Gamma Irradiation Influences the Survival and Regrowth of Antibiotic-Resistant Bacteria and Antibiotic-Resistance Genes on Romaine Lettuce

dc.contributor.authorDharmarha, Vaishalien
dc.contributor.authorGuron, Giselle K.P.en
dc.contributor.authorBoyer, Renee R.en
dc.contributor.authorNiemira, Brendan A.en
dc.contributor.authorPruden, Amyen
dc.contributor.authorStrawn, Laura K.en
dc.contributor.authorPonder, Monica A.en
dc.contributor.departmentCivil and Environmental Engineeringen
dc.contributor.departmentFood Science and Technologyen
dc.description.abstractContamination 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.en
dc.description.sponsorshipFunding was supported in part by USDA NIFA-AFRI #2014-05280 and #2017-68003-26498 and the Virginia Agricultural Experiment Station and the Hatch Program of the National Institute of Food and Agriculture, U.S. Department of Agriculture.en
dc.format.extent16 pagesen
dc.identifier.citationDharmarha V, Guron G, Boyer RR, Niemira BA, Pruden A, Strawn LK and Ponder MA (2019) Gamma Irradiation Influences the Survival and Regrowth of Antibiotic-Resistant Bacteria and Antibiotic-Resistance Genes on Romaine Lettuce. Front. Microbiol. 10:710. doi: 10.3389/fmicb.2019.00710en
dc.rightsCreative Commons Attribution 4.0 Internationalen
dc.subjectantibiotic resistanceen
dc.subjectEschericha coli O157:H7en
dc.subjectLettuce (lactuca sativa L.)en
dc.subjectphyllo epiphytic microbiotaen
dc.subjectgamma irradiationen
dc.subjectspoilage bacteriaen
dc.titleGamma Irradiation Influences the Survival and Regrowth of Antibiotic-Resistant Bacteria and Antibiotic-Resistance Genes on Romaine Lettuceen
dc.title.serialFrontiers in Microbiologyen
dc.typeArticle - Refereeden


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