title: Transfer of Escherichia coli O157:H7 from equipment surfaces to fresh-cut leafy greens during processing in a model pilot-plant production line with sanitizer-free water.
abstract: Escherichia coli O157:H7 contamination of fresh-cut leafy greens has become a public health concern as a result of several large outbreaks. The goal of this study was to generate baseline data for E. coli O157:H7 transfer from product-inoculated equipment surfaces to uninoculated  lettuce during pilot-scale processing without a sanitizer. Uninoculated cored heads of iceberg and romaine lettuce (22.7 kg) were processed using a commercial shredder, step conveyor, 3.3-m flume tank with sanitizer-free tap water, shaker table, and centrifugal dryer, followed by 22.7 kg of  product that had been dip inoculated to contain ∼10(6), 10(4), or 10(2) CFU/g of a four-strain avirulent, green fluorescent protein-labeled, ampicillin-resistant E. coli O157:H7 cocktail. After draining the flume tank and refilling the holding tank  with tap water, 90.8 kg of uninoculated product was similarly processed and collected in ∼5-kg aliquots. After processing, 42 equipment surface samples and 46 iceberg or 36 romaine lettuce samples (25 g each) from the collection baskets were quantitatively examined for E. coli O157:H7  by direct plating or membrane filtration using tryptic soy agar containing 0.6% yeast extract and 100 ppm of ampicillin. Initially, the greatest E. coli O157:H7 transfer was seen from inoculated lettuce to the shredder and conveyor belt, with all equipment surface populations decreasing  90 to 99% after processing 90.8 kg of uncontaminated product. After processing lettuce containing 10(6) or 10(4) E. coli O157:H7 CFU/g followed by uninoculated lettuce, E. coli O157:H7 was quantifiable throughout the entire 90.8 kg of product. At an inoculation  level of 10(2) CFU/g, E. coli O157:H7 was consistently detected in the first 21.2 kg of previously uninoculated lettuce at 2 to 3 log CFU/100 g and transferred to 78 kg of product. These baseline E. coli O157:H7 transfer results will help determine the degree of sanitizer  efficacy required to better ensure the safety of fresh-cut leafy greens.
authors.affiliation: Department of Food Science and Human Nutrition, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Annemarie L
authors.initials: AL
authors.lastname: Buchholz
authors.forename: Gordon R
authors.initials: GR
authors.lastname: Davidson
authors.forename: Bradley P
authors.initials: BP
authors.lastname: Marks
authors.forename: Ewen C D
authors.initials: EC
authors.lastname: Todd
authors.forename: Elliot T
authors.initials: ET
authors.lastname: Ryser
mesh_terms: D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D004866:Equipment Contamination; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005506:Food Contamination / Q000032:analysis*; D005511:Food Handling / Q000379:methods*; D006801:Humans; D018545:Lactuca / Q000382:microbiology*; D010865:Pilot Projects; D012499:Sanitation / Q000379:methods