(95b) Identification of Antibiotic Resistome in Urban Watersheds Via High-Throughput Screening

Urban watersheds from point sources are potential reservoirs of antibiotic resistance genes (ARGs). However, few studies have investigated urban watersheds of non-point source, which can provide information on the background level of antibiotic resistance in a bacterial community. Antibiotic resistance levels of two watersheds (R1, R3) were examined by employing heterotrophic plate counts (HPC) as a culturing method to obtain counts of bacteria resistant to seven antibiotics belonging to different classes (erythromycin, kanamycin, lincomycin, norfloxacin, sulfanilamide, tetracycline and trimethoprim). From the HPC study, 239 antibiotic resistant bacteria were characterized for resistance to more antibiotics. Furthermore, ARGs and antimicrobial biosynthesis genes were identified using GeoChip version 5.0 to elucidate the resistomes of surface waters in R1 and R3. GeoChip revealed similar ARGs in both watersheds, but with significantly higher intensities for tetX and β-lactamase B genes in R1 compared to R3. The genes with the highest average normalized intensities in R1 and R3 were tetracycline (tet) and fosfomycin (fosA) resistance genes, respectively. This study demonstrates that the use of a DNA microarray is useful for identifying naturally occurring resistomes and for comparing bacterial communities in urban watersheds of different land-use profiles.