Survival of Generic Escherichia coli on Plastic Mulch in Open-Field, Greenhouse, and Growth Chamber Environments

Plasticulture, the use of plastic mulch to control pests and enhance plant growth, is common in fresh produce production. Given that fruits and vegetables may come into direct or indirect contact with plastic mulch, assessing potential food safety risks associated with contaminated plastic mulch is needed. This study evaluated the survival of generic Escherichia coli on plastic mulch across three environments. Plastic mulch was cut into 100 × 15 mm coupons, placed in Petri dishes, and spot inoculated with 100 µL of green fluorescent protein-tagged generic E. coli (ca. 6 log CFU/cm2). After drying for 90 min, coupons were held in three different environments: open-field, greenhouse, or growth chamber. Samples were collected at 0, 0.06, 0.17, 0.41, 1, 2, 3, 5, and 7 d postinoculation (dpi) and enriched if counts were below the detection limit (<0.12 log CFU/cm2). All E. coli counts were confirmed by fluorescence. The reduction of E. coli on plastic mulch differed significantly by environment (p < 0.05). In the open-field, E. coli was reduced by >6 log CFU/cm2 within 0.17 dpi (4 h) and was undetectable by enrichment on 5 dpi. In the greenhouse, a 6 log CFU/cm2 reduction was also achieved; however, E. coli remained detectable up to 7 dpi. In the growth chamber, E. coli persisted at 4.0 log CFU/cm2 up to 7 dpi. E. coli demonstrated a die-off rate of −1.65 log CFU/cm2/h from 0 to 4 h in the open-field, compared to −0.21 and −0.01 log CFU/cm2/h from 0 to 3 h and 3 h onward, respectively, in the growth chamber. These results demonstrate that the survival of E. coli on plastic mulch is environment-dependent, indicating that not all production environments have the same risk. Field and greenhouse environments should also be included and prioritized in produce safety research as the laboratory-based experiment overestimated risk in the present study.