Soil Microclimate and Persistence of Foodborne Pathogens Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica Newport in Soil Affected by Mulch Type

The interplay between antimicrobial resistance, heavy metal pollution, and the role of microplastics

Environmental pollution with heavy metals (HMs) and microplastics (MPs) could enhance the global health challenge antimicrobial resistance (AMR). Herein, we explore the complicated mechanics of how HMs, MPs, and AMR are interlinked within microbial ecosystems, as well as the co-selection and cross-resistance mechanisms. Unlike antibiotics, HMs have influenced microbial evolution for billions of years, promoting resistance mechanisms that predate antibiotic resistance genes (ARGs). At the same time, this conundrum is further complicated by the pervasive spread of MPs in the aquatic and terrestrial environments, acting as substrates for bacterial pathogenic biofilms and accelerates the horizontal gene transfer (HGT) of ARGs and heavy metal resistance genes (MRGs). This review highlights that HMs such as lead (Pb), mercury (Hg), arsenic (As), chromium (Cr), cadmium (Cd), and nickel (Ni) have persistently selected for resistance traits through efflux systems and genetic co-regulation. Together, these interactions are amplified by MPs that create genetic exchange hotspots due to biofilm formation. These dynamics are modulated by organic matter, which serves both as a nutrient source and a mediator of HM bioavailability, directly influencing ARG abundance. Soil and water ecosystems, including riverine systems and landfill leachate, are reservoirs for ARGs and ARG-MRG combinations, with notable contributions originating from anthropogenic activities. This review also emphasizes the urgent need for integrated environmental and public health strategies to mitigate pollutant-driven AMR. This work seeks to approach HMs and MPs as synergistic drivers of AMR such that both HMs and MPs are upstream (causes) levers, a foundation from which future research on sustainable environmental management practices and health policy (One Health Approach), aimed at curbing the spread of resistance determinants can proceed.

Survival of Salmonella on Biodegradable Mulch, Landscape Fabric, and Plastic Mulch

Ground covers are used in produce production to enhance plant growth and control diseases and pests. While various factors are considered when selecting commercial ground covers, food safety, particularly the survival of foodborne pathogens, is often overlooked. This study aimed to assess the survival of Salmonella on different ground covers, including biodegradable mulch, landscape fabric, and plastic mulch. New rolls of each ground cover were cut to fit a 100 × 15 mm petri dish and spot inoculated with a seven-strain Salmonella cocktail at approximately 6 log CFU/cm2. The inoculated coupons were stored in a climate-controlled chamber (23°C, 55% relative humidity) and sampled at 0, 0.06 (1.5 h), 0.17 (4 h), 1, 2, 3, 5, 7, 30, 60, 90, and 140 days postinoculation (dpi). If counts dropped below the detection limit (<0.12 log CFU/cm2), enrichments were performed following the Food and Drug Administration's Bacteriological Analytical Manual Salmonella protocol. Salmonella survived 140 dpi on all tested ground covers, with reductions >5 log CFU/cm2. Survival rates at 140 dpi were highest on landscape fabric (83%, 25/30) followed by plastic mulch (50%, 15/30) and biodegradable mulch (13%, 4/30) coupons (p < 0.05). During the first 30 dpi, biodegradable mulch exhibited the smallest reduction in Salmonella (2.47 ± 0.26 log CFU/cm2), compared to landscape fabric (3.07 ± 0.30 log CFU/cm2) and plastic mulch (3.86 ± 0.72 log CFU/cm2). After 60 dpi, Salmonella reductions stabilized across all materials (∼4 log CFU/cm2) and by 90 dpi, no significant differences were observed between ground cover types (p > 0.05). Although Salmonella survival varied among ground covers in the short-term (0-30 dpi), a >5 log CFU/cm2 reduction of Salmonella was observed among all materials by 140 dpi. Findings suggest that ground cover material influences Salmonella survival and should be factored into food safety risk management strategies, especially when ground covers are reused.

Optimizing sustainable agriculture: A comprehensive review of agronomic practices and their impacts on soil attributes

This study explores agronomic management (AM) effects on soil parameters under diverse conditions. Investigating tillage practices (TP), nutrient management (NM), crop rotation (CR), organic matter (OM), irrigation management (IM), and mulching (MS), it aims to reveal impacts on soil productivity, nutrient availability, microbial activity, and overall health. Varied TP affect soil quality through compaction, porosity, and erosion risk. Proper NM is vital for nutrient cycling, preventing imbalances and acidification. CR disrupts pest cycles, reduces weed pressure, and boosts nutrient recycling. OM management enhances soil quality by influencing organic carbon, nutrient availability, pH, fertility, and water retention. Optimizing IM regulates soil water content without inducing waterlogging. MS contributes to OM content, nutrient retention, soil structure, and temperature-moisture regulation, benefiting soil biota, aggregation, soil health and agricultural productivity. The review emphasizes integrated nutrient, CR, and OM management's positive impact on fertility and microbial activity. Different TP and IM variations impact soil health and crop production. Judicious implementation of these practices is essential for sustainable agriculture. This synthesis identifies uncertainties and proposes research directions for optimizing productivity while ensuring environmental sustainability. Ongoing inquiry can guide a balanced approach between yields and resilient soil stewardship for future generations.

Rain splash-mediated dispersal of Escherichia coli from fecal deposits to field-grown lettuce in the mid- and south Atlantic U.S. regions is affected by mulch type

Introduction

Wildlife feces can contaminate vegetables when enteric bacteria are released by rain and splashed onto crops. Regulations require growers to identify and not harvest produce that is likely contaminated, but U.S. federal standards do not define dimensions for no-harvest zones. Moreover, mulching, used to retain soil moisture and maximize crop yield may impact rain-mediated bacterial dispersal from feces.

Methods

To assess Escherichia coli dissemination from a fecal point source to lettuce grown on various mulches, lettuce cv. 'Magenta' was transplanted into raised beds with plastic, biodegradable plastic, straw, or left uncovered at field sites in Maryland and Georgia. Eleven days post-transplant, 10 g of rabbit manure spiked with ~8 log CFU g-1 E. coli were deposited in each bed. One day following natural or simulated rain events, lettuce was sampled along 1.5 m transects on either side of fecal deposits. Lettuce-associated E. coli was semi-quantified with an MPN assay and dependence on fecal age (stale or fresh), lettuce age (baby leaf or mature head), distance from point source, mulch and post-rain days were statistically evaluated.

Results

Distance (p<0.001), fecal age (p<0.001) and mulch (p<0.01) were factors for E. coli transfer from point source to lettuce. The highest and lowest E. coli estimates were measured from lettuce grown on biodegradable plastic and straw, respectively, with a 2-log MPN difference (p<0.001). Mulch and distance were also significant factors in E. coli recovery 3 days post-rain (both p<0.001), where plastic mulches differed from bare ground and straw (p<0.01). For all treatments, fewer E. coli were retrieved from lettuce at 0.3 m, 3 days post-rain compared to 1 day (p<0.001). Fitting the data to a Weibull Model predicated that a 7-log reduction in E. coli from fecal levels would be achieved at 1.2-1.4 m from the point source on plastic mulches, 0.75 m on bare soil (p<0.05) and 0.43 m on straw (p<0.01).

Discussion

Straw and bare ground limited rain-mediated E. coli dispersal from feces to lettuce compared to plastic mulches. Fecal age was negatively associated with E. coli dispersal. These findings can inform harvesting recommendations for measures related to animal intrusion in vegetable production areas.