Transfer of Salmonella enterica and Enterococcus faecium from food-contact surfaces to stone fruits.

Abstract

Contaminated food-contact surfaces are a potential route for spreading microorganisms to stone fruit during postharvest handling. The objective of this study was to investigate the factors that affect the transfer of bacteria from food-contact surfaces to stone fruits. Coupons (1 × 1 cm) of polyurethane (PU) or polyvinyl chloride (PVC) were inoculated with rifampin-resistant variants of Salmonella (five-strain cocktail) or Enterococcus faecium NRRL B-2354 at ~5 or ~7 log CFU/cm². Inoculated coupons (n = 8-11) were attached to a texture analyzer, and uniform contact conditions (5 N, 5 s) were used to explore the impact of bacterial species, inoculation level, donor surface, the presence of dried peach juice or wax, recipient produce commodity, and the dryness of inoculum. Whole fruits were transferred to 20 mL of 0.1 % peptone, rubbed for 2 min, and then the diluent was plated onto tryptic soy agar supplemented with rifampin at 50 μg/mL. Whole fruits were enriched when populations were anticipated to fall below the limit of detection (1.6 log CFU/fruit). At an inoculum of ~5 log CFU/coupon, Salmonella and E. faecium were recovered from the fruit by enrichment but not by plating. At ~7 log CFU/coupon, transfer rates, i.e., ratio of populations on recipient fruit to donor surface, were not significantly (P > 0.05) influenced by either bacterial species (Salmonella [0.26 % ± 0.77 %] versus E. faecium [0.068 % ± 0.071 %]) or donor surface (PU [0.085 % ± 0.098 %] versus PVC [0.16 % ± 0.16 %]). The rates of transfer of E. faecium from contaminated PU to peaches (0.050 % ± 0.031 %), nectarines (0.066 % ± 0.076 %), and onion skins (0.048 % ± 0.059 %) were not significantly different. The mean transfer rates of E. faecium increased significantly (P < 0.05) in the presence of dried wax (18 % ± 16 %) or peach juice (1.3 % ± 2.6 %) on the PU surface compared with the control (0.080 % ± 0.086 %). The transfer rates of E. faecium from contaminated surfaces were also significantly influenced by the drying time post-inoculation; the drier the inoculum, the lower the transfer rates. The presence of residues or moisture on food-contact surfaces facilitated the transfer of microorganisms during dry handling of fresh stone fruits. The results underscore the importance of implementing adequate cleaning, sanitation and, where appropriate, drying of equipment surfaces to effectively remove organic residues and mitigate the risks of cross-contamination.