On the Origin and Distribution of Antibiotic Resistance: Permafrost Bacteria Studies

Abstract

The presented review summarizes the data obtained during the study of antibiotic-resistant bacteria isolated from the Arctic and Antarctic permafrost sediments. Comparative analysis of the molecular structure of the “ancient” environmental and modern clinical genes of resistance to β-lactams, streptomycin, spectinomycin, vancomycin, tetracycline, and sulfanilamides revealed a high level of their similarity, in some cases reaching 100%. The molecular structure of ancient bacterial plasmids carrying antibiotic resistance determinants was considered and compared with the plasmid structure of modern bacteria. A wide distribution of small plasmids among modern bacteria closely related to the ancient Acinetobacter plasmid carrying an autonomous streptomycin/spectinomycin resistance gene aadA27 has been revealed. The “ancient” integron structure, which agrees with the description of the hypothetical ancestor of the integrons of the subgroup aadA2, was described. By the examples of the Tn3 family transposons (Tn5393 and Tn21 subgroups) various mechanisms of formation of complex transposons simultaneously carrying several antibiotic-resistance genes were discussed. In particular, an important role of integrons in formation of complex transposons is demonstrated, and numerous cases of independent insertion of integrons with diverse cassette antibiotic-resistance genes into various base transposons of the Tn3 family are presented. Separately, the origin of the complex transposons of the Tn21 subgroup is discussed with the goal of revealing all the simple mobile elements, base ancestors for their formation, in permafrost. Together, the data presented are considered convincing evidence of the origin of both the clinical genes for antibiotic resistance and the mobile elements carrying them from the resistance determinants of bacteria inhabiting natural ecosystems.