CASE 25
LABORATORY STUDIES
Diagnostic Work-Up
Table 25-1 lists the likely causes of this woman’s illness. Investigational approach may include
TABLE 25-1 Differential Diagnosis and Rationale for Inclusion (consideration)
Rationale: A clinical diagnosis of urinary tract infection (UTI; uncomplicated cystitis) should be considered. The most common cause of uncomplicated cystitis in women is E. coli, often in relation to recent sexual intercourse. Infections due to S. saprophyticus are common among sexually active adolescent girls and young adult women. The other organisms in the list are almost exclusively seen in patients with other risk factors, usually hospitalized patients with indwelling urinary catheters.
MICROBIOLOGIC PROPERTIES
E. coli belongs to the family Enterobacteriaceae (see a partial list of species in Table 25-2). These bacteria are Gram-negative rods occurring singly or in pairs (Fig. 25-1). They are facultatively anaerobic bacteria; all ferment glucose (E. coli also ferments lactose; Fig. 25-2) and are oxidase negative. They are either nonmotile or motile by peritrichous flagella. All species are fast growing and appear as large, gray colonies on blood agar (see Fig. 25-2). These species may have the following two to three antigens:
TABLE 25-2 Other Major Species in the Enterobacteriaceae Family and Their Clinical and Epidemiologic Features
