''Aggregatibacter actinomycetemcomitans'' is a

Gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wa ...

, facultative anaerobe, nonmotile bacterium that is often found in association with

localized aggressive periodontitis Aggressive periodontitis describes a type of periodontal disease and includes two of the seven classifications of periodontitis as defined by the 1999 classification system: # Localized aggressive periodontitis (LAP) # Generalized aggressive periodo ...

, a severe infection of the

periodontium The periodontium is the specialized tissues that both surround and support the teeth, maintaining them in the maxillary and mandibular bones. The word comes from the Greek terms περί ''peri''-, meaning "around" and -''odont'', meaning "tooth" ...

. It is also suspected to be involved in

chronic periodontitis Chronic periodontitis is one of the seven categories of periodontitis as defined by the American Academy of Periodontology 1999 classification system. Chronic periodontitis is a common disease of the oral cavity consisting of chronic inflammation ...

. Less frequently, ''A. actinomycetemcomitans'' is associated with nonoral infections such as endocarditis. Its role in aggressive

periodontitis Periodontal disease, also known as gum disease, is a set of inflammatory conditions affecting the tissues surrounding the teeth. In its early stage, called gingivitis, the gums become swollen and red and may bleed. It is considered the main cau ...

was first discovered by

Danish Danish may refer to: * Something of, from, or related to the country of Denmark People * A national or citizen of Denmark, also called a "Dane," see Demographics of Denmark * Culture of Denmark * Danish people or Danes, people with a Danish a ...

-born

periodontist Periodontology or periodontics (from Ancient Greek , – 'around'; and , – 'tooth', genitive , ) is the specialty of dentistry that studies supporting structures of teeth, as well as diseases and conditions that affect them. The supporting ...

Jørgen Slots, a professor of dentistry and microbiology at the University of Southern California School of Dentistry. 'Bacterium actinomycetem comitans' was first described by Klinger (1912) as coccobacillary bacteria isolated with ''Actinomyces'' from actinomycotic lesions in humans. It was reclassified as ''Actinobacillus actinomycetemcomitans'' by Topley & Wilson (1929) and as ''Haemophilus actinomycetemcomitans'' by Potts ''et al.'' (1985). The species has attracted attention because of its association with localized aggressive periodontitis.

Nomenclature

Recent studies have shown a phylogenetic similarity of ''A. actinomycetemcomitans'' and ''Haemophilus aphrophilus'', ''H. paraphrophilus'', and ''H. segnis'', suggesting the new

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

''Aggregatibacter'' for them.

Importance

It is one of the

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

that might be implicated in destructive

periodontal disease Periodontal disease, also known as gum disease, is a set of inflammatory conditions affecting the tissues surrounding the teeth. In its early stage, called gingivitis, the gums become swollen and red and may bleed. It is considered the main caus ...

. Although it has been found more frequently in localized aggressive periodontitis, prevalence in any population is rather high. It has also been isolated from actinomycotic lesions (mixed infection with certain ''Actinomyces'' species, in particular ''A. israelii''). It possesses certain

virulence Virulence is a pathogen's or microorganism's ability to cause damage to a host. In most, especially in animal systems, virulence refers to the degree of damage caused by a microbe to its host. The pathogenicity of an organism—its ability to ...

factors that enable it to invade tissues, such as the pore-forming toxin leukotoxin A. It has also been isolated from women with bacterial vaginosis and as an etiologic agent in endocarditis. The pore-forming toxin LtxA of ''A. actinomycetemcomitans'' may be a trigger of the autoimmune disease

rheumatoid arthritis Rheumatoid arthritis (RA) is a long-term autoimmune disorder that primarily affects joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and hands are invol ...

due to its ability to stimulate protein citrullination, a post-translational protein modification targeted by autoantibodies in this disease.

Virulence factors

* Leukotoxin A: kills

granulocytes Granulocytes are cells in the innate immune system characterized by the presence of specific granules in their cytoplasm. Such granules distinguish them from the various agranulocytes. All myeloblastic granulocytes are polymorphonuclear. They ha ...

, monocytes, and other white blood cells expressing integrin beta-2 (CD18) * Cytolethal distending toxin * Immunosuppression factors that inhibit blastogenesis,

antibody An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and viruses. The antibody recognizes a unique molecule of the ...

production, and activate T-suppressor cells * Inhibition of granulocyte functions * Resistant to

complement A complement is something that completes something else. Complement may refer specifically to: The arts * Complement (music), an interval that, when added to another, spans an octave ** Aggregate complementation, the separation of pitch-clas ...

-mediated killing * Lipopolysaccharides * Surface antigens * Heat shock proteins * Antimicrobial resistance

''A. actinomycetemcomitans'' serotypes

* a strain, for example ATCC 29523, frequently in oral cavity, variable leukotoxin expression * b strain Y4, most frequently in localized aggressive periodontitis, high leukotoxin expression; of the b subset, clone Jp2 is particularly leukotoxic * c strain ATCC 33384, low leukotoxin expression * serotypes d, e, f, g * within each serotype, leukotoxin expression can be highly variable between strains

Small RNA

In bacteria, small RNAs are involved in gene regulation. Jorth et al. identified 9 sRNA by Northern blotting from computer-predicted candidates in strain VT1169 and 202 sRNA by RNA seq in strain 624. A systematic screen by RNA-seq and RT-PCR in HK1651 strain (a clinical isolate from an aggressive periodontitis patient), quantified 70 sRNAs and further identified 17 differentially expressed sRNAs during growth phases. Target prediction indicated possibility of sRNA interaction with several virulence genes. This study confirmed the presence of one of previously identified Fur regulated sRNAs JA04 identified in strain HK1651.

References

External links

Type strain of ''Aggregatibacter actinomycetemcomitans'' at Bac''Dive'' – the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q2174895 Pasteurellales Dentistry Capnophiles Bacterial vaginosis Bacteria described in 1912