LTCFs) and hospitals. As a result, except for certain pathotypes of intestinal pathogenic E. coli, these genera are global pathogens. The incidence of infection due to these agents is increasing because of the combination of an aging population and increasing antimicrobial resistance. In healthy humans, E. coli is the predominant species of GNB in the colonic microbiota, followed by Klebsiella and Proteus. GNB (primarily E. coli, Klebsiella, and Proteus) can also colonize the oropharynx and intact skin but, in healthy individuals, tend to do so only transiently. By contrast, in LTCFs and hospital settings, a variety of GNB emerge as the dominant colonizers of both mucosal and skin epithelial surfaces, particularly in association with antimicrobial use, severe illness, and extended length of stay. LTCFs are emerging as an important reservoir for resistant GNB. Such colonization with GNB may lead to subsequent extraintestinal infection; for example, oropharyngeal colonization may lead to pneumonia, and colonic/perineal colonization may lead to urinary tract infection (UTI). The use of ampicillin or amoxicillin was associated with an increased risk of subsequent infection due to the hypervirulent pathotype of Klebsiella pneumoniae in Taiwan; this association suggests that changes in the quantity or prevalence of colonizing bacteria may significantly influence the risk of infection. Serratia, Enterobacter, and, less commonly, ...

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