Microbiological status of reusable plastic containers in commercial grower/packer operations and risk of Salmonella cross-contamination between containers and cucumbers.

The sanitary status of reusable plastic containers (RPCs) in fresh produce packing/grower operations located in Ontario, British Columbia, and Quebec was evaluated. Visibly soiled, Ready-to-Use, RPCs and those visually clean, were considered sanitary using a criterion of <3 log relative light units (RLU)/100 cm2 in ATP testing, < 4 log colony forming units (CFU)/crate Total Aerobic Count (TAC), <3 log CFU/crate for yeast & mould, and <3 log CFU/crate Enterobacteriaceae, and coliforms along with the absence of Escherichia coli. Collectively, 162 RPCs (48 visibly soiled and 114 visually clean) were sampled with 10% (5/48) of the visibly soiled crates exceeding ATP RLU readings that compares to 81% of clean crates sampled. All visibly soiled crates exceeded the acceptable limits for TAC that compares to 83% of visually clean RPCs. The fail percentage of visibly soiled crates, with respect to Enterobacteriaceae and coliform counts, was 96% (23/24) and 25% (12/48) respectively, compared to 69% (48/70) and 3% (4.4/114) for clean crates. E. coli was recovered from five (3.5%; 5/114) of visually clean RPCs. It was concluded that visual assessment and ATP readings are poor metrics to assess the sanitary status of RPCs. In laboratory trials, Salmonella inoculated onto RPCs declined at a greater rate under low (55%) compared to high (88%) relative humidity (RH). However, the rate of decline of Salmonella was lower if cucumber homogenates were periodically introduced onto the surface of inoculated RPCs with growth occurring under high RH. Transfer of Salmonella from RPC to cucumbers occurred in a diphasic manner with an initial rapid phase followed by a slower rate of attachment with time. Sanitation cycles that included a caustic rinse followed by a peracetic acid treatment supported a 1.0–1.8 log reduction of Salmonella although residual survivors could be transferred from RPCs to cucumbers. The study demonstrated that Salmonella can persist for extended periods on RPCs and then be transferred to produce can occur if crates are inadequately sanitized. This result, coupled with the unsanitary condition of RPCs sampled in the field, reinforces the need to adequately sanitize crates between uses. • The sanitary status of RPCs in the field remains a key knowledge gap. • The study illustrated poor sanitary status of RPCs with associated food safety risk. • Salmonella can persist on RPCs over long periods with nutrients from produce exudates. • Salmonella can rapidly transfer between RPCs and fresh produces. • Current sanitation is insufficient to prevent Salmonella from surviving and transferring. [ABSTRACT FROM AUTHOR]