title: Theoretic and experimental analysis of the ability of a commercially prepared system to detect mixtures of bacteria.
abstract: The validity of the biochemical identification of bacteria presumes that the inoculum consists of a pure growth of bacteria. The detection of mixtures of bacteria with the Analytab Enteric (API 20E) system was tested. Using a computer to predict the response of the API 20E system to mixed cultures, the presence of a mixture was not detected in 15% of all pairwise combinations of 324 common organisms of the Enterobacteriaceae family and in 19% of all pairwise combinations of Enterobacteriaceae with four gram-positive cocci. These theoretic predictions were confirmed experimentally for selected mixtures in which the bacteria were combined in equal concentrations. These results indicate that a purity subculture plate must be used to insure the detection of mixtures of bacteria, because the API 20E system fails to detect a large number of mixtures and may erroneously identify the organisms in such mixtures.
mesh_terms: D001431:Bacteriological Techniques; D004755:Enterobacteriaceae; D013293:Enterococcus faecalis; D013210:Staphylococcus; D013211:Staphylococcus aureus; D013291:Streptococcus