Postharvest control of Escherichia coli O157:H7 on romaine lettuce using a novel pelargonic acid sanitizer

Ice can be used to chill romaine lettuce and maintain relative humidity during transportation. Escherichia coli O157:H7 may contaminate water used for ice. The objective of this study was to determine the potential for E. coli O157:H7 contamination of romaine lettuce from either ice contaminated with the pathogen or by transfer from lettuce surfaces via melting ice. In experiment 1, lettuce was spot inoculated with E. coli O157:H7 and chilled with ice prepared from uncontaminated tap water. In experiment 2, water inoculated with this pathogen was frozen and used to ice lettuce. Three heads of lettuce were stacked in each container and stored at 4 or 20°C. After the ice melted, E. coli O157:H7 attachment to and recovery from the lettuce leaves were determined. For experiment 1, the population of E. coli O157:H7 attached to inoculated sites averaged 3.8 and 5.5 CFU/cm2 at 4 and 20°C, respectively. Most of the uninoculated sites became contaminated with the pathogen due to ice melt. For experiment 2, 3.5 to 3.8 log CFU E. coli O157:H7 per cm2 was attached to the top leaf on the first head. After rinsing with chlorinated water (200 μg/ml), E. coli O157:H7 remained on the surface of the top head (1.8 to 2.0 log CFU/cm2). There was no difference in numbers of E. coli O157:H7 recovered from each sampling site at 4 and 20°C. Results show that E. coli O157:H7 can be transferred onto other produce layers in shipping containers from melted ice made of contaminated water and from contaminated to uncontaminated leaf surfaces.

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Behavior of Escherichia coli O157:H7 on Damaged Leaves of Spinach, Lettuce, Cilantro, and Parsley Stored at Abusive Temperatures

Journal of Food Protection ◽

10.4315/0362-028x-73.2.212 ◽

2010 ◽

Vol 73 (2) ◽

pp. 212-220 ◽

Cited By ~ 26

Author(s):

ROWAIDA K. KHALIL ◽

JOSEPH F. FRANK

Keyword(s):

Escherichia Coli ◽

Pathogenic Bacteria ◽

Leaf Damage ◽

Escherichia Coli O157 ◽

Oxidation Reactions ◽

Leaf Extracts ◽

Romaine Lettuce ◽

Growth And Survival ◽

E Coli ◽

Additional Information

Recent foodborne illness outbreaks associated with the consumption of leafy green produce indicates a need for additional information on the behavior of pathogenic bacteria on these products. Previous research indicates that pathogen growth and survival is enhanced by leaf damage. The objective of this study was to compare the behavior of Escherichia coli O157:H7 on damaged leaves of baby Romaine lettuce, spinach, cilantro, and parsley stored at three abusive temperatures (8, 12, and 15°C). The damaged portions of leaves were inoculated with approximately 105 CFU E. coli O157:H7 per leaf. The pathogen grew on damaged spinach leaves held for 3 days at 8 and 12°C (P < 0.05), with the population increasing by 1.18 and 2.08 log CFU per leaf, respectively. E. coli O157:H7 did not grow on damaged Romaine leaves at 8 or 12°C, but growth was observed after 8 h of storage at 15°C, with an increase of less than 1.0 log. Growth of E. coli O157:H7 on Romaine lettuce held at 8 or 12°C was enhanced when inocula were suspended in 0.05% ascorbic acid, indicating the possibility of inhibition by oxidation reactions associated with tissue damage. Damaged cilantro and Italian parsley leaves held at 8°C for 4 days did not support the growth of E. coli O157:H7. Behavior of the pathogen in leaf extracts differed from behavior on the damaged tissue. This study provides evidence that the damaged portion of a leafy green is a distinct growth niche that elicits different microbial responses in the various types of leafy greens.

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Impact of Preinoculation Culture Conditions on the Behavior of Escherichia coli O157:H7 Inoculated onto Romaine Lettuce (Lactuca sativa) Plants and Cut Leaf Surfaces

Journal of Food Protection ◽

10.4315/0362-028x-72.7.1553 ◽

2009 ◽

Vol 72 (7) ◽

pp. 1553-1559 ◽

Cited By ~ 24

Author(s):

CHRISTOPHER G. THEOFEL ◽

LINDA J. HARRIS

Keyword(s):

Escherichia Coli ◽

High Standard ◽

Culture Conditions ◽

Escherichia Coli O157 ◽

Late Stationary Phase ◽

Romaine Lettuce ◽

Preparation Methods ◽

E Coli ◽

Leaf Surfaces ◽

Inoculum Preparation

Inoculum preparation methods can impact growth or survival of organisms inoculated into foods, thus complicating direct comparison of results among studies. The objective of this study was to evaluate preinoculation culture preparation for impact on Escherichia coli O157:H7 inoculated onto leaves of romaine lettuce plants and cut leaf surfaces. E. coli O157:H7 was grown quiescently or shaken at 15, 25, or 37°C to different growth phases in tryptic soy or M9 minimal salts broth or agar. Cells were harvested, washed, and suspended in 0.1% peptone, Milli Q water, or well water and refrigerated for 0 or 18 h. Prepared inoculum was spotted onto cut romaine lettuce (10 μl; 3 × 104 CFU/10 g) or onto romaine lettuce plants (20 μl; 3 × 106 CFU per leaf). Cut lettuce was sealed in 100-cm2 bags (made from a commercial polymer film) and incubated at 5 or 20°C. Lettuce plants were held at 23°C for 24 h. For all tested conditions, levels of E. coli O157:H7 increased at 20°Concut lettuce and decreased on cut lettuce stored at 5°C or on leaves of lettuce plants. At 20°C, preinoculation culture conditions had little impact on growth of E. coli O157:H7 on cut lettuce. However, survival at 5°C was significantly better (P < 0.05) for cultures grown at 15 or 37°C in minimal medium and to late stationary phase. Impact of preinoculation handling on survival on lettuce plants was less clear due to relatively high standard deviations observed among samples.

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Comparative Examination of Escherichia coli O157:H7 Survival on Romaine Lettuce and in Soil at Two Independent Experimental Sites

Journal of Food Protection ◽

10.4315/0362-028x.jfp-11-306 ◽

2012 ◽

Vol 75 (3) ◽

pp. 480-487 ◽

Cited By ~ 32

Author(s):

GREG BEZANSON ◽

PASCAL DELAQUIS ◽

SUSAN BACH ◽

ROBIN McKELLAR ◽

ED TOPP ◽

...

Keyword(s):

Escherichia Coli ◽

Nalidixic Acid ◽

Abiotic Factors ◽

Decay Rates ◽

Escherichia Coli O157 ◽

Production Environment ◽

Romaine Lettuce ◽

Ecological Fitness ◽

E Coli ◽

Significant Difference

Little is known about the influence of abiotic factors such as climate and soil chemistry on the survival of Escherichia coli O157:H7 in field lettuce. We applied a nalidixic acid–resistant derivative of strain ATCC 700728 to field-grown romaine lettuce in two regions in Canada characterized by large variances in soil type and climate. Surviving populations in soil and on lettuce leaves were estimated on sorbitol MacConkey agar supplemented with nalidixic acid. Data were fitted with the Weibull decline function to permit comparison of decay rates in the two experimental sites. E. coli O157:H7 populations fell from 105 to <102 CFU/g on leaves, and <103 CFU/g in soil within 7 days after inoculation. Analysis revealed there was no significant difference between decay rates at the two experimental sites in either environment. The results of this study suggest that the inherent ecological fitness of E. coli O157:H7 ATCC 700728 determines the extent of survival in the production environment.

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Outbreaks of Escherichia coli O157:H7 Infections Linked to Romaine Lettuce in Canada from 2008 to 2018: An Analysis of Food Safety Context

Journal of Food Protection ◽

10.4315/jfp-20-029 ◽

2020 ◽

Vol 83 (8) ◽

pp. 1444-1462 ◽

Cited By ~ 1

Author(s):

GENEVIÈVE COULOMBE ◽

ANGELA CATFORD ◽

AMALIA MARTINEZ-PEREZ ◽

ENRICO BUENAVENTURA

Keyword(s):

Escherichia Coli ◽

The United States ◽

Escherichia Coli O157 ◽

Romaine Lettuce ◽

E Coli ◽

Leafy Greens ◽

Iceberg Lettuce ◽

Canadian Population ◽

The Difference ◽

Commercial Distribution

ABSTRACT Foodborne diseases are a major cause of illness in Canada. One of the main pathogens causing cases and outbreaks of foodborne illness in Canada is Escherichia coli O157:H7. From 2008 to 2018, 11 outbreaks of E. coli O157:H7 infection in Canada were linked to leafy greens, including 7 (63.6%) linked to romaine lettuce, 2 (18.2%) linked to iceberg lettuce, and 2 (18.2%) linked to other or unspecified types of leafy greens. The consumption of lettuce in Canada, the behavior of E. coli O157:H7 on lettuce leaves, and the production practices used for romaine and iceberg lettuce do not seem to explain why a higher number of outbreaks of E. coli O157:H7 infection were linked to romaine than to iceberg lettuce. However, the difference in the shape of iceberg and romaine lettuce heads could be an important factor. Among the seven outbreaks linked to romaine lettuce in Canada between 2008 and 2018, an eastern distribution of cases was observed. Cases from western provinces were reported only twice. The consumption of romaine and iceberg lettuce by the Canadian population does not seem to explain the eastern distribution of cases observed, but the commercial distribution, travel distances, and the storage practices used for lettuce may be important factors. In the past 10 years, the majority of the outbreaks of E. coli O157:H7 infection linked to romaine lettuce occurred during the spring (March to June) and fall (September to December). The timing of these outbreaks may be explained by the availability of lettuce in Canada, the growing region transition periods in the United States, and the seasonality in the prevalence of E. coli O157:H7. The consumption of romaine lettuce by the Canadian population does not explain the timing of the outbreaks observed. HIGHLIGHTS

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Nanoemulsified carvacrol as a novel washing treatment reduces Escherichia coli O157:H7 on spinach and lettuce

Journal of Food Protection ◽

10.4315/jfp-21-151 ◽

2021 ◽

Author(s):

Chi-Hung Chen ◽

Hsin-Bai Yin ◽

Zi Teng ◽

Suyeun Byun ◽

Yongguang Guan ◽

...

Keyword(s):

Escherichia Coli ◽

Fresh Produce ◽

Cell Aggregation ◽

The United States ◽

Water Soluble ◽

Escherichia Coli O157 ◽

Romaine Lettuce ◽

Iceberg Lettuce ◽

Leaf Surfaces ◽

Study Support

Fresh produce continues to be the main source of foodborne illness outbreaks in the United States implicating bacterial pathogens such as Escherichia coli O157:H7 (EHEC). The efficacy of nanoemulsified carvacrol (NCR) as a washing treatment in reducing EHEC on fresh produce was investigated. Fresh baby spinach, Romaine lettuce, and Iceberg lettuce leaves (2.5 cm diameter cores) were spot-inoculated with a five-strain cocktail of nalidixic acid resistant EHEC at ~ 6 log CFU/cm 2 . After air-drying for 1 h, 20 pieces of each inoculated produce leaves were immersed in water-based treatment solutions (200 ml/group), including water alone, 25 or 50 ppm free chlorine, and 0.25% or 0.75% NCR for 2 minutes. Inoculated produce leaves without any treatment served as baseline. Produce leaves were stored at 10°C and surviving EHEC populations were enumerated on days 0, 2, 7 and 14. The viability of EHEC following NCR treatments on the fresh produce was visualized under fluorescence microscope. NCR treatment at 0.75% immediately reduced EHEC populations on Iceberg lettuce by 1.3 log CFU/cm 2 as compared to the produce treated with water alone (P<0.05). Antimicrobial activity of NCR against EHEC was comparable to chlorine treatments on day 0 for all produce (P>0.05). After 14-days of storage at 10°C, populations of EHEC on 0.75% NCR treated Romaine lettuce were reduced by 2.3 log CFU/cm 2 as compared to the recovery from 50 ppm chlorine treated samples (P<0.05). Microscopic images revealed that EHEC cells were observed to be clustered on the baseline samples, indicating the development of cell aggregation, as compared to the scattered cells seen on NCR-treated leaf surfaces. Treatments with NCR did not significantly affect the color on the fresh produce leaves during the 14 days of storage at 10°C. Results of this study support the potential use of NCR as a water soluble natural antimicrobial wash treatment for controlling EHEC on fresh produce.

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Transfer of Escherichia coli O157:H7 from Simulated Wildlife Scat onto Romaine Lettuce during Foliar Irrigation

Journal of Food Protection ◽

10.4315/0362-028x.jfp-14-277 ◽

2015 ◽

Vol 78 (2) ◽

pp. 240-247 ◽

Cited By ~ 28

Author(s):

EDWARD R. ATWILL ◽

JENNIFER A. CHASE ◽

DAVID ORYANG ◽

RONALD F. BOND ◽

STEVEN T. KOIKE ◽

...

Keyword(s):

Escherichia Coli ◽

Bacterial Contamination ◽

Assessment Model ◽

Escherichia Coli O157 ◽

Romaine Lettuce ◽

E Coli ◽

Weighted Arithmetic ◽

Salinas Valley ◽

Mean Concentration ◽

Rabbit Feces

A field trial in Salinas Valley, California, was conducted during July 2011 to quantify the microbial load that transfers from wildlife feces onto nearby lettuce during foliar irrigation. Romaine lettuce was grown using standard commercial practices and irrigated using an impact sprinkler design. Five grams of rabbit feces was spiked with 1.29 × 108 CFU of Escherichia coli O157:H7 and placed −3, −2, and −1 days and immediately before a 2-h irrigation event. Immediately after irrigation, 168 heads of lettuce ranging from ca. 23 to 69 cm (from 9 to 27 in.) from the fecal deposits were collected, and the concentration of E. coli O157:H7 was determined. Thirty-eight percent of the collected lettuce heads had detectable E. coli O157:H7, ranging from 1 MPN to 2.30 × 105 MPN per head and a mean concentration of 7.37 × 103 MPN per head. Based on this weighted arithmetic mean concentration of 7.37 × 103 MPN of bacteria per positive head, only 0.00573% of the original 5 g of scat with its mean load of 1.29 × 108 CFU was transferred to the positive heads of lettuce. Bacterial contamination was limited to the outer leaves of lettuce. In addition, factors associated with the transfer of E. coli O157:H7 from scat to lettuce were distance between the scat and lettuce, age of scat before irrigation, and mean distance between scat and the irrigation sprinkler heads. This study quantified the transfer coefficient between scat and adjacent heads of lettuce as a function of irrigation. The data can be used to populate a quantitative produce risk assessment model for E. coli O157:H7 in romaine lettuce to inform risk management and food safety policies.

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