Isolation and Enumeration of Salmonella enterica from Fresh Lettuce (Lactuca sativa L.) Leaves and Its Susceptibility to Different Washing Protocols

Enumeration of Salmonella enterica in Lettuce and Efficacy of Washing

Abstract

Lettuce is one of the most consumed fresh produce items in the country, but it also serves as a vehicle for human pathogens, posing a risk of foodborne illness. This study used conventional microbiological and molecular analyses to obtain the concentration and prevalence of Salmonella enterica in fresh Green Ice and Iceberg lettuce leaves from selected supermarkets in Los Baños, Laguna, Philippines. The efficacy of different household washing procedures in reducing S. enterica on lettuce leaves was also investigated. Of the 19 composite Green Ice lettuce and 21 composite Iceberg lettuce samples tested, 5.26% and 4.76%, respectively, were contaminated with S. enterica, both with a 3.6 MPN g^–1 concentration. All washing procedures significantly reduced the number of S. enterica cells inoculated on both lettuce varieties versus the control (p < 0.05). Washing with baking soda solution (24 g L^–1, 15 min) yielded the highest log CFU reduction (1.293 ± 0.376 log CFU) for Green Ice lettuce, while the combination of soaking and rinsing resulted in the highest reduction (0.814 ± 0.148 log CFU) for Iceberg lettuce. Analysis of the p-values of log CFU reductions showed no significant difference among the washing treatments per lettuce variety (p > 0.05). Although the observed log reductions were minimal, reducing Salmonella cells on lettuce using common household washing procedures remains a viable strategy, especially considering the relatively low Salmonella concentrations detected.