Abstract
There is growing evidence that bacteria that live in diverse soil environments are gaining multidrug resistance. Recent functional screens and the growing information of metagenomic databases are also revealing the presence of an unexpected density of resistance genes in the environment, the antibiotic resistome. To explore this reservoir, we isolated 15000 morphologically diverse microorganisms directly from soil samples, and constructed a diverse library of 264 resistant isolates. Without exception, all the 264 isolates were found to be resistant to at least one antibiotic. Multi-drug resistance was observed for more than 3 antibiotics in 83% of the isolates, while five strains showed resistance to more than 10 antibiotics of the 15 antibiotics tested in the library. These results indicate that soil bacteria are a reservoir of antibiotic resistance with greater genetic diversity than previously accounted for.