Egg carton and eggshell: is there a possibility of Salmonella cross-contamination?

SUMMARY: Producers and consumers associated with small scale backyard egg production tend to reuse egg cartons. Egg cartons are also reused for arts and craft projects, gardening, and organization units for small items. The reuse of egg cartons is primarily driven by economic or ecological reasons. The ability of zoonotic bacteria, such as Salmonella Enteritidis (SE), to survive on the eggshell surface and a variety of food packaging materials makes the reuse of egg carton risky. This study was aimed at determining the scope of cross-contamination of SE between eggshell and different egg carton types using 2 experiments. Unwashed eggs from end-of-lay white Leghorn hens were used in the experiments. Two different SE strains were used with 3 independent tubes of inocula from each strain as replicates. In Experiment 1, 216 eggs from each SE strain (72/replicate) were inoculated with 10 μL of SE inoculum (~ 9.95 log cfu/mL), allowed to dry in room temperature, and placed in nonadjacent wells of noninoculated plastic, polystyrene foam, and pulp egg cartons. Egg cartons of each type were then stored either at refrigeration (4°C) or room temperature (25°C). After 24 h eggs were discarded and the carton-wells were swabbed for SE recovery. In Experiment 2, wells of egg cartons were inoculated with SE and uninoculated eggs were placed in them and stored similar to Experiment 1. A total of 216 wells within the egg cartons were inoculated for each SE strain (72/replicate). Eggshell samples were collected for SE recovery. Only 3 samples were detected positive for SE in Experiment 1 and no effect of carton type, SE strain, or incubation temperature was observed. In Experiment 2, 8 eggshell samples were SE positive – 6 from polystyrene foam and 2 from plastic carton. Statistical difference was observed for pulp versus polystyrene foam only (P < 0.05). These results indicate that transfer of SE between egg carton and eggshell surface is possible and that the risk of cross-contamination is associated with type of carton material.