| Haemophilus | |
|---|---|
 | |
| Haemophilus influenzae on aChocolate agar plate. | |
Scientific classification | |
| Domain: | Bacteria |
| Kingdom: | Pseudomonadati |
| Phylum: | Pseudomonadota |
| Class: | Gammaproteobacteria |
| Order: | Pasteurellales |
| Family: | Pasteurellaceae |
| Genus: | Haemophilus Winslow et al. 1917 |
| Species | |
H. aegyptius | |
Haemophilus is agenus ofGram-negative,pleomorphic,coccobacillibacteria belonging to the familyPasteurellaceae.[2][3] WhileHaemophilus 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.[4] The genus includescommensal organisms along with some significantpathogenic species such asH. influenzae—a cause of sepsis and bacterial meningitis in young children—andH. ducreyi, the causative agent ofchancroid. All members are eitheraerobic orfacultatively anaerobic. This genus has been found to be part of thesalivary microbiome.[5]
Most members of the genusHaemophilus require at least one of these blood factors for growth:hemin (sometimes called 'X-factor') and/ornicotinamide adenine dinucleotide (NAD; sometimes called 'V-factor'); they usually will not grow onblood agar plates. While NAD is released into blood agar by red blood cells, hemin is bound to the blood cells and is unavailable to bacteria in this medium which prevents the growth of manyHaemophilus species.[6] They are unable to synthesize important parts of the cytochrome system needed for respiration, and they obtain these substances from the heme fraction of blood hemoglobin. Clinical laboratories use tests for the hemin and NAD requirement to identify the isolates asHaemophilus species.[4] The species Haemophilus haemoglobinophilus is an exception to this, as it has been shown to grow well on both blood and chocolate agars.[7][self-published source?]
Chocolate agar is an excellentHaemophilus growth medium, as it allows for increased accessibility to these factors.[8] Alternatively,Haemophilus is sometimes cultured using the "Staph streak" technique: bothStaphylococcus andHaemophilus organisms are cultured together on a single blood agar plate. In this case,Haemophilus colonies will frequently grow in small "satellite" colonies around the largerStaphylococcus colonies because the metabolism ofStaphylococcus produces the necessary blood factor byproducts required forHaemophilus growth.
| Strain[9] | Needs hemin | Needs NAD | Hemolysis on HB/Rabbit blood |
|---|---|---|---|
| H. aegyptius | + | + | – |
| H. ducreyi | + | – | – |
| H. influenzae | + | + | – |
| H. haemolyticus | + | + | + |
| H. parainfluenzae | – | + | – |
| H. parahaemolyticus | – | + | + |
