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Microbiology

Organism Pathogenicity

This section focuses on the pathogenicity of the microorganisms discussed previously, covering their etiology (the cause of the disease), modes of transmission, and the virulence mechanisms they employ to cause infection and disease. A thorough understanding of these aspects is critical for effective prevention, diagnosis, and treatment of genital tract infections

Neisseria gonorrhoeae

Etiology

  • Organism: Gram-negative diplococcus, oxidase-positive, Neisseria gonorrhoeae
  • Disease: Gonorrhea, a sexually transmitted infection

Transmission

  • Mode: Primarily transmitted through sexual contact (vaginal, anal, or oral sex) with an infected partner
  • Other: Can be transmitted from mother to child during childbirth (causing ophthalmia neonatorum in the newborn)

Virulence Mechanisms

  • Attachment
    • Pili: Hair-like structures that mediate attachment to host cells (e.g., epithelial cells of the urethra, cervix, rectum, pharynx, and conjunctiva)
    • Opa Proteins: Surface proteins that promote adherence to host cells
  • Antigenic Variation
    • Pili Variation: The pili undergo antigenic variation, making it difficult for the host immune system to develop effective immunity
  • Invasion and Survival
    • Por Proteins: Promote bacterial survival by interfering with phagocytosis and complement activation
    • LOS (Lipooligosaccharide): Endotoxin that causes inflammation and tissue damage
    • IgA Protease: Cleaves IgA antibodies, preventing them from neutralizing the bacteria
  • Consequences
    • Inflammation: Triggers an inflammatory response in the infected tissues, leading to symptoms such as urethritis (in men), cervicitis (in women), and proctitis (in both sexes)
    • Disseminated Gonococcal Infection (DGI): In rare cases, the bacteria can disseminate to the bloodstream, causing septic arthritis, skin lesions, and endocarditis
    • Pelvic Inflammatory Disease (PID): In women, untreated gonorrhea can ascend the genital tract, leading to PID, which can cause infertility, ectopic pregnancy, and chronic pelvic pain
    • Ophthalmia Neonatorum: Infection of the newborn’s eyes, which can lead to blindness if not treated promptly

Chlamydia trachomatis

Etiology

  • Organism: Gram-negative obligate intracellular bacterium, Chlamydia trachomatis
  • Disease: Chlamydia, a sexually transmitted infection

Transmission

  • Mode: Primarily transmitted through sexual contact (vaginal, anal, or oral sex) with an infected partner
  • Other: Can be transmitted from mother to child during childbirth (causing conjunctivitis or pneumonia in the newborn)

Virulence Mechanisms

  • Invasion and Survival
    • Elementary Body (EB): The infectious form of the bacterium. The EB attaches to host cells and is internalized through endocytosis
    • Reticulate Body (RB): The metabolically active, replicating form of the bacterium, which resides within a vacuole (inclusion) inside the host cell
    • Inclusion Formation: Prevents fusion of the vacuole with lysosomes, allowing the bacteria to replicate within the host cell
  • Host Cell Damage
    • Cytokine Production: The infection triggers the release of inflammatory cytokines, leading to tissue damage
    • Cell Lysis: The bacteria eventually lyse the host cell, releasing new EBs to infect other cells
  • Consequences
    • Urethritis: In men, chlamydia can cause urethritis, leading to dysuria, and urethral discharge
    • Cervicitis: In women, chlamydia can cause cervicitis, often asymptomatic, but may cause vaginal discharge, bleeding, and pelvic pain
    • Pelvic Inflammatory Disease (PID): Untreated chlamydia can ascend the genital tract, leading to PID, which can cause infertility, ectopic pregnancy, and chronic pelvic pain
    • Epididymitis: In men, chlamydia can cause epididymitis (inflammation of the epididymis)
    • Proctitis: Inflammation of the rectum
    • Lymphogranuloma Venereum (LGV): A more invasive form of C. trachomatis infection caused by specific serovars, characterized by the formation of painful genital ulcers and swollen lymph nodes
    • Conjunctivitis: Can cause conjunctivitis in both adults and newborns
    • Pneumonia: Can cause pneumonia in newborns

Streptococcus agalactiae (Group B Streptococcus, GBS)

Etiology

  • Organism: Gram-positive coccus, Streptococcus agalactiae (GBS)
  • Disease: GBS infections, primarily in newborns

Transmission

  • Mode
    • Vertical Transmission: From mother to newborn during childbirth. The bacteria colonize the vagina and rectum of pregnant women, and the newborn can be exposed to the bacteria during passage through the birth canal
    • Colonization: GBS can colonize the genital tract and rectum of both men and women
  • Other: Rarely, transmission can occur through direct contact

Virulence Mechanisms

  • Capsule
    • Polysaccharide Capsule: The capsule is the primary virulence factor. It helps the bacteria evade phagocytosis and complement-mediated killing
    • Capsular Serotypes: The capsule is composed of different serotypes (Ia, Ib, II, III, IV, V, VI, VII, VIII), and the serotype of the GBS strain influences the severity of the infection
  • Surface Proteins
    • C5a Peptidase: Inactivates the complement component C5a, which is a chemoattractant for neutrophils
    • Beta-hemolysin/Cytolysin: Damages host cells
  • Consequences
    • Neonatal Infections
      • Early-Onset GBS Disease: Occurs within the first week of life, usually presenting as sepsis, pneumonia, or meningitis. The bacteria are acquired during delivery
      • Late-Onset GBS Disease: Occurs after the first week of life, often presenting as meningitis. The bacteria may be acquired from the mother or other sources
    • Maternal Infections
      • Chorioamnionitis: Infection of the amniotic fluid
      • Endometritis: Infection of the uterine lining
      • Wound Infections: After cesarean section or vaginal delivery
    • Other Infections: GBS can cause infections in adults, including bacteremia, pneumonia, skin and soft tissue infections, and endocarditis

Mycoplasma spp.

Etiology

  • Organisms: Mycoplasma hominis, Ureaplasma urealyticum, Mycoplasma genitalium
  • Diseases
    • M. hominis and U. urealyticum: Associated with bacterial vaginosis, postpartum fever, and pelvic inflammatory disease (PID)
    • M. genitalium: Associated with urethritis in men, cervicitis in women, and PID

Transmission

  • Mode: Primarily transmitted through sexual contact
  • Other: Vertical transmission (mother to child) can occur for U. urealyticum

Virulence Mechanisms

  • Adherence
    • Adhesins: Surface proteins that mediate attachment to host cells (e.g., epithelial cells of the genital tract)
  • Immune Evasion
    • Antigenic Variation: M. genitalium can undergo antigenic variation
  • Host Cell Damage
    • Production of Cytotoxins: Some mycoplasmas produce toxins that can damage host cells
    • Inflammation: The infection triggers an inflammatory response in the infected tissues
  • Consequences
    • Urethritis: M. genitalium is a significant cause of non-gonococcal urethritis (NGU) in men
    • Cervicitis: M. genitalium is associated with cervicitis in women
    • Pelvic Inflammatory Disease (PID): M. genitalium is associated with PID
    • Bacterial Vaginosis (BV): M. hominis and U. urealyticum are associated with BV
    • Postpartum Fever: M. hominis can cause postpartum fever
    • Infertility: Can contribute to infertility in both men and women

Key Considerations

  • Asymptomatic Carriage: Many individuals may be asymptomatic carriers of these pathogens, meaning they harbor the bacteria but do not experience symptoms. This can contribute to the spread of infection
  • Co-Infections: Co-infections with multiple pathogens are common
  • Risk Factors: Certain factors can increase the risk of genital tract infections, including:
    • Unprotected sexual intercourse
    • Multiple sexual partners
    • History of STIs
    • Young age
    • Pregnancy
    • Weakened immune system
  • Prevention: Prevention strategies include:
    • Safe sex practices (condom use)
    • Regular STI screening
    • Vaccination (for some infections, e.g., HPV)
    • Prompt treatment of infections
  • Public Health Significance: Genital tract infections have significant public health implications due to their high prevalence, potential for serious complications, and the risk of transmission to others
  • Antibiotic Resistance: The increasing prevalence of antibiotic resistance in N. gonorrhoeae is a major concern, and it can complicate treatment
  • Reporting: Laboratories are often required to report positive results for certain STIs (e.g., gonorrhea, chlamydia) to public health authorities for surveillance and control purposes

Key Terms

  • Etiology: The cause of a disease
  • Transmission: The process by which an infectious agent spreads
  • Virulence: The degree of pathogenicity or the ability of an organism to cause disease
  • Virulence Factors: Characteristics of an organism that contribute to its ability to cause disease
  • Pili: Hair-like structures on the surface of bacteria that mediate attachment
  • Opa Proteins: Surface proteins that promote bacterial adherence
  • Antigenic Variation: The ability of an organism to alter its surface antigens, making it difficult for the immune system to recognize and eliminate the pathogen
  • Endotoxin: A toxin (e.g., LOS) that is a component of the bacterial cell wall
  • IgA Protease: An enzyme that cleaves IgA antibodies
  • Phagocytosis: The process by which cells engulf and destroy bacteria
  • Complement Activation: A series of proteins in the blood that help to kill bacteria
  • Disseminated Infection: Spread of an infection to multiple sites in the body
  • Pelvic Inflammatory Disease (PID): An infection of the female reproductive organs
  • Ophthalmia Neonatorum: An eye infection in newborns
  • Elementary Body (EB): The infectious form of Chlamydia trachomatis
  • Reticulate Body (RB): The metabolically active, replicating form of Chlamydia trachomatis
  • Inclusion: A vacuole inside a host cell that contains bacteria
  • Cytokine: A signaling molecule that regulates the immune response
  • Capsule: A protective layer surrounding some bacteria
  • Serotype: A distinct variation within a species based on surface antigens
  • CAMP Test: A test used to identify Streptococcus agalactiae
  • Adhesins: Surface proteins that mediate attachment to host cells
  • Non-Gonococcal Urethritis (NGU): Urethritis not caused by Neisseria gonorrhoeae
  • Asymptomatic: Without symptoms
  • Carrier: An individual who harbors a pathogen but does not have symptoms
  • Co-infection: The presence of multiple infections
  • Risk Factors: Factors that increase the likelihood of developing a disease
  • Public Health: The health of the population as a whole
  • Antibiotic Resistance: The ability of bacteria to survive in the presence of antibiotics
  • Antigen: A substance that triggers an immune response