UCLA

The failing of current last line of defense antibiotics has raised concerns over the future treatability of common bacterial infections, drawing particular concern for antibiotic resistance genes (ARGs), which confer resistance and can be transferred among bacteria through horizontal gene transfer. ARGs are ubiquitous and rather than readily degrading, can proliferate in the presence of selective and co-selective pressures, as well as persist in the absence of a bacterial host. In this way, ARGs challenge current perceptions of contaminant behavior, with many questions concerning ARG fate and transport still yet to be answered. The four studies reported here explore ARG extent of dissemination, fate and transport, from the framework of prioritizing environmental compartments that may be of public health significance.

The first research chapter presents a survey of environmental ARG levels in California, sampling air, drinking water and soil across 26 public parks in four cities across California, USA. Data are analyzed by two methods and city values are compared to each other as well as to globally reported values. In conducting this study, city to city disparities in ARG levels are shown for the first time, providing insight into possible hotspots for ARG proliferation.

In the second chapter, Confined Animal Feeding Operations (CAFOs) are confirmed as possible sources for airborne ARGs. Air is sampled from areas directly downwind of agricultural activity and compared to locations regarded as “pristine,” or unassociated with agriculture. Antibiotic resistance is studied via culturally dependent and molecular methods, presenting data on ARGs in viable bacteria as well as found extracellularly.

The third research chapter explores commercial garden products as potential sources of ARG content near homes. Here a survey of the ARG content of 30 commercially available garden products is presented and contextualized in relation to branding, third party certifications and environmentally reported ARG quantities.

Lastly, the final research chapter explores the fate and transport of garden product-derived ARGs through microcosm experiments. Here, four garden products are used to supplement an ARG-free receiving soil and temporal profiles are created to determine short term decay and proliferation of ARGs from commercially available inputs