''Aggregatibacter actinomycetemcomitans'' is a

Gram-negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists ...

, facultative anaerobe, nonmotile bacterium that is often found in association with localized aggressive periodontitis, 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. Periodontics is the dental specialty that relates specifically to the care and maintenance of the ...

. It is also suspected to be involved in chronic periodontitis. 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 c ...

was first discovered by Danish-born periodontist Jørgen Slots, a professor of

dentistry Dentistry, also known as dental medicine and oral medicine, is the branch of medicine focused on the Human tooth, teeth, gums, and Human mouth, mouth. It consists of the study, diagnosis, prevention, management, and treatment of diseases, dis ...

and

microbiology Microbiology () is the branches of science, scientific study of microorganisms, those being of unicellular organism, unicellular (single-celled), multicellular organism, multicellular (consisting of complex cells), or non-cellular life, acellula ...

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 (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

''Aggregatibacter'' for them.

Importance

It is one of the

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 ...

that might be implicated in destructive periodontal disease. 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 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 Bacterial vaginosis (BV) is an infection of the vagina caused by excessive growth of bacteria. Common symptoms include increased vaginal discharge that often smells like fish. The discharge is usually white or gray in color. Burning with urina ...

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 synovial joint, joints. It typically results in warm, swollen, and painful joints. Pain and stiffness often worsen following rest. Most commonly, the wrist and h ...

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, that ...

monocytes Monocytes are a type of leukocyte or white blood cell. They are the largest type of leukocyte in blood and can differentiate into macrophages and monocyte-derived dendritic cells. As a part of the vertebrate innate immune system monocytes also i ...

, and other white blood cells expressing integrin beta-2 (CD18) *

Cytolethal distending toxin Cytolethal distending toxins (abbreviated CDTs) are a class of Protein trimer, heterotrimeric toxins produced by certain gram-negative bacteria that display DNase activity. These toxins trigger G2/M cell cycle arrest in specific mammalian cell l ...

* Immunosuppression factors that inhibit blastogenesis,

antibody An antibody (Ab) or immunoglobulin (Ig) is a large, Y-shaped protein belonging to the immunoglobulin superfamily which is used by the immune system to identify and neutralize antigens such as pathogenic bacteria, bacteria and viruses, includin ...

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