UCLA

Widespread prevalence of multidrug and pandrug-resistant bacteria has prompted substantial concern over the global dissemination of antibiotic resistance genes (ARGs). Environmental compartments can behave as genetic reservoirs and hotspots, wherein resistance genes can accumulate and be laterally transferred to clinically relevant pathogens. In this work, we explore the ARG copy quantities in three environmental media distributed across four cities in California and demonstrate that there exist city-to-city disparities in soil and drinking water ARGs. Statistically significant differences in ARGs were identified in soil, where differences in bla_SHV gene copies were the most striking; the highest copy numbers were observed in Bakersfield (6.0 × 10^-2 copies/16S-rRNA gene copies and 2.6 × 10⁶ copies/g of soil), followed by San Diego (1.8 × 10^-3 copies/16S-rRNA gene copies and 3.0 × 10⁴ copies/g of soil), Fresno (1.8 × 10^-5 copies/16S-rRNA gene copies and 8.5 × 10² copies/g of soil), and Los Angeles (5.8 × 10^-6 copies/16S-rRNA gene copies and 5.6 × 10² copies/g of soil). In addition, ARG copy numbers in the air, water, and soil of each city are contextualized in relation to globally reported quantities and illustrate that individual genes are not necessarily predictors for the environmental resistome as a whole.