Transmission of human enteric pathogens from artificially-inoculated flowers to vegetable sprouts/seedlings developed via contaminated seeds

Understanding the potential of fresh produce as vehicles of Salmonella enterica

This chapter presents an overview of Salmonella enterica as a contaminant in fresh produce, exploring outbreaks and recalls linked to them. It also provides information on potential sources of S. enterica contamination throughout the entire production chain of these products and presents food safety tools and new approaches for controlling this pathogen. S. enterica is recognized worldwide as a pathogen responsible for foodborne outbreaks, and there has been an increase in reported cases of salmonellosis linked to fresh produce. These products are susceptible to contamination throughout various stages of the farm-to-fork process. The potential sources of contamination are present from pre-harvest and harvest stages (e.g., soil, blossoms, seeds, irrigation water and gray/blackwater, wild and domestic animals/organic fertilizers, and distinctive traits of the plant) to post-harvest stages (e.g., processing, packaging, storage/retail, and preparing for consumption). Thus, controlling S. enterica contamination is extremely important for ensuring the safe consumption of fresh produce. However, obtaining practical, efficient, low-cost, and sustainable solutions that ensure the products' sensorial, nutritional, and food quality is still a challenge. As an alternative to conventional methods, recent studies report the use of new technologies, such as neutral, acidic or low chlorine electrolyzed oxidizing water, ultraviolet light, ultrasound, microemulsion of essential oils, cold plasma, irradiation, bacteriophages, and other methods, which can be used alone or in combination with the conventional ones. Therefore, understanding the main sources of S. enterica contamination in fresh produce and the effective approach for controlling this pathogen is crucial to reducing future outbreaks.

Assembly and Function of Seed Endophytes in Response to Environmental Stress

Seeds are colonized by diverse microorganisms that can improve the growth and stress resistance of host plants. Although understanding the mechanisms of plant endophyte-host plant interactions is increasing, much of this knowledge does not come from seed endophytes, particularly under environmental stress that the plant host grows to face, including biotic (e.g., pathogens, herbivores and insects) and abiotic factors (e.g., drought, heavy metals and salt). In this article, we first provided a framework for the assembly and function of seed endophytes and discussed the sources and assembly process of seed endophytes. Following that, we reviewed the impact of environmental factors on the assembly of seed endophytes. Lastly, we explored recent advances in the growth promotion and stress resistance enhancement of plants, functioning by seed endophytes under various biotic and abiotic stressors.

Salmonella Enteritidis survival in different temperatures and nutrient solution pH levels in hydroponically grown lettuce

Due to climate change, with contaminated and less fertile soils, and intense weather phenomena, a turn towards hydroponic vegetable production has been made. Hydroponic cultivation of vegetables is considered to be a clean, safe and environmentally friendly growing technique; however, incidence of microbial contamination i.e. foodborne pathogens, might occur, endangering human health. The aim of this study was to investigate the effects of different plant growth stages, pH (values 5, 6, 7, 8) and bacterial inoculum levels (3 and 6 log cfu/mL) on hydroponically cultivated lettuce spiked with Salmonella Enteritidis. The results revealed that the pH and inoculum levels affected the internalization and survival of the pathogen in the hydroponic environment and plant tissue. Younger plants were found to be more susceptible to pathogen internalization compared to older ones. Under the current growing conditions (hydroponics, pH and inoculum levels), no leaf internalization was observed at all lettuce growth stages, despite the bacterium presence in the hydroponic solution. Noticeably, bacteria load at the nutrient solution was lower in low pH levels. These results showed that bacterium presence initiates plant response as indicated by the increased phenols, antioxidants and damage index markers (H2O2, MDA) in order for the plant to resist contamination by the invader. Nutrient solution management can result in Taylor-made recipes for plant growth and possible controlling the survival and growth of S. Enteritidis by pH levels.

Fate and mitigation of Salmonella contaminated in lettuce (Lactuca sativa) seeds grown in a hydroponic system

AIMS

We investigated the fate of Salmonella in lettuce seeds grown in a hydroponic system and the potentials of applying photodynamic inactivation (PDI) to enhance microbial safety of hydroponic farming systems.

METHODS AND RESULTS

Lettuce was grown from Salmonella-contaminated seeds, and rose bengal-mediated PDI was applied. Without intervention, Salmonella could persist in plants and hydroponic farming environment throughout 6 weeks of lettuce growth. Cross-contamination from Salmonella-inoculated to noninoculated seedlings was observed. PDI significantly decreased Salmonella from 3.90 ± 0.31 log colony-forming unit (CFU) per plant to 2.77 ± 0.49 log CFU per plant without extra illumination needed (p < 0.01) by week six.

CONCLUSIONS

Salmonella from contaminated seeds could survive for an extended period in lettuce and hydroponic farming environment and posed serious cross-contamination risks. Rose bengal-mediated PDI showed promise in controlling Salmonella contamination in lettuce in a hydroponic farming setting.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shed light on the serious food safety implications that Salmonella-contaminated lettuce seeds might entail in a hydroponic farming environment and demonstrated rose bengal-mediated PDI as a potential mitigation strategy. These findings contribute to the increasingly relevant field of urban farming systems and their associated food safety concerns.

Microbial Contamination of Fresh Produce: What, Where, and How?

Promotion of healthier lifestyles has led to an increase in consumption of fresh produce. Such foodstuffs may expose consumers to increased risk of foodborne disease, as often they are not subjected to processing steps to ensure effective removal or inactivation of pathogenic microorganisms before consumption. Consequently, reports of ready-to-eat fruit and vegetable related disease outbreak occurrences have increased substantially in recent years, and information regarding these events is often not readily available. Identifying the nature and source of microbial contamination of these foodstuffs is critical for developing appropriate mitigation measures to be implemented by food producers. This review aimed to identify the foodstuffs most susceptible to microbial contamination and the microorganisms responsible for disease outbreaks from information available in peer-reviewed scientific publications. A total of 571 outbreaks were identified from 1980 to 2016, accounting for 72,855 infections and 173 deaths. Contaminated leafy green vegetables were responsible for 51.7% of reported outbreaks. Contaminated soft fruits caused 27.8% of infections. Pathogenic strains of Escherichia coli and Salmonella, norovirus, and hepatitis A accounted for the majority of cases. Large outbreaks resulted in particular biases such as the observation that contaminated sprouted plants caused 31.8% of deaths. Where known, contamination mainly occurred via contaminated seeds, water, and contaminated food handlers. There is a critical need for standardized datasets regarding all aspects of disease outbreaks, including how foodstuffs are contaminated with pathogenic microorganisms. Providing food business operators with this knowledge will allow them to implement better strategies to improve safety and quality of fresh produce.