Normally, the urine and urinary tract above the entrance to the bladder are essentially free of microorganisms; the lower urethra, however, has a normal resident flora. Species of Lactobacillus, Staphylococcus (coagulase-negative), Corynebacterium, Haemophilus, Streptococcus, and Bacteroides are common inhabitants.
The normal flora of the genital tract of women is influenced by the action of estrogen hormones on the epithelial cells of the vaginal mucosa. When estrogens are present, glycogen is deposited in these cells. The glycogen is converted to lactic acid by lactobacilli, resulting in an acidic pH that inhibits the growth of many potential pathogens. Lactobacilli may also release hydrogen peroxide, a powerful inhibitor of some anaerobic bacteria, as a by-product of metabolism. Thus, the normal flora and resistance to infection of the female genital tract vary considerably with the person's hormonal status. For example, prepubertal girls, having low estrogen levels, are much more susceptible to vaginal infections with Streptococcus pyogenes and Neisseria gonorrhoeae than women during the child-bearing years. ■ lactobacilli, p. 275
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