Haemophilus influenzae
One-Sentence Definition
Haemophilus influenzae is a fastidious Gram-negative coccobacillus causing otitis, sinusitis, pneumonia, and — historically via type b capsule — pediatric meningitis; conjugate vaccination transformed invasive Hib epidemiology.
Taxonomy & Morphology
- Gram-negative coccobacillus; requires X (hemin) and/or V (NAD) factors
- Grows on chocolate agar; satellite growth around S. aureus on blood agar
- Typeable (capsule a–f, Hib = type b) vs nontypeable (NTHi, unencapsulated)
Virulence Highlights
- Hib Capsule (PRP) — major invasive disease driver pre-vaccine
- NTHi: adhesins, biofilm in middle ear / airways (Biofilm)
- IgA protease; LOS endotoxin
Clinical Syndromes
- Hib (unvaccinated): meningitis, epiglottitis, bacteremia, septic arthritis
- NTHi: otitis media, sinusitis, COPD exacerbations, community pneumonia
- Non-b encapsulated types (a, e, f) cause residual invasive disease
Diagnosis
- Culture on chocolate; MALDI; CSF/blood PCR panels
- Capsule typing for invasive isolates (surveillance)
Treatment Notes (conceptual)
- Empiric meningitis regimens cover Hib; definitive therapy by AST
- β-lactamase-producing strains common — ampicillin resistance historically important
- Vaccination prevents most Hib disease (Vaccination)
AMR
- TEM β-lactamases → ampicillin resistance
- BLNAR (β-lactamase-negative ampicillin-resistant) via PBP changes
- Watch β-lactamase + altered PBP combinations
Genomics & Computational Notes
- Capsule loci and BLNAR mutations detectable by WGS
- NTHi population structure highly diverse — recombination (Recombination in Bacterial Phylogenies)
Related Notes
- Bacterial Meningitis · Community-Acquired Pneumonia · Capsule · Neisseria meningitidis
- MOCs: MOC - Bacteriology · MOC - Diseases by System · MOC - Public Health & Epidemiology
Active Recall
- X and V factors — which media supplies both?
- Hib vs NTHi — typical disease patterns after mass vaccination?
- What does BLNAR mean?