Date of Award

2018

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Animal Science

First Advisor

John Barlow

Abstract

While commonly thought of as a waste product, food scraps and residuals represent an important opportunity for energy and nutrient recapture within the food system. As demands on production continue to increase, conservation of these valuable resources has become a priority area. In the wake of new legislation in Vermont, Act 148, the Universal Recycling Law, the fate of microbial species in food waste, scraps and residuals is increasingly important. The presence of antimicrobial resistance genes in all types of foods calls for an increased need to estimate risk of antibiotic resistance transfer and maintenance across all segments of food production and distribution systems, from farm to fork. Specifically, the fate of antibiotic resistance genes (ARGs) in these co-mingled food wastes has not been sufficiently characterized; as legislative programs increase in popularity, surveillance of these materials is pressing and should be documented to assess the risk and potential measures for mitigation and management as we approach commercial scales of implementation

Previous studies have relied on a combination of targeted techniques, such as 16S rRNA sequencing and qPCR on a specific subset of ARGs; however, these may not cover the full extent of resistance or microorganisms of concern in any given sample. As sequencing technologies improve and costs continue to drop, more comprehensive tools, such as shotgun metagenomic sequencing, can be applied to these problems for both surveillance and novel gene discovery. In this study, we leveraged the increased screening power of the Illumina HiSeq and shotgun metagenomic sequencing to identify and characterize ARGs, microbial communities, and associated virulence factors of food scraps, on-farm composts, and several consumer products. Isolates were also screened for antibiotic resistance to demonstrate the functionality of ARGs identified.

The resistome, microbiome, and virulence genes were characterized in all samples. Fifty unique ARGs were identified that spanned 8 major drug classes. Most frequently found were genes related to aminoglycoside, macrolide, and tetracycline resistance. Additionally, 54 distinct virulence factors and 495 bacterial species were identified. Virulence factors were present across the farm setting and mainly included gene transfer mechanisms, while bacteria clustered distinctly into site and farm, as well as separate on farm niches. The relationship between these categories was also assessed by both Pearson correlation and co-inertia analysis, with the most significant relationship being between ARGs and virulence factors (P = 0.05, RV = 0.67). While limited in this study, these patterns reinforce the finding that spread of antibiotic resistance genes may be dependent on the virulence factors present enabling transfer, rather than total microbial community composition.

Language

en

Number of Pages

103 p.

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