Reducing Listeria Species and Escherichia coli O157:H12 on Cantaloupes at Pre-harvest Level by Octenidine Hydrochloride

Introduction: Cantaloupes have been increasingly implicated in outbreaks of human illnesses in recent years. The cantaloupe industry has traditionally relied on various chemical wash treatments to reduce pathogens at post-harvest level. Effective interventions applied at the pre-harvest level could also decrease pathogens on the fruit, and reduce the risk of foodborne outbreaks.

Purpose: To determine the efficacy of a potent and safe bispyridinamine compound, octenidine dihydrochloride (OH) was applied as a pre-harvest spray for reducing Listeria spp. and Escherichia coli O157:H12 on cantaloupes.

Methods: Cantaloupe plants grown for 3 weeks in a growth chamber were transplanted in a high-tunnel. Mature fruits (n = 60) were dip-inoculated for 10 s in a fecal slurry containing L. innocua or E. coli O157:H12, allowed to air-dry for 15 min, and then sprayed with 15 ml of 0.1% ethanol (n = 20), 0.1% OH (n = 20) or 0.2% OH (n = 20). Three cantaloupes from each group were harvested on days 0, 14, and 28; 2-cm dia cores (n = 21) were sampled from each cantaloupe and sub-grouped into three samples of 7 cores each. These core samples were analyzed for surviving Listeria and E. coli O157:H12 by direct-plating on selective media and MPN.

Results:  Initial Listeria and E. coli O157:H12 populations on control cantaloupes were 6.4 and 4.6 log CFU/cm², respectively. Spraying cantaloupes with 0.1% ethanol did not result in significant reductions in pathogen counts. All OH treatments reduced Listeria and E. coli on cantaloupes by 1.0 and 1.5 log CFU/cm², respectively, on day 0. On day 28, Listeria was reduced by ~ 2 log CFU/cm², whereas E. coli populations were reduced to undetectable levels on OH-treated cantaloupes.

Significance: The results of this study indicate that OH is effective in reducing E. coli and Listeria spp. and could potentially be used for decontaminating cantaloupes at the farm level.