Chapter 1 Infection

Genitourinary tract the urinary tract is sterile in

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Genitourinary Tract The urinary tract is sterile in health above the distal 1 cm of the urethra, which has a scanty flora derived from the perineum. Thus, in health the urine in the bladder, ureters, and renal pelvis is sterile. The vagina has a flora that varies according to hormonal influences at different ages. Before puberty and after menopause, it is mixed, nonspecific, and relatively scanty, and it contains organisms derived from the flora of the skin and colon. During the childbearing years, it is composed predominantly of anaerobic and microaerophilic members of the genus Lactobacillus , with smaller numbers of anaerobic Gram-negative rods, Gram-positive cocci, and yeasts that can survive under the acidic conditions produced by the lactobacilli. These conditions develop because glycogen is deposited in vaginal epithelial cells under the influence of estrogenic hormones and metabolized to lactic acid by lactobacilli. This process results in a vaginal pH of 4 to 5, which is optimal for growth and survival of the lactobacilli, but inhibits many other organisms. Roles in Health and Disease Opportunistic Infection Many species among the normal flora are opportunists in that they can cause infection when they reach protected areas of the body in sufficient numbers. For example, certain strains of E coli can reach the urinary bladder by ascending the urethra and cause acute urinary tract infection. Perforation of the colon from a ruptured diverticulum or a penetrating abdominal wound releases feces into the peritoneal cavity; this contamination may be followed by peritonitis or intra-abdominal abscesses caused by the more opportunistic members of the flora. Reduced innate defenses or immunologic responses can result in local invasion and disease by normal floral organisms. Caries and periodontal disease are caused by organisms that are members of the normal oral flora (see Chapter 60). Exclusionary Effect Balancing the prospect of opportunistic infection is the tendency of the normal flora to produce conditions that compete with extraneous pathogens and thus reduce their ability to establish a niche in the host. The flora in the colon of the breastfed infant produces an environment inimical to colonization by enteric pathogens, as does a vaginal flora dominated by lactobacilli. The benefit of this exclusionary effect has been demonstrated by what happens when it is removed. Antibiotic therapy, particularly with broad- spectrum agents, may so alter the normal flora of the gastrointestinal tract that antibiotic-resistant organisms multiply in the ecologic vacuum. Under these conditions, the spore-forming Clostridium difficile has a selective advantage that allows it to survive, proliferate, and produce a toxic colitis.
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Genitourinary Tract The urinary tract is sterile in health...

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