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 as representing a threat level of “urgent” and “priority one, critical,” respectively. Enterobacteriaceae are responsible for a significant proportion of the deaths attributed to resistant bacteria, the number of which has been estimated at 23,000 and 25,000 annually in the United States and the European Union, respectively, with numbers three- to fivefold greater (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) that are members of the family Enterobacteriaceae. Salmonella, Shigella, and Yersinia, also in the family Enterobacteriaceae, are discussed in Chaps. 160, 161, and 166, respectively.
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; Klebsiella and Proteus are less prevalent. GNB (primarily E. coli, Klebsiella, and Proteus) colonize the oropharynx and skin of healthy individuals only transiently. By contrast, in LTCFs and hospital settings, a variety of GNB emerge as the dominant colonizers of both mucosal and skin surfaces, particularly in association with antimicrobial use, severe illness, and extended length of stay. LTCFs are emerging as an important reservoir for resistant GNB. This colonization may lead to subsequent 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 and Enterobacter infection may be acquired directly through a variety of infusates (e.g., medications, blood products). Edwardsiella infections are acquired through freshwater and marine environment exposures ...