That's because gut phage from mice treated with one drug carried high levels of
genes that confer
resistance to different drugs, which means that the phage could serve as backup when bacteria must find
ways to withstand a variety of
antibiotics.
That background makes it important to characterize «both the natural occurrence of the
antibiotic -
resistance genes and the anthropogenic load, and where those
genes come from, and it's good to do it in a quantitative
way,» as Pruden's team did for the South Platte, says Joakim Larsson of the University of Gothenburg, Sweden, who has tracked
antibiotics and
resistance genes in India and Sweden.