Survival and transfer of salmonella enteritidis in lettuce cultivated in hydroponics as affected by different ph of nutrient solution

Abstract

The consumption of leafy vegetables has been linked with outbreaks of listeriosis and salmonellosis. Hydroponics is a novel soilless cultivation system used for the growth of fresh produce/leafy vegetables that is gaining increased interest nowadays. In this study, lettuce (Lactuca sativa) plants of different ages (young and old plants) were grown in hydroponic solution with four different pH values (5, 6, 7 and 8) and inoculated with two bacterial populations of Salmonella Enteritidis (low: 3 log cfu mL-1 and high: 6 log cfu mL-1). Plants were harvested for old plants: After 13 and 26 days post inoculation (dpi) and for young plants: After 14 dpi and microbiological assessment on plant tissue (leaves, roots), root rinse and hydroponic solution was performed. The results revealed that the pathogen present in high populations was internalized in roots at 26 dpi (at all pH), while the pathogen was found around the roots (root rinse) independently of the pH of the hydroponic solution or the bacterial population. Interestingly, low bacterial internalization frequencies were observed in low pH values (5 and 6) of the hydroponic solution, while no internalization in leaves was noted. Therefore, a suitable management of the nutrient solution can possibly lead to safer leafy vegetable production.