Susceptibility of 117 L. monocytogenes strains isolated during three time periods (1950–1980; 2000–2005, and 2018–2021) to 23 antibiotics was tested by the disk diffusion method. All strains were sensitive to aminoglycosides (gentamicin, kanamycin, neomycin, streptomycin), glycopeptides (vancomycin and teicoplanin), clarithromycin, levofloxacin, amoxicillin/clavulanic acid, and trimethoprim/sulfamethoxazole. Resistance to clindamycin was observed in 35.5% of strains. Resistance to carbapenems, imipenem and meropenem was found in 4% and 5% of strains, respectively. Resistance to erythromycin, penicillin G, trimethoprim, and ciprofloxacin was found in 4%, 3%, 3%, and 2.5% of strains, respectively. Resistance to tylosin, ampicillin, enrofloxacin, linezolid, chloramphenicol, and tetracycline was found in less than 2%. Three strains with multiple antibiotic resistance and 12 strains with resistance to two antibiotics were revealed. Comparison of strains isolated in different time periods showed that the percentage of resistant strains was the lowest among strains isolated before 1980, and no strains with multiple antibiotic resistance were found among them. Statistical analysis demonstrated that the temporal evolution of resistance in L. monocytogenes has an antibiotic-specific character. While resistance to some antibiotics such as ampicillin and penicillin G has gradually decreased in the population, resistance to other antibiotics acquired by particular strains in recent years has not been accompanied by changes in resistance of other strains.

Totally, 45 L. monocytogenes strains isolated from meat, poultry, dairy, and fish products in the Central European part of Russia in 2001–2005 and 2019–2020 were typed using a combined MLST and internalin profile (IP) scheme. Strains belonged to 14 clonal complexes (CCs) of the phylogenetic lineages I and II. Almost half of the strains (20 of 45) belonged to six CCs previously recognized as epidemic clones (ECs). ECI and ECV strains were isolated during both studied periods, and ECII, ECIV, ECVI, and ECVII strains were isolated in 2001–2005, but not in 2019–2020. ECI, ECIV, ECV, and ECVII strains were isolated from products of animal origin. ECII and ECVI were isolated from fish. Testing of invasion efficiencies of 10 strains isolated in different years and from different sources and belonging to distinct CCs revealed a statistically significant difference between phylogenetic lineage I and II strains but not between ECs and non-EC CCs or strains differing by year and source of isolation. Strains isolated in 2001–2005 were characterized by higher phylogenetic diversity and greater presentation of ECs and CCs non-typical for natural and anthropogenic environments of the European part of Russia comparatively to isolates obtained in 2019–2020.Closing of the Russian market in 2019–2020 for imported food might be responsible for these differences.

Elizabethkingia anophelis is an emerging multidrug-resistant pathogen that causes severe nosocomial and community-acquired infections worldwide. We report the first case of E. anophelis isolation in Russia and the first isolation from raw cow’s milk. The ML-44 demonstrated resistance to 28 antimicrobials of 33 tested in the disk-diffusion test. Whole genome-based phylogeny showed ML-44 strain clustered together with the F3201 strain isolated from a human patient in Kuwait in 1982. Both strains were a part of the “endophytica” clade. Another clade was formed by subsp. anophelis strains. Each of the E. anophelis compared genomes carried 18 to 21 antibiotic resistance determinants. The ML-44 chromosome harbored nine efflux system genes and three beta-lactamase genes, along with six other antimicrobial resistance genes. In total, 72 virulence genes were revealed. The set of virulence factors was quite similar between different E. anophelis strains and included LPS and capsule encoded genes, type IV pili, oxidative stress response genes, and genes encoding TIVSS and TVISS effectors. The particular interest caused the mip and zmp1 gene homologs, which can be essential for intracellular survival. In sum, our findings suggest that raw milk might be a source of E. anophelis harboring a set of virulence factors and a broad resistance to generally used antimicrobials.

Aeromonas spp. are gram-negative facultatively anaerobic bacilli recovered mainly from aquatic environments. Aeromonas spp. were reported to be associated with infections primarily in aquatic and to a lesser extent in terrestrial animals as well as in humans. Up-to-date little is known about aeromonads associated with wild animals, especially with rodents. This study reported the first isolation and characterization of two Aeromonas spp. from internal organs of apparently healthy wild rodents Apodemus uralensis and Apodemus flavicollis captured in the wild environment in the European part of Russia. Isolates were identified as A. hydrophila M-30 and A. encheleia M-2 using the multilocus sequence analysis (MLSA) approach. The isolation of the A. encheleia from rodents is the first described case. Both strains demonstrated beta-hemolytic activity towards human erythrocytes. Antimicrobial susceptibility testing showed that both Aeromonas strains were resistant and intermediate to carbapenems and piperacillin-tazobactam, which was caused by the expression of the genus-specific CphA carbapenemases. A. hydrophila M-30 also demonstrated trimethoprim resistant phenotype. This is usually caused by the carriage of the dfrA or dfrB genes in aeromonads which are frequently associated with integron class I. The latter however was absent in both isolates. Our results expand our understanding of possible aeromonad reservoirs and demonstrate the likelihood of the formation of natural foci of Aeromonas infection and a new link in the chain of the spread of antimicrobial resistance as well.

Objective. To determine the current state-of-art of acquired resistance to antimicrobial drugs among L. monocytogenes strains associated with listeriosis in humans and food contamination in Moscow. Materials and Methods. We used 39 L. monocytogenes strains isolated in Moscow in 2019–2021 from clinical material (n = 24) and food (n = 15). Resistance to 12 antibiotics of the first and second lines of defense was studied using disk-diffusion method. The parameters recommended for L. monocytogenes were used to interpret the results; in the absence of recommendations for L. monocytogenes, the criteria for Staphylococcus aureus and/or Enterococcus spp. were used. Results. All strains were susceptible to ampicillin, benzylpenicillin, erythromycin, vancomycin, imipenem, linezolid, and the amoxicillin/clavulanic acid. Resistance was observed to gentamicin (23%) as well as to meropenem, trimethoprim/sulfamethoxazole and ciprofloxacin (5%, 74% and 28% of strains, respectively). A total of 15 strains with multiple antibiotic resistance were identified (13 and 2 isolates were resistant to three and four antibiotics, respectively). Simultaneous resistance to trimethoprim/sulfamethoxazole, ciprofloxacin and levofloxacin was observed in 9 strains, 6 strains were resistant to gentamicin and trimethoprim/sulfamethoxazole, including 3 strains – to gentamicin, trimethoprim/sulfamethoxazole, levofloxacin, and 2 strains – to gentamicin, trimethoprim/sulfamethoxazole, ciprofloxacin. Comparison of the growth inhibition zones by ampicillin and benzylpenicillin in the studied strains with historical data on the strains isolated in Russia in 1950–1980 showed a significant downward shift in the size of growth inhibition zones. Comparison of the distribution of strains with different diameters of growth inhibition zones depending on the source of isolation did not show significant differences between clinical strains and strains of food origin isolated in 2019–2021. Conclusions. A wide spread of acquired resistance was shown among L. monocytogenes strains of clinical and food origin isolated in Moscow in 2019–2021. Despite the fact that all strains were susceptible to penicillins, the distribution of growth inhibition zone diameters showed a significant shift towards decreasing sensitivity to ampicillin and benzylpenicillin in strains isolated in 2019–2021 compared with L. monocytogenes strains isolated in Russia before 1980.