title: Chromogenic agar medium for detection and isolation of Escherichia coli serogroups O26, O45, O103, O111, O121, and O145 from fresh beef and cattle feces.
abstract: Non-O157 Shiga toxin-producing Escherichia coli (STEC) strains are clinically important foodborne pathogens. Unlike E. coli O157:H7, these foodborne pathogens have no unique biochemical characteristics to readily distinguish them from other E. coli strains  growing on plating media. In this study, a chromogenic agar medium was developed in order to differentiate among non-O157 STEC strains of serogroups O26, O45, O103, O111, O121, and O145 on a single agar medium. The ability of this chromogenic agar medium to select and distinguish among these  pathogens is based on a combination of utilization of carbohydrates, b -galactosidase activity, and resistance to selective agents. The agar medium in combination with immunomagnetic separation was evaluated and successfully allowed for the detection and isolation of these six serogroups from  artificially contaminated fresh beef. The agar medium in combination with immunomagnetic separation also allowed successful detection and isolation of naturally occurring non-O157 STEC strains present in cattle feces. Thirty-five strains of the top six non-O157 STEC serogroups were isolated  from 1,897 fecal samples collected from 271 feedlot cattle. This chromogenic agar medium could help significantly in routine screening for the top six non-O157 STEC serogroups from beef cattle and other food.
authors: U.S. Department of Agriculture, Agricultural Research Service, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center, Nebraska 68933-0166, USA. norasak.kalchayanand@ars.usda.gov
authors: Norasak
authors: N
authors: Kalchayanand
authors: Terrance M
authors: TM
authors: Arthur
authors: Joseph M
authors: JM
authors: Bosilevac
authors: James E
authors: JE
authors: Wells
authors: Tommy L
authors: TL
authors: Wheeler
mesh_terms: D000362:Agar; D000818:Animals; D002417:Cattle / Q000382:microbiology*; D015169:Colony Count, Microbial / Q000379:methods; D005243:Feces / Q000382:microbiology*; D005506:Food Contamination / Q000032:analysis*; D018189:Immunomagnetic Separation / Q000379:methods; D008460:Meat / Q000382:microbiology; D012703:Serotyping; D054323:Shiga-Toxigenic Escherichia coli / Q000145:classification / Q000302:isolation & purification*
chemical_list: D000362:Agar