ACTINOMYCOSIS
Actinomycosis is a chronic suppurative or granulomatous bacterial infection caused by branching, non–spore-forming, gram-positive bacteria belonging to the genus Actinomyces. Actinomyces spp. are strict or facultative anaerobes. Their cellular morphology is variable, usually diphtheroid or filamentous, although bacillary and coccoid forms may also occur. Actinomyces are true bacteria; their filaments are narrower than fungal hyphae; and unlike the latter, they readily fragment into bacillary forms. In addition, Actinomyces spp. reproduce by binary fission and not by spore formation or budding as in fungi. They are part of normal oral flora within gingival crevices and tonsillar crypts. Their prevalence is increased with poor oral hygiene, in periodontal pockets, in dental plaques, and on carious teeth.
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Actinomycosis
is a cosmopolitan, sporadically occurring endogenous infection. Males are 1.5
to 3.0 times more likely to have the disease than females. Actinomyces
israelii is the usual cause of actinomycosis, although several other
species can occasionally cause human disease. Clinical types of actinomycosis
and their incidence include cervicofacial (55%), pulmonary (20%), abdominal
(20%), and disseminated (5%). A hallmark of actinomycosis is the tendency to
spread through anatomic barriers, including fascial planes, and the development
of multiple sinus tracts. Cervicofacial infection usually follows tooth
extraction or other trauma to the oral mucosa and is characterized by a firm
indurated mass in the region of the jaw (“lumpy jaw”) that often suppurates and
gives rise to multiple cutaneous fistulas. Poor oral hygiene is important as a
predisposing factor. Other predisposing conditions include diabetes, immunosuppression,
malnutrition, and local tissue damage.
Pulmonary
actinomycosis may result directly from a cervicofacial focus or from extension
through the diaphragm from an intraabdominal lesion. As a rule, it is secondary
to aspiration of the organism from the mouth, and generally the lower lobes are
involved. Initial symptoms include mild fever and cough with purulent sputum.
With abscess formation, the sputum may become blood streaked. If it is not
treated, the infection often spreads to the pleura and through the thoracic
wall, causing subsequent empyema, soft tissue abscesses, and multiple draining
sinuses. The clinical and radiographic signs of pulmonary actinomycosis are
similar to those of nocardiosis, tuberculosis, and other lung disorders.
Abdominal
infection most often occurs after appendectomy or bowel perforation, which may
be either traumatic or spontaneous. Abdominal actinomycosis is more common in
the cecum and appendix, where it is frequently associated with sinus formation.
In disseminated actinomycosis, virtually any organ may be involved.
Actinomyces spp. form
characteristic sulfur granules in infected tissue but not in vitro. Pus should
be placed in a sterile Petri dish and examined with a hand lens against a dark
background for these granules. If present, these granules are yellowish white
to white firm flecks that vary in size from a barely visible speck to 5 mm in
diameter. Under an oil immersion lens, Gram stain of the granules reveals an
internal tangle of delicate gram-positive filaments with a rosette of peripheral
clubs. Similar granules may be formed by other microorganisms such as Nocardia
brasiliensis, Streptomyces madurae, and Staphylococcus aureus.
However, these other granules lack the rosette of peripheral clubs.
Diagnosis of
actinomycosis is confirmed by culture and occasionally by histopathologic
evidence of Actinomyces infection. Actinomyces spp. are
slow-growing, fastidious organisms, which require an enriched medium, anaerobic
or microaerophilic conditions, and up to 14 to 21 days for optimal growth. Therefore,
the clinical microbiology laboratory should be informed if Actinomyces spp.
are suspected. Actinomyces spp. are almost invariably isolated as part
of a polymicrobial flora. However, the significance of these coexisting bacteria
in the pathogenesis of actinomycosis is unclear, and these pathogens do not
need to be specifically treated with antibiotics.
TREATMENT
Management of
patients with actinomycosis often requires prolonged courses of antibiotics and
surgical intervention in
complicated cases. High-dose penicillin is the treatment of choice for
actinomycosis. For mild infections without significant suppuration or fistulous
tracts, oral penicillin V or amoxicillin for 2 to 6 months is recommended.
Acceptable alternatives to penicillin include the tetracyclines, erythromycin,
and clindamycin. In patients with more severe cervicofacial actinomycosis that
requires surgery, intravenous penicillin G for 4 to 6 weeks followed by oral
penicillin V for 6 to 12 months is recommended.
In addition to
antibiotics, surgical intervention may be required for excision of necrotic
tissue or recalcitrant fibrotic lesions and for drainage of extensive abscesses
with marsupilation of persisting sinus tracts. Prognosis is excellent with a
combined medical-surgical approach. However, recurrences can occur, so prolonged
observation of
patients after treatment is recommended.
