What causes excessive growth of staphylococcus aureus?

The composition of the aerobic human vaginal microfloras has been extensively studied . These floras are dominated by lactobacilli; however, other aerobic bacteria may also be present, including Staphylococcus aureus. The bacterial density of S. aureus changes dramatically during menstruation, increasing logarithmically in the vagina compared to during nonmenses . A major end product of Lactobacillus metabolism, lactic acid, is responsible for maintaining the vaginal pH at approximately 4 at times other than menstruation. During menstruation, lactobacilli appear to be unable to maintain vaginal pH, and the rise in pH corresponds with rises in S. aureus levels.