Medical Microbiology Lecture 11

Medical Microbiology Lecture (11)

• The lecture covers an overview of bacterial infections, focusing on Neisseria gonorrhoeae, Helicobacter pylori, Vibrio cholerae, Mycoplasma pneumoniae, and Chlamydia trachomatis.

Neisseria gonorrhoeae

• Common Name: Gonorrhea or Gonococcus
• Transmission: Sexually transmitted infection (oral, vaginal, or anal intercourse).
• Characteristics:
  • Gram-negative diplococci (paired, coffee-bean shaped)
  • Aerobic (requires oxygen to grow)
  • Size: 0.6-1.0 µm
• Virulence Factors:
  • Pili/Fimbriae: Attachment to host cells
  • Outer Membrane Proteins (OMPs): Immune evasion
  • IgA Protease: Degrades IgA antibodies (mucosal immunity)
  • Lipooligosaccharide (LOS): Endotoxin, contributes to inflammation
• Clinical Manifestations:
  • Men: Painful urination (dysuria), yellowish/greenish discharge, epididymitis
  • Women: Increased vaginal discharge, painful urination, pelvic pain, lower abdominal pain, abnormal vaginal bleeding
  • Other: Rectal infections (pain, itching, discharge, bleeding)
  • Neonatal: Eye infection (conjunctivitis) in newborns
• Laboratory Diagnosis:
  • Sample Collection: Urethral swabs (men), endocervical swabs (women), eye swabs (newborns)
  • Microscopy: Gram-negative diplococci
  • Culture: Chocolate agar
  • Molecular Tests (available)

Helicobacter pylori (H. pylori)

• Description: A bacterium that infects the stomach and the first part of the small intestine (duodenum).
• Transmission: Fecal–oral, person-to-person via saliva, contaminated food/water
• Characteristics:
  • Gram-negative
  • Spiral-shaped (helical)
  • Microaerophilic (needs oxygen at a lower concentration)
  • Highly Motile (flagella used for colonization)
• Virulence Factors: - Urease: Neutralizes stomach acid; helps colonization - Flagella: Facilitates movement through gastric mucus - Cytotoxin-Associated Gene A (CagA): Increased cancer risk - Vacuolating Cytotoxin A (VacA): Cell damage - Lipopolysaccharides (LPS): Immune evasion
• Clinical Manifestations:
  • Acute/Chronic Gastritis: Epigastric pain, nausea, bloating
  • Peptic Ulcer Disease: Burning pain, nausea, possible bleeding
  • Gastric Cancer: Chronic inflammation increases cancer risk (adenocarcinoma)
  • Mucosa-Associated Lymphoid Tissue (MALT) lymphoma: Chronic infection stimulates lymphoid tissue.
• Diagnosis:
  • Invasive Methods: Endoscopy, biopsy, rapid urease test, histology, culture.
  • Non-Invasive Methods: Urea breath test (detects active infection), stool antigen test.
• Prevention:
  • Good hygiene practices
  • Good handwashing
  • Clean drinking water
  • Safe food handling
  • Health education

Vibrio cholerae

• Description: Cholera is an intestinal infection caused by the bacterium Vibrio cholerae.
• Transmission: Contaminated water/food
• Characteristics:
  • Gram-negative
  • Comma-shaped (curved rods)
  • Facultative anaerobe
  • Motile (single flagella)
• Virulence Factors: - Cholera Toxin (CT): Secretion of water and electrolytes - Toxin-Coregulated Pili (TCP): Attachment - Accessory Colonization Factor (ACF): Enhanced intestinal colonization - Zonula Occludens Toxin (Zot): Disrupts intestinal tight junctions - Hemagglutinin Protease (HAP): Facilitates bacterial spread
• Clinical Manifestations:
  • Sever Diarrhea (rice water stool)
  • Dehydration & Electrolyte imbalance
  • Mild/asymptomatic cases in low infective doses
• Diagnosis:
  • Microscopy (dark-field): Detection of motile, comma-shaped bacteria in stool.
  • Culture: Selective media
  • Serotyping: Identifying O1 or O139 Antigens
  • Molecular Tests: Polymerase Chain Reaction (PCR) to detect toxin genes (ctxA, ctxB)
• Prevention:
  • Hygiene and sanitation (clean water, handwashing)
  • Oral Cholera Vaccines (OCVs)

Mycoplasma pneumoniae

• Description: A bacteria that causes respiratory infections, featuring dry cough, fever, and mild shortness of breath
• Transmission: Respiratory droplets (highly contagious)
• Characteristics:
  • Smallest free-living organisms
  • Pleomorphic (various shapes)
  • Lacks a cell wall
  • Resistant to beta-lactam antibiotics
  • Aerobic
  • Slow growing.
• Pathogenesis: - Uses adhesions protein(P1) to attach to respiratory epithelial cells. - Produces Community-Acquired Respiratory Distress Syndrome (CARDS) toxin, causing inflammation - Strong immune response contributes to symptoms.
• Clinical Manifestations:
  • Dry Cough (hallmark symptom)
  • Fever, sore throat, headache, malaise
  • Skin Rashes
  • Neurological: Meningitis and Encephalitis
  • Hematologic: Hemolytic anemia due to cold agglutinins
• Diagnosis: - Culture: Requires specialized media (e.g. Eaton's agar) - Serology: Detection of antibodies against M. pneumoniae - Molecular tests: Detection of M. pneumoniae DNA - Chest X-ray: Used for diagnosis
• Prevention:
  • Good hygiene
  • Avoidance of close contact with infected individuals
  • Isolation

Chlamydia trachomatis

• Description: Gram-negative bacterium, common cause of sexually transmitted infections (STIs) and eye infections (trachoma).
• Transmission:
  • Sexual contact (vaginal, anal, oral)
  • Vertical transmission (mother to newborn)
  • Eye contact (trachoma)
  • Fomites (rare) / contaminated towels/ surfaces
• Characteristics:
  • Elementary Body (EB): Infective, extracellular form
  • Reticulate Body (RB): Non-infective, intracellular form
• Pathogenesis:
  • Infects epithelial cells of urethra, cervix, rectum, and eyes.
  • EB enters via endocytosis, transforms into RB, replicates, then matures back into EB, which releases to infect other cells
• Clinical Manifestations:
  • Urogenital Infections:
    • Women: Vaginal discharge, cervicitis, pelvic inflammatory disease (PID), infertility
    • Men: Urethritis, epididymitis, prostatitis
  • Neonates: Neonatal conjunctivitis, pneumonia
• Diagnosis:
  • Clinical symptoms
  • Nucleic acid amplification tests (NAATs): Detecting DNA or RNA in urine/swab samples
  • Chlamydia culture
  • Serological tests (e.g., DFA, ELISA): Detecting antigens/antibodies
• Prevention:
  • Safe sexual practices (condoms)
  • Screening for sexually active individuals
  • Partner notification & treatment
  • Hygiene practices (in trachoma-endemic areas)