Actinomyces naeslundii is a gram-positive, rod-shaped, non-spore-forming, non-acid-fast, facultative anaerobe found in the oral cavity of humans and other animals. This non-motile bacillus is one of only a few gram-positive bacteria characterized as having fimbriae (Wu et al., 2001). The type 1 fimbriae of A. naeslundii mediate adhesion of this organism to the tooth surface (Chen et al., 2007). This microorganism is mesophilic and grows in temperatures ranging from 15°C to 40°C with an optimum growing temperature of 37°C, the normal human body temperature. Actinomyces naeslundii is commonly found in large numbers in the oral cavity and is a major component of dental plaque. It has also been linked to root caries, periodontal disease and even opportunistic infections such as actinomycosis.
Actinomycosis is a chronic bacterial infection caused by certain species of the genus Actinomyces such as A. naeslundii, A. viscosus and A. odontolyticus. The most common clinical form of actinomycosis is cervicofacial, but thoracic and abdominal actinomycosis, as well as pelvic actinomycosis in women, are also possible. Common infection sites are decayed teeth, the lungs and the intestines. However, Actinomycosis can occur in nearly every organ and the infection is usually a mix of several Actinomyces and other bacterial species, including gram-negative species (NCBI). Actinomycosis is often hard to identify and is sometimes referred to as the "most misdiagnosed disease" (Jin et al., 2001).