Haemophilus

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iHaemophilus

Scientific classification

Kingdom:	Bacteria
Phylum:	Proteobacteria
Class:	Gamma Proteobacteria
Order:	Pasteurellales
Family:	Pasteurellaceae
Genus:	Haemophilus Winslow et al. 1917

Species

H. aegyptius
H. aphrophilus
H. avium
H. ducreyi
H. felis
H. haemolyticus
H. influenzae
H. paracuniculus
H. parahaemolyticus
H. pittmaniae
etc.

Haemophilus is a genus of Gram-negative, pleomorphic, coccobacilli bacteria.<ref name=Bergeys>Holt JG (editor) (1994). Bergey's Manual of Determinative Bacteriology, 9th ed., Williams & Wilkins. ISBN 0-683-00603-7.</ref> While Haemophilus bacteria are typically small coccobacilli, they are categorized as pleomorphic bacteria because of the wide range of shapes they occasionally assume. The genus includes commensal organisms along with some significant pathogenic strains such as H. influenzae—a cause of septicemia and bacterial meningitis in young children—and H. ducreyi, the causative agent of chancroid. All members are either aerobic or facultatively anaerobic.

Haemophilus species are classified by characterization of their capsule: seven serogroups exist, a—f and e′.<ref name=Barron>Musher DM (1996). Haemophilus Species. In: Baron's Medical Microbiology (Barron S et al, eds.), 4th ed., Univ of Texas Medical Branch. (via NCBI Bookshelf) ISBN 0-9631172-1-1.</ref> Capsule type b (Hib) is the most clinically significant because of its virulence.

[edit] Metabolism

Members of the Haemophilus genus are typically cultured on blood agar plates as all species require at least one of the following blood factors for growth: hemin (factor X) and/or nicatinamide adenine dinucleotide (factor V). Chocolate agar is an excellent Haemophilus growth media as it allows for increased accessibility to these factors.<ref name=Sherris>Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology, 4th ed., McGraw Hill. ISBN 0-8385-8529-9.</ref> Alternatively, Haemophilus is sometimes cultured using the "Staph streak" technique: both Staphylococcus and Haemophilus organisms are cultured together on a single blood agar plate. In this case, Haemophilus colonies will frequently grow in small "satellite" colonies around the larger Staphylococccus colonies because the metabolism of Staphylococcus produces the necessary blood factor by-products required for Haemophilus growth.