Survival of Escherichia coli on Lettuce under Field Conditions Encountered in the Northeastern United States

Abstract

Although wildlife intrusion and untreated manure have been associated with microbial contamination of produce, relatively few studies have examined the survival of Escherichia coli on produce under field conditions following contamination (e.g., via splash from wildlife feces). This experimental study was performed to estimate the die-off rate of E. coli on preharvest lettuce following contamination with a fecal slurry. During August 2015, field-grown lettuce was inoculated via pipette with a fecal slurry that was spiked with a three-strain cocktail of rifampin-resistant nonpathogenic E. coli. Ten lettuce heads were harvested at each of 13 time points following inoculation (0, 2.5, 5, and 24 h after inoculation and every 24 h thereafter until day 10). The most probable number (MPN) of E. coli on each lettuce head was determined, and die-off rates were estimated. The relationship between sample time and the log MPN of E. coli per head was modeled using a segmented linear model. This model had a breakpoint at 106 h (95% confidence interval = 69, 142 h) after inoculation, with a daily decrease of 0.70 and 0.19 log MPN for 0 to 106 h and 106 to 240 h following inoculation, respectively. These findings are consistent with die-off rates obtained in similar studies that assessed E. coli survival on produce following irrigation. Overall, these findings provide die-off rates for E. coli on lettuce that can be used in future quantitative risk assessments.

Effect of surrounding vegetation on microbial survival or die‐off on watermelon surface in an agriculture setting

“…In our study, the night time (i.e., between 12 hr (6 p.m.) and 24 hr (6 a.m.) may have allowed adequate time for the bacterial cells to recover from damage and resume their growth. Studies reported that relative humidity and temperature could affect microbial survival or die‐off rate on produce surface (Del Rosario & Beuchat, ; Stine, Song, Choi, & Gerba, ; Weller et al, ). During the current study, the relative humidity ranged from 62% to 74%, and the average temperature ranged from 25 °C to 28.56 °C (Table ).…”

“…This result was consistent with the results reported by other studies, especially on lettuce surface matrix. In field conditions, Weller et al () observed that the average daily die‐off rate of E. coli on lettuce head was 0.52 log from their 10 days of die‐off study. In a similar study, Bezanson et al () observed an average daily die‐off rate of E. coli O157:H7 on lettuce by 0.56 log.…”

“…The intrusion of crops by wild animals, birds, reptiles, and rodents, as well as insects and nematodes, act as a vector for transferring various pathogens (Brandl, 2006). The survival and growth of microorganisms is influenced by several environmental factors and agricultural practices such as, exposure to solar UV radiation, temperature changes, humidity, and poor fertilizer regimes (Bezanson et al, 2012;Brandl, 2006;Nyeleti, Cogan, & Humphrey, 2004;Tomas-Callejas et al, 2011;Weller et al, 2017).…”

“…This result was consistent with the results reported by other studies, especially on lettuce surface matrix. In field conditions,Weller et al (2017) observed that the average daily die-off rate of E. coli on lettuce head was 0.52 log from their 10 days of die-off study.…”

Evaluation of ultraviolet (UV‐C) light treatment for microbial inactivation in agricultural waters with different levels of turbidity

“…Produce safety has become the forefront in agricultural issues that address potential public health risks due to an increase in foodborne disease outbreaks (Breitenmoser, Fretz, Schmid, Besl, & Etter, 2011;CDC, 2015;Fan, Annous, Beaulieu, & Sites, 2008;Mazari-Hiriart et al, 2008). Preharvest environment and farm activities are the major sources of microbial contamination in fresh produce (Chhetri, Fontenot, et al, 2019;Weller et al, 2017). Agricultural water is one of the important vehicles for human pathogens (Cooley et al, 2007;Ijabadeniyi, Debusho, Vanderlinde, & Buys, 2011;Park et al, 2012).…”