TRICHODERMA VIRENS APPLIED TO PLANT ROOTS SUPPRESSES COLONIZATION OF LEAVES BY SALMONELLA ENTERICA SEROVER TYPHIMURIUM

Human pathogens like Salmonella enterica are opportunistic colonizers of fruits, vegetables and leafy greens. Consequently, a large number of produce-associated foodborne outbreaks are increasingly reported. Strategies to minimize colonization of human pathogens are thus very important in agriculture and crop protection. Trichoderma species, an already well-established biocontrol agent, with various beneficial effects on plants including the induction of systemic resistance (ISR), may serve as a good candidate for preventing contamination in crops. As a model, we infected Arabidopsis thaliana (A. thaliana) and parsley with S. enterica serovar Typhimurium (S. Typhimurium) and Trichoderma virens. Trichoderma colonizes plant roots whereas S. Typhimurium colonizes the roots, the leaves and the stalks, depending on the irrigation method, so any effect detected may be either direct or indirect. In order to evaluate the potential of Trichoderma to attenuate S. Typhimurium growth, we exposed S. Typhimurium to culture filtrates from Trichoderma virens (or Trichoderma co-cultured with Arabidopsis seedlings) and assessed S. Typhimurium growth rates and its ability to produce biofilm. After demonstrating that Trichoderma had a dramatic effect on both these parameters, we performed in planta colonization assays with S. Typhimurium, comparing plants pre-treated with Trichoderma vs. untreated ones. As estimated visually by confocal microscopy and bacterial viable counts in plant tissue, S. Typhimurium colonization in A. thaliana was significantly decreased by pre-treating the plants with T. virens. This was also demonstrated in parsley. We have shown that in addition to all the known beneficial effects of Trichoderma, these biocontrol fungi may provide a potentially powerful and environmentally friendly tool to diminish the contamination of fresh produce by the human pathogens S. Typhimurium.