Haemophilus and HACEK Group

Haemophilus Intro - X & V Factor Fiends

• Gram-negative coccobacilli or pleomorphic rods.
• Require growth factors for culture:
  • X factor (hemin).
  • V factor (NAD - Nicotinamide Adenine Dinucleotide).
• Grow on chocolate agar (provides both X and V factors).
• Exhibit satellitism on blood agar: grow around Staphylococcus aureus colonies.
  • S. aureus lyses RBCs (releasing X factor) and synthesizes V factor.

⭐ Haemophilus means 'blood-loving', referring to its requirement for blood-derived factors for growth.

H. influenzae - Tiny Troublemaker Tyke

• Gram-negative coccobacillus.
• Virulence: Polysaccharide capsule (type b - Hib: Polyribitol Ribose Phosphate - PRP), IgA protease, pili, LOS.
• Diseases:
  • Hib (Encapsulated): Meningitis (3m-3y), Acute Epiglottitis (thumbprint sign), Septic Arthritis, Pneumonia, Cellulitis.
  • NTHi (Non-typeable): Otitis media, Sinusitis, Bronchitis, Conjunctivitis, Pneumonia (COPD).
• Hib Vaccine: Conjugate (PRP-protein), T-cell dependent, effective <2 years.

⭐ Acute epiglottitis (Hib): dysphagia, drooling, distress, inspiratory stridor; cherry-red epiglottis.

Other Haemophilus - Niche Nuisance Crew

• H. ducreyi:
  • Causes chancroid: painful genital ulcer (ragged edges), tender suppurative inguinal lymphadenopathy (buboes).
  • Gram stain: 'school of fish'/'railroad track' coccobacilli.
  • Requires special culture media.

  ⭐ H. ducreyi causes a PAINFUL genital ulcer, differentiating it from syphilis (painless chancre).

• H. aegyptius (Koch-Weeks bacillus):
  • Acute purulent conjunctivitis ('pink eye').
  • Brazilian Purpuric Fever (BPF) by certain strains: fulminant pediatric septicemia.
• H. parainfluenzae:
  • Normal Upper Respiratory Tract (URT) flora.
  • Opportunistic: endocarditis, otitis media.

HACEK Group Intro - Endocarditis Entourage

• 📌 Haemophilus species (often Aggregatibacter), Aggregatibacter actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella kingae.
• General characteristics: Gram-negative bacilli/coccobacilli; fastidious (specific growth needs), slow-growing; capnophilic (enhanced growth in 5-10% CO₂).
• Normal flora: Oropharynx.
• Primary clinical significance: Subacute bacterial endocarditis (SBE), particularly in patients with pre-existing valvular damage or prosthetic valves. Characterized by large vegetations and frequent systemic emboli.

⭐ HACEK organisms are a significant cause of culture-negative or slow-to-detect infective endocarditis.

HACEK Members & Dx/Tx - Slow-Grow Pathogen Parade

• HACEK: Gram-negative, fastidious, slow-growing coccobacilli. Cause culture-negative endocarditis (large vegetations).
• Key Features:
  • Aggregatibacter spp.: Endocarditis. A. actinomycetemcomitans (Aa): star-shaped colonies, juvenile periodontitis.
  • Cardiobacterium hominis: Pleomorphic (rosettes), endocarditis.
  • Eikenella corrodens: Pits agar, bleach odor. Human bites, clenched-fist injuries.
  • Kingella kingae: β-hemolytic. Osteoarticular (kids <4 yrs), endocarditis.
• Lab Dx: Prolonged blood culture (1-3 wks). Notify lab.
• Tx: Ceftriaxone, Amp-Sulbactam. β-lactamase possible.

⭐ Eikenella corrodens: notorious for infections post human bite/clenched-fist injuries.

High‑Yield Points - ⚡ Biggest Takeaways

• H. influenzae type b (Hib): Causes meningitis, epiglottitis (unvaccinated); PRP capsule is key virulence factor.
• Requires X & V factors; grows on chocolate agar; shows satellitism.
• H. ducreyi: Causes painful chancroid and inguinal buboes.
• HACEK group: Fastidious Gram-negatives causing culture-negative endocarditis, often on damaged valves.
• Eikenella corrodens: Linked to human bite wounds; pits agar, bleach-like odor.
• Kingella kingae: Causes septic arthritis and osteomyelitis in young children.