title: Quantitative transfer of Escherichia coli O157:H7 to equipment during small-scale production of fresh-cut leafy greens.
abstract: Postharvest contamination and subsequent spread of Escherichia coli O157:H7 can occur during shredding, conveying, fluming, and dewatering of fresh-cut leafy greens. This study quantified E. coli O157:H7 transfer from leafy greens to equipment surfaces during simulated  small-scale commercial processing. Three to five batches (22.7 kg) of baby spinach, iceberg lettuce, and romaine lettuce were dip inoculated with a four-strain cocktail of avirulent, green fluorescent protein-labeled, ampicillinresistant E. coli O157:H7 to contain ∼10(6),  10(4), and 10(2) CFU/g, and then were processed after 1 h of draining at ∼23°C or 24 h of storage at 4°C. Lettuce was shredded using an Urschel TransSlicer at two different blade and belt speeds to obtain normal (5 by 5 cm) and more finely shredded (0.5 by 5 cm)  lettuce. Thereafter, the lettuce was step conveyed to a flume tank and was washed and then dried using a shaker table and centrifugal dryer. Product (25-g) and water (40-ml) samples were collected at various points during processing. After processing, product contact surfaces (100 cm(2))  on the shredder (n = 14), conveyer (n = 8), flume tank (n = 11), shaker table (n = 9), and centrifugal dryer (n = 8) were sampled using one-ply composite tissues. Sample homogenates diluted in phosphate or neutralizing buffer were plated, with or without  prior 0.45- m m membrane filtration, on Trypticase soy agar containing 0.6% yeast extract supplemented with 100 ppm of ampicillin to quantify green fluorescent protein-labeled E. coli O157:H7 under UV light. During leafy green processing, ∼90% of the E. coli O157:H7  inoculum transferred to the wash water. After processing, E. coli O157:H7 populations were highest on the conveyor and shredder (P<0.05), followed by the centrifugal dryer, flume tank, and shaker table, with ∼29% of the remaining product inoculum lost during centrifugal  drying. Overall, less (P<0.05) of the inoculum remained on the product after centrifugally drying iceberg lettuce that was held for 1 h (8.13%) as opposed to 24 h (42.18%) before processing, with shred size not affecting the rate of E. coli O157:H7 transfer.
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; D004866:Equipment Contamination; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005506:Food Contamination; D005511:Food Handling / Q000379:methods*; D006801:Humans; D018545:Lactuca / Q000382:microbiology*; D018724:Spinacia oleracea / Q000382:microbiology*; D013997:Time Factors