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 Enterobacteriaceae is a large family (biology), 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 ...

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 f ...

. 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'' was the first organism to have its genome 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), 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 microb ...

, pneumonia,

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 accidenta ...

. 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 s ...

'', '' 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 ''Actinobacillus succinogenes'' is a bacterium. It is a succinic acid-producing strain first isolated from the bovine rumen. It is a facultatively anaerobic, pleomorphic, Gram-negative Gram-negative bacteria are bacteria that do not retain ...

'', '' Haemophilus influenzae'', ''

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 ''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 s ...

'', while the other includes '' Actinobacillus minor'', ''

Actinobacillus pleuropneumoniae ''Actinobacillus pleuropneumoniae'' (previously ''Haemophilus pleuropneumoniae''), is a Gram-negative, facultative anaerobic, respiratory pathogen found in pigs. It was first reported in 1957, and was formally declared to be the causative agent o ...

'', '' Haemophilus ducreyi'', ''

Haemophilus parasuis ''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 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 mucosal ...

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

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 co ...

'' 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, 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 The Aeromonadales are an order of Pseudomonadota, with 10 genera in two families. Aeromonadales

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

References

{{Taxonbar, from=Q142666 Pasteurellales