Survival of Escherichia coli and Listeria innocua on Lettuce after Irrigation with Contaminated Water in a Temperate Climate

Microbial disease outbreaks related to fresh produce consumption, including leafy green vegetables, have increased in recent years. Where contamination occurs, pathogen persistence may represent a risk for consumers’ health. This study analysed the survival of E. coli and L. innocua on lettuce plants watered with contaminated irrigation water via a single irrigation event and within stored irrigation water. Separate lettuce plants (Lactuca sativa var. capitata) were irrigated with water spiked with Log10 7 cfu/mL of each of the two strains and survival assessed via direct enumeration, enrichment and qPCR. In parallel, individual 20 L water microcosms were spiked with Log10 7 cfu/mL of the individual strains and sampled at similar time points. Both strains were observed to survive on lettuce plants up to 28 days after inoculation. Direct quantification by culture methods showed a Log10 4 decrease in the concentration of E. coli 14 days after inoculation, and a Log10 3 decrease in the concentration of L. innocua 10 days after inoculation. E. coli was detected in water samples up to 7 days after inoculation and L. innocua was detected up to 28 days by direct enumeration. Both strains were recovered from enriched samples up to 28 days after inoculation. These results demonstrate that E. coli and L. innocua strains are able to persist on lettuce after a single contamination event up until the plants reach a harvestable state. Furthermore, the persistence of E. coli and L. innocua in water for up to 28 days after inoculation illustrates the potential for multiple plant contamination events from stored irrigation water, emphasising the importance of ensuring that irrigation water is of a high quality.

Give and Take: Salmonella Enterica Alters Macrosteles Quadrilineatus Feeding Behaviors Resulting in Altered S. Enterica Populations and Distribution on Leaves

Hemipteran insects are ubiquitous inhabitants of the phyllosphere. Changes in microbial phyllosphere communities have recently been demonstrated following infestation by Macrosteles quadrilineatus (Aster Leafhopper). Although epiphytic Salmonella enterica populations naturally decline in the phyllosphere of plants, M. quadrilineatus infestation facilitated the growth of the bacterial pathogen populations. Here, we demonstrate that cellular damage by insect stylet penetration results in a localized beneficial niche on the leaf surface, leading to enhanced S. enterica populations. We measured S. enterica populations and colonization patterns on plants infested with Hemipterans with distinct feeding behaviors. M. quadrilineatus infestation resulted in higher solute leakage and significantly greater bacterial populations than plants absent of insects. Following immigration via contaminated irrigation water, the highest populations of S. enterica are naturally found on the tips of tomato leaflets. We discovered M. quadrilineatus feeding preference altered the natural distribution of S. enterica populations, and that the presence of S. enterica altered the distribution of probing attempts. These findings elucidate how cellular damage resulting from insect feeding drives changes in bacterial colonization of the phyllosphere.

Mechanistic understanding and holistic approach of phytoremediation: A review on application and future prospects

Rapid industrialisation, increased rate of waste production, higher agricultural inputs, mining, industrial waste,and contaminated irrigation water are increasing the heavy metal contamination in agricultural land andfreshwater sources. These heavy metals contaminated resources are used by humans for food production thatultimately get accumulated in the food chain. Biomagnification of heavy metals can pose solemn health threatsto human life, such as mutations, endocrine disruption, nephro-toxicity, etc. There has long been a need fordecontamination of these resources and prevention from the further contamination to avert the negative effectson human health. The “phytoremediation” process is a very promising and eco-friendly approach for heavymetal remediation from contaminated sites with some limitations. An effort has been made to present thescattered information of phytoremediation technique in a single paper through this review. The present reviewdescribes the fundamentals of phytoremediation including the different associated processes, mechanism, andinfluencing factors. The mechanism of tolerance and detoxification of heavy metals by plants has also beendiscussed in brief. The possible amelioration/modification of a particular phytoremediation strategy has beenadvocated to increase its potential efficacy and further development of these strategies for future reference. Thereview tries to cover all the essential and adequate information of the relevant published data with some recentadvances in phytoremediation approaches. It is recommended to apply the combination of different availabletechniques or phytoremediation techniques with modern chemical, biological and genetic engineering tools foran easy and effective decontamination of heavy metals from soil and agricultural land. The review advocates thedevelopment of site specific, farmer driven, sequential and phytoremediation strategies along with policy supportfor effective decontamination.

The Effect of Picloram Plus 2,4-Dichlorphenoxyacetic Acid on Peanut Growth and Yield

ABSTRACT Picloram (4-amino-3,5,6-trichloropicolinic acid) injury, in the form of leaf roll, is often observed in peanut fields due to short crop rotations, contaminated irrigation water, treated hay, and contaminated livestock waste. Limited data on peanut response to picloram is available. Field trials were conducted near Tifton, GA from 2015-2017 to determine the effects of picloram plus 2,4-D (2,4-dichlorophenoxyacetic acid) on peanut growth and yield. Picloram plus 2,4-D was applied to ‘GA-06G' peanut at four different timings: preemergence (PRE), 30 d after planting (DAP), 60 DAP, and 90 DAP. At each timing, three rates of picloram plus 2,4-D were applied including the following: 1/10thX (0.18 + 0.67 kg ai/ha); 1/100thX (0.018 + 0.067 kg ai/ha); and 1/300thX (0.006 + 0.023 kg ai/ha). A non-treated control (NTC) or 0 rate was included for comparison. Peanut plant density was not influenced by any rate or timing of picloram plus 2,4-D. For peanut injury (leaf roll), a significant rate x timing interaction was observed (P=0.047). At 120 DAP, leaf roll was significant for the 1/10thX rate applied at 30, 60, and 90 DAP, the 1/100thX rate applied at 60 and 90 DAP, and for the 1/300thX rate applied at 90 DAP. When averaged over timing, peanut height at 120 DAP was significantly reduced by the 1/10thX and 1/100thX rates. When averaged over rate, peanut height reductions were greatest when picloram plus 2,4-D was applied at 60 DAP. When averaged over timing, only the 1/10thX rate caused significant yield reductions (11%). When averaged over rate, timing had no effect on yield (P=0.5403). Peanut fields unintentionally exposed to picloram plus 2,4-D rates ≤ 1/100thX can exhibit typical injury symptoms but most likely will not experience yield losses.