Heavy metal pollution and co-selection for antibiotic resistance: a microbial palaeontology approach

The introduction of heavy metals into the environment can modify the microbial community and their activity. Due to the persistence of metals in soils and sediments, it is implicated that increased tolerance to heavy metals may be a driving factor in the maintenance of antibiotic resistance in the environment due to co-selective mechanisms of resistance. This study marks the first attempt to address the effects of industrial heavy metal contaminants on both the cultivable and the total microbial population of a sediment core that covers a time scale spanning approximately a century, through both phenotypic analysis and with the use of high throughput sequencing technologies, providing a deeper understanding of the heavy metal driven response in microbial diversity through time. We assess the selective pressure of zinc as a driving force for the maintenance and proliferation of antibiotic resistance through phenotypic analysis of resistance in microbial isolates and the quantification of a gene conferring resistance to both metals and antibiotics (IntI1). We demonstrate a positive correlation between the level of zinc resistance in the microbial population and zinc in the environment, and the proportion of zinc resistant isolates with proportion of resistance to three clinically relevant antibiotics (oxacillin, cefotaxime and trimethoprim). We assess the effects of selective pressures imposed by heavy metals on total microbial community composition with the use of high-throughput sequencing technologies. These data show that zinc plays a significant role in shaping the structure of community diversity over time and is driving the population towards higher levels of resistance to zinc, resulting in the co-selection of antibiotic resistant organisms in the environment.