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.
Highlights
Fresh produce is highly implicated in foodborne disease outbreaks [1,2,3]
The present study examined the die-off rate and attachment behavior of E. coli on watermelon surfaces in an agricultural field setting in a south central part of the U.S.A
Coliforms and E. coli were uniformly distributed on the watermelon surfaces
Summary
Fresh produce is highly implicated in foodborne disease outbreaks [1,2,3]. Produce is estimated to be responsible for 20 million illnesses, resulting in the loss of $38.6 billion annually in the US [4]. During 2010–2014, produce was on the top list of food categories responsible for Salmonella and shiga toxin–producing E. coli associated outbreaks [1]. Die-off of Escherichia coli on watermelon pre-harvest events as important causes of microbial contamination [5,6,7,8]. Produce is typically consumed raw or minimally processed. Appropriate risk management strategies should be in place in the field production stage to minimize food safety risks
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