QUANTIFYING ANTIBIOTIC RESISTANCE IN THE SEDIMENTS OF A MIXED-LANDSCAPE RIVER

The purpose of this study was to quantify the occurrence of antibiotic resistance in the sediments of the mixed-landscape Cache La Poudre River. This river has previously been studied and shown to have high concentrations of antibiotics correlating with urban and agricultural activity. Molecular and culture-based methods for assessing antibiotic resistance in environmental samples were developed and applied to the river sediments. PCR detection assays were conducted for seven sulfonamide resistance gene families using newly designed primers and eight tetracycline resistance gene families using previously published primers. Sul(I), sul(II), tet(W), and tet(O) gene families were quantified by real-time quantitative polymerase chain reaction (Q-PCR). Resistances to four classes of antibiotics (tetracyclines, sulfonamides, ionophores, and macrolides) was also investigated using a culture-based approach on antibiotic media. The quantities of the resistance genes were as high as 1.32×108 copies/gram sediment at impacted sites versus 9.55×104 copies/gram sediment at a pristine site, while resistant CFU were as high as 1.1×106 CFU/gram sediment at impacted sites versus 8.0×102 CFU/gram sediments at the pristine site. Overall the findings indicated that land-use impacts the overall concentration of antibiotic resistance genes in sediments.