Effect of irrigation regimes on persistence of Salmonella enterica serovar Newport in small experimental pots designed for plant cultivation

Increased outbreaks of foodborne illness throughout the world have raised concern over the potential health hazard of pre-harvest colonization of crops by human pathogens originating from contaminated irrigation water, or manure-amended soil. Contradictory reports currently exist concerning the ability of pathogenic bacteria to penetrate internal plant tissues via the root and translocate to edible aerial tissues, which suggest dependence of the process on experimental variables employed. Mechanistic investigations of internalization into plants require development of regulated, experimental, co-cultivation systems for the plant and the bacteria. In the present study, we have evaluated the effect of three irrigation regimes: 'no-irrigation' and irrigation with or without leachate, on the capacity of Salmonella enterica serovar Newport to survive in a potting medium in small experimental pots designed for internalization studies. The duration of bacterial survival in the potting-medium varied under the irrigation regimes employed, ranging from 4.7 to 10 weeks. The survival duration under irrigation without leachate was longer than in the 'no-irrigation' treatment. Leaching reduced the concentration of Salmonella in the experimental pots, presumably by a washing effect and consequently shortened the duration of survival from 70 to 33 days. The observed dependency of Salmonella viability in the experimental pots, upon the irrigation schemes applied, points at the need to consider the irrigation conditions in experimental systems aimed at studying the interactions between human enteric pathogen and the plant ecosystem.