| dc.description.abstract | Antimicrobial resistance poses an ever-increasing threat to global health services. The environment is considered a major reservoir of antimicrobial resistance genes (ARGs), in large part due to anthropogenic pollution. Our understanding of the predominant factors affecting the prevalence and persistence of ARGs in the environment is still limited, and thus was the focus of the current study.
To investigate antimicrobial resistance in the aquatic environment, ARGs were first quantified by qPCR in samples collected from a wastewater treatment plant (WWTP) and the receiving marine ecosystem. Five of the seven target ARGs (ermB, qnrB, sul1, tetB, tetD) and the class one integron integrase gene, intI1, were detected in wastewater samples. Across all samples, the sulfonamide resistance gene, sul1, was the most frequently detected and abundant, and so was the focus of further analysis. The WWTP process was observed to be only partially effective at removing sul1, and as such the effluent could be considered a source of ARGs detected in the receiving environment. In a subsequent study of the River Dee, Aberdeenshire, spatiotemporal variation was observed in both the relative abundances of ARGs (sul1, ermB and tetB) and microbial community composition, evaluated by Illumina sequencing of the 16S rRNA V4 region. The sul1 gene exhibited a positive relationship with intI1 and both genes further correlated with compositional shifts in the microbial community.
The study thereafter investigated ARGs in the soil environment, with a focus on sul1, a gene which has been identified as a widespread contaminant in the current and previous works, despite limited current clinical usage. In a microcosm experiment, pig manure was applied to four distinct Scottish soils and the relative abundance of sul1 was tracked over 100 days by qPCR. Manure amendment significantly increased sul1 relative abundance, which continued to increase over the first quarter of the experimental run, before decreasing to background levels across the remainder of the time course. Significant differences in sul1 relative abundance were observed between soil types over the experiment, in both untreated and autoclaved soil microcosms. The introduction of manure microbiota significantly altered microbial community composition; however, the native soil microbiota recovered within the early stages of the experimental run. The relative abundance of sul1 displayed a significant positive relationship with the intI1 gene, and mobility potential was indicated to be associated with gene persistence. The presence of sul1 on class one integrons was subsequently validated by inverse PCR and Nanopore sequencing.
Overall, sul1, ermB and tetB were the highest occurring ARGs of those investigated and sul1 was revealed to be an especially prevalent environmental contaminant, whose fate is shaped by multiple interconnected factors. With the agricultural industry and wastewater identified as considerable point sources, a greater focus on ARG removal is necessary if the dissemination of ARGs is to be mitigated in the future. | en |
