Potential role of Mercury pollutants in the success of Methicillin-Resistant Staphylococcus aureus USA300 in Latin America

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) lineage known as USA300-North American (NA) has become highly prevalent in North America whilst a USA300 variant known as USA300-LV, harboring a mercury resistance element (COMER), has become dominant in South America. We investigated whether mercury pollution, which is common in South America notably because of artisanal gold mining, may explain the local dominance pattern of USA300-LV. Density-based estimation of epidemic success in 245 genomes of the ST8 lineage revealed that the acquisition of COMER in USA300 progenitors increased success in South American countries but decreased success elsewhere. The fitness of USA300-LV was impaired in vitro compared with USA300-NA, but the addition of sub-inhibitory concentration of mercury provided a strong fitness advantage to USA300-LV and triggered an overexpression of major virulence factors. The success of USA300-LV in South America may result from low-level mercury exposure selecting resistant and virulent strains.