A collection of bacterial antibiotic resistance strains isolated from arctic permafrost subsoil sediments of various age and genesis was created. The collection included approximately 100 strains of Gram-positive (Firmicutes, Arthrobacter) and Gram-negative bacteria (Bacteroidetes, γ-Proteobacteria, and α-Proteobacteria) resistant to aminoglycoside antibiotics (gentamicin, kanamycin, and streptomycin), chloramphenicol and tetracycline. Antibiotic resistance spectra were shown to differ in Gram-positive and Gram-negative bacteria. Multidrug resistance strains were found for the first time in ancient bacteria. In studies of the molecular nature of determinants for streptomycin resistance, determinants of the two types were detected: strA-strB genes coding for aminoglycoside phosphotransferases and genes aadA encoding aminoglycoside adenylyltransferases. These genes proved to be highly homologous to those of contemporary bacteria.

A Psychrobacter psychrophilus strain resistant to tetracycline and streptomycin was isolated from a 15 000–35 000-year-old permafrost subsoil sedimen

This review briefly summarizes the data on the mechanisms of development of the adaptability of Acinetobacters to various living conditions in the environment and in the clinic. A comparative analysis of the genomes of free-living and clinical strains of A. lwoffii, as well as the genomes of A. lwoffii and A. baumannii, has been carried out. It has been shown that plasmids, both large and small, play a key role in the formation of the adaptability of Acinetobacter to their living conditions. In particular, it has been demonstrated that the plasmids of various strains of Acinetobacter differ from each other in their structure and gene composition depending on the lifestyle of their host bacteria. Plasmids of modern strains are enriched with antibiotic-resistant genes, while the content of genes involved in resistance to heavy metals and arsenic is comparable to plasmids from modern and ancient strains. It is concluded that Acinetobacter plasmids may ensure the survival of host bacteria under conditions of various types of environmental and clinical stresses. A brief overview of the main mechanisms of horizontal gene transfer on plasmids inherent in Acinetobacter strains is also given.

Transposons closely related to the streptomycin resistance transposon of modern bacteria, Tn 5393, were detected in the bacterial isolates from permafrost resistant to streptomycin. Many transposons...