Comparison of two methods for same-day identification of Enterobacteriaceae

Two commercial methods, API 20E (as modified for same-day enterobacterial identification) and Micro-ID, were evaluated for ability to provide useful same-day information of 368 clinically isolated Enterobacteriaceae. Organisms included Escherichia coli (54), Shigella (7), Edwardsiella tarda (1), Salmonella enteritidis (10), Citrobacter (30), Klebsiella (55), Enterobacter (68), Hafnia alvei (2), Serratia (33), Proteus (64), Morganella morganii (24), Providencia (18), and Yersinia enterocolitica (2). Methods were those of manufacturers without supplemental tests. API at five hours identified 78.5% of strains to species, 9.5% to genus only, 10.1% as part of a spectrum of identifications (SI), and 1.9% incorrect. Micro-ID at four hours yielded 90.0% correct identification to species and 3.3% to genus only, 4.0% SI, and 2.7% incorrect. API identification of many Serratia, Citrobacter, Providencia strains was to genus only; most incorrect results occurred in Serratia marcescens. Micro-ID identified most organisms to species; incorrect identifications were mainly S. marcescens and Klebsiella pneumoniae. Both systems provided excellent identification of E. coli. Both methods sacrifice a degree of accuracy that varies with the species tested, as compared to overnight systems, but both provide rapid information of potential clinical value.