Performance of two four-hour identification systems with atypical strains of Enterobacteriaceae

Two four-hour systems (Rapid 20E and Micro-ID) for identification of Enterobacteriaceae were evaluated using 66 strains isolated from clinical specimens which could not be identified by conventional methods. API 20E was used as reference method. Both systems had an acceptable identification rate (84.8% for Rapid 20E and 74.2% for Micro-ID). After referral to API's computer facilities the identification rate of Rapid 20E rose to 92.4%. Micro-ID incorrectly identified 16.7% of the strains and Rapid 20E only 1.5%. On the other hand, no identification was achieved in 13.6% of the strains using Rapid 20E versus 6% using Micro-ID. On the basis of these findings Rapid 20E is considered the more suitable system for the rapid identification of Enterobacteriaceae strains which cannot be identified by conventional methods.