Acid medium of vaginal maintained by:
A. Trichomonasvaginalis
B. Staphylococci
C. Doderlein’s bacilli
D. E. coli
Correct Answer: C. Doderlein’s bacilli
Explanation: The acidic pH (normally 3.5–4.5) of the vagina is primarily maintained by **lactobacilli** (also called lactic acid bacteria or Döderlein’s bacilli).
Mechanism:
1. Glycogen breakdown:
• The vaginal epithelium (under the influence of estrogen) is rich in glycogen.
• Vaginal epithelial cells shed and release this glycogen.
2. Lactobacilli fermentation:
• Dominant healthy vaginal flora consists of Lactobacillus species (especially L. crispatus, L. iners, L. gasseri, L. jensenii).
• These bacteria metabolize glycogen → lactic acid (mainly L-lactic and D-lactic isomers).
3. Result:
• Production of lactic acid lowers the vaginal pH to 3.5–4.5.
• This acidic environment inhibits the growth of pathogenic bacteria (e.g., Gardnerella, Prevotella, Mobiluncus) and yeast.
Additional contributing factors:
• Minor contribution from organic acids produced by other vaginal bacteria or epithelial cells.
• Estrogen (maintains thick glycogen-rich epithelium; hence acidity is lost after menopause or in hypoestrogenic states).
Summary (most common exam answer):
The acidic medium of the vagina is maintained by lactobacilli through the production of lactic acid from glycogen.
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Writer: Vandita Singh, Lucknow (GS India Nursing Group)