title: Comparison of different sample preparation procedures for the detection and isolation of Escherichia coli O157:H7 and Non-O157 STECs from leafy greens and cilantro.
abstract: The FDA Bacteriological Analytical Manual (BAM) method for the detection/isolation of Shiga toxin-producing Escherichia coli (STEC) involves enrichment of produce rinses, blended homogenates or stomached homogenates. However, the effectiveness of rinsing produce to remove attached bacteria is largely unknown. Moreover, PCR inhibitors can be released under physical treatment. The study objective was to determine the relative effectiveness of recovery methods for STEC contaminated produce. Spinach, lettuce, and cilantro were contaminated with E. coli O157:H7 or a non-O157 STEC, subjected to both the BAM method and a soak method, and tested by real-time PCR and cultural methods. For O157:H7 and non-O157:H7 STECs, the soak method was significantly more productive than leafy green rinses. Of 320 test portions, PCR of recovered colonies confirmed 148 were positive by rinsing and 271 were positive by soaking (an 83% increase in sensitivity). For recovery of O157:H7 from cilantro, of 60 test portions, positives were 38 by soaking, 41 by stomaching, and 28 by blending. Soaking and stomaching were significantly more productive than blending, although soaking was only arithmetically superior to stomaching. Based upon these results, it is recommended that a soak method replace the current BAM procedures.
authors.affiliation: Division of Microbiology, Microbial Methods Development Branch, Office of Regulatory Sciences, Center for Food Safety and Applied Nutrition, United States Food and Drug Administration, 5100 Paint Branch Parkway, Rm 3E-023, HFS - 711 College Park, MD 20740, USA. julie.kase@fda.hhs.gov
authors.forename: Julie A
authors.initials: JA
authors.lastname: Kase
authors.forename: Anna
authors.initials: A
authors.lastname: Maounounen-Laasri
authors.forename: Insook
authors.initials: I
authors.lastname: Son
authors.forename: Deanne M
authors.initials: DM
authors.lastname: Deer
authors.forename: Stacey
authors.initials: S
authors.lastname: Borenstein
authors.forename: Samantha
authors.initials: S
authors.lastname: Prezioso
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Hammack
mesh_terms: D002623:Chemistry Techniques, Analytical / Q000379:methods*; D028526:Coriandrum / Q000382:microbiology*; D019453:Escherichia coli O157 / Q000235:genetics / Q000302:isolation & purification*; D005506:Food Contamination / Q000032:analysis*; D018545:Lactuca / Q000382:microbiology*; D018515:Plant Leaves / Q000382:microbiology; D054323:Shiga-Toxigenic Escherichia coli / Q000235:genetics / Q000302:isolation & purification*; D018724:Spinacia oleracea / Q000382:microbiology*