Notes on Neisseria and Listeria

Neisseria Species

  • Overview

    • Gram-negative, kidney bean-shaped diplococci.

    • Aerobic, capnophilic bacteria.

    • Prefer high CO₂ concentrations and optimal growth in moist atmosphere.

Virulence Factors of Neisseria

  • Capsule

    • Prevents phagocytosis, aiding in survival within the host.

  • Pili

    • Facilitates attachment and genetic exchange between cells, also prevents phagocytosis.

  • Cell Wall Proteins

    • Contributes to evasion from the host immune response.

  • Endotoxins

    • Mediate damage to host tissues, enhancing virulence.

  • IgA Protease

    • Cleaves IgA on mucosal surfaces, allowing for further invasion.

Pathogenic Neisseria Species

  • Neisseria gonorrhoeae

    • Frank pathogen responsible for gonorrhea.

    • Symptoms: acute pyogenic infection, urethritis, purulent discharge, dysuria.

    • Short incubation period of 2 to 7 days.

    • Complications in males: prostatitis, epididymitis.

    • Asymptomatic carriers are rare in men (3-5%).

  • Neisseria meningitidis

    • Frank pathogen causing epidemic and endemic meningitis, meningococcemia.

    • Found in nasopharynx/oropharynx of 3-30% of asymptomatic individuals.

    • Source of infection through respiratory droplets from carriers.

    • Symptoms include fever, headache, stiff neck, with potential petechial skin lesions leading to bacteremia.

Complications Associated with Neisseria gonorrhoeae

  • In Women

    • Untreated gonococcal cervicitis may lead to pelvic inflammatory disease (PID), causing sterility or ectopic pregnancy.

  • In Newborns

    • Risk of ophthalmia neonatorum during vaginal delivery, potentially causing blindness if untreated.

Other Neisseria/Related Species

  • Neisseria catarrhalis (Branhamella)

    • Normal flora of respiratory tract causing opportunistic infections like pneumonia, sinusitis, and otitis media.

Listeria monocytogenes

  • Overview

    • Gram-positive, aerobic, non-spore forming bacilli.

    • Found in soil, water, vegetation, and animal products.

Virulence Factors

  • Hemolysin (Listeriolysin O)

    • Damages cell membranes to evade killing by host defense.

  • Catalase, Superoxide Dismutase, Phospholipase C

    • Enzymatic components that enhance survival.

Clinical Manifestations

  • In Pregnant Women

    • Increased risk during the 3rd trimester; symptoms can resemble flu (fever, headache, myalgia).

    • Can lead to spontaneous abortion or stillbirth.

  • Neonatal Listeriosis

    • Two forms:

    • Early-Onset: Intrauterine infection resulting in symptoms at or shortly after birth.

    • Late-Onset: Appears several days to weeks after birth.

    • High mortality rate in untreated neonates (50% fatality).

Transmission

  • Occurs via consumption of contaminated foods: milk, cheese, meats, coleslaw, fruits, fish.

  • Infection may be self-limiting if the source is eliminated (e.g., birth).