Actinomyces are rod-shaped bacteria of the order Actinomycetales, which are also called ray fungi due to their characteristic appearance under the microscope. The bacteria preferentially colonize vertebrates and appear either parasitic or commensal. An infection leads to an actinomycosis of the oral cavity and partly lung or liver.

What are Actinomyces?

Actinomyzetaceae form a family within the bacterial order Actinomycetales, which contains five subgenera. The Actinomyces are a genus of this family. They contain most species within the Actinomyzetaceae. All Actinomycetaceae characteristically consist of elongated, branched cells and have gram-positive properties.

Actinomyces have a slightly curved to straight rod shape and thus belong to the bacillus bacteria. The diameter of the cells is between 0.2 and 3.0 microns. Although the length can vary, most members of the genus are rather langf├Ądig and reach lengths of more than 50 microns. In part, they also form small-branched mycelia. For active movement, the bacteria are unable.

There are numerous representatives within the bacterial genus Actinomyces. Human pathogens are, for example, the species Actinomyces israelii, naeslundii, viscosus and odontolyticus or Actinomyces meyeri and pyogenes. Apart from actinomycosis, the diseases associated with them include, among other things, purulent inflammations.

Due to their microscopic appearance and their radial-filamentous branches, the bacteria of the genus Actinomyces sometimes remind of fungi. In this context, the descriptive generic name ray fungus was introduced.

Occurrence, distribution & characteristics

Actinomycetes are largely anaerobic. So you do not need oxygen for your metabolism and survival. While oxygen is toxic to some anaerobic life forms, Actinomyces does not. Many of the species are facultative aerobic and can use oxygen for metabolism. Only a few Actinomyces have catalase enzymes. A high concentration of CO2 or HCO3 in the nutrient medium allows most actinomycetes to grow under aerobic conditions.

Almost all actinomycetes rely on a complex supply of nutrients to grow. Their energy pathway corresponds in most cases to a fermentative energy metabolism. Carbohydrates are used in this type of energy metabolism to organic acids.

The preferred habitat of most species is equivalent to warm-blooded vertebrates populated by the bacteria as pathogens or commensal. A commensal is a living creature that lives on food residues and waste products of a host organism and therefore does not harm the host. The opposite is the classical parasitic colonization, which deprives the host of substances that he himself needs to survive. Parasitic colonization damages the host accordingly and should be classified as pathogenic. Amongst the parasitic pathogenic colonies associated with Actinomyces is infection with the species Actinomyces israelii.

For the growth of Actinomyces is a temperature optimum between 30 to 37 degrees Celsius. For this reason, living organisms with a constant body temperature in this temperature range offer the bacteria the best level. Above all, bacteria of the genus Actinomyces are decaying for reproduction. This decay corresponds to a segmentation into short cells. Endospores do not work the bacteria.

Actinomyces have a radicular hyphae structure due to their one-point growth and have been mistaken for fungi in the past because of their appearance before being classified as bacteria. The bacteria are not transmitted exclusively species-specific, but are transferable from one species to another. This transmission is called zoonosis. More specifically, since the bacteria colonize the gastrointestinal tract and oral cavity of animals, the transmission to humans is a zooanthroponosis. In the body of the host, some species of the Acitomyces can carry out hematogenous scattering and thus reach the lungs or the liver via the blood. However, this distribution of bacteria is a rather rare form.

Diseases & complaints

Actinomyces can cause various diseases. In most cases, the disorders are mixed infections by microaerophilic, facultative anaerobic or anaerobic bacteria that produce anaerobic environmental conditions. Since the anaerobic bacteria depend on anaerobic environments, they create the required milieu accordingly. In this context, in the context of actinomycosis, pustules develop, which in most cases are associated with the formation of fistulas. The abscesses release sulfur yellow drusen.

Actinomycosis is a pseudomycosis mainly associated with abscesses in the oral cavity, lung and gastrointestinal tract. In the context of actinomkyoses, the accumulations of pus tend to spread rapidly to the surrounding tissue. The accumulations are surrounded by connective tissue or granulation tissue of rough consistency. In addition to abscess formation, actinomycetes can also cause tooth decay or periodontitis.

Actinomycosis is differentiated into different forms. The cervicofacial form is the most relevant and is mainly caused by Actinomyces israelii. The infection is often based on an injury within the oral cavity, so that there may be an endogenous infection. To distinguish this form is the thoracic actinomycosis, which can arise in the context of saliva aspiration from a cervicofacial actinomycosis. In abdominal actinomycosis, injuries of the intestine or the female genital area are considered as origin. Cutaneous actinomycosis occurs after injury with salivary transmission. In rare cases, the liver is also affected by the infection. Even rarer, but possible, is a colonization of the tear ducts. Tags: 

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