Cucumber Waxing Significantly Enhances the Survival of Salmonella enterica Serovar Newport on the Fruit Surface

Introduction: A 2014 multistate foodborne illness outbreak caused by Salmonella enterica serovar Newport was responsible for 275 illnesses and traced back to contaminated cucumbers. In 2015, an outbreak caused by Salmonella Poona-contaminated cucumbers caused over 900 illnesses in the United States. Few studies have investigated the persistence of Salmonellaon the surface of cucumbers. Further, waxing is a common practice to preserve the water content and hence the turgidity of fruit. However, little is known about the effect of wax on epiphytic bacteria, including enteric pathogens.

Purpose: This study investigated the survival of Salmonella Newport on the surface of six cucumber cultivars of varying surface topographies. The effect of a commercial wax on the persistence of Salmonella Newport was also studied.

Methods: Salmonella Newport adapted for rifampicin resistance (~6.5 log CFU/ml) were spot inoculated (100 μl) on the surface (~2 cm spot) of cultivars Marketmore, Patio Snacker, Corinto (rough, spined varieties), Bella, Pepinex, and Summer Dance (smooth, spineless varieties). Inoculated spots of half the samples of each cultivar were covered with 20 μl wax using a sterile toothbrush. Cucumbers were held at room temperature for 24 h. Salmonella Newport was enumerated by direct plate count onto tryptic soy agar amended with 50 µg/ml rifampicin.

Results: Waxing significantly lessened population decline on cucumber surfaces after 24 h (P<0.01). While there was ~ three log CFU/g decline in populations on unwaxed cucumbers, the decline on waxed cucumbers was ~ two log CFU/g. For both treatments, cultivars with rough surfaces supported smaller populations than smooth cultivars (P<0.01).

Significance: This study provided evidence that commercial wax may enhance the risk of foodborne illness by enhancing persistence of Salmonella. It also provides evidence for cucumber cultivar differences in Salmonella survival; where cucumbers with spines or ridges may harbor smaller populations than smooth-skinned cultivars.