The Pasteurellaceae comprise a large family of Gram-negative

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 am ...

. Most members live as

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 ...

s on mucosal surfaces of birds and mammals, especially in the upper respiratory tract. Pasteurellaceae are typically

rod-shaped A bacillus (), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name '' Baci ...

, and are a notable group of

facultative anaerobe 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 '' Staphylococ ...

s. Their biochemical characteristics can be distinguished from the related

Enterobacteriaceae Enterobacteriaceae is a large family of Gram-negative bacteria. It was first proposed by Rahn in 1936, and now includes over 30 genera and more than 100 species. Its classification above the level of family is still a subject of debate, but o ...

by the presence of oxidase, and from most other similar bacteria by the absence of

flagella A flagellum (; ) is a hairlike appendage that protrudes from certain plant and animal sperm cells, and from a wide range of microorganisms to provide motility. Many protists with flagella are termed as flagellates. A microorganism may have fro ...

. Bacteria in the family Pasteurellaceae have been classified into a number of genera based on metabolic properties, but these classifications are not generally accurate reflections of the evolutionary relationships between different species. ''

Haemophilus 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 bact ...

'' was the first organism to have its

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...

sequenced and has been studied intensively by genetic and molecular methodologies. The genus ''

Haemophilus ''Haemophilus'' is a genus of Gram-negative, pleomorphic, coccobacilli bacteria belonging to the family Pasteurellaceae. While ''Haemophilus'' bacteria are typically small coccobacilli, they are categorized as pleomorphic bacteria because of ...

'' is a notorious human pathogen associated with

bacteremia Bloodstream infections (BSIs), which include bacteremias when the infections are bacterial and fungemias when the infections are fungal, are infections present in the blood. Blood is normally a sterile environment, so the detection of microbe ...

pneumonia Pneumonia is an inflammatory condition of the lung primarily affecting the small air sacs known as alveoli. Symptoms typically include some combination of productive or dry cough, chest pain, fever, and difficulty breathing. The severit ...

meningitis Meningitis is acute or chronic inflammation of the protective membranes covering the brain and spinal cord, collectively called the meninges. The most common symptoms are fever, headache, and neck stiffness. Other symptoms include confusion or ...

and

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 accident ...

. Other pathogenic members of the family Pasteurellaceae include '' Aggregatibacter'', ''

Mannheimia ''Mannheimia'' is a Gram-negative, anaerobic, non-spore-forming and non-motile bacterial genus from the family Pasteurellaceae The Pasteurellaceae comprise a large family of Gram-negative bacteria. Most members live as commensals on mucosal ...

'', '' Pasteurella'', and ''

Actinobacillus ''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 family Pasteurellaceae. The bacteria are facul ...

'' species.

Molecular signatures and phylogenetic position

Comparative analyses of Pasteurellaceae genomes have identified large numbers (>20) of

conserved signature indels Conserved signature inserts and deletions (CSIs) in protein sequences provide an important category of molecular markers for understanding phylogenetic relationships. CSIs, brought about by rare genetic changes, provide useful phylogenetic markers ...

(CSIs) in different important proteins that are uniquely shared by all sequenced Pasteurellaceae species/strains, but are not found in any other bacteria. Based upon many other CSIs that are specific for subgroups of Pasteurellaceae species, it has been proposed to divide the family into at least two clades . One proposed clade includes '' Aggregatibacter'', '' Pasteurella'', '' Actinobacillus succinogenes'', ''

'', ''

Haemophilus somnus ''Haemophilus'' is a genus of Gram-negative, pleomorphic, coccobacilli bacteria belonging to the family Pasteurellaceae. While ''Haemophilus'' bacteria are typically small coccobacilli, they are categorized as pleomorphic bacteria because of ...

'', and '' Mannheimia succiniciproducens'', while the other includes ''

Actinobacillus minor ''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 family Pasteurellaceae. The bacteria are facul ...

'', '' Actinobacillus pleuropneumoniae'', '' Haemophilus ducreyi'', '' Haemophilus parasuis'', and ''

Mannheimia haemolytica ''Mannheimia'' is a Gram-negative, anaerobic, non-spore-forming and non-motile bacterial genus from the family Pasteurellaceae The Pasteurellaceae comprise a large family of Gram-negative bacteria. Most members live as commensals on mucos ...

''. Molecular signatures in the form of CSIs have also been used to help resolve

polyphyletic A polyphyletic group is an assemblage of organisms or other evolving elements that is of mixed evolutionary origin. The term is often applied to groups that share similar features known as homoplasies, which are explained as a result of conver ...

distribution of three main genera within the family Pasteurellaceae: ''Actinobacillus'', ''Haemophilus'', and ''Pasteurella''.Olsen I, Dewhirst FE, Paster BJ, Busse HJ (2005) Family I. Pasteurellaceae. In: Bergey’s Manual of Systematic Bacteriology, edn. 2, vol 2, pp. 851–856. Eds Brenner D. J., Krieg N. R., Garrity G. M., Staley J. T. Springer-: New York. These genera demonstrate extensive polyphyly across the family, however, CSIs have been found to be consistently shared by certain species that form a

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gr ...

group within each respective genus. The distribution of CSIs corresponds to ''

sensu stricto ''Sensu'' is a Latin word meaning "in the sense of". It is used in a number of fields including biology, geology, linguistics, semiotics, and law. Commonly it refers to how strictly or loosely an expression is used in describing any particular c ...

'' clades of "true" ''Actinobacillus'', ''Haemophilus'', and ''Pasteurella'' species, respectively. Since they are indicative of common ancestry, it has been postulated that the CSI distribution can be used to determine genus identity, where the species that do not share the CSI may be reclassified as a different genus. CSIs have also been found that are specific for ''Aggregatibacter'' and ''Mannheimia'' , two clinically relevant genera. The Pasteurellales, along with

Enterobacterales Enterobacterales is an order of Gram-negative, non-spore forming, facultatively anaerobic, rod-shaped bacteria with the class Gammaproteobacteria. The type genus of this order is ''Enterobacter.'' The name Enterobacterales is derived from th ...

, are of the most recently divergent orders within the

Gammaproteobacteria Gammaproteobacteria is a class of bacteria in the phylum Pseudomonadota (synonym Proteobacteria). It contains about 250 genera, which makes it the most genera-rich taxon of the Prokaryotes. Several medically, ecologically, and scientifically imp ...

. Their distinction from all other orders are supported by the presence of several conserved signature proteins (CSPs) that are shared by these two orders, and absent from all other bacteria. Pasteurellales also share additional CSPs with Enterobacterales,

Vibrionales The Vibrionaceae are a family of Pseudomonadota given their own order, Vibrionales. Inhabitants of fresh or salt water, several species are pathogenic, including the type species ''Vibrio cholerae'', which is the agent responsible for cholera. Mo ...

, Aeromonadales, and Alteromonadales, adding additional resolution to their evolutionary branching and phylogenetic position among the large Gammaproteobacteria class.

References

{{Taxonbar, from=Q142666 Pasteurellales