Isolating E. coli from Ready-to-Eat Foods

A total of 252 strains of Enterobacteriaceae were isolated from 2000 RTE food samples in Guangdong, China, in 2021. To isolate Escherichia coli, 25 g of foodstuff was transferred to an aseptic bag and mixed with 225 mL of Butterfield's phosphate‐buffered solution. The sample was homogenized for 2 min at 230 rpm using a stomach machine and diluted 10‐fold. The diluent was inoculated into fermentation tubes containing lactose broth and incubated at 37°C for 24–48 h. A loopful of the suspension extracted from positive cultures (those showing lactose fermentation and gas production) was smeared onto CHROMagar E. coli agar plates and cultured at 37°C for 18–24 h. Finally, one colony from each plate was selected, analyzed, and identified using API 20E (bioMérieux) (Qinghua et al., 2018 (link)).