Dataset Information

Assessments of total and viable Escherichia coli O157:H7 on field and laboratory grown lettuce.

ABSTRACT: 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 10(6) 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 10(4) 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.

SUBMITTER: Moyne AL

PROVIDER: S-EPMC3728298 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Assessments of total and viable Escherichia coli O157:H7 on field and laboratory grown lettuce.

Moyne Anne-Laure AL Harris Linda J LJ Marco Maria L ML

PloS one 20130730 7

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 organi ...[more]

PMID: 23936235

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Project description:Leafy green vegetables, such as lettuce, have been increasingly implicated in outbreaks of foodborne illnesses due to contamination by Escherichia coli O157:H7. While E. coli can survive in soils, colonize plants, and survive on produce, very little is known about the interaction of E. coli with the roots of growing lettuce plants. In these studies, a combination of microarray analyses and surface enhanced Raman spectroscopy (SERS) were used to gain a comprehensive understanding of bacterial genes involved in the colonization and growth of E. coli O157:H7 on lettuce roots and compared to E. coli K12 using a hydroponic system (HS) which we have reported in the previous studies. Using microarray, after three days of interaction with lettuce roots, 94 and 109 genes of E. coli O157:H7 were significantly up-regulated and down-regulated at least 1.5 fold, respectively. Only 8 genes were also found in the E. coli K12 up-regulated genes. No genes were found in the down-regulated genes clusters between those two strains. For E. coli O157:H7, forty out of the 94 up-regulated genes (43%) were involved in protein synthesis and were highly repressed compared to 40 out of 193 (23%) E. coli K12 up-regulated genes associated with protein synthesis. The wildtype of E.coli O157:H7 colonized two log CFU per root less compared to E. coli K12. Genes involved in biofilm modulation (bhsA and ybiM) were significantly up-regulated in E. coli O157:H7 and curli production (crl and csgA) were found important for E. coli K12 to attach to lettuce roots in the previous studies. BhsA mutant of E. coli O157:H7 was impaired in the colonization of lettuce roots. The SERS spectra of E. coli K12 and O157 controls (cells without interacting with roots) were very similar. The spectra of E. coli K12 and O157 exposed to the hydroponic system (HS) showed some differences in the nucleic acid, protein, and lipid regions compared with controls. The spectra of E. coli K12 HS cells exhibited significant differences compared to spectra from E. coli O157 HS cells in the RNA and protein regions. The overall band intensity of amide regions declined for E. coli O157 HS cells, while it increased for E. coli K12 HS cells. The intensity of the RNA bands of E. coli K12 HS cells were also found much higher than those of E. coli O157 HS cells. These findings were in agreement to our Microarray data. Our microarray and SERS data showed that E. coli K12 and O157:H7 behavior dramatically differently in colonizing on lettuce roots. Compared to K12, E. coli O157:H7 colonized less efficiently on lettuce roots.

Dataset Information

Assessments of total and viable Escherichia coli O157:H7 on field and laboratory grown lettuce.

Publications

Assessments of total and viable Escherichia coli O157:H7 on field and laboratory grown lettuce.

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