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

Bezanson, G. S.; Delaquis, Pascal; Bach, Susan; McKellar, R.C.; Topp, Edward; Gill, Alexander; Blais, Burton W.; Gilmour, Matthew W.

doi:10.4315/0362-028x.jfp-11-306

Cited by 52 publications

(47 citation statements)

References 34 publications

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“…Following inoculation, E. coli O157:H7 ATCC 700728 did not survive in high quantities in the lettuce phyllosphere, and culturable cells were no longer detectable on most plants 7 days after inoculation. This result is agreement with field and laboratory studies on E. coli O157:H7 epiphytic fitness (28, 29, 37–41). Despite an inability to survive on lettuce, E. coli O157:H7 altered the composition of the other bacteria present on the plants on replicate plants in two independent trials.…”

Section: Discussionsupporting

confidence: 91%

Phyllosphere Microbiota Composition and Microbial Community Transplantation on Lettuce Plants Grown Indoors

Williams

Marco

2014

mBio

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The aerial surfaces of plants, or phyllosphere, are microbial habitats important to plant and human health. In order to accurately investigate microbial interactions in the phyllosphere under laboratory conditions, the composition of the phyllosphere microbiota should be representative of the diversity of microorganisms residing on plants in nature. We found that Romaine lettuce grown in the laboratory contained 10- to 100-fold lower numbers of bacteria than age-matched, field-grown lettuce. The bacterial diversity on laboratory-grown plants was also significantly lower and contained relatively higher proportions of Betaproteobacteria as opposed to the Gammaproteobacteria-enriched communities on field lettuce. Incubation of field-grown Romaine lettuce plants in environmental growth chambers for 2 weeks resulted in bacterial cell densities and taxa similar to those on plants in the field but with less diverse bacterial populations overall. In comparison, the inoculation of laboratory-grown Romaine lettuce plants with either freshly collected or cryopreserved microorganisms recovered from field lettuce resulted in the development of a field-like microbiota on the lettuce within 2 days of application. The survival of an inoculated strain of Escherichia coli O157:H7 was unchanged by microbial community transfer; however, the inoculation of E. coli O157:H7 onto those plants resulted in significant shifts in the abundance of certain taxa. This finding was strictly dependent on the presence of a field-associated as opposed to a laboratory-associated microbiota on the plants. Phyllosphere microbiota transplantation in the laboratory will be useful for elucidating microbial interactions on plants that are important to agriculture and microbial food safety.

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Section: Discussionsupporting

confidence: 91%

Phyllosphere Microbiota Composition and Microbial Community Transplantation on Lettuce Plants Grown Indoors

Williams

Marco

2014

mBio

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“…Shortly after application of (non-toxigenic) E. coli O157:H7 onto lettuce in production regions, culturable populations of the pathogen rapidly declined [12]–[14], regardless of the season [14] or location (e.g. Salinas Valley, California, USA [14]; Tifton, Georgia, USA [12]; or Summerland, B.C., and Kentville, Nova Scotia, Canada [13]). However, E. coli O157:H7 can apparently survive, at least in low quantities, on field-grown plants, and viable cells were found on a fraction of lettuce plants for several weeks after inoculation [12]–[15].…”

Section: Introductionmentioning

confidence: 99%

Assessments of Total and Viable Escherichia coli O157:H7 on Field and Laboratory Grown Lettuce

2013

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Leafy green produce has been associated with numerous outbreaks of foodborne illness caused by strains of Escherichia coli O157:H7. While the amounts of culturable E. coli O157:H7 rapidly decline after introduction onto lettuce in the field, it remains to be determined whether the reduction in cell numbers is due to losses in cell viability, cell injury and a subsequent inability to be detected by standard laboratory culturing methods, or a lack of adherence and hence rapid removal of the organism from the plants during application. To assess which of these options is most relevant for E. coli O157:H7 on leafy green produce, we developed and applied a propidium monoazide (PMA) real-time PCR assay to quantify viable (with PMA) and total (without PMA) E. coli O157:H7 cells on growth chamber and field-grown lettuce. E. coli O157:H7, suspended in 0.1% peptone, was inoculated onto 4-week-old lettuce plants at a level of approximately 106 CFU/plant. In the growth chamber at low relative humidity (30%), culturable amounts of the nontoxigenic E. coli O157:H7 strain ATCC 700728 and the virulent strain EC4045 declined 100 to 1000-fold in 24 h. Fewer E. coli O157:H7 cells survived when applied onto plants in droplets with a pipette compared with a fine spray inoculation. Total cells for both strains were equivalent to inoculum levels for 7 days after application, and viable cell quantities determined by PMA real-time PCR were approximately 104 greater than found by colony enumeration. Within 2 h after application onto plants in the field, the number of culturable E. coli ATCC 700728 was reduced by up to 1000-fold, whereas PCR-based assessments showed that total cell amounts were equivalent to inoculum levels. These findings show that shortly after inoculation onto plants, the majority of E. coli O157:H7 cells either die or are no longer culturable.

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“…While the occurrence of the pathogen in leafy greens on that same sample date was relatively low, subsequent dissemination of high levels of E. coli O157:H7 from the feedlot surface to the plots may have increased the contamination of leafy greens that were sampled on the later dates. Numerous studies have evaluated the risks associated with preharvest contamination of leafy vegetables and have found that E. coli O157:H7 can persist on spinach and lettuce for days up to weeks (31)(32)(33)(34)(35)(36)(37)(38). Both growth chamber and field studies indicate that after inoculation onto leafy greens to mimic a contamination event, populations of E. coli O157:H7 initially decrease rapidly, followed by a more gradual rate of decline of remaining cells.…”

Section: Resultsmentioning

confidence: 99%

Effect of Proximity to a Cattle Feedlot on Escherichia coli O157:H7 Contamination of Leafy Greens and Evaluation of the Potential for Airborne Transmission

Berry

Wells

Bono

et al. 2015

Appl Environ Microbiol

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cThe impact of proximity to a beef cattle feedlot on Escherichia coli O157:H7 contamination of leafy greens was examined. In each of 2 years, leafy greens were planted in nine plots located 60, 120, and 180 m from a cattle feedlot (3 plots at each distance). Leafy greens (270) and feedlot manure samples (100) were collected six different times from June to September in each year. Both E. coli O157:H7 and total E. coli bacteria were recovered from leafy greens at all plot distances. E. coli O157:H7 was recovered from 3.5% of leafy green samples per plot at 60 m, which was higher (P < 0.05) than the 1.8% of positive samples per plot at 180 m, indicating a decrease in contamination as distance from the feedlot was increased. Although E. coli O157:H7 was not recovered from air samples at any distance, total E. coli was recovered from air samples at the feedlot edge and all plot distances, indicating that airborne transport of the pathogen can occur. Results suggest that risk for airborne transport of E. coli O157:H7 from cattle production is increased when cattle pen surfaces are very dry and when this situation is combined with cattle management or cattle behaviors that generate airborne dust. Current leafy green field distance guidelines of 120 m (400 feet) may not be adequate to limit the transmission of E. coli O157:H7 to produce crops planted near concentrated animal feeding operations. Additional research is needed to determine safe set-back distances between cattle feedlots and crop production that will reduce fresh produce contamination.T he consumption of fresh produce increasingly has been linked to human food-borne disease (1-4). In particular, leafy vegetables, such as spinach and lettuce, have become significant vehicles for the transmission of food-borne pathogens. Produce-associated outbreak surveillance data from the Centers for Disease Control and Prevention (CDC) for the period from 2000 to 2009 showed that among produce commodities, leafy greens were the most frequently linked to outbreaks (5). An analysis of published reports of U.S. fresh produce-associated outbreaks with an attribution risk ranking tool categorized the combination of leafy greens and Escherichia coli O157:H7 with the highest risk ranking score, followed by Salmonella enterica in tomatoes ranking second and S. enterica in leafy greens ranking third (6). For all U.S. foodborne disease outbreaks caused by Shiga toxin-producing E. coli (STEC) in the period of 1998 to 2008, leafy vegetables were the second most common implicated commodity, following beef (2). In addition, spinach, lettuce, and cilantro were commodities most associated with the recovery of STEC in produce market basket surveys conducted within the USDA Agricultural Marketing Service Microbiological Data Program from 2002 to 2012 (7). Leafy greens typically are consumed raw, so protecting these products from microbial contamination in the preharvest environment is critical to reducing the risk for food-borne illness. Potential sources of pathogens for preharvest produ...

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

Cited by 52 publications

References 34 publications

Phyllosphere Microbiota Composition and Microbial Community Transplantation on Lettuce Plants Grown Indoors

Phyllosphere Microbiota Composition and Microbial Community Transplantation on Lettuce Plants Grown Indoors

Assessments of Total and Viable Escherichia coli O157:H7 on Field and Laboratory Grown Lettuce

Effect of Proximity to a Cattle Feedlot on Escherichia coli O157:H7 Contamination of Leafy Greens and Evaluation of the Potential for Airborne Transmission

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