Attachment strength and on-farm die-off rate of Escherichia coli on watermelon surfaces

Abstract

Pre-harvest contamination of produce has been a major food safety focus. Insight into the behavior of enteric pathogens on produce in pre-harvest conditions will aid in developing pre-harvest and post-harvest risk management strategies. In this study, the attachment strength (SR) and die-off rate of E. coli on the surface of watermelon fruits and the efficacy of aqueous chlorine treatment against strongly attached E. coli population were investigated. Watermelon seedlings were transplanted into eighteen plots. Prior to harvesting, a cocktail of generic E. coli (ATCC 23716, 25922 and 11775) was inoculated on the surface of the watermelon fruits (n = 162) and the attachment strength (SR) values and the daily die-off rates were examined up to 6 days by attachment assay. After 120 h, watermelon samples were treated with aqueous chlorine (150 ppm free chlorine for 3 min). The SR value of the E. coli cells on watermelon surfaces significantly increased (P<0.05) from 0.04 to 0.99 in the first 24 h, which was primarily due to the decrease in loosely attached population, given that the population of strongly attached cells was constant. Thereafter, there was no significant change in SR values, up to 120 h. The daily die-off rate of E. coli ranged from -0.12 to 1.3 log CFU/cm2. The chlorine treatment reduced the E. coli level by 4.2 log CFU/cm2 (initial level 5.6 log CFU/cm2) and 0.62 log CFU/cm2 (initial level 1.8 log CFU/cm2), on the watermelons that had an attachment time of 30 min and 120 h respectively. Overall, our findings revealed that the population of E. coli on watermelon surfaces declined over time in an agricultural environment. Microbial contamination during pre-harvest stages may promote the formation of strongly attached cells on the produce surfaces, which could influence the efficacy of post-harvest washing and sanitation techniques.

Effectiveness of Aqueous Chlorine Dioxide in Minimizing Food Safety Risk Associated with Salmonella, E. coli O157:H7, and Listeria monocytogenes on Sweet Potatoes

“…Aqueous ClO 2 (3 ppm) reduced the L. monocytogenes population by 3.7 log CFU when bell pepper surfaces were not injured and by 0.44 when injured [38]. Reduced efficacy of the treatments in our study may be due to a higher level of bruises and attached soiled particles which may have allowed bacterial cells to hide better in the surfaces limiting the access to the sanitizer solutions [43,44]. However, a further rigorous study is needed to better understand the influence of individual factors on the efficacy of the sanitizer.…”

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

“…The number of contaminated cantaloupes was higher in December, September, and June in 2010, 2011, and 2012, respectively (Denis et al, ). This seasonal variation in the microbial population may be attributed to the changes in weather conditions such as temperature, humidity, and day length (Ailes et al, ; Chhetri, Fontenot, et al, ; Chhetri et al, ). However, further study is needed to establish relationships between year‐round weather conditions and microbial quality of produce.…”

“…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, ; CDC, ; Fan, Annous, Beaulieu, & Sites, ; Mazari‐Hiriart et al, ). Preharvest environment and farm activities are the major sources of microbial contamination in fresh produce (Chhetri, Fontenot, et al, ; Weller et al, ). Agricultural water is one of the important vehicles for human pathogens (Cooley et al, ; Ijabadeniyi, Debusho, Vanderlinde, & Buys, ; Park et al, ).…”

Evaluation of the Effectiveness of Aeration and Chlorination during Washing to Reduce E. coli O157:H7, Salmonella enterica, and L. innocua on Cucumbers and Bell Peppers

“…Additionally, washing aids in the reduction of the microbial load present on the surface of fresh produce, improving the quality, shelf-life, and safety of the produce [ 11 ]. However, during the washing process, microorganisms loosely adhering to contaminated surfaces can be released into the water, risking cross-contamination of other produce [ 12 ]. The use of sanitizers such as peroxyacetic acid, ozone, chlorine, and chlorine dioxide during washing can minimize the risk of cross-contamination [ 13 ].…”