Aggregatibacter actinomycetemcomitans (Aa) is an oral commensal found also in severe infections in the oral cavity, mainly the periodontium

Periodontium

Periodontium refers to 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 peri-, meaning "around" and -odons, meaning "tooth." Literally taken, it means that which is "around the tooth"...

. A. actinomycetemcomitans, previously Actinobacillus actinomycetemcomitans, is a gram negative facultative non-motile rod. It is also associated with non-oral infections. Its role in periodontitis was first discovered by Danish

Denmark

Denmark is a Scandinavian country in Northern Europe. The countries of Denmark and Greenland, as well as the Faroe Islands, constitute the Kingdom of Denmark . It is the southernmost of the Nordic countries, southwest of Sweden and south of Norway, and bordered to the south by Germany. Denmark...

-born periodontist Jørgen Slots

Jørgen Slots

Jørgen Slots is a Danish periodontist and professor of dentistry and microbiology at the University of Southern California School of Dentistry.-Biography:...

, currently a professor of dentistry

Dentistry

Dentistry is the branch of medicine that is involved in the study, diagnosis, prevention, and treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is widely considered...

 and microbiology

Microbiology

Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell , cell clusters or no cell at all . This includes eukaryotes, such as fungi and protists, and prokaryotes...

 at University of Southern California School of Dentistry

University of Southern California School of Dentistry

The Herman Ostrow School of Dentistry was established in 1897 as simply the "University of Southern California School of Dentistry," and graduated its first class of 11 students in 1900. In 2010, the school was renamed after a $35 million dollar donation by a USC alumnus, and the school was...

.

Bacterium actinomycetem comitans’ was described by Klinger (1912) as coccobacillary bacteria isolated together with Actinomyces from actinomycotic lesions of man. 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

Aggressive periodontitis

Aggressive periodontitis describes a type of periodontal disease and includes two of the seven classifications of periodontitis:# Localized aggressive periodontitis # Generalized aggressive periodontitis...

 (Slots & Ting, 1999; Haubek et al., 2001).

Nomenclature

Recent studies have shown a phylogenetic similarity of Actinobacillus actinomycetemcomitans and Haemophilus aphrophilus, Haemophilus paraphrophilus, and Haemophilus segnis suggesting the new genus

Genus

In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 Aggregatibacter for them.

Importance

It is one of the bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 which might be implicated in destructive periodontal disease

Periodontal disease

Periodontitis is a set of inflammatory diseases affecting the periodontium, i.e., the tissues that surround and support the teeth. Periodontitis involves progressive loss of the alveolar bone around the teeth, and if left untreated, can lead to the loosening and subsequent loss of teeth...

. 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 Actinomyces israelii).
It possesses certain virulence

Virulence

Virulence is by MeSH definition the degree of pathogenicity within a group or species of parasites as indicated by case fatality rates and/or the ability of the organism to invade the tissues of the host. The pathogenicity of an organism - its ability to cause disease - is determined by its...

 factors that enable it to invade tissues, such as leukotoxin.

Virulence Factors

- Leukotoxin; kills PMNs

Granulocyte

Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. They are also called polymorphonuclear leukocytes because of the varying shapes of the nucleus, which is usually lobed into three segments...

 and monocytes.

- Cytolethal distending toxin

Cytolethal distending toxin

In molecular biology, cytolethal distending toxin is a toxin produced by Proteobacteria, including Escherichia coli, Haemophilus spp and Campylobacter spp.This toxin causes distension in certain cell lines, which eventually disintegrate and die. It consists of three subunits: A, B and C. Their...

- Immunosuppression factors that inhibit blastogenesis, antibody

Antibody

An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...

 production and activate T-suppressor cells

- Inhibition of PMNs

Granulocyte

Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. They are also called polymorphonuclear leukocytes because of the varying shapes of the nucleus, which is usually lobed into three segments...

 functions

- Resistant to complement

Complement system

The complement system helps or “complements” the ability of antibodies and phagocytic cells to clear pathogens from an organism. It is part of the immune system called the innate immune system that is not adaptable and does not change over the course of an individual's lifetime...

mediated killing.

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, leukotoxin expression.

- c strain ATCC 33384, low leukotoxin.

- serotypes d, e