''Haemophilus'' is a genus of Gram-negative, 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 belonging to the family Pasteurellaceae. 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 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 Chancroid ( ) is a bacterial sexually transmitted infection characterized by painful sores on the genitalia. Chancroid is known to spread from one individual to another solely through sexual contact. However, there have been reports of accidenta ...

. All members are either aerobic or facultatively anaerobic. This genus has been found to be part of the

salivary microbiome The salivary microbiome consists of the nonpathogenic, commensal bacteria present in the healthy human salivary glands. It differs from the oral microbiome which is located in the oral cavity. Oral microorganisms tend to adhere to teeth. The oral m ...

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 (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 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 NCBIbr>bookshelf
. {{Taxonbar, from=Q311275 Bacteria genera