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Microbiology

Genital Tract

This section covers the key aspects of bacteriological analysis of genital tract specimens, from specimen collection to understanding the organisms’ disease-causing potential. It provides a framework for understanding the diagnostic process and the critical information needed for accurate patient care

Specimen Sources

  • Female
    • Vaginal swabs
    • Cervical swabs
    • Endocervical swabs
  • Male
    • Urethral swabs
    • First-catch urine
    • Prostatic fluid (obtained via prostatic massage)
    • Semen
  • Considerations
    • Proper collection technique is crucial for accurate results
    • Specimen site must be specified on the lab request
    • Transport media and conditions are vital for organism viability

Indigenous Organisms: Colony and Gram Stain Morphology

  • Understanding the Normal Flora: Differentiating between normal flora and pathogens requires knowledge of the expected bacterial communities in each anatomical site
  • Key Organisms and Characteristics
    • Vagina (Female)
      • Dominant: Lactobacillus spp. (Gram-positive, large rods)
      • Others: Gram-positive cocci (CoNS, streptococci), Gram-negative/variable bacteria (e.g., Gardnerella vaginalis), Yeast (Candida spp.)
    • Cervix (Female)
      • Less diverse: Gram-positive cocci (CoNS, streptococci), Gram-negative cocci (Neisseria spp.)
      • Others: Gram-positive bacilli (Corynebacterium spp., Lactobacillus spp.)
    • Urethra (Male)
      • Similar to Cervix: Gram-positive cocci (CoNS, streptococci), Gram-negative cocci (Neisseria spp.)
      • Others: Gram-positive bacilli (Corynebacterium spp., Lactobacillus spp.)
    • Prostate (Male)
      • Generally Sterile: Some organisms that are found in the urethra may be present
  • Importance
    • Provides a baseline for identifying deviations from normal flora
    • Helps interpret the clinical significance of isolated organisms

Methods for Detection of Pathogens Associated with Vaginitis

  • Focus: Trichomonas vaginalis, Candida spp., and the diagnosis of bacterial vaginosis (BV)
  • Methods and Applications
    • Trichomonas vaginalis
      • Wet Mount: Microscopic examination for motile protozoa
      • Culture: Specific culture media for growth
      • Rapid Antigen Tests: Immunoassays for antigen detection
      • NAATs: Nucleic acid amplification tests (highly sensitive)
    • Candida spp.
      • Wet Mount: Microscopic examination for budding yeast and hyphae
      • Gram Stain: Identification of yeast cells
      • Culture: Growth on selective media for identification and species determination
      • Rapid Tests: Germ tube test, antigen detection
    • Bacterial Vaginosis (BV)
      • Amsel’s Criteria: Clinical diagnostic criteria (discharge, pH, amine odor, clue cells)
      • Wet Mount: Clue cells, decreased Lactobacilli, increased other bacteria
      • Gram Stain (Nugent Score): Scoring of bacterial morphotypes
      • Culture: Not routinely used
  • Importance
    • Allows for the identification of the specific cause of vaginitis
    • Guides appropriate treatment

Culture and/or Molecular Detection

  • Focus: Neisseria gonorrhoeae, Chlamydia trachomatis, Streptococcus agalactiae, and Mycoplasma spp
  • Methods and Applications
    • Neisseria gonorrhoeae
      • Culture: Selective media (TMA, NYC) followed by identification (Gram stain, oxidase, carbohydrate utilization) and AST (antibiotic susceptibility testing)
      • Molecular Detection: NAATs (highly sensitive)
    • Chlamydia trachomatis
      • Culture: Cell culture
      • Molecular Detection: NAATs (highly sensitive)
    • Streptococcus agalactiae
      • Culture: Blood agar, identification (Gram stain, CAMP test, serotyping)
      • Molecular Detection: PCR
    • Mycoplasma spp.
      • Culture: Specialized media
      • Molecular Detection: PCR
  • Importance
    • Provides definitive identification of pathogens
    • Enables antibiotic susceptibility testing for N. gonorrhoeae
    • Allows for rapid and sensitive detection, especially with molecular methods

Organism Pathogenicity

  • Focus: Understanding the mechanisms by which the identified organisms cause disease
  • Key Aspects
    • Etiology: The specific causative agent (e.g., Neisseria gonorrhoeae causes gonorrhea)
    • Transmission: How the pathogen is spread (e.g., sexual contact, mother-to-child)
    • Virulence Mechanisms: How the pathogen causes disease
      • Adherence: Pili, Opa proteins (for N. gonorrhoeae)
      • Invasion/Survival: EB/RB cycle (for C. trachomatis), capsule (for S. agalactiae)
      • Immune Evasion: Antigenic variation, IgA protease
      • Host Cell Damage: Cytotoxins, inflammation
      • Consequences: Specific diseases (e.g., urethritis, PID, neonatal infections)
  • Importance
    • Essential for understanding the clinical presentation of infections
    • Guides the selection of appropriate treatments
    • Informs infection prevention strategies
    • Helps assess the severity and potential complications of infections