[A case of inactive Escherichia coli isolated from feces initially suspected to be Shigella boydii subgroup C serotype 14 by conventional biochemical tests in tubes].

A small number of colorless colonies grew from DHL agar of feces culture taken as part of a complete physical for a 42 year-old woman who had lived in Singapore for several years. When cultured for first-stage identification using conventional biochemical tests in tubes for Enterobacteriaceae, such as TSI agar slant and SIM medium, the results for lactose reaction (-), saccharose reaction (-), gas (very weak +) and motility (-) were obtained, and Shigella spp. was suspected. Serological tests (by serotype) for Shigella spp. were then conducted. As a result, clear C14 agglutination was observed. Based on these results, the isolate was strongly suspected to be Shigella boydii serotype 14, but since the woman had no symptoms of abdominal pain, diarrhea or fever, such identification was still questionable. When further identification test was carried out using Walk-Away 96 and VITEK 2, non-Shigella spp. identification results were obtained. In second-stage identification, xylolytic activity, acetate salt utilization and use of carbon sources in CA (citrate-acetate) medium were checked, all results were positive, and the isolate was ultimately identified as Inactive Escherichia coli. While Shigella spp. and E. coli are taxonomically similar, they are quite different from each other in terms of pathogenicity. Accurate and rapid identification of Shigella spp. is therefore important.