Gram-Negative Cocci and Meningitis Overview

Gram-Negative Cocci

• Gram-negative cocci are a group of bacteria that includes Neisseria, Moraxella, and Kingella.
• They are oxidase-positive except for Acinetobacter.
• Neisseria and Moraxella are catalase-positive, while Kingella are catalase-negative.

Neisseria meningitidis (Meningococcus)

• Habitat: Human upper respiratory tract
• Diseases:
  • Meningitis: Inflammation of the meninges (brain and spinal cord).
  • Meningococcemia: Bacterial infection of the bloodstream.
• Transmission: Via respiratory droplets.
• Diagnosis:
  • Gram-negative "kidney-bean" shaped diplococci.
  • Oxidase-positive.
  • Large polysaccharide capsule.
• Risk factors for meningitis:
  • Skipping vaccinations.
  • Age.
  • Living in a community setting.
  • Pregnancy.
  • Weakened immune system.
  • Environmental factors like low humidity.
• Pathogenesis:
  • Reaches the meninges via the bloodstream.
  • Endotoxin in cell wall causes symptoms of septic shock.
  • Produces IgA protease.
  • Capsule is antiphagocytic.
  • Characteristic skin rash (purpura) of meningococcal septicemia.
• Treatment:
  • Penicillin G (no significant resistance).
• Prevention:
  • Vaccine contains capsular polysaccharides of strains A, C, Y & W-135.
    • Two types exist: one with polysaccharides coupled to a carrier protein (diphtheria toxoid) and another with only polysaccharides.
  • Rifampin or ciprofloxacin given to close contacts to decrease oropharyngeal carriage.

Neisseria gonorrhoeae (Gonococcus)

• Habitat: Human genital tract.
• Diseases:
  • Gonorrhea.
  • Neonatal conjunctivitis.
  • Pelvic inflammatory disease.
• Transmission:
  • Adults: Sexual contact.
  • Neonates: During birth.
• Diagnosis:
  • Gram-negative "kidney-bean" shaped diplococci.
  • Oxidase-positive.
  • Insignificant capsule.
• Treatment:
  • Ceftriaxone for uncomplicated cases.
• Prevention:
  • No drug or vaccine.
  • Trace contacts and treat to interrupt transmission.
  • Treat newborns' eyes with erythromycin ointment or silver nitrate to prevent conjunctivitis.

Moraxella catarrhalis

• Characteristic: Small coccobacillary gram-negative rod.
• Habitat: Found only in humans.
• Diseases:
  • Otitis media & sinusitis in children.
  • Bronchitis & pneumonia in older people with chronic obstructive pulmonary disease.
• Transmission: Respiratory aerosol.

Veillonella parvula

• Characteristic: Anaerobic gram-negative diplococcus.
• Habitat: Normal flora of the mouth, colon, and vagina.
• Disease: A rare opportunistic pathogen that causes abscesses of the sinuses, tonsils, and brain.
• Infection type: Usually part of mixed anaerobic infections.

Explore the characteristics of gram-negative cocci, focusing on the genus Neisseria and its significance in meningitis. This quiz details the habitat, diseases caused by Neisseria meningitidis, transmission methods, and key risk factors. Test your knowledge on the pathogenesis and diagnosis of this important bacterial infection.