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Careful studies of the antibiotic susceptibilities of mixtures of bacteria likely to be encountered in clinical cultures have shown that the results obtained are completely unreliable. Mixtures of resistant and sensitive species appeared either as "resistant" or "sensitive" depending upon the organisms and the drug. A number of sensitive species gave reactions interpreted as resistant when tested in combination. Since reactions of bacterial mixtures are completely unpredictable, the authors emphasize that antibiotic susceptibility testing be limited to pure cultures.

Two rapid systems for the identification of anaerobes were compared to a conventional growth system aided by a computer. The rapid systems (AN-Ident and RapID-ANA) are non-growth-dependent micronmethods that identify anaerobes in 4 h by the action of various constitutive enzymes on chromogenic substrates. The organisms tested were 98 anaerobes, most of which were clinical isolates. The AN!Ident system identified 76 of these to species level and 86 to genus level; the RapID-ANA system correctly identified 74 of the organisms to species level and identified 93 to genus level. The PRAS Il system correctly identified 77 to species level and 96 to genus level. In most instances, adequate identification could be obtained with either of the two rapid systems, but the conventional PRAS II system remains the most accurate.