Infections caused by anaerobic bacteria are common, and may be serious and life-threatening. Anaerobes predominant in the bacterial flora of normal human skin and mucous membranes, and are a common cause of bacterial infections of endogenous origin. Infections due to anaerobes can evolve all body systems and sites. The predominate ones include: abdominal, pelvic, respiratory, and skin and soft tissues infections. Because of their fastidious nature, they are difficult to isolate and are often overlooked. Failure to direct therapy against these organisms often leads to clinical failures. Their isolation requires appropriate methods of collection, transportation and cultivation of specimens. Treatment of anaerobic bacterial infection is complicated by the slow growth of these organisms, which makes diagnosis in the laboratory only possible after several days, by their often polymicrobial nature and by the growing resistance of anaerobic bacteria to antimicrobial agents.

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 Actinomycosis is an uncommon, chronic suppurative and  granulomatous infection.  Localized swelling with suppuration, abscess formation, tissue fibrosis, and draining sinuses characterize this disease that spreads contiguously forming often draining sinuses that extrude characteristic but not pathognomonic “sulfur granules.”20  Oral and cervicofacial infections are most common, however, any body site can be infected.  Other regions that are often affected are the thoracic, abdomin-pelvic,21 and the central nervous system.22


 Actinomyces israelli is the most common species causing human disease.  Other species include Actinomyces naeslundii, Actinomyces odontolyticus, Actinomyces viscosus, Actinomyces meyeri, and Propionibacterium propionicum (formerly Arachnia propionica).20  Most actinomycotic infections are polymicrobial, involving other aerobic and anaerobic bacteria.  The most commom co-isolates depend on the infection site and are Actinobacillus actinomycetemcomitans, Eikenella corrodens, Bacteroides, Fusobacterium, Capnocytophaga, Staphylococcus, Streptococcus, and Enterobacteriaceae.

Gram stain of Actinomyces

Pathogenesis and pathology

 Actinomyces species are of low pathogenicity and require disruption of the mucosal barrier to cause disease.  Oral and cervicofacial diseases commonly are associated with dental procedures, oral surgery, trauma, or dental sepsis.  Pulmonary infections usually arise after aspiration of oropharyngeal or gastrointestinal secretions.  Gastrointestinal infection frequently follows loss of mucosal integrity, such as with surgery, appendicitis, diverticulitis, trauma, or foreign bodies.20  The use of intrauterine contraceptive devices (IUDs) was linked to the development of female genital tract actinomycosis.  Other predisposing factors are steroid use, immunosuppression, and human immunodeficiency viral infections.

Clinical manifestations:


 It is usually observed in a setting of poor oral hygiene with tooth decay, periodontal disease, or gingivitis, in which mucosal integrity is disrupted by dental manipulations or other injury.  Chronic tonsillitis, mastoiditis, and otitis also are important risk factors.

 The infection generally evolves as a chronic or subacute painless or painful soft-tissue swelling or mass involving the submandibular or paramandibular region.23  The swelling may have ligneous consistency caused by tissue fibrosis.  More rapidly developing lesions often simulate pyogenic infections.  Periapical infection can also occur.23  Trismus may be present, and advanced lesions may discharge odorless pus containing sulfur granules through one or more sinuses.  The infection can extend to the carotid artery, tongue, sinuses, ears, mastoid orbit, salivary glands, pharynx, larynx, trachea, or thorax. 


 This is an indolent, slow process involving the pulmomonary parenchyma and pleural space.  This form often results from aspiration of infective material from the oropharynx, and rarely following esophageal perforation, by extension into the mediastinum from the neck, from an abdominal site, or hematogenous spread.  The mediastinum, pericardium, and myocardium can also rarely be affected. 

  The most common symptoms are chest pain, a productive cough, dyspnea, weight loss, and fever.  Anemia, mild leukocytosis, and an elevated sedimentation rate are relatively common.  The pulmonary lesion is either a mass lesion or pneumonitis and may resemble tuberculosis, and blastomycosis.  Pleural thickening, effusion, or emphysema are common.

Pulmonary actinomycosis


 The inflammatory process is a chronic, localized, and is preceded by the breaking of the integrity of the gastrointestinal mucosa by intestinal perforated.  The ileocecal region is involved most frequently .  The infection extends to contiguous organs.  Hepatic, renal, and splenic disseminations are uncommon and persistent draining sinuses may form.  The extensive fibrosis often mimics tumor.  Constitutional symptoms and signs are nonspecific; the most common are fever, diarrhea or constipation, weight loss, nausea, vomiting, pain, and sensation of mass. 21

Abdominal CT scan shoing enhancing mass (arrow) in anterior abdominal wall due to actinomycosis


 This is observed in women who had prolonged use of IUD, and may also occur from extension of intestinal infection.  Manifestations may range from a chronic vaginal discharge to pelvic inflammatory disease with tubo-ovarian abscesses or pseudomalignant masses. 24  Patients generally present with abnormal vaginal bleeding or discharge, abdominal or pelvic pain, menorrhagia, fever, and weight loss.

  Endometritis is the earlier form of the infection, followed by tubo-ovarian abscesses.  Extension to the uterus, bladder, rectal area, abdominal wall, peritoneum, pelvic bones, thorax, and systemic can also occur.

CT pelvic actinomycosis misdiagnosed as tubo-ovarian abscess

Central nervous system (CNS)

 CNS infections are rare and generally manifest as single or multiple encapsulated brain abscesses that appear as ring-enhancing lesions with thick wall that may be irregular or nodular  on CT with intravenous contrast material. 22  Headache and focal neurological signs are the most common finding.  Most infections hematogenously seeded from a distant site; however, direct extension of cervicofacial disease can occur. Actinomyces meningitis is chronic and basilar in location, with lymphocytic pleocytosis. 

MRI brain show a ring-like enhancing lesion in the right frontal lobe due to actinomyces


 A combination of appropriate microbiological and pathological studies are essential for diagnosis. 20  A high index of suspicion should be communicated to the microbiology diagnostic laboratory, along with material from draining sinuses, from deep-needle aspiration, or from biopsy specimens.  Anaerobic culture is required, and no selective media are available to restrict overgrowth of the slow-growing Actinomyces by associated microflora.  The presence, in pus or tissue specimens, of non-acid-fast, Gram-positive organisms with filamentous branching is suggestive of the diagnosis.  The characteristic morphology of sulfur granules and the presence of Gram-positive organisms within are helpful.  Direct fluorescent antibody conjugates and immunofluorescence testing can be.

 Penicillin G is the drug of choice for treating an infection caused by any of the Actinomyces. 20  It is given in high dosage over a prolonged period, to prevent recurrance.  Most deep-seated infections can be expected to respond to IV penicillin G, 10 to 20 million units/day given for 2 to 6 weeks, followed by an oral phenoxypenicillin ( 2 to 4 g/day ).  A few additional weeks of oral penicillin therapy may suffice for uncomplicated cervicofacial disease; complicated cases and extensive pulmonary or abdominal disease may require treatment for 12 to 18 months.  Alternative first-line agents include amoxicillin, tetracycline, erythromycin, and clindamycin.  First-generation cephalosporins, ceftriaxone, and imipenem also have been used successfully.  Metronidazole, aminoglycosides, and antifungal drugs are not active against these organisms. 

 Since many of the association organisms are known pathogens, coverage is desirable for them as well.  This is especially important in lower-abdominal infections.  Surgical removal of infected tissue may be needed if extensive necrotic tissue or fistulas are present. When well-defined IUD-related symptoms and Papanicolaou smears demonstrate Actinomyces, the IUD should be removed.  Antibiotic administration for a 2-week period may be indicated but more serious infections require prolonged therapy.


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