Antibiotic resistance genes in freshwater biofilms along a whole river

A key problem challenging public health officials' efforts to stem the spread of antibiotic resistance is the potential increase of resistance in the environment. Yet, despite recent and significant changes to agricultural land in New Zealand, as well as the sector's high antibiotic use, the influence on antibiotic resistance in the environment remained uncharacterised. Spatial and temporal dynamics of antibiotic resistance genes in freshwater biofilms from NZ's fourth longest river as it transitioned between low and high intensity farming were examined for 1 year. Polymerase chain reaction was employed to gauge the level of resistance present. Biofilms were screened for 10 genes conferring resistance to antibiotics used in humans only and both humans and agricultural animals. Three genes were detected, one which conferred resistance to the important human-only use antibiotic vancomycin. Detected at the two downstream sites only, and those subject to the highest combined land-use stressors, the three genes indicated an elevated presence of antibiotic resistance in relation to surrounding land use; 7.7% versus 2% across the whole river system. The detection of a gene conferring resistance to an important human-only use antibiotic was particularly concerning and highlighted human-based contamination sources along the river, in addition to those of agricultural origin.