title: Suitability of selective plating media for recovering heat- or freeze-stressed Escherichia coli O157:H7 from tryptic soy broth and ground beef.
abstract: The efficacy of tryptic soy agar (TSA), modified sorbitol MacConkey agar (MSMA), modified eosin methylene blue (MEMB) agar, and modified SD-39 (MSD) agar in recovering a five-strain mixture of enterohemorrhagic Escherichia coli O157:H7 and five non-O157 strains of E. coli heated in tryptic soy broth at 52, 54, or 56 degrees C for 10, 20, and 30 min was determined. Nonselective TSA supported the highest recovery of heated cells. Significantly (P < or = 0.05) lower recovery of heat-stressed cells was observed on MSMA than on TSA, MEMB agar, or MSD agar. The suitability of MEMB agar or MSD agar for recovery of E. coli O157:H7 from heated or frozen (-20 degrees C) low- or high-fat ground beef was determined. Recovery of E. coli O157:H7 from heated ground beef was significantly (P < or = 0.05) higher on TSA than on MEMB agar, which in turn supported higher recovery than MSD agar did; MSMA was inferior. Recovery from frozen ground beef was also higher on MEMB and MSD agars than on MSMA. Higher populations were generally recovered from high-fat beef than from low-fat beef, but the relative performance of the recovery media was the same. The inability of MSMA to recover stressed cells of E. coli O157:H7 underscores the need to develop a better selective medium for enumerating E. coli O157:H7.
authors.affiliation: Department of Food Science and Technology, University of Georgia, Griffin 30223-1797, USA.
authors.forename: M
authors.initials: M
authors.lastname: Rocelle
authors.forename: S
authors.initials: S
authors.lastname: Clavero
authors.forename: L R
authors.initials: LR
authors.lastname: Beuchat
mesh_terms: D000362:Agar; D000818:Animals; D001431:Bacteriological Techniques; D002417:Cattle; D015169:Colony Count, Microbial; D003470:Culture Media; D004196:Disease Outbreaks; D004926:Escherichia coli / Q000145:classification / Q000302:isolation & purification* / Q000472:pathogenicity; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology; D005069:Evaluation Studies as Topic; D005517:Foodborne Diseases / Q000453:epidemiology / Q000382:microbiology; D005615:Freezing; D006358:Hot Temperature; D006801:Humans; D008460:Meat / Q000382:microbiology*
chemical_list: D003470:Culture Media; D000362:Agar