Actinomyces

Overview
Actinomyces is a genus of Gram-positive bacteria. Some species are anaerobic, while others are facultatively anaerobic. Actinomyces species do not form spores, and, while individual bacteria are rod-shaped, morphologically Actinomyces colonies form fungus-like branched networks of hyphae.

Many Actinomyces species are opportunistic pathogens of humans and other mammals, particularly in the oral cavity. In rare cases, these bacteria can cause actinomycosis, a disease characterized by the formation of abscesses in the mouth, lungs, or the gastrointestinal tract.

Some species are responsible for the smell of topsoil, which is often particularly noticeable after rain.

Disease
Actinomycosis is most frequently caused by Actinomyces israelii and is sometimes known as the "most misdiagnosed disease," as it is frequently confused with neoplasms. A. israelii is a normal colonizer of the vagina, colon, and mouth. Infection is established first by a breach of the mucosal barrier thru various procedures (dental, GI), aspiration, or pathologies such as diverticulitis. The chronic phase of this disease is also known the "classic phase" because the acute, early phase is often missed by health care providers. This is characterized by slow contiguous growth that ignores tissue planes and forms a sinus tract that can spontaneously heal and recur, leading to a densely fibrotic lesion. This lesion is often characterized as "wooden." Sulfur granules form in a central purulence surrounded by neutrophils. This conglomeration of organisms is virtually diagnostic of Actinomyces israelii. Oral-cervicofacial disease is the most common form of actinomycosis. It is characterized by a painless "lumpy jaw." Lymphadenopathy is uncommon in this form of the disease. Another form of actinomycosis is thoracic disease, which is often misdiagnosed as a neoplasm, as it forms a mass that extends to the chest wall. It arises thru aspiration of organisms from the oropharynx. Symptoms include chest pain, fever, and weight loss. Abdominal disease is another manifestation of actinomycosis. This can lead to a sinus tract that drains to the abdominal wall or the perianal area. Pelvic actinomycosis is often caused by intrauterine devices (IUD). Symptoms include fever, abdominal pain, and weight loss. Actinomyces sp. have also been shown to infect the central nervous system in a dog "without history or evidence of previous trauma or other organ involvement." 

Treatment
Treatment for actinomycosis consists of antibiotics such as penicillin or amoxicillin for six to twelve months, as well as surgery if the disease is extensive.

Diagnosis
Consider actinomycosis when the patient has chronic progression of disease across tissue planes that is mass-like at times, sinus tract development that may heal and recur, and refractory infection after a typical course of antibiotics.