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ARS Home » Plains Area » Clay Center, Nebraska » U.S. Meat Animal Research Center » Meat Safety and Quality » Research » Research Project #442725

Research Project: Evaluation of Media Formulated to Aid in Isolation of Shiga Toxin-producing E. Coli

Location: Meat Safety and Quality

Project Number: 3040-42000-021-010-N
Project Type: Non-Funded Cooperative Agreement

Start Date: Aug 1, 2022
End Date: Jul 31, 2023

Objective:
Determine if Cooperator’s media formulated to aid in isolation of Shiga toxin-producing E. coli can meet needs of ARS and FSIS.

Approach:
Evaluate cooperator’s media in the following ways: 1) Screen target and non-target E. coli (those that are STEC and non-STEC) for growth and identification on cooperators media. Specifically, 90-100 isolates of E. coli O157 including H7; 90-100 isolates each of non-O157 STEC serogroups O103 and O26; 40-50 isolates each of non-O157 STEC serogroups O45, O111, O121, and O145. These E. coli O157 and non-O157 STEC will include background organisms commonly mistaken for the targeted E coli type. Further, 90-100 isolates of STEC determined to be potentially pathogenic and belonging to non-Top 7 serogroups (ex: O5, O118, O74, O172, etc…) will be included. Background E. coli, arbitrarily selected from 498 samples of US ground beef, will serve as negative controls. Any strains expected to present as a STEC that do not, and vice versa will be reexamined and characterized to resolve the discrepancy. Results from the above E. coli screening will be compared to the results of the same isolates grown on media currently used to identify STEC: modified Rainbow Agar, CHROMagar STEC, washed sheeps blood agar/SHIBAM, and modified BGIC-SMAC. 2) Assuming the cooperator’s media performs as described, then the cooperators media will be used during routine STEC isolation attempts from field lab provided beef enrichment broths. 100-300 broths depending on the providing labs, will be cultured for STEC using targeted IMS for the most common STEC serogroups if indicated by molecular assay (O26, O45, O103, O111, O121, O145 and O157) and but direct plating to identify STEC in a serogroup independent fashion.