''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 ...

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

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 In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

species such as ''

H. influenzae ''Haemophilus influenzae'' (formerly called Pfeiffer's bacillus or ''Bacillus influenzae'') is a Gram-negative, non-motile, coccobacillary, facultatively anaerobic, capnophilic pathogenic bacterium of the family Pasteurellaceae. The bacteria ...

''—a cause of sepsis and bacterial meningitis in young children—and '' H. ducreyi'', the causative agent of chancroid. All members are either

aerobic Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cel ...

facultatively anaerobic A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent. Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...

. This genus has been found to be part of the salivary microbiome.

Metabolism

Members of the genus ''Haemophilus'' will not grow on

blood agar An agar plate is a Petri dish that contains a growth medium solidified with agar, used to Microbiological culture, culture microorganisms. Sometimes selective compounds are added to influence growth, such as antibiotics. Individual microorganism ...

plates, as all species require at least one of these blood factors for growth:

hemin Hemin (haemin; ferric chloride heme) is an iron-containing porphyrin with chlorine that can be formed from a heme group, such as heme B found in the hemoglobin of human blood. Chemistry Hemin is protoporphyrin IX containing a ferric iron (Fe3 ...

(X-factor) and/or

nicotinamide adenine dinucleotide Nicotinamide adenine dinucleotide (NAD) is a coenzyme central to metabolism. Found in all living cells, NAD is called a dinucleotide because it consists of two nucleotides joined through their phosphate groups. One nucleotide contains an aden ...

(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 Chocolate agar (CHOC) or chocolate blood agar (CBA), is a nonselective, enriched growth medium used for isolation of pathogenic bacteria. It is a variant of the blood agar plate, containing red blood cells that have been lysed by slowly heating ...

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.

References

External links

''Haemophilus'' chapter
in Baron's ''Medical Microbiology'' (online at the

NCBI The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The ...

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. {{Taxonbar, from=Q311275 Bacteria genera