- Anaerobic bacteria are organisms capable of growing in a reduced oxygen environment, either exclusively (obligate anaerobes) or in addition to growing in air (facultative anaerobes).
- Anaerobic bacteria can cause invasive and serious infections.
- Anaerobic bacteria tend to participate with other anaerobic and aerobic flora in causing polymicrobial infections.
- Although anaerobic bacteremia is less frequent in children than in adults, other anaerobic infections such as chronic sinusitis or chronic otitis media are common in children.
- Because of their fastidious nature, the ability of microbiology laboratories to identify anaerobic bacteria is highly dependent on proper collection and transport of culture specimens; hence, anaerobic bacteria are often missed and likely underreported.
- Impaired host immunity
- Splenic dysfunction
- Presence of devitalized tissue
- Surgery, trauma
- Vascular insufficiency
- Poorly controlled diabetes
- Presence of foreign bodies
- Anaerobic infections commonly derive from the normal flora of the oropharynx, skin, intestines, or the female genital tract; thus, anaerobic infections occur when there is a loss of integrity of anatomic or epithelial barriers at these sites.
- Virulence factors include production of exotoxins (e.g., Clostridia spp.), endotoxins (e.g., Fusobacterium spp.), and presence of phagocyte-inhibiting capsules (e.g., Bacteroides spp.).
The most common clinically-relevant anaerobes include the following:
- Gram-negative rods (Bacteroides, Prevotella, Porphyromonas, Fusobacterium)
- Gram-positive cocci (Peptostreptococcus, Peptococcus)
- Spore-forming gram-positive bacilli (Clostridia)
- Non–spore-forming gram-positive bacilli (Eubacterium, Bifidobacterium, Propionibacterium, Actinomyces, Lactobacillus)
- Gram-negative cocci (Veillonella, Acidaminococcus)
- Spirochetes (many of which are anaerobic)
Commonly Associated Conditions
- CNS infections:
- Brain abscess due to bacteremia
- Subdural empyema
- Epidural abscess (most commonly due to complications from sinusitis)
- Head and neck infections:
- Sinusitis (generally polymicrobial)
- Chronic otitis media
- Ludwig angina (infection of the submandibular space)
- Cervical adenitis
- Peritonsillar abscess
- Dental abscess
- Actinomycosis of jaw
- Lemierre disease
- Septic thrombophlebitis of the internal jugular vein owing to anaerobic bacteremia
- Most commonly with Fusobacterium spp., often resulting in pulmonary abscess formation and metastatic infection
- Pleuropulmonary infections:
- Aspiration of infected amniotic or vaginal secretions in neonates
- Aspiration of oral or gastrointestinal fluids in children (severe gingival or periodontal may be a risk factor)
- Pneumonia, abscess formation due to aspirated foreign bodies
- Peritonitis/peritoneal abscess:
- Appendiceal abscess
- Perforated viscus
- Postoperative complication
- Ascending infection may occur following biliary tract surgery (e.g., Kasai procedure).
- Soft tissue infections:
- Pilonidal cyst
- Hidradenitis suppurativa
- Crepitant cellulitis
- Necrotizing fasciitis
- Gas gangrene (Clostridium spp.)
- Infected decubitus ulcers (may result in contiguous osteomyelitis)
- Penetrating wounds (may lead to tetanus)
- Infections of the female genital tract:
- Tubo-ovarian or adnexal abscess
- Pelvic inflammatory diseases
- Pelvic abscess
- Bartholin gland, vulvar, or perineal abscess
- Bacterial vaginosis
- Infected bite wounds
- Anaerobes isolated from 50% of human or animal bites
- Often associated with focal primary site of involvement (gastrointestinal disease, abscess)
- Neonatal infections:
- Cellulitis at fetal monitoring sites
- Aspiration pneumonia
- Infant botulism
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