UCLA

The rising level of antibiotic resistance is a serious public health issue, posing a global threat to human health. The common practice of applying sub-therapeutic dosages of antibiotics to livestock has been shown to foster the development of antibiotic resistant bacteria (ARB). ARB originating in livestock can reach the general population via multiple pathways: air downwind of animal feeding operations and transportation vehicles, indoor air, soil following land application, surface and groundwater, and retail meat and poultry. Likewise, antibiotic resistance genes (ARGs) confer antibiotic resistance through various mechanisms, and are themselves considered to be emerging contaminants. In Chapter 2, we demonstrate the presence of both ARB and ARGs emanating from cattle production in air. This study is unique in that it is the first to compare resistance in airborne bacteria near conventional and organic beef farms. We used two methods to assess antibiotic resistance: our newly developed high throughput method (HT) for liquid cultures (n= 1295), and a common method, disk diffusion (DD), which involves culturing on solid media. By the HT method, conventional beef production sites showed a greater average fraction of ARB than organic production for most of the six antibiotics at the low and high concentrations, some with statistical significance. Regular surveillance of ARB and ARGs from beef cattle farms is suggested to detect the spread of ARB and ARG to the community via air trajectories.

This body of work also demonstrates ARB originating from retail meat. In Chapter 3, we present results that suggest that the presence of antibiotic resistant E. coli differs depending on the type of poultry production system. In this study, we cultured Escherichia coli from retail poultry falling into three categories of farming practices: Conventional, No Antibiotics, and Pristine Organic. We examined the antibiotic resistance of the E. coli isolates (n = 424) by exposing them to seven common antibiotics via a high-throughput, liquid culture-based method. Our findings were that the fraction resistant of the E. coli bacteria from the Pristine Organic was significantly lower than the Conventional and No Antibiotic categories, while the latter categories had similar fractions of isolates resistant. It is the first study to suggest that a particular type of organic meat production shows a significant improvement in antibiotic resistance over typical organic brands.

In Chapter 4, the study addresses the gap in literature where there are few studies that address the release of ARGs specifically from poultry CAFOs. To investigate this, upwind and downwind of the farms, bioaerosols were collected and examined for antibiotic resistant genes. To our knowledge, this is the first study to examine air samples collected upwind and downwind of CAFOs for elevated levels of ARGs. Our findings show that there are higher frequency of blaSHV downwind than upwind in two poultry CAFO sites and also, a higher frequency of erm(F) downwind than upwind in three poultry CAFO sites. The higher frequency of ARG detection near downwind versus upwind of poultry farms collectively show the occurrence of antibiotic resistance in the environment, which may imply potential exposure to ARGs via an air pathway downwind of poultry farm. Regular monitoring and surveillance of ARG from poultry sources is suggested to detect development of airborne antimicrobial resistance that can be spread to surrounding community, especially humans living near farms and workers, via wind air trajectories. The microbiome of family workers can be impacted by these ARG’s and research into the public health should be investigated.