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Overview
The Haemophilus species inhabit the mucosal epithelium of the upper respiratory and lower genital tract. They cause suppurative infections due to the release of pro-inflammatory cytokines, released from macrophages. This includes serofibrinous to fibrinopurative infections of the lungs, body cavities and joints. The colonisation of meningeal vessels causes a thrombotic vasculitis leading to encephalitis and meningitis.
Characteristics
Haemophilus species are morphologically variable Gram-negative bacilli, ranging from short rods to long filaments. They are facultative anaerobes and are typically oxidase positive. They depend on beta-nicotinamide adenine dinucleotide (NAD) (V factor) and/or Haemin (X fector) for growth.
Heated blood agar (Chocolate Agar) is required for growth of NAD-dependent strains. Haemin-dependent strains grow on Blood Agar but do not grow on MacConkey agar.