Verification of the abbreviated identification method for Escherichia coli based on CLSI guidelines

Abstract

Although rapid identification tests using a mass spectrometer are becoming mainstream, such tests are not applicable in all facilities because some of the facilities do not have a mass spectrometer. M35-A2 published by the Clinical and Laboratory Standards Institute (CLSI) details rapid and simple identification methods for bacteria and yeast. In this study, the identification method for Escherichia coli described in the CLSI guidelines (CLSI method) was verified with the method of York et al. (original method), which is the basis of the CLSI method, using clinical isolates. Of the 543 strains (E. coli strains, 478; non-E. coli strains, 65) of gram-negative bacilli that were oxidase-negative and spot indole-positive, all E. coli strains were correctly identified by both methods and 99% of these strains could be identified within 30 minutes. However, six non-E. coli strains identified using the CLSI method and one non-E. coli strain identified using the original method were misidentified as E. coli. In more detail, one strain of PYR test-negative Klebsiella oxytoca was misidentified by both methods, and five strains of β-hemolytic Morganella morganii were misidentified only by the CLSI method. These results suggest that the original method was more suitable for routine laboratory test. We hope that this identification method is used meaningfully according to the situation of each laboratory.