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HAEMOPHILUS INFLUENZAE osms.it/haemophilus-influenzae PATHOLOGY & CAUSES ▪ Haemophilus: blood loving ▪ Characteristics ▫ Catalase, oxidase positive ▪ Virulence factors ▫ Polysaccharide capsule: prevents phagocytosis; causes ciliostasis, evades mucociliary clearance of bacteria; classiﬁed into six serotypes based on capsular antigens (A, B, C, D, E, F); some strains unencapsulated (AKA nontypable); most clinical isolates Haemophilus inﬂuenzae type B (Hib)/ nontypable ▫ IgA1 protease, adherence factors, antigenic variation, bioﬁlm formation ▪ Gram stain of exudate shows bacteria arranged in chains (“school of ﬁsh”) ▪ Culture ▫ Isolation specimen: cerebrospinal ﬂuid (CSF), urine, serum, synovial ﬂuid ▫ Media: chocolate agar/Fildes medium (hemolyzed erythrocytes) with factor X (hemin), V (nicotinamide adenine dinucleotide) supplementation in aerobic, only factor X supplementation in anaerobic environment ▫ Convex, smooth, grey/transparent colonies ▪ Gram-negative coccobacillus → meningitis, respiratory tract infections ▪ Nontypeable strains colonize nasopharynx of 40–80% children, adults ▪ Hib colonizes 3–5% children TYPES Hib ▪ Epiglottitis in older children, adults ▪ Cellulitis (most common in young children) ▪ Pneumonia ▫ Sometimes with meningitis, epiglottitis ▪ Meningitis, septic arthritis, osteomyelitis 354 OSMOSIS.ORG Nontypable ▪ Less invasive due to lack of capsule; causes mild localized respiratory tract disease in children, adults ▪ More severe in immunocompromised/ predisposed individuals ▫ Otitis media, sinusitis, purulent conjunctivitis, bacterial pneumonia in children (in low-income countries), neonatal bacteremia ▫ Community-acquired pneumonia in adults with underlying lung disease ▫ Exacerbation of chronic obstructive pulmonary disease (COPD) ▫ Meningitis in individuals with predisposition/conditions causing leakage of CSF ﬂuid (e.g. sinusitis, otitis media, head trauma) Transmission ▪ Direct contact with respiratory tract secretions/airborne respiratory droplets Pathogenesis ▪ Inoculation → passage through upper respiratory tract → adherence to respiratory epithelium, LPS inhibits mucociliary clearance → colonization spreads throughout respiratory tract → sinuses, otitis, pneumonia ▪ IgA1 protease, antigenic variation, paracytosis, bioﬁlm formation → perseverance of bacteria RISK FACTORS ▪ Viral infection, sickle-cell disease, asplenia, HIV infection, malignancies, congenital deﬁciencies of complement components COMPLICATIONS ▪ Nontypable in neonates, immunocompromised individuals → septicemia, meningitis, septic arthritis ▪ Hib meningitis → subdural effusion/ empyema; ischemic/hemorrhagic cortical

Haemophilus influenzae

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Haemophilus influenzae

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(Encapsulated/Unencapsulated) strains of Haemophilus influenzae are most often associated with pneumonia.

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A 28-year-old woman comes to the clinic because of purulent, bilateral eye discharge that began this morning. She is a medical student and uses contact lenses. Culture and microscopic investigation show gram-negative, oxidase positive, catalase positive coccobacilli. Which of the following is the most likely microbe responsible for this patient's symptoms?

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