Co-selection of Mercury and Antibiotic Resistance in Sphagnum Core Samples Dating Back 2000 Years

Metal exposure might induce multiple drug resistance (MDR) in bacteria in environments devoid of antibiotics via the process of co-selection, but the extent is poorly known. Core samples from two sphagnum peat bogs in central Maine, USA, were analyzed for total Hg content and were radiocarbon dated. Culturable bacteria isolated from various core depths were assayed for antibiotic- and Hg-resistance and the presence of merA (mercuric reductase). Our results show that sphagnum peat bogs represent natural ecosystems that contain ambient levels of Hg that select for indigenous bacterial strains that are not only Hg resistant, but also possess the MDR phenotype.