Basic Antibiotic Resistance of Bacteria Isolated from Different Biotopes

Soil is not only a habitat of antibiotic-resistant microorganisms and a natural source of antibiotic resistance genes, but also an environment in which clinical determinants of antibiotic resistance may be accumulated and transferred. Quantitative assessment of antibiotic-resistant bacteria in polluted soils used in agriculture and its comparison to the so-called baseline content of resistant bacteria and their resistance genes in the soil is therefore urgent. However, the data on the study of antibiotic-resistant bacteria in pristine soils (with minimal anthropogenic impact) are practically absent. Comparative study was therefore carried out on the spectra of resistance to natural and synthetic antibiotics among gram-negative bacteria isolated from various soils: pristine (Arctic and Antarctic soils); sites with possible pollution (Albic Retisols (IUSS Working Group WRB, 2015) of a woodland park area in the Moscow region), and moderately polluted soils with high mercury content (near the Khaidarkan mercury mine). It was revealed that strains resistant to one or more of the used natural antibiotics, with the exception of tetracycline, were found in all types of biotopes. About one third of the studied strains, both isolated from soils of polar regions with low anthropogenic impact, and from polluted soils near the Khaidarkan mercury mine, exhibited multiple drug resistance. These results suggest that the presence of multiple antibiotic resistance among bacteria is not solely a response to anthropogenic pollution. Bacterial strains with multidrug antibiotic resistance isolated from the biotopes formed in extremely cold conditions belonged mainly to the genera among the representatives of which intrinsic resistance is widespread, due to the specific structure of their cell walls, preventing antibiotic penetration into the cell, and to the presence of various nonspecific efflux systems of release of toxic substances from the cell.