20 plus species including:


Haemophilus aegyptius
Haemophilus aphrophilus (recently reclassified as Aggregatibacter aphrophilus )
Haemophilus avium
Haemophilus ducreyi
Haemophilus haemoglobinophilus
Haemophilus haemolyticus
Haemophilus influenzae
Haemophilus paracuniculus
Haemophilus paragallinarum
Haemophilus parahaemolyticus
Haemophilus parahrohaemolyticus
Haemophilus parainfluenzae
Haemophilus paraphrophilus
Haemophilus parasuis
Haemophilus pleuropneumoniae
Haemophilus segnis (recently reclassified as Aggregatibacter segnis )


Gram Stain: Negative.
Morphology: Pleomorphic, spherical, oval, coccobacilli and rod-shaped; sometimes forming threads or filaments.
Size: 0.4-1.0 micrometers in diameter by 2.0 micrometers in length.
Motility: Non-motile.
Capsules: Yes. Responsible for pathogenesis in some species, aids in the determination of type specificity, and production of anti-infective immunity.
Spores: None.
Other: Some Haemophilus spp. produce "mouse-nest" like odors.


Surface colonies of Haemophilus species on sufficiently rich media are usually non-pigmented or slightly yellowish, flat, and convex. Most species produce smooth colonies. Other strains produce slight granular growth.



Facultatively anaerobic; fermentative and respiratory type metabolism. Glucose, not lactose, is fermented. Chemoorganotrophic. Aerobic growth in H. influenzae needs X-factor (hemin) and V-factor (NAD) or (NADP), both found in lysed red blood cells. All species can attack carbohydrates fermentatively, yielding various acids (i.e. acetic, lactic, and succinic) as end products in glucose broth.


These organisms are strictly parasitic. Obligate parasites on the mucous membranes of the upper respiratory tract, mouth, vagina and intestinal canal of humans animals and birds.


Among the Haemophilus species that colonize man, H. influenzae is the most important from a clinical point of view. Although not responsible for epidemic influenza, it is involved in a variety of important and severe infections. These infections can be divided into two groups: (a) acute, pyogenic, and usually invasive infections in which H. influenzae is the primary pathogen, and (b) infections (usually chronic) in which H. infuenzae seems to play a secondary part. (2)

The acute infections include meningitis in children, of which H. influenzae is the leading cause, and other septicemic conditions with local implications such as epiglottitis, cellulitis, arthritis and osteomyelitis. The H. influenzae organisms that can be isolated from these conditions virtually always posses a serovar b capsule. Capsulated strains of several serovars may also cause pneumonia in adults.

Non-capsulated strains of H. influenzae are often implicated in chronic bronchitis, sinusitis, conjunctivitis, and otitis media, and occur frequently in lower respiratory tract of patients with cystic fibrosis during acute exacerbations. (2)

H. ducreyi appears to be the causative agent of the venereal disease soft chancre or chancroid. Other strains such as H. parainfluenzae , H. parahaemolyticus , H. segnis *, and H. aphrophilus *, which occur in the mouth and nasopharynx of healthy persons, are only opportunistic pathogens. The oral cavity is usually a likely source of the etiologic agents in infections caused by these organisms. Such infections include endocarditis, brain abscesses, jaw infections and infections following human bites or finger sucking. Other strains of the Haemophilus species have been implicated in diseases like Glasser's disease in swine and urogenital inflammatory disease in dogs.

* H. segnis recently reclassified as Aggregatibacter segnis and H. aphrophilus recently reclassified as Aggregatibacter aphrophilus .


For culture: Chocolate Agar, Blood Agar, Enriched Nutrient Agar, or RTF Casman, Mueller Hinton Broth, and FB Broth.
For selective isolation: Chocolate with Bacitracin, or RTF Casman, Selective Agar.
For maintenance: Skim Milk and Leventhal Broth cultures. Lyophilization may be used for long-term preservation.


Temperature: 33-37 degrees C.
Time: 18-24 hours.
Atmosphere: Aerobic, Facultatively Anaerobic, or CO 2 (5-10%).


1. Holt, J.G., et al. 1994. Bergey's Manual of Determinative Bacteriology , 9th ed. Williams & Wilkins, Baltimore, MD.

2. Holt, J.G., et al. 1986. Bergey's Manual of Systemic Bacteriology , Vol. I & II. Williams & Wilkins, Baltimore, MD.

3. The Oxoid Vade-Mecum of Microbiology . 1993. Unipath Ltd., Basingstoke, UK3.

4. Murray, P.R., et al. 2003. Manual of Clinical Microbiology , 8th ed. American Society for Microbiology, Washington, D.C.

5. Internet: www.hardlink.com /Bacterial Database Search, February, 1998.

6. Hensyl, B.R., et al. 1990. Stedman's Medical Dictionary , 25th ed. Williams & Wilkins, Baltimore, MD.

7. Koneman, et al. 1997. Color Atlas and Textbook of Diagnostic Microbiology , 5th ed. Lippincott, Philadelphia, PA.