Microbiology · MU Sofia

110. Microbiological Aspects of Sexually Transmitted Infections (STIs)

Covers the main sexually transmitted infections and the bacterial, viral, protozoal and fungal agents behind them, with a classification table grouping the common pathogens. It then goes through six key organisms in turn, giving features, clinical presentations, diagnostic methods and treatments, followed by a diagnostic summary table and a closing section on prevention and public health.

Inside: 6 sections · 7 labelled pictures · 2 tables · 16 flashcards · 2 min

Topic 110 of 113 in the MU Sofia syllabus for Microbiology (Dental Medicine, Year 2). The free AceMed note covers it in 6 sections, about 235 words (2 min of reading), with 16 flashcards.

In this note

  1. Microbiological Aspects of Sexually Transmitted Infections (STIs)
  2. I. Overview of STIs
  3. II. Classification of Major STIs
  4. III. Key Pathogens and Features
  5. IV. Diagnosis of STIs
  6. V. Prevention and Public Health

I. Overview of STIs

  • STIs are infections transmitted primarily through sexual contact, including vaginal, anal, and oral routes.
  • Involve bacteria, viruses, protozoa, and fungi.
  • Can lead to local (genital) symptoms or systemic complications (e.g., infertility, malignancies, neurologic disease).

III. Key Pathogens and Features

1. Neisseria gonorrhoeae:

  • Gram-negative diplococcus, oxidase-positive.
  • Causes urethritis, cervicitis, PID, conjunctivitis.
  • Virulence: pili, IgA protease.
  • Diagnosis: Gram stain (PMNs + GN diplococci), culture on Thayer-Martin agar, NAAT.
  • Treat with ceftriaxone + doxycycline (for possible Chlamydia co-infection).

2. Chlamydia trachomatis (serovars D–K):

  • Intracellular bacterium, not seen on Gram stain.
  • Causes urethritis, cervicitis, neonatal conjunctivitis, PID.
  • Diagnosis: NAAT (urine or swab).
  • Treatment: doxycycline or azithromycin.

3. Treponema pallidum (syphilis):

  • Spirochete, not culturable.
  • Painless chancre → rash (palms/soles) → tertiary syphilis (neuro/cardiac).
  • Diagnosis: Dark field microscopy, RPR/VDRL (screen), FTA-ABS (confirm).
  • Treatment: Benzathine penicillin G.

4. Herpes Simplex Virus (HSV-2 > HSV-1):

  • Enveloped DNA virus, causes painful genital ulcers, systemic symptoms.
  • Diagnosis: Tzanck smear (multinucleated giant cells), PCR.
  • Treatment: Acyclovir or valacyclovir.

5. Human Papillomavirus (HPV):

  • Types 6, 11: genital warts (condylomata acuminata)
  • Types 16, 18: cervical, anal, penile cancers
  • Diagnosis: Pap smear, HPV DNA testing
  • Prevention: Vaccination (Gardasil)

6. Trichomonas vaginalis:

  • Flagellated protozoan.
  • Causes foul-smelling, greenish discharge, strawberry cervix.
  • Diagnosis: Wet mount (motile trichomonads), NAAT.
  • Treatment: Metronidazole (treat partner too).

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