Not to be confused with Haemophilia
|Haemophilus influenzae on a blood agar plate.|
Winslow et al. 1917
Haemophilus is a genus of Gram-negative, pleomorphic, coccobacilli bacteria belonging to the Pasteurellaceae family. 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 species such as H. influenzae—a cause of sepsis and bacterial meningitis in young children—and H. ducreyi, the causative agent of chancroid. All members are either aerobic or facultatively anaerobic.
Members of the Haemophilus genus will not grow on blood agar plates, as all species require at least one of these blood factors for growth: hemin (factor X) and/or nicotinamide adenine dinucleotide (factor V). Chocolate agar is an excellent Haemophilus growth medium, as it allows for increased accessibility to these factors. 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 Staphylococcus colonies because the metabolism of Staphylococcus produces the necessary blood factor byproducts required for Haemophilus growth.
- Holt JG (editor) (1994). Bergey's Manual of Determinative Bacteriology (9th ed.). Williams & Wilkins. ISBN 0-683-00603-7.
- Kuhnert P; Christensen H (editors). (2008). Pasteurellaceae: Biology, Genomics and Molecular Aspects. Caister Academic Press. ISBN 978-1-904455-34-9. .
- Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9.
- Haemophilus chapter in Baron's Medical Microbiology (online at the NCBI bookshelf).
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