Environmental inactivation and irrigation-mediated regrowth of Escherichia coli O157:H7 on romaine lettuce when inoculated in a fecal slurry matrix

Jennifer A. Chase, Melissa L. Partyka, Ronald F. Bond, Edward R Atwill

Research output: Contribution to journalArticle

1 Citation (Scopus)

Abstract

Field trials were conducted in July-August and October 2012 to quantify the inactivation rate of Escherichia coli O157:H7 when mixed with fecal slurry and applied to romaine lettuce leaves. Lettuce was grown under commercial conditions in Salinas Valley, California. One-half milliliter of rabbit, chicken, or pig fecal slurry, containing an average of 4.05 10 7 CFU E. coli O157:H7 (C 0 ), was inoculated onto the upper (adaxial) surface of a lower leaf on 288 heads of lettuce per trial immediately following a 2.5 h irrigation event. To estimate the bacterial inactivation rate as a function of time, fecal matrix, irrigation and seasonal climate effects, sets of lettuce heads (n = 28) were sampled each day over 10 days and the concentration of E. coli O157:H7 (C t ) determined. E. coli O157:H7 was detected on 100% of heads during the 10-day duration, with concentrations ranging from 340 MPN/head (∼5-log reduction) to >3.45 10 12 MPN/head (∼5-log growth). Relative to C 0 , on day 10 (C t = 12 ) we observed an overall 2.6-log and 3.2-log mean reduction of E. coli O157:H7 in July and October, respectively. However, we observed relative maximum concentrations due to bacterial growth on day 6 (maximum C t = 8 ) apparently stimulated by foliar irrigation on day 5. From this maximum there was a mean 5.3-log and 5.1-log reduction by day 10 (C t = 12 ) for the July and October trials, respectively. This study provides insight into the inactivation and growth kinetics of E. coli O157:H7 on romaine lettuce leaves under natural field conditions. This study provides evidence that harvesting within 24 h post irrigation has the potential to increase the concentration of E. coli O157:H7 contamination, if present on heads of romaine lettuce; foliar irrigation can temporarily stimulate substantial regrowth of E. coli O157:H7.

Original languageEnglish (US)
Article numbere6591
JournalPeerJ
Volume2019
Issue number3
DOIs
StatePublished - Jan 1 2019

Fingerprint

romaine lettuce
Lettuce
Escherichia coli O157
Irrigation
regrowth
Escherichia coli
inactivation
irrigation
Head
head lettuce
Growth
leaves
Erythroid Precursor Cells
Growth kinetics
Climate
lettuce
microbial growth
Chickens
field experimentation
Contamination

Keywords

  • E. coli O157:H7
  • Enumeration
  • Fecal contamination
  • Field trial
  • Foliar irrigation
  • Food safety
  • Produce
  • Romaine lettuce
  • Slurry
  • Survival

ASJC Scopus subject areas

  • Neuroscience(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Agricultural and Biological Sciences(all)

Cite this

Environmental inactivation and irrigation-mediated regrowth of Escherichia coli O157:H7 on romaine lettuce when inoculated in a fecal slurry matrix. / Chase, Jennifer A.; Partyka, Melissa L.; Bond, Ronald F.; Atwill, Edward R.

In: PeerJ, Vol. 2019, No. 3, e6591, 01.01.2019.

Research output: Contribution to journalArticle

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abstract = "Field trials were conducted in July-August and October 2012 to quantify the inactivation rate of Escherichia coli O157:H7 when mixed with fecal slurry and applied to romaine lettuce leaves. Lettuce was grown under commercial conditions in Salinas Valley, California. One-half milliliter of rabbit, chicken, or pig fecal slurry, containing an average of 4.05 10 7 CFU E. coli O157:H7 (C 0 ), was inoculated onto the upper (adaxial) surface of a lower leaf on 288 heads of lettuce per trial immediately following a 2.5 h irrigation event. To estimate the bacterial inactivation rate as a function of time, fecal matrix, irrigation and seasonal climate effects, sets of lettuce heads (n = 28) were sampled each day over 10 days and the concentration of E. coli O157:H7 (C t ) determined. E. coli O157:H7 was detected on 100{\%} of heads during the 10-day duration, with concentrations ranging from 340 MPN/head (∼5-log reduction) to >3.45 10 12 MPN/head (∼5-log growth). Relative to C 0 , on day 10 (C t = 12 ) we observed an overall 2.6-log and 3.2-log mean reduction of E. coli O157:H7 in July and October, respectively. However, we observed relative maximum concentrations due to bacterial growth on day 6 (maximum C t = 8 ) apparently stimulated by foliar irrigation on day 5. From this maximum there was a mean 5.3-log and 5.1-log reduction by day 10 (C t = 12 ) for the July and October trials, respectively. This study provides insight into the inactivation and growth kinetics of E. coli O157:H7 on romaine lettuce leaves under natural field conditions. This study provides evidence that harvesting within 24 h post irrigation has the potential to increase the concentration of E. coli O157:H7 contamination, if present on heads of romaine lettuce; foliar irrigation can temporarily stimulate substantial regrowth of E. coli O157:H7.",
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