''Haemophilus'' is a
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
Gram-negative
Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...
,
pleomorphic,
coccobacilli
A coccobacillus (plural coccobacilli), or bacilluscocco, is a type of bacterium with a shape intermediate between cocci (spherical bacteria) and bacilli (rod-shaped bacteria). Coccobacilli, then, are very short rods which may be mistaken for cocci ...
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
belonging to the family
Pasteurellaceae
The Pasteurellaceae comprise a large family of Gram-negative bacteria. Most members live as commensals on mucosal surfaces of birds and mammals, especially in the upper respiratory tract. Pasteurellaceae are typically rod-shaped, and are a notabl ...
.
While ''Haemophilus'' bacteria are typically small coccobacilli, they are categorized as pleomorphic bacteria because of the wide range of shapes they occasionally assume. These organisms inhabit the mucous membranes of the upper respiratory tract, mouth, vagina, and intestinal tract.
The genus includes
commensal
Commensalism is a long-term biological interaction (symbiosis) in which members of one species gain benefits while those of the other species neither benefit nor are harmed. This is in contrast with mutualism, in which both organisms benefit fro ...
organisms along with some significant pathogenic species such as ''Haemophilus influenzae, H. influenzae''—a cause of sepsis and bacterial meningitis in young children—and ''Haemophilus ducreyi, H. ducreyi'', the causative agent of chancroid. All members are either Aerobic organism, aerobic or Facultative anaerobic organism, facultatively anaerobic. This genus has been found to be part of the salivary microbiome.
Metabolism
Members of the genus ''Haemophilus'' will not grow on blood agar plates, as all species require at least one of these blood factors for growth: hemin (X-factor) and/or nicotinamide adenine dinucleotide (V-factor). They are unable to synthesize important parts of the cytochrome system needed for respiration, and they obtain these substances from the heme fraction, known as the X factor, of blood hemoglobin. The culture medium must also supply the cofactor nicotinamide adenine dinucleotide (from either NAD+ or NADP+), which is known as the V factor. Clinical laboratories use tests for the requirement of the X and V factors to identify the isolates as ''Haemophilus'' species.
[
Chocolate agar is an excellent ''Haemophilus'' growth medium, as it allows for increased accessibility to these factors.]
References
External links
''Haemophilus'' chapter
in Baron's ''Medical Microbiology'' (online at the National Center for Biotechnology Information, NCBI]
bookshelf
.
{{Taxonbar, from=Q311275
Haemophilus,
Bacteria genera