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Anaerobes form the predominant bacterial components of the normal
human skin and mucous membranes. They are responsible either alone
or in combination with aerobes for a wide variety of infections
ranging from superficial skin infections to intra-abdominal and
intracranial infections.
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Epidemiology
and Pathogenesis
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Anaerobic organisms are widely distributed in nature. They are
present in the soil as well as the skin, mucous membranes, and gastrointestinal
tracts of animals and humans. Only a few of these organisms have
been identified as responsible for disease in humans (eTable 249.1).
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Infection with these organisms usually results secondary to disruption
in the normal skin or mucous membrane barriers of the host, resulting
in entry of the bacteria into deeper tissues and leading to, at
times, potentially severe infections from an individual’s
own endogenous flora. Although some are strict anaerobes, others
may be facultative anaerobes, able to survive in conditions with or
without oxygen. The presence of devitalized tissues, low oxygen
tension, and low pH serve to greatly contribute to the pathogenesis
of anaerobic infections. Other conditions that may play a role include
host defense mechanisms, virulence factors (bacterial adherence
factors), production of toxins (eg, Clostridium species),
and the presence of other bacteria in polymicrobial infections.
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Due to their fastidious nature, as well as inconsistent use of
adequate methods for isolation and identification, anaerobic bacteria
are not easily isolated, which makes their exact frequency difficult
to ascertain.1 Although anaerobes have been reported
to account for 8% to 11% of episodes of bacteremia
in adults, anaerobic organisms have rarely been isolated from blood cultures
in pediatric patients.2,3 This may partly be explained
by higher prevalence of chronic or debilitating conditions in adults,
like malignant neoplasms, secondary immunodeficiencies, diabetes,
obstetric and gynecologic surgery, and the presence of decubitus
ulcers.
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Clinical Manifestations
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Commonly encountered diseases caused by anaerobic bacteria in
children are listed in Table 249-1. The principal
sites of infection are deep soft tissue infections around the mouth
and oropharynx, peritonitis and peritoneal abscesses following appendicitis,
or bowel rupture, and brain and lung abscesses. In females, beyond menarche,
anaerobic bacteria may cause different pelvic infections, such as
salpingitis, tuboovarian abscesses, pelvic inflammatory disease, as
well as bacterial vaginosis. Recently, various eye infections have
been associated with contact lens use, such as conjunctivitis and
keratitis. Overuse of antibiotics leading to pseudomembranous colitis,
which may be quite refractory to treatment, has also emerged as
a significant problem, more so in adults than in children.
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