title: Rapid Identification of Shiga Toxin-Producing Escherichia coli O Serogroups from Fresh Produce and Raw Milk Enrichment Cultures by Luminex Bead-Based Suspension Array.
abstract: The U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM) Chapter 4a describes a Luminex microbead-based suspension array used to screen colonies for 11 clinically relevant Shiga toxin-producing Escherichia coli (STEC) serogroups: O26, O45, O91, O103, O104, O111, O113, O121, O128, O145, and O157. We evaluated the usefulness of this method to identify STEC-positive enrichment samples before agar plating. Twelve E. coli strains were added to three types of fresh produce (bagged baby spinach, alfalfa sprouts, and cilantro) at levels near the detection limit of the test. A subset of these strains (six O serogroups) was similarly evaluated in raw milk. For comparison, portions of each of the 168 enrichment cultures were analyzed for serogroup by a real-time PCR assay and a Bio-Plex 200 assay with the bead-based suspensions. No false-positive results were obtained. Of the 112 samples with a reported cycle threshold (CT) value, 101 undiluted, diluted, or extracted enrichment cultures also produced ratios above 5.0 in the Bio-Plex assay. When PCR CTvalues approached or were greater than 35, Bio-Plex detection became less reliable. Using undiluted or extracted enrichment cultures resulted in a significantly larger number of positive results. With the same enrichment material prepared for real-time PCR analysis as described in the BAM Chapter 4a, the STEC microbead-based suspension array can accurately screen food enrichment cultures.
authors.affiliation: U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, Division of Microbiology, College Park, Maryland 20740.
authors.forename: Julie A
authors.initials: JA
authors.lastname: Kase
authors.affiliation: U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, Division of Microbiology, College Park, Maryland 20740.|Oak Ridge Research Institute for Science and Education, Oak Ridge, Tennessee 37830.
authors.forename: Anna
authors.initials: A
authors.lastname: Maounounen-Laasri
authors.affiliation: U.S. Food and Drug Administration, Office of Regulatory Affairs, San Francisco Laboratory, Alameda, California 94502, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Lin
mesh_terms: D000362:Agar; D000818:Animals; D008892:Milk; D060888:Real-Time Polymerase Chain Reaction; D065288:Serogroup; D054323:Shiga-Toxigenic Escherichia coli / Q000145:classification*
chemical_list: D000362:Agar
keywords: Bio-Plex 200 instrumentation; Food enrichment; Luminex; O serogroup identification; Shiga toxin–producing Escherichia coli