24. Gram-negative bacteria causing air-borne infections. Haemophilus influenzae. Morphology, biology, antigenic structure. Pathogenic factors. Diseases. Immunity. Microbiological diagnosis. Specific prophylaxis and therapy. The causative agent of Whooping cough (Bordetella pertussis). Morphology, biology. Pathogenic factors. Pathogenicity and immunity. Microbiological diagnosis. Specific prophylaxis and therapy. Neisseria meningitidis. Morphology, biology. Pathogenic factors. Pathogenicity and clinical forms of meningococcal infection. Immunity. Microbiological diagnosis. Specific prophylaxis and therapy. Neisseria gonorrhoeae. Morphology, biology. Pathogenic factors. Pathogenicity and clinical forms of gonococcal infection. Immunity. Microbiological diagnosis. Prophylaxis and therapy.

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. Invasive (mostly type b):

• Meningitis (especially in unvaccinated children)
• Epiglottitis (acute, life-threatening airway obstruction)
• Septic arthritis, cellulitis, bacteremia

2. Localized (usually non-typeable strains):

• Otitis media
• Sinusitis
• Conjunctivitis
• Bronchitis & pneumonia (especially in COPD patients)

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