Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1317 page)

   Specimens may be collected from sites that are not the primary site of active infection (even though there may be signs of inflammation at the site).

   Inadequate site preparation may result in false-positive cultures due to specimen contamination with endogenous flora. Contaminated specimens may also mask the recognition of slow-growing or fastidious pathogens in the culture.

ANAEROBIC CULTURE

   Definition and Use

   Anaerobic cultures are indicated for evaluation of patient specimens taken from sites with signs and symptoms of bacterial infection (e.g., swelling, redness, heat, pus, or exudate). Infections associated with anaerobic pathogens include surgical and traumatic wounds, sinusitis and pararespiratory infections, pelvic and intra-abdominal infections, osteomyelitis, myositis, gangrene, and necrotic wounds, abscesses, and actinomycosis and infections associated with fistula formation.

   Anaerobic cultures are used for the detection of common anaerobic bacterial pathogens from patient specimens. Site-specific aerobic bacterial cultures (e.g., tissue culture, abscess culture, wound culture) are recommended, if available. Specimens are inoculated on several types of anaerobic culture media. (see “Aerobic Culture” for a general discussion about media). Media should be fresh and prereduced. Typical media for aerobic cultures include

   Supportive agar media, like Schaedler agar or CDC anaerobic blood agar

   Selective/differential agar media:

   Phenylethyl alcohol or CNA agar for anaerobic gram-positive pathogens

   Kanamycin–vancomycin–laked blood agar, for anaerobic gram-negative bacilli

   Bacteroide bile–esculin agar, for
Bacteroides fragilis
group

   Egg yolk agar, for characterization of
Clostridium
species

   Cycloserine–cefoxitin–egg yolk–fructose agar (CCFA), for
Clostridium difficile