Ans. b. Meningitis (Ref: Ananthanarayan 8/e p331)Meningitis is not caused by non-typable Hib.'Diseases due to H. influenza may be considered under two groups, invasive and noninvasive.In the first group, the bacillus acts as a primary pathogen, causing acute invasive infections. The bacilli spread through blood, being protected from phagocytes by their capsule. Haemophilus meningitis is the most important infection in this group, others being laryngoepiglottits, conjunctivitis, bacteremia, pneumonia, arthritis, endocarditis and pericarditis. These infections are usually seen in children and are caused by the capsulated strains, type b accounting for most cases. In the second group, the bacillus spreads by local invasion along mucosal surfaces and causes secondary or superadded infections, usually of the respiratory tract. These include otitis media, sinusitis and exacerbations of chronic bronchitis and bronchiectasis. These are usually seen in adults and are often caused the non-capsulated strains. Ananthanarayan 8/e p331Hemophilus influenzae (Pfeiffer's bacillus)Morphology:Non-motile. non-sporing, oxidase positive, gram negative bacilliQCapsulated coccobacilli shows pleomorphismQStained by Loeffler's methylene blueQ or Dilute carbol fuschinQDivided into 8 biotypes on the basis of indole production, urease and ornithine decarboxyalse activityQCulture:Fildes agar is the best for primary' isolationQOn Levinthal's mediumQ, capsulated strains show distinctive iridesecenceRequires both X factor (heat stable hemin) and V factor (heat labile coenzyme present in RBC), so heated or boiled blood agar is superior to plain agarQShows 'Satellitism'Q (dependence on V factor) when S. aureus is streaked across the blood agar.Antigenic properties:Hemophilus influenzae is the first free living organism whose complete genome is sequencedQThere are three major surface antigen- the capsular polysaccharide, the outer membrane protein, and lipo-oligosaccharideQHemophilus influenzae (Pfeiffer's bacillus)Major antigenic determinant is capsular polysaccharideQ based on which, it is typed into six capsular typesMost isolates from acute invasive infections belong to type bQType b capsule has unique structure containing pentose sugar (ribose and ribitol) in the form of polyribosyl ribitol phosphate (PRP)Q instead of hexose and hexosaminesTypes of Hemophilus influenzaeInvasiveNon-invasive* Bacillus acts as a primary pathogen, causing acute invasive infectionsQ* Bacilli spread through blood, being protected from phagocytes by their capsuleQ.* Meningitis is the most important infection in this group.* Others: Laryngoepiglottits, conjunctivitis, bacteremia, pneumonia, arthritis, endocarditis and pericarditis.* Usually seen in children* Caused by the capsulated strains, type b accounting for most cases* Bacillus spreads by local invasion along mucosal surfacesQ* Causes secondary or superadded infections, usually of the respiratory tractQ.* These include otitis media, sinusitis and exacerbations of chronic bronchitis and bronchiectasisQ.* Usually seen in adultsQ* Caused by non-capsulated strainsQClinical Features:Meningitis and respiratory tract infection are the most common presentationQMeningitisMost frequently caused by biotype-1QOccur in childrenQ due to absence of PRP antibodiesSubdural effusionQ is the MC complicationDOC is ceftriaxone or cefotaximeQRemember:Hemophilus influenzae is called Pfeiffers bacillus but Pfieffer's phenomenon (bacteriolysis in vivo) is associated with V. choleraQ (cholera vibrios were lysed when injected intraperitoneally into specifically immunized guinea pigs)