AUTHOR=Martinez Jose L. TITLE=Natural Antibiotic Resistance and Contamination by Antibiotic Resistance Determinants: The Two Ages in the Evolution of Resistance to Antimicrobials JOURNAL=Frontiers in Microbiology VOLUME=3 YEAR=2012 URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2012.00001 DOI=10.3389/fmicb.2012.00001 ISSN=1664-302X