Inactivation of Escherichia coli O157: H7 on romaine lettuce when inoculated in a fecal slurry matrix

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

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

A field trial was conducted in July 2011 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, CA. One-half milliliter of rabbit fecal slurry, containing 6.3×107 CFU of E. coli O157:H7, was inoculated onto the upper (adaxial) surface of a lower leaf on 240 heads of lettuce within 30 min after a 2.5-h irrigation event. Forty-eight romaine lettuce heads were collected per event at 2.5 h (day 0.1), 19.75 h (day 0.8), 43.25 h (day 1.8), 67.25 h (day 2.8), and 91.75 h (day 3.8) postinoculation and were analyzed for the concentration of E. coli O157:H7 (Ct). E. coli O157:H7 was detected on 100% of collected heads in concentrations ranging from 340 to 3.40 × 1010 most probable number (MPN) per head. Enumeration data indicate substantial growth of E. coli O157:H7 postinoculation (2.5 h), leading to elevated concentrations, 1 to 3 log above the starting inoculum concentration (Co). By the end of the 92-h trial, we observed a net 0.8-log mean reduction of E. coli O157:H7 compared with Co; however, after accounting for the substantial bacterial growth, there was an overall 2.3-log reduction by the final sampling event (92 h). On the basis of two different regression models that used either the raw data for Ct or log-transformed values of Ct/Co during the period 2.5 to 91.75 h postinoculation, there was an estimated 76 to 80% reduction per day in bacterial counts; however, more accurate predictions of MPN per head of lettuce were generated by using non-log-transformed values of Ct. This study provides insight into the survival of E. coli O157:H7 transferred via splash from a contaminated fecal source onto produce during irrigation. Moreover, these findings can help generate inactivation times following a potential contamination incident.

Original languageEnglish (US)
Pages (from-to)792-798
Number of pages7
JournalJournal of Food Protection
Volume80
Issue number5
DOIs
StatePublished - May 1 2017

Fingerprint

romaine lettuce
Lettuce
Escherichia coli O157
inactivation
head lettuce
Head
irrigation
Erythroid Precursor Cells
Bacterial Load
Growth
plate count
lettuce
microbial growth
leaves
field experimentation
inoculum
valleys
rabbits
Rabbits
prediction

Keywords

  • Escherichia coli O157:H7
  • Fecal contamination
  • Field trial
  • Produce
  • Slurry
  • Survival

ASJC Scopus subject areas

  • Microbiology
  • Food Science

Cite this

Inactivation of Escherichia coli O157 : H7 on romaine lettuce when inoculated in a fecal slurry matrix. / Chase, Jennifer A.; Atwill, Edward R; Partyka, Melissa L.; Bond, Ronald F.; Oryang, David.

In: Journal of Food Protection, Vol. 80, No. 5, 01.05.2017, p. 792-798.

Research output: Contribution to journalArticle

Chase, Jennifer A. ; Atwill, Edward R ; Partyka, Melissa L. ; Bond, Ronald F. ; Oryang, David. / Inactivation of Escherichia coli O157 : H7 on romaine lettuce when inoculated in a fecal slurry matrix. In: Journal of Food Protection. 2017 ; Vol. 80, No. 5. pp. 792-798.
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