Microbiology · MU Sofia

62. Haemophilus influenzae. Moraxella catrrhalis.

Covers Haemophilus influenzae, first its growth requirements (factors X and V, chocolate agar, CO2) and virulence factors, then invasive versus localised disease, pathogenesis, laboratory diagnosis, treatment and the Hib vaccine. It then turns to Moraxella catarrhalis, outlining its Neisseria-like appearance, β-lactamase production, respiratory infections, diagnosis, antibiotic susceptibility and prevention. Tables summarise virulence factors, Moraxella's diseases and diagnostic steps.

Inside: 3 sections · 8 labelled pictures · 4 tables · 13 flashcards · 4 min

Topic 62 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 3 sections, about 444 words (4 min of reading), with 13 flashcards.

In this note

  1. Haemophilus influenzae. Moraxella catarrhalis
  2. Haemophilus influenzae
  3. Moraxella catarrhalis

Haemophilus influenzae

General Characteristics

  • Gram stain: Gram-negative, small pleomorphic coccobacilli
  • Oxygen: Aerobic / Facultatively anaerobic
  • Motility: Non-motile
  • Spores: Non-spore-forming
  • Capsule: Present in typeable strains (especially type b), anti-phagocytic polysaccharide capsule
  • Growth requirements:
  • Factor X (hemin) – heat-stable
  • Factor V (NAD) – heat-labile
  • Grows on chocolate agar, not on blood agar (unless "satellitism" with S. aureus)
  • Requires 5–10% CO₂ atmosphere
  • Colonies: Small, round, translucent after 24h incubation at 35–37°C

Virulence Factors

Diseases Caused

  1. 1. Invasive (mostly type b):
  • Meningitis (especially in unvaccinated children)
  • Epiglottitis (acute, life-threatening airway obstruction)
  • Septic arthritis, cellulitis, bacteremia
  1. 2. Localized (usually non-typeable strains):
  • Otitis media
  • Sinusitis
  • Conjunctivitis
  • Bronchitis & pneumonia (especially in COPD patients)
  1. 3. Other rare cases:
  • Endocarditis
  • Osteomyelitis

Pathogenesis

  • Enters via respiratory tract
  • Attaches using pili
  • Type b capsule evades phagocytosis, spreads hematogenously
  • IgA protease aids mucosal colonization
  • Can cross blood-brain barrier → meningitis

Laboratory Diagnosis

  • Specimens: Blood, CSF, sputum, middle ear aspirates, nasopharyngeal swab
  • Microscopy: Gram-negative coccobacilli, seen in Gram and Loeffler stains
  • Culture:
  • Chocolate agar (contains X + V factors), 24h, 35–37°C, CO₂ enriched
  • Satellite phenomenon: grows near S. aureus on blood agar
  • Serology: Latex agglutination to detect capsular antigens (esp. in CSF)
  • Biochemical:
  • Catalase: +
  • Glucose fermentation: +
  • Rapid tests: PCR available for strain typing in critical settings

Treatment

  • First-line for serious infections:
  • 3rd gen cephalosporins (e.g., ceftriaxone, cefotaxime)
  • Mild infections:
  • Amoxicillin-clavulanate, macrolides (azithromycin), fluoroquinolones
  • Note: Many strains produce β-lactamase – test for resistance

Prevention

  • Vaccine:
  • Hib (Haemophilus influenzae type b) conjugate vaccine
  • Contains polyribosylribitol phosphate (PRP) conjugated to tetanus toxoid
  • Administered in infancy (part of routine immunization)
  • Chemoprophylaxis: Rifampin for close contacts of invasive Hib cases
  • General:
  • Proper hygiene
  • Avoid crowding in daycare centers
  • Early vaccination coverage

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