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Recent studies have shown that the presence of antimicrobial-resistance genes (ARGs) long predated the clinical use of antibiotics (NEJM JW Infect Dis April 25 2012). New work on soil microorganisms has extended these observations, revealing a vast array of ARGs — most of them distinct from known ARGs in human pathogens.
Using functional metagenomics, researchers screened agricultural and grassland soil samples from two sites for the presence of ARGs active against any of 18 antibiotics from eight drug classes. The 2895 ARGs that they identified conferred resistance to 15 of the 18 antibiotics and represented all major resistance mechanisms. Only 15 of these ARGs had perfect amino acid identity to those recorded in the National Center for Bi…