All of the following are true regarding Haemophilus influenzae EXCEPT:

Explanation

## Haemophilus influenzae: Key Structural & Biochemical Features **Key Point:** Not all H. influenzae isolates produce beta-lactamase. Ampicillin resistance occurs via two mechanisms: beta-lactamase production (BLPRO) and altered penicillin-binding proteins (BLNAR — beta-lactamase negative ampicillin-resistant). BLNAR strains are increasingly prevalent and do NOT produce beta-lactamase, yet remain ampicillin-resistant. ### Growth Requirements & Identification | Feature | Details | |---------|----------| | **Gram stain** | Gram-negative coccobacillus (pleomorphic) | | **X factor** | Hemin (iron-containing porphyrin) | | **V factor** | NAD^+^ (nicotinamide adenine dinucleotide) | | **Culture media** | Chocolate agar (heated blood provides both factors); NOT on plain blood agar | | **Growth** | Fastidious; requires enriched media | ### Capsular Polysaccharide **High-Yield:** Type b H. influenzae (Hib) capsule is composed of **polyribose phosphate (PRP)** — a polymer of ribose and phosphate. This is the target of the conjugate Hib vaccine (PRP-protein conjugate). ### Antibiotic Resistance Mechanisms 1. **BLPRO (Beta-Lactamase Producing):** Produces TEM or ROB-1 beta-lactamase; susceptible to beta-lactamase inhibitors (amoxicillin-clavulanate, ampicillin-sulbactam) 2. **BLNAR (Beta-Lactamase Negative Ampicillin-Resistant):** Altered PBPs; NOT detected by standard beta-lactamase testing; requires susceptibility testing 3. **BLNAR-BLPRO:** Dual resistance **Clinical Pearl:** Ampicillin cannot be assumed effective in H. influenzae without susceptibility testing. Third-generation cephalosporins (ceftriaxone, cefotaxime) remain reliable. ### Epidemiology & Reservoir **Key Point:** H. influenzae is an **obligate human pathogen** — no animal reservoir. Transmission is via respiratory droplets. Colonization of the nasopharynx is common; invasive disease occurs when mucosal defenses are breached. **Mnemonic — H. influenzae Risk Factors:** **ASPLENIC** = Asplenia, Sickle cell, Premature infants, Low immunoglobulin, Epiglottitis predisposition, Neonate, Immunocompromised, Chronic lung disease