LB 29-291 - Investigating the microbial resistome of pristine and anthropogenically disturbed soils

Background/Question/Methods:

The continual emergence of antibiotic resistant strains of bacteria causes concern for the future of public and environmental health and is likely to become a global pandemic. Soils are important reservoirs of antibiotic resistance and antibiotic production genes. Antibiotic resistance genes (ARGs) from environmental sources can spread to pathogenic species through a variety of mechanisms, including horizontal gene transfer, with potential to impact animal and human health. Historical and naturally occurring antibiotic resistance has been noted in soils free from anthropogenic effects, therefore determining naturally occurring ARGs versus acquired can aid in tracking evolution of resistant pathogens and epidemiological modeling. However, the largest contributor to rising antibiotic resistance within the environment is the use of antibiotics in animal husbandry and human health. We assessed antibiotic resistance in Wyoming soils and how anthropogenic disturbances affect the ecology of microbial communities. Soils from three locations with different levels of anthropogenic disturbances were used for microbial culturing and qPCR for select antibiotic resistance genes. Selected cultured bacterial isolates were tested for antibiotic resistance using a minimum inhibitory concentration assay (MIC).

Results/Conclusions:

Several ARGs showed increased abundances in soils from heavily grazed grasslands: acrd, intI1, intI3, bla_OXA, mefE, tetA, and tetX. The genes in higher abundance represent resistance to several different classes of antibiotics and associated antibiotic mechanisms, as well as resistance mechanisms (e.g. efflux pumps, enzymes). Analysis of MIC from selected isolates from each soil location revealed a high level of resistance to penicillin compared with other antibiotics. Anthropogenically disturbed soils exhibited a trend of more resistance as measured by MIC than undisturbed soils. Recently, it has been suggested that intI1 can be used as a proxy for monitoring environmental pollution because it is linked to antibiotic resistance, heavy metal tolerance, is found in a variety of pathogenic and nonpathogenic bacteria, and can be acquired by horizontal gene transfer. Abundance measurements of this ARG and others, combined with assessment of the level of resistance through MIC assays can help us to understand the historical levels of antibiotic resistance and measure the effects of anthropogenic disturbances on the environment.