The Pasteurellaceae comprise a large family of Gram-negative

bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

. 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 f ...

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

rod-shaped Bacterial cellular morphologies are the shapes that are characteristic of various types of bacteria and often key to their identification. Their direct examination under a light microscope enables the classification of these bacteria (and archae ...

, and are a notable group of facultative anaerobes. Their biochemical characteristics can be distinguished from the related

Enterobacteriaceae Enterobacteriaceae is a large family (biology), family of Gram-negative bacteria. It includes over 30 genera and more than 100 species. Its classification above the level of Family (taxonomy), family is still a subject of debate, but one class ...

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

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

. 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, Motility, non-motile, Coccobacillus, coccobacillary, facultative anaerobic organism, facultatively anaerobic, Capnophile, capnophili ...

'' was the first organism to have its

genome 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 genes, other functional regions of the genome such as ...

sequenced and has been studied intensively by genetic and molecular methodologies. The genus '' Haemophilus'' is a notorious human pathogen associated with

bacteremia Bloodstream infections (BSIs) are infections of blood caused by blood-borne pathogens. The detection of microbes in the blood (most commonly accomplished by blood cultures) is always abnormal. A bloodstream infection is different from sepsis, wh ...

pneumonia Pneumonia is an Inflammation, inflammatory condition of the lung primarily affecting the small air sacs known as Pulmonary alveolus, alveoli. Symptoms typically include some combination of Cough#Classification, productive or dry cough, ches ...

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, intense headache, vomiting and neck stiffness and occasion ...

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 accidenta ...

. Other pathogenic members of the family Pasteurellaceae include '' Aggregatibacter'', '' Mannheimia'', '' Pasteurella'', and '' Actinobacillus'' species.

Molecular signatures and phylogenetic position

Comparative analyses of Pasteurellaceae genomes have identified large numbers (>20) of conserved signature indels (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'', ''

'', '' Histophilus somni'', and '' Mannheimia succiniciproducens'', while the other includes '' Actinobacillus minor'', '' Actinobacillus pleuropneumoniae'', '' Haemophilus ducreyi'', '' Glaesserella parasuis'', and '' Mannheimia haemolytica''. Molecular signatures in the form of CSIs have also been used to help resolve

polyphyletic A polyphyletic group is an assemblage that includes organisms with mixed evolutionary origin but does not include their most recent common ancestor. The term is often applied to groups that share similar features known as Homoplasy, homoplasies ...

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 biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

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 bacteria, Gram-negative, non-spore forming, Facultative anaerobic organism, facultatively anaerobic, rod-shaped bacteria with the class Gammaproteobacteria. The type genus of this order is ''Enterob ...

, 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 genus-rich taxon of the Prokaryotes. Several medically, ecologically, and scienti ...

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

Etymology

This taxonomical group of bacteria was named after

Louis Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist, pharmacist, and microbiologist renowned for his discoveries of the principles of vaccination, Fermentation, microbial fermentation, and pasteurization, the la ...

, a name formally accepted in 1981. The designation was conceived to accommodate a collection of Gram-negative organisms currently representing 33 genera and 110 species, described as "specialized commensals, primarily and potential pathogens of vertebrates–mainly mammals and birds."

References

{{Authority control Pasteurellales