Comparative study of three methods of identification of Enterobacteriaceae

Abstract

Three separate hospital clinical microbiology laboratories using 3 different identification systems participated in the identification of Enterobacteriaceae from a central pool of unknown clinical [human] isolates. With conventional tubed media, API-20E (Analytab Products Inc.) and R/B tube (Corning Diagnostics) systems, there was a 91.1% agreement in the species designation. No significant differences at the 95% confidence level were found among the systems. Evaluation of individual tests within the systems used revealed lysine decarboxylase of the conventional and citrate of the API-20E system to be significantly different from the same test within the other two systems. The lysine decarboxylase of the conventional system had species relatedness; the differences in citrate of the API-20E system were not related to a particular species. These individual test variations did not affect final organism identification. Reproducibility, evaluated as the system''s ability to designate the same identification of 2 separate occasions, was 92-94% for each system. Exact duplication of selected sets of reactions was 60% for conventional, 45% for API-20E and 61% for R/B. The variations in sets of reactions differed with the system and with the organism involved. The findings suggest equivalency among the 3 systems in ability to identify common clinical isolates of Enterobacteriaceae and point out the limited usefulness of these systems for biochemical biotyping.