At the end of XX and in the first decade of the XXI century, new, previously unknown microorganisms have been emerging all over thr world, while "old" and forgotten strains of bacteria were becoming more active; antibiotic resistance of infectious agents is becoming more common. This problem is especially acute due to the growing number of patients with immune deficiency conditions, high frequency of severe, combined, common, atypical and complicated forms of disease, mixed infections, the emergence and rapid spread of the so-called "new" and re-emerging infections.