Actinomyces naeslundii

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Actinomyces naeslundii
Histopathological changes due to A. naeslundii.
Scientific classification edit
Domain: Bacteria
Phylum: Actinomycetota
Class: Actinomycetia
Order: Actinomycetales
Family: Actinomycetaceae
Genus: Actinomyces
A. naeslundii
Binomial name
Actinomyces naeslundii
corrig. Thompson and Lovestedt 1951 (Approved Lists 1980)
  • Actinomyces naeslundi Thompson and Lovestedt 1951 (Approved Lists 1980)

Actinomyces naeslundii is a Gram-positive, rod-shaped bacterium found in the mouth of humans. The species has been implicated in periodontal disease, as well as various tooth cavities.[1] In other cases, A. naeslundii is associated with good oral health. It is one of the first bacteria to occupy the oral cavity and colonize the tooth's surface. It has also been isolated from women with bacterial vaginosis.[2]


A. naeslundii appears Gram-positive and pleomorphic by microscopy. It does not form spores, and is considered anaerobic or microaerophilic.[3]

In 2009, the species A. naeslundi was split. Bacteria formerly known as "Actinomyces naeslundi genospecies 2" were reclassified under the new species name Actinomyces oris. Those formerly known as "Actinomyces naeslundi genospecies WVA 963" were reclassified as Actinomyces johnsonii.[3]


a)Bronchoalveolar lavage (BAL) sample gram's stain b)culture showing white dry pinpoint colonies, c)gram's stain from the colonies show filamentous branching d) modified Ziehl–Neelsen staining from colony

Many species of the genus Actinomyces, including A. naeslundii, cause a chronic disease called actinomycosis, which is characterized by swelling and formation of an abscess which may exude pus. This can be accompanied by tissue fibrosis.[4]

Infections of the mouth, face, and neck are the most commonly recognized infections; however, the thoracic region, abdomen, pelvis, and the central nervous system can also be involved.[1]


  1. 1.0 1.1 Nanna Sarkonen (August 2007). "Oral Actinomyces Species in Health and Disease: Identification, Occurrence and Importance of Early Colonization" (PDF). National Public Health Institute, Helsinki, Finland. Archived (PDF) from the original on 21 February 2023. Retrieved 24 July 2016.
  2. Africa, Charlene; Nel, Janske; Stemmet, Megan (2014). "Anaerobes and Bacterial Vaginosis in Pregnancy: Virulence Factors Contributing to Vaginal Colonisation". International Journal of Environmental Research and Public Health. 11 (7): 6979–7000. doi:10.3390/ijerph110706979. ISSN 1660-4601. PMC 4113856. PMID 25014248.
  3. 3.0 3.1 Henssge, U.; Do, T.; Radford, D. R.; Gilbert, S. C.; Clark, D.; Beighton, D. (2009). "Emended description of Actinomyces naeslundii and descriptions of Actinomyces oris sp. nov. And Actinomyces johnsonii sp. nov., previously identified as Actinomyces naeslundii genospecies 1, 2 and WVA 963". International Journal of Systematic and Evolutionary Microbiology. 59 (3): 509–16. doi:10.1099/ijs.0.000950-0. PMC 2884933. PMID 19244431.
  4. Quinonez JM. "Pediatric Actinomycosis". Medscape. Archived from the original on 30 March 2008. Retrieved 22 May 2016.

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