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Not to be confused with Haemophilia.

Haemophilus influenzae.jpg
Haemophilus influenzae on a Chocolate agar plate.
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gammaproteobacteria
Order: Pasteurellales
Family: Pasteurellaceae
Winslow et al. 1917

H. aegyptius
H. avium
H. ducreyi
H. felis
H. haemoglobinophilus [1]
H. haemolyticus
H. influenzae
H. parainfluenzae
H. paracuniculus
H. parahaemolyticus
H. paraphrohaemolyticus [1]
H. parasuis [1]
H. pittmaniae
H. piscium [1]
H. segnis
H. sputorum [1]


Haemophilus is a genus of Gram-negative, pleomorphic, coccobacilli bacteria belonging to the family Pasteurellaceae. [2] [3] 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. [4] The genus includes commensal organisms along with some significant pathogenic species such as H. influenzae a cause of sepsis and bacterial meningitis in young childrenand H. ducreyi , the causative agent of chancroid. All members are either aerobic or facultatively anaerobic. This genus has been found to be part of the salivary microbiome. [5]

A genus is a taxonomic rank used in the biological classification of living and fossil organisms, as well as viruses, in biology. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclature, the genus name forms the first part of the binomial species name for each species within the genus.

In microbiology, pleomorphism(from greek πλέω- more, and -μορφή form) is the ability of some micro-organisms to alter their shape or size in response to environmental conditions. Pleomorphism has been observed in some members of the Deinococcaceae family. The modern definition of pleomorphism in the context of bacteriology is based on variation of size or shape of the cell, rather than a change of shape as previously believed.


A coccobacillus is a type of bacterium with a shape intermediate between cocci and bacilli. Coccobacilli, then, are very short rods which may be mistaken for cocci.


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.< [4]

Hemin chemical substance

Hemin is an iron-containing porphyrin with chlorine that can be formed from a haem group, such as haem b found in the haemoglobin of human blood.

Chocolate agar is an excellent Haemophilus growth medium, as it allows for increased accessibility to these factors. [6] 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.

Chocolate agar Growth medium

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 to 80°C. Chocolate agar is used for growing fastidious respiratory bacteria, such as Haemophilus influenzae and Neisseria meningitidis. In addition, some of these bacteria, most notably H. influenzae, need growth factors such as nicotinamide adenine dinucleotide and hemin, which are inside red blood cells; thus, a prerequisite to growth for these bacteria is the presence of red blood cell lysates. The heat also inactivates enzymes which could otherwise degrade NAD. The agar is named for its color and contains no chocolate products.

Strain [7] Needs X-FactorNeeds V-FactorHemolysis on HB/Rabbit blood
H. aegyptius ++
H. ducreyi +
H. influenzae ++
H. haemolyticus +++
H. parainfluenzae +
H. parahaemolyticus ++

Related Research Articles

<i>Streptococcus</i> genus of bacteria

Streptococcus is a genus of gram-positive coccus or spherical bacteria that belongs to the family Streptococcaceae, within the order Lactobacillales, in the phylum Firmicutes. Cell division in streptococci occurs along a single axis, so as they grow, they tend to form pairs or chains that may appear bent or twisted.

Agar plate

An agar plate is a Petri dish that contains agar as a solid growth medium plus nutrients, used to culture microorganisms. Sometimes selective compounds are added to influence growth, such as antibiotics.

Microbiological culture multiplying microorganisms by letting them reproduce in culture media

A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture medium under controlled laboratory conditions. Microbial cultures are foundational and basic diagnostic methods used extensively as a research tool in molecular biology.

<i>Haemophilus influenzae</i> species of bacterium

Haemophilus influenzae is a Gram-negative, coccobacillary, facultatively anaerobic pathogenic bacterium belonging to the Pasteurellaceae family. H. influenzae was first described in 1892 by Richard Pfeiffer during an influenza pandemic.

<i>Corynebacterium</i> genus of bacteria

Corynebacterium is a genus of bacteria that are Gram-positive and aerobic. They are bacilli (rod-shaped), and in some phases of life they are, more particularly, club-shaped, which inspired the genus name.

Pasteurellaceae family of bacteria

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 notable group of facultative anaerobes. Their biochemical characteristics can be distinguished from the related Enterobacteriaceae by the presence of oxidase, and from most other similar bacteria by the absence of flagella.

Coliform bacteria

Coliform bacteria are defined as rod-shaped Gram-negative non-spore forming and motile or non-motile bacteria which can ferment lactose with the production of acid and gas when incubated at 35–37°C. They are a commonly used indicator of sanitary quality of foods and water. Coliforms can be found in the aquatic environment, in soil and on vegetation; they are universally present in large numbers in the feces of warm-blooded animals. While coliforms themselves are not normally causes of serious illness, they are easy to culture, and their presence is used to indicate that other pathogenic organisms of fecal origin may be present. Such pathogens include disease-causing bacteria, viruses, or protozoa and many multicellular parasites. Coliform procedures are performed in aerobic or anaerobic conditions.

Growth medium liquid or gel used for the growth of microorganisms or cells

A growth medium or culture medium is a solid, liquid or semi-solid designed to support the growth of microorganisms or cells, or small plants like the moss Physcomitrella patens. Different types of media are used for growing different types of cells.

<i>Staphylococcus epidermidis</i> species of bacterium

Staphylococcus epidermidis is a Gram-positive bacterium, and one of over 40 species belonging to the genus Staphylococcus. It is part of the normal human flora, typically the skin flora, and less commonly the mucosal flora. It is a facultative anaerobic bacteria. Although S. epidermidis is not usually pathogenic, patients with compromised immune systems are at risk of developing infection. These infections are generally hospital-acquired. S. epidermidis is a particular concern for people with catheters or other surgical implants because it is known to form biofilms that grow on these devices. Being part of the normal skin flora, S. epidermidis is a frequent contaminant of specimens sent to the diagnostic laboratory.

Hemolysis (microbiology)

Hemolysis is the breakdown of red blood cells. The ability of bacterial colonies to induce hemolysis when grown on blood agar is used to classify certain microorganisms. This is particularly useful in classifying streptococcal species. A substance that causes hemolysis is a hemolysin.

Streaking (microbiology) microbiological method for isolation

In microbiology, streaking is a technique used to isolate a pure strain from a single species of microorganism, often bacteria. Samples can then be taken from the resulting colonies and a microbiological culture can be grown on a new plate so that the organism can be identified, studied, or tested.

Moraxella is a genus of Gram-negative bacteria in the Moraxellaceae family. It is named after the Swiss ophthalmologist Victor Morax. The organisms are short rods, coccobacilli, or as in the case of Moraxella catarrhalis, diplococci in morphology, with asaccharolytic, oxidase-positive, and catalase-positive properties. M. catarrhalis is the clinically most important species under this genus.

Mannitol salt agar culture medium used in microbiology

Mannitol salt agar or MSA is a commonly used selective and differential growth medium in microbiology. It encourages the growth of a group of certain bacteria while inhibiting the growth of others. This medium is important in medical laboratories as one method of distinguishing pathogenic microbes in a short period of time. It contains a high concentration of salt (NaCl), making it selective for Gram-positive bacteria since this level of salt is inhibitory to most other bacteria. It is also a differential medium for mannitol-fermenting staphylococci, containing carbohydrate mannitol and the indicator phenol red, a pH indicator for detecting acid produced by mannitol-fermenting staphylococci. Staphylococcus aureus produces yellow colonies with yellow zones, whereas other coagulase-negative staphylococci produce small pink or red colonies with no colour change to the medium. If an organism can ferment mannitol, an acidic byproduct is formed that causes the phenol red in the agar to turn yellow. It is used for the selective isolation of presumptive pathogenic (pp) Staphylococcus species.

<i>Actinobacillus</i> genus of bacteria

Actinobacillus is a genus of Gram-negative, nonmotile and non-spore-forming, oval to rod-shaped bacteria occurring as parasites or pathogens in mammals, birds, and reptiles. It is a member of the Pasteurellaceae family. The bacteria are facultatively aerobic or anaerobic, capable of fermenting carbohydrates, and of reducing nitrates. The genomic DNA contains between 40 and 47 mol % guanine plus cytosine.

Mueller-Hinton agar culture medium used in microbiology

Müller-Hinton agar is a microbiological growth medium that is commonly used for antibiotic susceptibility testing. It is also used to isolate and maintain Neisseria and Moraxella species.

Bacterial cellular morphologies

Bacteria are classified by direct examination with the light microscope according to their morphology and arrangement.

Victivallis vadensis is a Gram-negative, coccus-shaped, bacteria found in the human digestive tract. It measures approximately 0.5-1.3 micrometers in diameter, is non-motile and chemoorganotrophic, and does not form spores. Victivallis vadensis is strictly anaerobic, as are 90 percent of the bacteria in the human gastrointestinal system.

Salivary microbiome

The Salivary microbiome is the nonpathogenic, commensal bacteria present in the healthy human salivary glands. It is distinct from bacteria that may cause infection in the glands. It differs from the oral microbiome which is located in the oral cavity. Oral microorganisms tend to adhere to teeth. The oral microbiome possesses its own characteristic microorganisms found there. Resident microbes of the mouth adhere to the teeth and gums. "[T]here may be important interactions between the saliva microbiome and other microbiomes in the human body, in particular, that of the intestinal tract."

Histophilus somni is a Gram-negative, pleomorphic, coccobacillus bacterium belonging to the family Pasteurellaceae.


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