Anti-listerial properties of chemical constituents of Eruca sativa (rocket salad): From industrial observation to in vitro activity

Exploring the biocontrol potential of rocket (Eruca sativa) extracts and associated microorganisms against Verticillium wilt

AIMS

This study aimed to assess the impact of rocket (Eruca sativa) extract on Verticillium wilt in eggplants, explore rhizospheric microorganisms for disease biocontrol, and evaluate selected strains' induced systemic resistance (ISR) potential while characterizing their genomic and biosynthetic profiles.

METHODS AND RESULTS

Rocket extract application led to a significant reduction in Verticillium wilt symptoms in eggplants compared to controls. Isolated microorganisms from treated soil, including Paraburkholderia oxyphila EP1, Pseudomonas citronellolis EP2, Paraburkholderia eburnea EP3, and P. oxyphila EP4 and EP5, displayed efficacy against Verticillium dahliae, decreasing disease severity and incidence in planta. Notably, strains EP3 and EP4 triggered ISR in eggplants against V. dahliae. Genomic analysis unveiled shared biosynthetic gene clusters, such as ranthipeptide and non-ribosomal peptide synthetase-metallophore types, among the isolated strains. Additionally, metabolomic profiling of EP2 revealed the production of metabolites associated with amino acid metabolism, putative antibiotics, and phytohormones.

CONCLUSIONS

The application of rocket extract resulted in a significant reduction in Verticillium wilt symptoms in eggplants, while the isolated microorganisms displayed efficacy against V. dahliae, inducing systemic resistance and revealing shared biosynthetic gene clusters, with metabolomic profiling highlighting potential disease-suppressing metabolites.

Surveillance of Listeria monocytogenes: Early Detection, Population Dynamics, and Quasimetagenomic Sequencing during Selective Enrichment

In this study, we addressed different aspects regarding the implementation of quasimetagenomic sequencing as a hybrid surveillance method in combination with enrichment for early detection of Listeria monocytogenes in the food industry. Different experimental enrichment cultures were used, comprising seven L. monocytogenes strains of different sequence types (STs), with and without a background microbiota community. To assess whether the proportions of the different STs changed over time during enrichment, the growth and population dynamics were assessed using dapE colony sequencing and dapE and 16S rRNA amplicon sequencing. There was a tendency of some STs to have a higher relative abundance during the late stage of enrichment when L. monocytogenes was enriched without background microbiota. When coenriched with background microbiota, the population dynamics of the different STs was more consistent over time. To evaluate the earliest possible time point during enrichment that allows the detection of L. monocytogenes and at the same time the generation of genetic information that enables an estimation regarding the strain diversity in a sample, quasimetagenomic sequencing was performed early during enrichment in the presence of the background microbiota using Oxford Nanopore Technologies Flongle and Illumina MiSeq sequencing. The application of multiple displacement amplification (MDA) enabled detection of L. monocytogenes (and the background microbiota) after only 4 h of enrichment using both applied sequencing approaches. The MiSeq sequencing data additionally enabled the prediction of cooccurring L. monocytogenes strains in the samples.

IMPORTANCE We showed that a combination of a short primary enrichment combined with MDA and Nanopore sequencing can accelerate the traditional process of cultivation and identification of L. monocytogenes. The use of Illumina MiSeq sequencing additionally allowed us to predict the presence of cooccurring L. monocytogenes strains. Our results suggest quasimetagenomic sequencing is a valuable and promising hybrid surveillance tool for the food industry that enables faster identification of L. monocytogenes during early enrichment. Routine application of this approach could lead to more efficient and proactive actions in the food industry that prevent contamination and subsequent product recalls and food destruction, economic and reputational losses, and human listeriosis cases.