Gram-Negative Cocci and Neisseria Pathogens

Gram-Negative Cocci

• Gram-negative cocci are usually diplococci
• Catalase positive
• Oxidase positive
• Most grow on sheep and chocolate agar
• Identified by CTA sugar fermentation patterns
• Aerobic
• Nonmotile
• Non-spore-forming

Pathogenicity and Host Range

• Table 17-1 shows pathogenicity and host range for Neisseria and Moraxella species.
• Table 17-5 details characteristics of significant species
• N. gonorrhoeae: primary pathogen, humans only
• N. meningitidis: primary pathogen, humans only
• N. lactamica, N. cinerea, N. sicca, N. flavescens: opportunistic pathogens, warm-blooded animals; N. subflava, N. mucosa: opportunistic pathogens, warm-blooded animals
• Moraxella catarrhalis: opportunistic pathogen, humans only

Cellular Structure of Pathogenic Neisseria

• The cell wall of pathogenic Neisseria has components like LOS and pili

Virulence Factors of Neisseria

• Pili aid in attachment and prevent phagocytosis; exchange of genetic material
• Capsule prevents phagocytosis
• Cell-outer membrane proteins cause antigenic variation and prevent effective antibody binding
• Major outer membrane porin proteins (Por, Opa, Rmp) block host serum bactericidal action and facilitate adherence
• Lipooligosaccharides (LOS) lead to tissue damage
• IgA protease cleaves IgA at mucosal surfaces
• Receptors for human transferrin allow for iron competition

Neisseria meningitidis

• Found only in humans
• Normal flora of the upper respiratory tract and urogenital tracts
• May be a commensal or an invasive pathogen
• Infections include endemic and epidemic meningitis and meningococcemia

Neisseria meningitidis: Epidemiology

• Spread through crowded living conditions (military recruits, college students)
• Transmission via respiratory droplets from carriers to new hosts
• Highest incidence in infants and adolescents
• Populations at risk of invasive disease include asplenic patients and those with complement deficiencies
• Factors contributing to spread include crowded living conditions and military/college settings

Neisseria meningitidis: Clinical Infections

• Symptoms include abrupt onset of headaches, stiff neck, fever, etc.
• Death may occur within 12-48 hours after symptoms appear
• Meningococcemia is characterized by purpuric skin lesions and may or may not accompany meningitis.
• Complications may include arthritis, pericarditis, pneumonia, conjuntivitis, and urethritis
• Can lead to Waterhouse-Friderichsen syndrome (adrenal hemorrhage)

Laboratory Diagnosis of Neisseria meningitidis

• Specimens like CSF, blood, or nasopharyngeal swabs are used
• Need to grow on SBA and chocolate agar requiring CO2
• Identification is based on colony morphology, microscopic morphology, and oxidase test

Neisseria gonorrhoeae

• Humans are the only natural hosts for gonorrhea
• Urogenital tract, pharynx, and conjunctiva of the eye are common infection sites
• Infections in men: Acute urethritis, Prostatitis, epididymitis
• Infections in women: Endocervix (common), cervical or vaginal discharge, dysuria, lower abdominal pain, vaginal bleeding; untreated infections can lead to PID and sterility; complications may also include ectopic pregnancy and/or perihepatitis (Fitz-Hugh-Curtis syndrome)
• Disseminated infections can lead to purulent arthritis and septicemia
• Blood-borne disseminated infections can cause fever and rash on extremities.

Neisseria gonorrhoeae: Identification

• Direct microscopic examinations use Gram stains to look for gram-negative intracellular/extracellular diplococci
• Cultures are crucial for confirmation using enriched media (like Modified Thayer-Martin (MTM) agar), with 35-37°C incubation and 3-10% CO2

Neisseria gonorrhoeae: Treatment and Resistance

• Penicillin for confirmed meningitis use
• Chloramphenicol, third-generation cephalosporins, azithromycin, ciprofloxacin, or sulfonamides for penicillin-allergic patients.
• Chemoprophylaxis with rifampin, ciprofloxacin, or sulfonamides may be used for people in close contact.
• Antimicrobial-resistant strains exist (PPNG, CMRNG, TRNG)
• Fluoroquinolones are no longer recommended due to resistance.
• Ceftriaxone is currently the recommended treatment.

Nonpathogenic Neisseria Species

• Gram-negative cocci
• Normal parts of upper respiratory microbiota.
• Include N. bacilliformis, N. canis, N. cinerea, N. flavescens, N. elongata, N. mucosa, N. ovis, N. shayeganii, N. sicca, N. subflava, N. wadsworthii, N. zoodegmatis
• Clinical diagnosis often involves growth in culture

Moraxella Species

• Family Moraxellaceae
• 22 species (constantly revised), identified by being catalase-positive and oxidase-positive
• Found in the upper respiratory tract as normal microbiota
• One commercially important species is Moraxella catarrhalis, found in children and older adults and generally identified by being catalase positive and oxidase positive