Human Pathogen Colonization of Lettuce Dependent Upon Plant Genotype and Defense Response Activation.

Cristián Jacob,Maeli Melotto

doi:10.3389/fpls.2019.01769

Abstract

Fresh produce contaminated with human pathogens may result in foodborne disease outbreaks that cause a significant number of illnesses, hospitalizations, and death episodes affecting both public health and the agribusiness every year. The ability of these pathogens to survive throughout the food production chain is remarkable. Using a genetic approach, we observed that leaf colonization by Salmonella enterica serovar Typhimurium 14028s (S. Typhimurium 14028s) and Escherichia coli O157:H7 was significantly affected by genetic diversity of lettuce (Lactuca sativa L. and L. serriola L.). In particular, there was a significant variation among 11 lettuce genotypes in bacterial attachment, internalization, and apoplastic persistence after surface- and syringe-inoculation methods. We observed a significant correlation of the bacterial leaf internalization rate with stomatal pore traits (width and area). Moreover, bacterial apoplastic populations significantly decreased in 9 out of 11 lettuce genotypes after 10 days of surface inoculation. However, after syringe infiltration, populations of E. coli O157:H7 and S. Typhimurium 14028s showed positive, neutral, or negative net growth in a 10-day experimental period among seedlings of different lettuce types. The relative ability of the bacteria to persist in the apoplast of lettuce genotypes after syringe inoculation was minimally altered when assessed during a longer period (20 days) using 3.5- to 4-week-old plants. Interestingly, contrasting bacterial persistence in the lettuce genotypes Red Tide and Lollo Rossa was positively correlated with significant differences in the level of reactive oxygen species burst and callose deposition against S. Typhimurium 14028s and E. coli O157:H7 which are related to plant defense responses. Overall, we characterized the genetic diversity in the interaction between lettuce genotypes and enterobacteria S. Typhimurium 14028s and E. coli O157:H7 and discovered that this genetic diversity is linked to variations in plant immune responses towards these bacteria. These results provide opportunities to capitalize on plant genetics to reduce pathogen contamination of leaves.

Highlights

During the last two decades, the number, severity, and distribution of outbreaks of human diseases linked to the consumption of fresh produce have attracted the attention of farmers, the food industry, consumers, politicians, and scientists
The discovery that plant genetic diversity affects the interaction between the phyllosphere and human pathogenic bacteria provided an unprecedented opportunity to dissect the plant components associated with bacterial colonization and persistence phenotypes
We observed a significant variation in bacterial attachment among the lettuce genotypes and the differences were dependent upon the bacterial species (Figure 1)

Summary

Introduction

During the last two decades, the number, severity, and distribution of outbreaks of human diseases linked to the consumption of fresh produce have attracted the attention of farmers, the food industry, consumers, politicians, and scientists. The most common etiologic agents identified were norovirus (54% of outbreaks), Salmonella enterica (21%), and Shiga toxin-producing Escherichia coli (10%) (Bennett et al, 2018). This is concerning considering the current upward trend and the steady promotion of fresh produce consumption. The yearly sales of bagged salads have been growing in the U.S, reaching $3.7 billion in 2015 (Cook, 2016), which represents an important change in the consumers’ behavior towards purchasing ready-toeat and/or minimally processed salads

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Results

Conclusion