Survival of Salmonella spp. and Listeria monocytogenes on Pressed Card and Plastic Polyethethylene Board from the Farmers' Market and Validated Commercial Sanitizers to Decontaminate Salmonella spp. and Listeria monocytogenes

Introduction: Salmonella and Listeria are present on fresh produce at farmers’ markets. Uncleaned containers could be a potential contamination source.

Purpose: This study evaluated the potential differences in survival of Salmonella and Listeria monocytogenes (Lm) on pressed-card and plastic polyethethylene surfaces during storage and evaluated antimicrobial efficacy of commercial sanitizers.

Methods:   Study I, an anonymous survey, assessed postharvest practices of handling storage containers from 28 vendors at the Morgantown, WV, farmers’ market. In Study II, pressed-card (green moulded-pulp produce basket) and plastic containers, obtained from the farmers’ market, were trimmed (4 cm by 4 cm) and inoculated with Salmonella Typhimurium and Tennessee and three strains of Lm, stored at 4°C and 25°C (22 days), and periodically analyzed for survivals of inoculated microorganisms. Study III, evaluated pressed-card and plastic board inoculated with Salmonella and Lm, stored at 4°C for 1 and 24 h, treated by immersion into tap water, sodium hypochlorite (200 ppm), lactic acid (5%), peroxyacetic acid (PAA, 1,000 ppm), and H₂O₂-PAA mix (SaniDate-5.0, 0.25%) for 60 s. Surviving bacteria were analyzed on XLT-4 (Salmonella) and Modified-Oxford (Lm) agar. Data (two replicates/three samples/replicate) were analyzed using the mixed-model procedure of SAS and USDA Integrated Predictive Modeling Program software.

Results: Plastic (81%) and paper baskets (52%) were used by vendors. Forty-one percent of vendors did not sanitize containers. The pathogens died slower (P<0.05) at 4°C and on pressed-card (fit Reparamerized Gompertz survival model) than at 25°C and on plastic board (fit linear model without tail). At 4°C, Salmonella decreased from 4.2 to 4.4 to 3.1 to 3.2 log CFU/cm²; Lm decreased from 6.3 to 6.4 to 3.9 to 4.2 log CFU/cm² during 22-day storage on both surfaces. At 25°C, pathogens decreased from 4.5 to 6.2 log CFU/cm² to <0.3 log CFU/cm² after two to four days on plastic board, which is shorter (P<0.05) than pressed-card (22 days). At 1 and 24 h, all sanitizers reduced Salmonella and Lm to <0.3 log CFU/cm².

Significance: Farmers’ market vendors should choose plastic container to store fresh produce and avoid putting the containers in a cooler.