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The vaginal flora of a normal, asymptomatic reproductive-aged woman includes multiple aerobic, facultative anaerobic, and obligate anaerobic species (Table 3-1). Of these, anaerobes predominate and outnumber aerobic species approximately 10 to 1 (Bartlett, 1977). These bacteria exist in a symbiotic relationship with the host and are alterable, depending on the microenvironment. They localize where their survival needs are met and have exemption from the infection-preventing destructive capacity of the human host. The function of this vaginal bacterial colonization, however, remains unknown.
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Within this vaginal ecosystem, some microorganisms produce substances such as lactic acid and hydrogen peroxide that inhibit nonindigenous organisms (Marrazzo, 2006). Several other antibacterial compounds, termed bacteriocins, play a similar role. For protection from many of these toxic substances, a secretory leukocyte protease inhibitor is found in the vagina. This protein protects local tissues against toxic inflammatory products and infection.
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Certain bacterial species normally found in vaginal flora have access to the upper reproductive tract. The female upper reproductive tract is not sterile, and the presence of these bacteria does not indicate active infection (Hemsell, 1989; Spence, 1982). Together, these findings do illustrate the potential for infection following gynecologic surgery and the need for antimicrobial prophylaxis. They also explain the potential acceleration of a local acute infection if a pathogen, such as Neisseria gonorrhoeae, gains access to the upper tract.
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Typically, the vaginal pH ranges between 4 and 4.5. Although not completely understood, Lactobacillus species contribute by production of lactic acid, fatty acids, and other organic acids. Other bacteria can also add organic acids from protein catabolism, and anaerobic bacteria donate by amino acid fermentation.
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Glycogen, which is present in healthy vaginal mucosa, provides nutrients for many vaginal ecosystem species and is metabolized to lactic acid (Boskey, 2001). Accordingly, as glycogen content within vaginal epithelial cells diminishes after menopause, this decreased substrate for acid production leads to a rise in vaginal pH. Specifically, if no pH-altering pathogens are present, a vaginal pH of 6.0 to 7.5 is strongly suggestive of menopause (Caillouette, 1997).
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Changing any element of this ecology may alter the prevalence of various species. For example, postmenopausal women not ...