The key to diagnosis of anaerobic infections are clinical suspicion and appropriate cultures.
Clinical suspicion is aided by site of infection and clinical situation, presence of gas (not just anaerobes cause gas) or cavitary disease (lung), and smell (which is usually foul/pungent).
Specimen collection - preferably pus, not swabs, and use of appropriate anaerobic transport media. Immediate transport to the clinical Micro-lab for culture anaerobically. These specimens should never be refrigerated -- this will kill most anaerobes. Cultures are performed on selective media (Figure 33-4), and detectable growth requires 48 - 72o. Identification of anaerobes require several fermentation tests that are not done at all hospitals.