Actinomyces are branching Gram-positive bacilli.
They are a group of bacteria which are having branching filaments that resembles fungi.
Actinomyces israelii is the medically important Actinomyces species belongs to this group.
Actinomyces live in oral and intestinal normal flora in humans.
Some organisms belong to this group are free living and most are found in soil.
They are facultative anaerobes.
However, in primary cultures, they fail to grow in aerobic conditions.
They can be grown under anaerobic or micro-aerophilic conditions.
Addition of 5–10% carbon dioxide enhances the growth of this organism.
Actinomycosis is caused by this bacterium.
Actinomycosis causes abscess (chronic granulomatous infections/ Sulphur granules) and draining of pus through sinus tracts.
Usually, they cause infections in the jaw, following the extraction of a tooth.
However, they cause infections in the abdomen and very occasionally causes infections in brain and lungs.
Laboratory diagnosis
Depending on the site of infection specimen collection is done.
Normally pus, sputum, infected tissues are accepted for the laboratory diagnosis.
They are group of gram-positive bacilli and forming branching filaments and some are fragmented forms.
These filaments easily fragment into slender rods.
They are prokaryotic bacteria.
Though these filaments resemble fungal hyphae, Moreover, fragmented forms resemble diphtheroids.
In actinomycosis
Sulfur granules in draining pus can be identified under microscope as small, yellowish and firm particles. Usually, Actinomyces granules are yellow.
But they also can be seen in brown colour. These granules are round, and have a diameter about 0.5–5 µm.
Granules are stained by Gram and Ziehl–Neelsen stains to identify the mycelia and the acid-fast organisms.
When stained the crushed granules with modified Ziehl-Neelsen stain, the filamentous branches are not acid fast.
However, radiating clubs are acid fast.
Furthermore, by using fluoresence-conjugated specific antisera sulphur granules and mycelia in tissue sections can be identified.
PCR also has been used for the diagnosis of Actinomyces in tissue biopsies.
These organisms can be grown anaerobically and microaerophilically on enriched media.
Granules are cultured on enrichment media.
Enrichment media are blood agar, brain heart infusion or thioglycolate broth.
Normally they are slow growers.
To see visible growth on blood agar, it takes about 5 to 7 day at 35–37º.
The colonies are small, cream colour or white.
They have a rough nodular surface.
Actinomyces gives spider colonies that resembles molar teeth, after several days of incubation.
Biochemical identification of Actinomyces israelii gives catalase negative, indole negative and urease negative reactions.
They do not reduce nitrates. It hydrolyzes aesculin.
They ferment sugars like glucose, lactose, mannitol, and some other sugars.
Confirmation of Actinomyces can be done by biochemical tests, specific fluorescent antisera or by using gas chromatography of metabolic products which originated from carbohydrate fermentation.
Treatment
They are sensitive to many antibiotic drugs.
However, it may vary depending on the penetration ability of the drug into the fibrotic diseased tissue.
Penicillin G was used for the treatment of actinomycosis.
But it should be done prolonged basis. Therefore, instead of penicillin G, amoxicillin with clavulanic acid or cephalosporins are used.
Especially ceftriaxone is used.
Moreover, tetracyclines, macrolides, fluoroquinolones and imipenem are used.
It is necessary to use additional drugs like aminoglycosides and metronidazole for the treatment, when contaminant organisms are present,
Always it is necessary perform formal antibiotic susceptibility testing to ensure the optimal antibiotic therapy.
Prolonged antibiotic therapy and surgical drainage of the lesions is important to eliminate the infection.
Normally recurrence infection of Actinomyces is uncommon.
Prevention
There is no special vaccine or prophylactic drug available for Actinomycosis.
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