Browsing by Author "Guron, Giselle K.P."

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    Effects of Dairy Manure-Based Amendments and Soil Texture on Lettuce-and Radish-Associated Microbiota and Resistomes
    Guron, Giselle K.P.; Arango-Argoty, Gustavo; Zhang, Liqing; Pruden, Amy; Ponder, Monica A. (American Society for Microbiology, 2019)
    Dairy cattle are routinely treated with antibiotics, and the resulting manure or composted manure is commonly used as a soil amendment for crop production, raising questions regarding the potential for antibiotic resistance to propagate from “farm to fork.” The objective of this study was to compare the microbiota and “resistomes” (i.e., carriage of antibiotic resistance genes [ARGs]) associated with lettuce leaf and radish taproot surfaces grown in different soils amended with dairy manure, compost, or chemical fertilizer only (control). Manure was collected from antibiotic-free dairy cattle (DC) or antibiotic-treated dairy cattle (DA), with a portion composted for parallel comparison. Amendments were applied to loamy sand or silty clay loam, and lettuce and radishes were cultivated to maturity in a greenhouse. Metagenomes were profiled via shotgun Illumina sequencing. Radishes carried a distinct ARG composition compared to that of lettuce, with greater relative abundance of total ARGs. Taxonomic species richness was also greater for radishes by 1.5-fold. The resistomes of lettuce grown with DC compost were distinct from those grown with DA compost, DC manure, or fertilizer only. Further, compost applied to loamy sand resulted in twofold-greater relative abundance of total ARGs on lettuce than when applied to silty clay loam. The resistomes of radishes grown with biological amendments were distinct from the corresponding fertilizer controls, but effects of composting or antibiotic use were not measureable. Cultivation in loamy sand resulted in higher species richness for both lettuce and radishes than when grown in silty clay loam by 2.2-fold and 1.2-fold, respectively, when amended with compost.
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    Gamma Irradiation Influences the Survival and Regrowth of Antibiotic-Resistant Bacteria and Antibiotic-Resistance Genes on Romaine Lettuce
    Dharmarha, Vaishali; Guron, Giselle K.P.; Boyer, Renee R.; Niemira, Brendan A.; Pruden, Amy; Strawn, Laura K.; Ponder, Monica A. (Frontiers, 2019-04)
    Contamination of romaine lettuce with human pathogens, antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARGs) occurs during production. Post-harvest interventions are emplaced to mitigate pathogens, but could also mitigate ARB and ARGs on vegetables. The objective of this research was to determine changes to lettuce phyllosphere microbiota, inoculated ARB, and the resistome (profile of ARGs) following washing with a sanitizer, gamma irradiation, and cold storage. To simulate potential sources of pre-harvest contamination, romaine lettuce leaves were inoculated with compost slurry containing antibiotic-resistant strains of pathogenic (Escherichia coli O157:H7) and representative of spoilage bacteria (Pseudomonas aeruginosa). Various combinations of washing with sodium hypochlorite (50 ppm free chlorine), packaging under modified atmosphere (98% nitrogen), irradiating (1.0 kGy) and storing at 4°C for 1 day versus 14 days were compared. Effects of post-harvest treatments on the resistome were profiled by shotgun metagenomic sequencing. Bacterial 16S rRNA gene amplicon sequencing was performed to determine changes to the phyllosphere microbiota. Survival and regrowth of inoculated ARB were evaluated by enumeration on selective media. Washing lettuce in water containing sanitizer was associated with reduced abundance of ARG classes that confer resistance to glycopeptides, b-lactams, phenicols, and sulfonamides (Wilcoxon, p < 0.05). Washing followed by irradiation resulted in a different resistome chiefly due to reductions in multidrug, triclosan, polymyxin, b-lactam, and quinolone ARG classes (Wilcoxon, p < 0.05). Irradiation followed by storage at 4°C for 14 days led to distinct changes to the b-diversity of the host bacteria of ARGs compared to 1 day after treatment (ANOSIM, R = 0.331; p = 0.003). Storage of washed and irradiated lettuce at 4°C for 14 days increased the relative abundance of Pseudomonadaceae and Carnobacteriaceae (Wilcoxon, p < 0.05), two groups whose presence correlated with detection of 10 ARG classes on the lettuce phyllosphere (p < 0.05). Irradiation resulted in a significant reduction (~3.5 log CFU/g) of inoculated strains of E. coli O157:H7 and P. aeruginosa (ANOVA, p < 0.05). Results indicate that washing, irradiation and storage of modified atmosphere packaged lettuce at 4C are effective strategies to reduce antibiotic-resistant E. coli O157:H7 and P. aeruginosa and relative abundance of various ARG classes.
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    Microbiota and Antibiotic Resistome of Lettuce Leaves and Radishes Grown in Soils Receiving Manure-Based Amendments Derived From Antibiotic-Treated Cows
    Fogler, Kendall; Guron, Giselle K.P.; Wind, Lauren L.; Keenum, Ishi M.; Hession, W. Cully; Krometis, Leigh-Anne H.; Strawn, Laura K.; Pruden, Amy; Ponder, Monica A. (Frontiers, 2019-04-10)
    Cattle are commonly administered antibiotics, resulting in excretion of antibiotics, antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARGs). The aim of this study was to determine if the use of dairy manure collected during antibiotic administration influences the bacterial microbiota of lettuce and radishes, including carriage of ARB and ARGs, when applied as a soil amendment and if composting mitigates the effects. Lettuce and radishes were grown in field-plots amended with raw manure from antibiotic-treated (cephapirin, pirlimycin) cows, composted manure from antibiotic-treated cows, composted manure from antibiotic-free cows, or an inorganic chemical fertilizer (control; 12 plots, n = 3). Surficial vegetable bacteria and antibiotic resistomes (i.e., total ARGs) were characterized using heterotrophic plate counts (HPCs) on antibiotic-containing media, 16S rRNA gene amplicon sequencing, quantitative polymerase chain reaction (qPCR), and shot-gun metagenomics. The different manure and compost amendments did not result in significant changes to the surficial vegetable bacteria at the phylum level; however, some minor changes at the class and family level were observed. Beta-diversities of the ARGs detected by shotgun metagenomic sequencing were distinctly different between vegetable type (R = 0.30, p = 0.04), with small separations between the resistomes associated with amendment type in unrarefied analysis (R = 0.27, p = 0.02), but not rarefied analysis, of the data. Network analysis highlighted that multi-drug ARG classes commonly co-occurred with plasmid-associated genes and could be a driver of co-and cross-selection of ARGs in the different conditions. Carriage of sul1 and tet(W) ARGs on vegetables quantified by qPCR were strong indicators of manure-based amendment relative to chemical fertilizer, with some reduction incurred via composting (p < 0.05). Also, increased HPCs resistant/tolerant to clindamycin, a class of antibiotics administered to cattle, were on lettuce grown in biological soil amendments relative to chemical fertilizer (p < 0.05). This study demonstrates that amending soil with rawmanure collected fromdairy cows during antibiotic administration may affect the composition of microbiota and resistomes associated with vegetable surfaces. Composting may be an important strategy to reduce some ARGs on fresh produce, but differences in the resistomes of lettuce and radishes suggest the extent of soil contact should be considered.