Survival and Growth of Escherichia coli O157:H7 Inoculated onto Cut Lettuce Before or After Heating in Chlorinated Water, Followed by Storage at 5 or 15°C

2001 ◽  
Vol 64 (3) ◽  
pp. 305-309 ◽  
Author(s):  
YUE LI ◽  
ROBERT E. BRACKETT ◽  
JINRU CHEN ◽  
LARRY R. BEUCHAT
Keyword(s):  
Escherichia Coli ◽  
Escherichia Coli O157 ◽  
Marked Influence ◽  
E Coli ◽  
Iceberg Lettuce ◽  
Survival And Growth ◽  
Fresh Cut ◽  
Subsequent Storage ◽  
Efficacy Of Treatment ◽  
Treatment Water

This study determined the effects of mild heat and chlorine treatment followed by storage for up to 18 days at 5°C or 7 days at 15°C on the survival and growth of Escherichia coli O157:H7 inoculated onto fresh-cut iceberg lettuce. The efficacy of treatment with 20 ppm chlorine in killing the pathogen on lettuce at 50°C was determined. Treatment of lettuce with 20 ppm chlorine at either 20 or 50°C did not result in significantly greater reductions in populations of E. coli O157:H7 compared to respective treatments in water without chlorine. The pathogen steadily decreased in viability on treated lettuce throughout subsequent storage at 5°C for 18 days. The population increased by 2.3 to 3.2 log10 CFU/g within 2 days, then continued to increase at a slower rate through 7 days of storage at 15°C. At 4 and 7 days, significantly (α = 0.05) higher populations were reached on lettuce that had been treated at 50°C, compared to respective samples that had been treated at 20°C, regardless of the presence of 20 ppm chlorine in the treatment water. Treatment of lettuce with 20 ppm chlorine at 50 or 20°C before or after inoculation with E. coli O157:H7 did not have a marked influence on behavior of the pathogen during subsequent storage at 5 or 15°C.

Tracking an Escherichia coli O157:H7–Contaminated Batch of Leafy Greens through a Pilot-Scale Fresh-Cut Processing Line

2014 ◽  
Vol 77 (9) ◽  
pp. 1487-1494 ◽  
Author(s):  
ANNEMARIE L. BUCHHOLZ ◽  
GORDON R. DAVIDSON ◽  
BRADLEY P. MARKS ◽  
EWEN C. D. TODD ◽  
ELLIOT T. RYSER
Keyword(s):  
Escherichia Coli ◽  
Membrane Filtration ◽  
Fluorescent Protein ◽  
Pilot Scale ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Leafy Greens ◽  
Iceberg Lettuce ◽  
Processing Line ◽  
Fresh Cut

Cross-contamination of fresh-cut leafy greens with residual Escherichia coli O157:H7–contaminated product during commercial processing was likely a contributing factor in several recent multistate outbreaks. Consequently, radicchio was used as a visual marker to track the spread of the contaminated product to iceberg lettuce in a pilot-scale processing line that included a commercial shredder, step conveyor, flume tank, shaker table, and centrifugal dryer. Uninoculated iceberg lettuce (45 kg) was processed, followed by 9.1 kg of radicchio (dip inoculated to contain a four-strain, green fluorescent protein–labeled nontoxigenic E. coli O157:H7 cocktail at 106 CFU/g) and 907 kg (2,000 lb) of uninoculated iceberg lettuce. After collecting the lettuce and radicchio in about 40 bags (~22.7 kg per bag) along with water and equipment surface samples, all visible shreds of radicchio were retrieved from the bags of shredded product, the equipment, and the floor. E. coli O157:H7 populations were quantified in the lettuce, water, and equipment samples by direct plating with or without prior membrane filtration on Trypticase soy agar containing 0.6% yeast extract and 100 ppm of ampicillin. Based on triplicate experiments, the weight of radicchio in the shredded lettuce averaged 614.9 g (93.6%), 6.9 g (1.3%), 5.0 g (0.8%), and 2.8 g (0.5%) for bags 1 to 10, 11 to 20, 21 to 30, and 31 to 40, respectively, with mean E. coli O157:H7 populations of 1.7, 1.2, 1.1, and 1.1 log CFU/g in radicchio-free lettuce. After processing, more radicchio remained on the conveyor (9.8 g; P < 0.05), compared with the shredder (8.3 g), flume tank (3.5 g), and shaker table (0.1 g), with similar E. coli O157:H7 populations (P > 0.05) recovered from all equipment surfaces after processing. These findings clearly demonstrate both the potential for the continuous spread of contaminated lettuce to multiple batches of product during processing and the need for improved equipment designs that minimize the buildup of residual product during processing.

Efficacy of Sanitizer Treatments on Survival and Growth Parameters of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on Fresh-Cut Pieces of Cantaloupe during Storage†

2015 ◽  
Vol 78 (7) ◽  
pp. 1288-1295 ◽  
Author(s):  
DIKE O. UKUKU ◽  
LIHAN HUANG ◽  
CHRISTOPHER SOMMERS
Keyword(s):  
Escherichia Coli ◽  
Listeria Monocytogenes ◽  
Storage Temperature ◽  
Growth Parameters ◽  
Bacterial Pathogens ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Mesophilic Bacteria ◽  
Survival And Growth ◽  
Fresh Cut

For health reasons, people are consuming fresh-cut fruits with or without minimal processing and, thereby, exposing themselves to the risk of foodborne illness if such fruits are contaminated with bacterial pathogens. This study investigated survival and growth parameters of Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and aerobic mesophilic bacteria transferred from cantaloupe rind surfaces to fresh-cut pieces during fresh-cut preparation. All human bacterial pathogens inoculated on cantaloupe rind surfaces averaged ~4.8 log CFU/cm2, and the populations transferred to fresh-cut pieces before washing treatments ranged from 3 to 3.5 log CFU/g for all pathogens. A nisin-based sanitizer developed in our laboratory and chlorinated water at 1,000 mg/liter were evaluated for effectiveness in minimizing transfer of bacterial populations from cantaloupe rind surface to fresh-cut pieces. Inoculated and uninoculated cantaloupes were washed for 5 min before fresh-cut preparation and storage of fresh-cut pieces at 5 and 10°C for 15 days and at 22°C for 24 h. In fresh-cut pieces from cantaloupe washed with chlorinated water, only Salmonella was found (0.9 log CFU/g), whereas E. coli O157:H7 and L. monocytogenes were positive only by enrichment. The nisin-based sanitizer prevented transfer of human bacteria from melon rind surfaces to fresh-cut pieces, and the populations in fresh-cut pieces were below detection even by enrichment. Storage temperature affected survival and the growth rate for each type of bacteria on fresh-cut cantaloupe. Specific growth rates of E. coli O157:H7, Salmonella, and L. monocytogenes in fresh-cut pieces were similar, whereas the aerobic mesophilic bacteria grew 60 to 80% faster and had shorter lag phases.

Microbial Antagonists of Escherichia coli O157:H7 on Fresh-Cut Lettuce and Spinach

2009 ◽  
Vol 72 (7) ◽  
pp. 1569-1575 ◽  
Author(s):  
MICHAEL A. JOHNSTON ◽  
MARK A. HARRISON ◽  
RUTH A. MORROW
Keyword(s):  
Escherichia Coli ◽  
Inhibitory Activity ◽  
Antagonistic Activity ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Iceberg Lettuce ◽  
Naturally Occurring ◽  
Pathogen Load ◽  
Natural Microflora ◽  
Fresh Cut

Fresh-cut lettuce and spinach can become contaminated with pathogens at numerous points from the field to the retail market. Natural microflora present on fresh produce may help reduce the pathogen load. The objective of this study was to isolate natural microflora from fresh-cut iceberg lettuce and baby spinach and to determine whether these bacteria were antagonistic toward Escherichia coli O157:H7. Samples were collected under conditions that mimicked actual practices between production and retail sale. Evidence of naturally occurring microorganisms on fresh lettuce (295 isolates) and spinach (200 isolates) and of possible antagonistic activity toward E. coli O157:H7 was documented. Inhibitory activity by several isolates was due to either acid production or antimicrobial peptides. Bacteria with inhibitory activity were isolated from every step in the processing and handling of the fresh-cut iceberg lettuce and baby spinach.

Survival and Growth of Listeria monocytogenes and Escherichia coli O157:H7 in Ready-to-Eat Iceberg Lettuce Washed in Warm Chlorinated Water

2002 ◽  
Vol 65 (3) ◽  
pp. 459-464 ◽  
Author(s):  
PASCAL DELAQUIS ◽  
SANDRA STEWART ◽  
SANDRA CAZAUX ◽  
PETER TOIVONEN
Keyword(s):  
Escherichia Coli ◽  
Listeria Monocytogenes ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Iceberg Lettuce ◽  
Before And After ◽  
Survival And Growth ◽  
Spoilage Microflora ◽  
Storage Temperatures

Cut iceberg lettuce inoculated with Escherichia coli O157:H7 and Listeria monocytogenes before and after washing for 3 min in cold (4°C) and warm (47°C) water containing 100 mg/liter total chlorine was stored at 1 and 10°C in oxygen-permeable film packages (6,000 to 8,000 cc/m2/24 h). Cold chlorinated water was detrimental to the survival of E. coli O157: H7 and L. monocytogenes at both storage temperatures. In contrast, washing in warm chlorinated water favored the growth of both pathogens in lettuce stored at 10°C. There was no evidence of a relationship between the magnitude of spoilage microflora and the fate of either bacterium.

Quantitative Transfer of Escherichia coli O157:H7 to Equipment during Small-Scale Production of Fresh-Cut Leafy Greens

2012 ◽  
Vol 75 (7) ◽  
pp. 1184-1197 ◽  
Author(s):  
ANNEMARIE L. BUCHHOLZ ◽  
GORDON R. DAVIDSON ◽  
BRADLEY P. MARKS ◽  
EWEN C. D. TODD ◽  
ELLIOT T. RYSER
Keyword(s):  
Escherichia Coli ◽  
Green Fluorescent Protein ◽  
Fluorescent Protein ◽  
Small Scale ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Leafy Greens ◽  
Iceberg Lettuce ◽  
Fresh Cut ◽  
Green Fluorescent

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, ampicillin-resistant E. coli O157:H7 to contain ∼106, 104, and 102 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 cm2) 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-μm 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.

Effectiveness of Bacteriophages in Reducing Escherichia coli O157:H7 on Fresh-Cut Cantaloupes and Lettuce†

2009 ◽  
Vol 72 (7) ◽  
pp. 1481-1485 ◽  
Author(s):  
MANAN SHARMA ◽  
JITENDRA R. PATEL ◽  
WILLIAM S. CONWAY ◽  
SEAN FERGUSON ◽  
ALEXANDER SULAKVELIDZE
Keyword(s):  
Escherichia Coli ◽  
Foodborne Illness ◽  
Escherichia Coli O157 ◽  
E Coli ◽  
Iceberg Lettuce ◽  
Fresh Cut ◽  
Phosphate Buffered Saline

Consumption of produce contaminated with Escherichia coli O157:H7 has resulted in cases of foodborne illness. We determined the efficacy of a mixture of three E. coli O157:H7–specific bacteriophages (ECP-100) in reducing the number of viable E. coli O157:H7 on contaminated fresh-cut iceberg lettuce and cantaloupe. E. coli O157:H7 was spot inoculated on lettuce pieces (9 cm2) with a population of 3.76 log CFU/cm2, allowed to dry, and then sprayed with a control (phosphate-buffered saline) or ECP-100 to deliver 7.98 log PFU/cm2 to lettuce stored for 2 days at 4°C. Cut pieces of cantaloupe were spot inoculated with E. coli O157:H7 (4.55 log CFU/ml) and treated with the control or ECP-100 (6.69 log PFU/ml), and then stored at 4 or 20°C for up to 7 days. On days 0, 2, 5, and 7, cantaloupe samples were homogenized, and populations of E. coli O157:H7 were enumerated. Populations of E. coli O157:H7 on lettuce treated with ECP-100 on 0, 1, and 2 days (0.72, <0.22, and 0.58 log CFU/cm2 of lettuce) and stored at 4°C were significantly (P < 0.05) lower than those treated with the control (2.64, 1.79, and 2.22 log CFU/cm2), respectively. Populations on cut cantaloupes treated with ECP-100 on days 2, 5, and 7 (0.77, 1.28, and 0.96 log CFU/ml) and stored at 4°C were significantly lower than those cut cantaloupes treated with the control (3.34, 3.23, and 4.09 log CFU/ml), respectively. This study is the first to show the effectiveness of bacteriophages to reduce E. coli O157:H7 on fresh-cut lettuce and cantaloupes.

Fate of Escherichia coli O157:H7 in the Presence of Indigenous Microorganisms on Commercially Packaged Baby Spinach, as Impacted by Storage Temperature and Time†

2009 ◽  
Vol 72 (10) ◽  
pp. 2038-2045 ◽  
Author(s):  
YAGUANG LUO ◽  
QIANG HE ◽  
JAMES L. McEVOY ◽  
WILLIAM S. CONWAY
Keyword(s):  
Escherichia Coli ◽  
Product Quality ◽  
Elevated Temperatures ◽  
Storage Temperature ◽  
Escherichia Coli O157 ◽  
Indigenous Microorganisms ◽  
E Coli ◽  
Psychrotrophic Bacteria ◽  
Survival And Growth

This study investigated the effect of storage temperature and time on the survival and growth of Escherichia coli O157:H7, the growth of indigenous microorganisms, and the changes in product quality of packaged baby spinach. Commercial packages of spinach within 2 days of processing were cut open at one end, sprayed with fine mists of E. coli O157:H7 inoculum, resealed, and then stored at 1, 5, 8, and 12°C for 12 days until their labeled best-if-used-by dates. Microbial enumeration and product quality evaluation were conducted on day(s) 0, 3, 6, 9, and 12 postinoculation. Spinach held at 12°C supported significant (P < 0.001) E. coli O157:H7 growth, with a 1.0-log CFU/g increase within 3 days postinoculation, which was followed by additional growth during continued storage. E. coli O157:H7 grew slowly when held at 8°C, with a significant (P < 0.01) level of growth reached after 6 days of storage. However, on products held at 1 and 5°C, E. coli O157:H7 populations declined significantly (P < 0.01 and P < 0.001, respectively) within 3 days of storage. Aerobic mesophilic bacteria, psychrotrophic bacteria, and yeast and mold populations increased significantly at all storage temperatures, with more growth on products held at elevated temperatures. Product quality scores remained high within the first 6 days of storage, with a sharp decline noted on samples held at 12°C on day 9. Results suggest that E. coli O157:H7 can grow significantly on commercially packaged spinach held at 8°C or above before significant product quality deterioration occurs.

Influence of Curli Expression by Escherichia coli O157:H7 on the Cell's Overall Hydrophobicity, Charge, and Ability To Attach to Lettuce

2007 ◽  
Vol 70 (6) ◽  
pp. 1339-1345 ◽  
Author(s):  
RENEE R. BOYER ◽  
SUSAN S. SUMNER ◽  
ROBERT C. WILLIAMS ◽  
MERLE D. PIERSON ◽  
DAVID L. POPHAM ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Surface Charge ◽  
Extracellular Proteins ◽  
Escherichia Coli O157 ◽  
Fruit And Vegetable ◽  
E Coli ◽  
Iceberg Lettuce ◽  
Escherichia Coli Cells ◽  
Abiotic Surfaces ◽  
Plant Surfaces

Curli fibers are produced by some Escherichia coli cells in response to environmental stimuli. These extracellular proteins enhance the cell's ability to form biofilms on various abiotic surfaces. E. coli O157:H7 cells readily attach to a variety of fruit and vegetable surfaces. It is not known whether the expression of curli influences the cell's ability to attach to produce surfaces. In this study, the effect of curli expression on the cell's overall hydrophobicity, charge, and ability to attach to cut and whole iceberg lettuce surfaces was examined. All strains, regardless of curli expression, attached preferentially to the cut edges of lettuce (P < 0.05). The curli-producing cells of E. coli O157:H7 strain E0018 attached in significantly greater numbers to both cut and whole lettuce pieces than did the non–curli-producing E0018 cells (P < 0.05); however, no significant attachment differences were observed between the curli-producing and non–curli-producing cells of E. coli O157:H7 strains 43894 and 43895. All curli-producing E. coli O157:H7 strains were significantly more hydrophobic (P < 0.01); however, no association between the cells' hydrophobic characteristics and lettuce attachment was observed. Overall surface charge of the cells did not differ among strains or curli phenotypes. Results indicate that overall hydrophobicity and cell charge in E. coli O157:H7 strains do not influence attachment to iceberg lettuce surfaces. The presence of curli may not have any influence on attachment of E. coli O157:H7 cells to produce items. Additional factors may influence the attachment of E. coli O157:H7 to plant surfaces and should be further examined.

Is There a Relation between the Microscopic Leaf Morphology and the Association of Salmonella and Escherichia coli O157:H7 with Iceberg Lettuce Leaves?

2016 ◽  
Vol 79 (10) ◽  
pp. 1784-1788 ◽  
Author(s):  
INGE VAN der LINDEN ◽  
MARKUS ERIKSSON ◽  
MIEKE UYTTENDAELE ◽  
FRANK DEVLIEGHERE
Keyword(s):  
Escherichia Coli ◽  
Stomatal Density ◽  
Fresh Produce ◽  
Morphological Structure ◽  
Bacterial Attachment ◽  
Escherichia Coli O157 ◽  
Stages Of Development ◽  
E Coli ◽  
Iceberg Lettuce ◽  
Morphological Differences

ABSTRACT To prevent contamination of fresh produce with enteric pathogens, more insight into mechanisms that may influence the association of these pathogens with fresh produce is needed. In this study, Escherichia coli O157:H7 and Salmonella were chosen as model pathogens, and fresh cut iceberg lettuce was chosen as a model fresh produce type. The morphological structure of iceberg lettuce leaves (stomatal density and length of cell margins per leaf area) was quantified by means of leaf peels and light microscopy of leaves at different stages of development (outer, middle, and inner leaves of the crop) on both leaf sides (abaxial and adxial) and in three leaf regions (top, center, and bottom). The morphology of the top region of the leaves was distinctly different from that of the center and base, with a significantly higher stomatal density (up to five times more stomata), different cell shape, and longer cell margins (two to three times longer). Morphological differences between the same regions of the leaves at different stages of development were smaller or nonsignificant. An attachment assay with two attenuated E. coli O157:H7 strains (84-24h11-GFP and BRMSID 188 GFP) and two Salmonella strains (serovars Thompson and Typhimurium) was performed on different regions of the middle leaves. Our results confirmed earlier reports that these pathogens have a higher affinity for the base of the lettuce leaf than the top. Differences of up to 2.12 log CFU/g were seen (E. coli O157:H7 86-24h11-GFP). Intermediate attachment occurred in the central region. The higher incidence of preferential bacterial attachment sites such as stomata and cell margins or grooves could not explain the differences observed in the association of the tested pathogens with different regions of iceberg lettuce leaves.

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