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The vaginal flora of a normal, asymptomatic reproductive-aged woman includes multiple aerobic or facultative species as well as 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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Table 3-1. Lower Reproductive Tract Bacterial Flora
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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, provide a similar role and include peptides such as acidocin and lactacin. Moreover, some microbe species have the ability to produce proteinaceous adhesions and attach to vaginal epithelial cells.

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For protection from many of these toxic substances, the vagina secretes leukocyte protease inhibitor. 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. One study of 55 asymptomatic reproductive-aged women found a mean of 4.2 bacterial species recovered from the endocervix, and 2.1 from the endometrial cavity (Hemsell, 1989). Of the species recovered, 17 percent were recovered from the endometrium only, 50 percent were recovered from the endocervix only, and the remainder was recovered from both sites. Also reported is the finding of bacteria in cul-de-sac peritoneal fluid of asymptomatic women undergoing elective tubal sterilization (Spence, 1982). These and other studies show that the female upper reproductive tract is not sterile, but the presence of these bacteria does not indicate active infection. Together, these findings do illustrate the potential for infection following gynecologic surgery and the necessity for antimicrobial prophylaxis (Chap. 39). 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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Vaginal pH

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Typically, the vaginal pH ranges between 4 and 4.5. Although not completely understood, it is believed to result from Lactobacillus species' production of lactic acid, fatty acids, and other organic acids. Other bacteria can also contribute organic acids from protein catabolism, and anaerobic ...

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