P131: Antibiotic Resistant Bacteria in Soil, Sediments, and Runoff from a Soybean Farm

The purpose of this study was to compare the antibiotic resistances (ABR) in bacterial isolates in active soybean farm soil and runoff exposed to fertilizers, pesticides and herbicides. The samples were selected to represent a control group of untreated soil, active farm soil exposed to agricultural chemicals, and sediment and runoff beyond the cultivated farm. Similar viable bacteria counts (10⁶ CFU/g) were found in the farmland soil samples and in untreated soil (10⁷ CFU/g). Bacterial isolates from the samples were tested for minimum inhibitory concentrations of antibiotic resistance using agar dilution methods and were then screened for ABR and integron genes using standard PCR protocols. The results indicated that bacteria within the soil/water/sediment population were resistant to individual and combinations of antibiotics used for the treatment of human infections. The most prevalent ABR in 180 Gram-negative bacteria were ampicillin (AMP) 85%, followed by chloramphenicol (CHL) 76%, gentamicin (GEN) 9%, tetracycline (TET) 7% and ciprofloxacin (CIP) 3% of the isolates. Of 165 Gram-positive isolates, 32% showed resistance to AMP, erythromycin (ERM) and vancomycin (VAN), 20% to CHL, 6% to GEN, 4% to TET and 1% to CIP.  The presence of int1 in the soil indicates a possible mechanism for ABR gene transfer in agricultural soil, although vanA and vanB were not detected. The findings from this study indicate the potential for the development of resistant bacteria under typical farming conditions of exposure to chemical treatments, which impact crop yields and can potentially impact human health, welfare and the environment.