Numerical evaluation of minimal biochemical test combinations for the identification of Enterobacteriaceae species.

Species identification of 572 clinical isolates of Enterobacteriaceae was determined using an in-house biochemical test panel and API 20E. The overall agreement was 82.7 per cent. When a numerical identification programme for Enterobacteriaceae was used to analyze the results of 440 E.coli isolates, the agreement with API 20E increased from 81.4 to 91.1 per cent. Numerical identification was then employed to evaluate 14 routine biochemical test panels used in 12 Swedish laboratories, and an additional 18 potential new test panel variants. The theoretical identification power of the panels was measured by a scoring system, based on simulated test results for the 14 most common species of Enterobacteriaceae. The results showed wide variations in the performance of different panels, with a number of panels being of insufficient quality. Among the 32 test panels, 6 panels indicated excellent performance. These should be further evaluated for routine laboratory performance. Numerical identification methods constitute powerful tools in the hands of the clinical microbiologist to aid in species identification as well as to analyze the quality of identification charts in use.