Urogenital microbiome

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Vaginal Flora - Lactobacillus Land

  • Primary Colonizers: Predominantly Lactobacillus species (L. crispatus, L. iners).
  • Protective Acid Shield:
    • Metabolize glycogen from epithelial cells to produce lactic acid ($C_3H_6O_3$).
    • Maintains an acidic vaginal pH (< 4.5), which is hostile to most pathogens.
    • Some strains also produce H₂O₂ to suppress anaerobic bacteria.
  • Flora Disruption: A decrease in Lactobacillus can lead to:
    • Bacterial Vaginosis (BV): Overgrowth of anaerobes (e.g., Gardnerella vaginalis).
    • Candidiasis: Fungal overgrowth (e.g., Candida albicans).

⭐ High estrogen levels promote glycogen deposition in the vaginal epithelium, fostering a healthy Lactobacillus-dominant microbiome. This is why pre-pubertal and post-menopausal women are more susceptible to vaginal infections.

Vaginal Epithelial Cells: Healthy vs. Bacterial Vaginosis

Hormonal Axis - Estrogen's Empire

  • Estrogen's Role: The primary driver of a healthy vaginal ecosystem.

    • ↑ Estrogen levels promote the maturation and glycogenation of the vaginal epithelium.
    • Lactobacillus species metabolize this glycogen into lactic acid.
    • This creates an acidic vaginal environment (pH < 4.5), which inhibits the growth of pathogenic microbes.
  • Hormonal Fluctuations:

    • Pre-puberty & Post-menopause: ↓ Estrogen → ↓ glycogen → ↑ vaginal pH. This increases susceptibility to infections like bacterial vaginosis and atrophic vaginitis.
    • Reproductive Years: Cyclical estrogen maintains a protective, acidic state.

High-Yield: In low-estrogen states (e.g., menopause), the vaginal pH rises >4.5, creating a favorable environment for pathogens like E. coli, leading to recurrent UTIs and vaginitis.

Estrogen, Glycogen, and Lactobacillus in Vaginal Health

Dysbiosis Drama - When Guards Go Down

  • The Shift: A decline in protective Lactobacillus species is the central event, disrupting the vaginal ecosystem's balance.

  • Primary Triggers:

    • Broad-spectrum antibiotics (e.g., clindamycin, amoxicillin)
    • Douching, spermicides
    • Hormonal shifts (menstruation, pregnancy, menopause)
  • The Cascade: ↓ Lactobacillus → ↓ Lactic acid production → ↑ Vaginal pH > 4.5 → Pathogen overgrowth.

Normal vaginal flora vs. bacterial vaginosis microscopy

  • Key Conditions:
    • Bacterial Vaginosis (BV): Polymicrobial overgrowth, primarily Gardnerella vaginalis. Presents with thin, grey-white discharge and a "fishy" odor. Diagnosed by clue cells on microscopy.
    • Vulvovaginal Candidiasis (VVC): Overgrowth of Candida albicans. Thick, white, "cottage cheese" discharge and intense pruritus. Normal pH.

Exam Favorite: Diagnosis of Bacterial Vaginosis often relies on the Amsel Criteria. Requires 3 of 4:

  1. Thin, white, homogenous discharge.
  2. Vaginal pH > 4.5.
  3. Positive whiff-amine test.
  4. Clue cells on microscopy.

Male Microbiome - A Quick Tour

  • Distal Urethra: Primarily skin & gut commensals.
    • Staphylococcus epidermidis, Enterococcus faecalis, Corynebacteria, Lactobacilli.
  • Coronal Sulcus (Uncircumcised): Rich in anaerobic bacteria (Prevotella, Porphyromonas).
  • Semen: Generally low bacterial biomass, reflecting urethral flora.

Male Urogenital Microbiome Sites and Associated Bacteria

⭐ Circumcision significantly reduces anaerobic bacteria in the coronal sulcus. This microbial shift is linked to a lower risk for HIV and HPV acquisition.

High‑Yield Points - ⚡ Biggest Takeaways

  • Lactobacillus is the dominant microbe in a healthy vagina, producing lactic acid to maintain an acidic pH (< 4.5).
  • Estrogen promotes glycogen, which Lactobacillus metabolizes, linking hormonal status to vaginal health.
  • Bacterial Vaginosis (BV) is a dysbiosis, a shift from Lactobacillus to anaerobes like Gardnerella vaginalis.
  • An elevated vaginal pH (> 4.5) is a key indicator of BV or trichomoniasis.
  • The upper urinary tract (bladder, kidneys) is normally sterile.
  • Candida albicans overgrowth, often post-antibiotics, causes candidiasis.

Practice Questions: Urogenital microbiome

Test your understanding with these related questions

A 28-year-old woman comes to the physician because of a 4-day history of lower abdominal pain and pain with urination. Five months ago, she was treated for gonococcal urethritis. She recently moved in with her newlywed husband. She is sexually active with her husband and they do not use condoms. Her only medication is an oral contraceptive. Her temperature is 37.5°C (99.7°F) and blood pressure is 120/74 mm Hg. There is tenderness to palpation over the pelvic region. Pelvic examination shows a normal-appearing vulva and vagina. Laboratory studies show: Leukocyte count 8,400/mm3 Urine pH 6.7 Protein trace WBC 60/hpf Nitrites positive Bacteria positive Which of the following is the most likely causal organism?

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Flashcards: Urogenital microbiome

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_____ vaginalis presents with clue cells on wet mount microscopy

TAP TO REVEAL ANSWER

_____ vaginalis presents with clue cells on wet mount microscopy

Gardnerella

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