Cultivation conditions of leafy vegetables determine phyllosphere bacterial community structures and ultimately affect growth of L. monocytogenes post-harvest

Abstract

Cultivation conditions including plant species, variety, cultivation method and seasonality are all at least co-factors of epiphytic growth of L. monocytogenes. Meanwhile, phyllosphere associated bacteria were found to influence colonisation of invading pathogens. Thus, the main objective of this study was to determine whether cultivation conditions are factors in the development of the bacterial phyllosphere community on leafy vegetables which consequently influences L. monocytogenes growth. Indeed, this study revealed that vegetable cultivation condition was a more influential determinant of phyllosphere development than plant species. Of the identified phyllosphere associated bacteria presence of Pseudomonadaceae had a positive correlation with L. monocytogenes populations on all tested produce. Yet, Pseudomonadaceae content appeared to be more important for L. monocytogenes growth on spinach F1 Trumpet. From day 7 to 9 of storage, Pseudomonadaceae increases on open field spinach F1 Trumpet were associated with L. monocytogenes largest increase (0.94 log10 cfu g-1), whereas Pseudomonadaceae content decreased for polytunnel spinach F1 Trumpet and the corresponding L. monocytogenes populations remained unchanged. Carnobacteriaceae were present on spinach F1 Trumpet from polytunnel but not on other spinach produce with higher associated L. monocytogenes growth. Pectobacteriaceae (genus Dickeya) increased for spinach F1 Trumpet polytunnel but decreased for other spinach produce with lower associated L. monocytogenes growth. Similarly, polytunnel rocket Esmee had an increasing relative abundance of Pectobacteriaceae whereas it remained constant for polytunnel rocket Buzz. Compared to summer spinach F1 Trumpet produce, winter produce had significantly greater Streptococcaceae content and was correlated with a decrease in L. monocytogenes growth. Finally, higher phyllosphere alpha diversity putatively limited L. monocytogenes growth. Ultimately, this study revealed that cultivation conditions determine bacterial phyllosphere community structure which consequently influences L. monocytogenes growth.