Sensitivity, specificity, and reproducibility of the automicrobic system (with the Enterobacteriaceae-plus biochemical card) for identifying clinical isolates of Gram- negative bacilli

Abstract

Two independent laboratories tested 1,743 clinical isolates by using the Enterobacteriaceae-plus Biochemical Card in the AutoMicrobic system (AMS) and identical standard reference methods. Included were 55 isolates representing 11 species that cannot be identified by the enterobacteriaceae-plus Biochemical Card computer program; 3 or these isolates were incorrectly identified as Pseudomonas cepacia. With the other 1,688 isolates, 5% of the AMS identifications were considered to be equivocal (probability value, less than 0.80), and the remaining test were 97% accurate (sensitive), Difficulty was observed in the ability of the AMS to identify some H2S-negative Citrobacter freundii species. An AMS response of P. cepacia was also considered nonspecific, because several other organisms were misidentified at P. cepacia. Reproducibility of the system was documented by testing 125 strains on 3-separate days; only 6 strains produced significantly variable results. The AMS (with the Enterobacteriaceae-plus Biochemical Card) was a very satisfactory, automated system for accurately identifying most gram-negative bacilli within 8 to 13 h.