Bacterial Antibiotic Resistance in Soils Irrigated with Reclaimed Municipal Wastewater.

Wastewater reclamation for municipal irrigation and groundwater recharge is an increasingly attractive option for extending water supplies. However, public health concerns include the potential for development of antibiotic resistance (AR) in soil bacteria after exposure to residual chemicals in reclaimed water. Though scientific studies have reported high levels of AR in soils irrigated with wastewater, these works often fail to address the natural occurrence of AR in soil bacteria. The Gilbert Riparian Preserve in Gilbert, Arizona has been utilizing reclaimed municipal wastewater for groundwater recharge for nearly 20 years. We are comparing AR patterns in Gram positive (enterococci) soil bacteria isolated from sediments of the Riparian Preserve and comparing these to bacterial AR in sediments collected from a nearby agricultural irrigation pond with no exposure to reclaimed water. Resistance to 16 antibiotics is being quantified from the soil surface (0-5 cm) to a depth of 30 cm. Results reveal high levels of resistance to selected antibiotics (daptomycin and lincomycin) in soils from both sites, but while 35% of enterococci isolated from sediments of the Riparian Preserve showed no antibiotic resistance, only 7% of isolates from the irrigation pond sediments displayed the same trend. Furthermore, multi-drug resistance (resistance to more than 4 antibiotics) was far higher in irrigation pond isolates (32%) than in enterococci from the Riparian Preserve (15%). Comparing the development of AR in soil bacteria at these two sites will increase current understanding of environmental and public health impacts of using reclaimed water for irrigation and recharge.