Haemophilus species - Overview

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Phylum Proteobacteria
Class Gamma Proteobacteria
Order Pasteurellales
Family Pasteurellaceae
Genus Haemophilus
Haemophilus influenzae. ((Bobjgalindo 2005, Wikimedia commons)


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.


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.

See here for a list of Haemophilus species

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