++
Anaerobic bacteria comprise most normal human flora. Normal microbial flora of the mouth (anaerobic spirochetes, Prevotella, fusobacteria), the skin (anaerobic diphtheroids), the large bowel (Bacteroides, anaerobic cocci, clostridia), and the female genitourinary tract (Bacteroides, anaerobic cocci, fusobacteria) produce disease when displaced from their normal sites into tissues or closed body spaces.
++
Anaerobic infections tend to be polymicrobial and abscesses are common. Pus and infected tissue often are malodorous. Septic thrombophlebitis and metastatic infection can occur; the latter may require incision and drainage. Diminished blood supply that favors proliferation of anaerobes because of reduced tissue oxygenation may interfere with the delivery of antimicrobials to the site of anaerobic infection. Cultures, unless carefully collected under anaerobic conditions, may yield negative results.
++
Important types of infections caused by anaerobic organisms are listed below. Treatment of these infections may consist of surgical exploration and judicious excision in conjunction with antimicrobial drugs.
+++
1. HEAD & NECK INFECTIONS
++
Prevotella species and anaerobic spirochetes are commonly involved in periodontal infections. These organisms, fusobacteria, and peptostreptococci may cause chronic sinusitis, peritonsillar abscess, chronic otitis media, and mastoiditis. F necrophorum has been recognized as a cause of pharyngitis in adolescents and young adults. F necrophorum infection has also been associated with septic internal jugular thrombophlebitis (Lemierre syndrome) and can cause septic pulmonary embolization. Surgical debridement and drainage are as important in treatment as antimicrobials. Penicillin alone is inadequate treatment for infections from oral anaerobic organisms because of penicillin resistance, usually due to beta-lactamase production. Therefore, ampicillin/sulbactam 1.5–3 g intravenously every 6 hours (if parenteral therapy is required), or amoxicillin/clavulanic acid 875 mg/125 mg orally twice daily can be used for coverage of oral anaerobes. Antimicrobial treatment is continued for a few days after symptoms and signs of infection have resolved. Indolent, established infections (eg, mastoiditis or osteomyelitis) may require prolonged courses of therapy, eg, 4–6 weeks or longer, using antimicrobials that penetrate bone.
++
Usually in the setting of poor oral hygiene and periodontal disease, aspiration of saliva may lead to necrotizing pneumonia, lung abscesses, and empyema. Polymicrobial infection is common, and anaerobes—particularly Prevotella species, fusobacteria, and peptostreptococci—are often among the etiologic agents. Most pulmonary infections respond to antimicrobial therapy alone. Percutaneous chest tube or surgical drainage is indicated for empyema.
++
Preferred regimens include ampicillin-sulbactam (3 gm intravenously every 6 hours, followed by amoxicillin/clavulanic acid 875/125 mg orally twice daily) or moxifloxacin (400 mg intravenously or orally once daily). Clindamycin (300–450 mg orally three times daily) could also be used. Metronidazole does not cover facultative streptococci, which often are present, and if used, a second agent that is active against streptococci, such as ceftriaxone, 1 g intravenously or intramuscularly daily, should be added. Because these infections respond slowly, a prolonged course of therapy (eg, 4–6 weeks) may be recommended for complicated infections.