Purpose: To develop and validate a novel method for large-scale sampling of produce and quantification of indicator microorganisms in cantaloupe, melon, and jalapeño pepper.
Methods : Cantaloupe melons and jalapeño peppers were decontaminated using chlorine and ethanol. A cocktail containing 106 CFU of Escherichia coli, Salmonella (surrogate of fecal coliforms) and Enterococcus faecalis was inoculated on the produce surface by spots (melon) or submersion (jalapeño). After allowing the inoculum to dry, microorganisms were quantified using the stomacher, swab or a novel rinse/filtration method. The latter method consisted of rinsing one melon or one jalapeño with peptone water, filtering the rinsate by membrane filtration to concentrate microbes, and incubating the filter over KF and RapidEcoli2 agars for Enterococcus and E .coli/coliforms, respectively. Six replicates, by three individuals over multiple days were analyzed by the Kruskal-Wallis and Tukey’s tests.
Results: The rinse/filtration method was similar or more sensitive in microbial recovery efficiency when compared with the stomacher or swab methods. On inoculated melons, recovery efficiency of Salmonella was significantly better (P < 0.05) by the rinse/filtration method (3 - 4.5 log CFU versus 2 - 3.5 log CFU for the other methods). For recovery of E. coli and Enterococcus, the three methods were similar (2.5 - 3.5 log CFU for E. coli and 3 – 4.7 log CFU for Enterococcus). For jalapeños, the rinse/filtration and swab methods provided better recoveries than did the stomacher method.
Significance: The rinse/filtration method is similar or better in recovery sensitivity than swab or stomacher methods and is logistically easy to use in large-scale sampling of produce.