During the childbearing years, the normal flora of the vagina is predominantly which organism?

• A. Enterococcus
• B. Lactobacillus
• C. Propionibacterium
• D. Coagulase-negative Staphylococcus

Answer: (B)

Lactobacillus species predominate in the vagina during the reproductive years. This dominance is driven by estrogen, which increases glycogen in vaginal epithelial cells. Lactobacilli metabolize that glycogen into lactic acid, lowering the vaginal pH to roughly 3.8–4.5. This acidic environment helps suppress many potential pathogens and supports a protective microbial balance. Some lactobacilli may also produce hydrogen peroxide, contributing to antimicrobial activity. The other organisms listed are common in skin or gut environments and do not typically form the dominant vaginal flora in reproductive-age women. After menopause, decreased estrogen reduces glycogen, the pH rises, and the flora shifts away from lactobacilli dominance.