Food products may be a source of Salmonella, one of the main causal agents of food poisoning, especially after the emergence of strains resistant to antimicrobial preparations. The present work dealt with investigation of the occurrence of resistance to antimicrobial preparations among S. enterica strains isolated from food. The isolates belonged to 11 serovars, among which Infantis (28%), Enteritidis (19%), and Typhimurium (13.4%) predominated. The isolates were most commonly resistant to trimethoprim/sulfamethoxazole (n = 19, 59.38%), cefazolin (n = 15, 46.86%), tetracycline (n = 13, 40.63%), and amikacin (n = 9, 28.13%). Most of the strains (68.75%) exhibited multiple resistance to commonly used antibiotics. High-throughput sequencing was used to analyse three multidrug-resistant strains (resistant to six or more antibiotics). Two of them (SZL 30 and SZL 31) belonged to S. Infantis, while one strain belonged to S. Typhimurium (SZL 38). Analysis of the genomes of the sequenced strains revealed the genes responsible for antibiotic resistance. In the genomes of strains SZL 30 and SZL 31 the genes of antibiotic resistance were shown to be localized mostly in integrons within plasmids, while most of the antibiotic resistance genes of strain SZL 38 were localized in a chromosomal island (17,949 nt). Genomes of the Salmonella strains SZL 30, SZL 31, and SZL 38 were shown to contain full-size pathogenicity islands: SPI-1, SPI-2, SPI-4, SPI-5, SPI-9, SPI-11, SPI-13, SPI-14, and CS54. Moreover, the genome of strain SZL 38 was also found to contain the full-size pathogenicity islands SPI-3, SPI-6, SPI-12, and SPI-16. The emergence of multidrug-resistant strains of various Salmonella serovars indicates that further research on the transmission pathways for these genetic determinants and monitoring of the distribution of these microorganisms are necessary.

Biofilm contamination in food production threatens food quality and safety, and causes bacterial infections. Study of food biofilms (BF) is of great importance. The taxonomic composition and structural organization of five foods BF taken in different workshops of a meat-processing plant (Moscow, RF) were studied. Samples were taken from the surface of technological equipment and premises. Metagenomic analysis showed both similarities in the presented microorganisms dominating in different samples, and unique families prevailing on certain objects were noted. The bacteria found belonged to 11 phyla (no archaea). The dominant ones were Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. The greatest diversity was in BFs taken from the cutting table of raw material. Biofilms’ bacteria may be the cause of meat, fish and dairy products spoilage possible representatives include Pseudomonas, Flavobacterium, Arcobacter, Vagococcus, Chryseobacterium, Carnobacterium, etc.). Opportunistic human and animal pathogens (possible representatives include Arcobacter, Corynebacterium, Kocuria, etc.) were also found. Electron-microscopic studies of BF thin sections revealed the following: (1) the diversity of cell morphotypes specific to multispecies BFs; (2) morphological similarity of cells in BFs from different samples, micro-colonial growth; (3) age heterogeneity of cells within the same microcolony (vegetative and autolyzed cells, resting forms); (4) heterogeneity of the polymer matrix chemical nature according to ruthenium red staining.

In order to control pathogenic microorganisms, three polymer compositions were prepared and tested. First, a water-soluble positively charged polycomplex was synthesized via the electrostatic binding of anionic polyacrylic acid to an excess of polyethylenimine to enhance the biocidal activity of the polycation. Second, an aqueous solution of AgNO₃ was added to the polycomplex, thus forming a ternary polycation-polyanion-Ag¹⁺ complex with an additional antimicrobial effect. Third, the resulting ternary complex was subjected to UV irradiation, which ensured the conversion of Ag¹⁺ ions into Ag nanoparticles ranging in size mainly from 10 to 20 nm. Aqueous solutions of the polymer compositions were added to suspensions of the Gram-positive bacteria S. aureus and the Gram-negative bacteria P. aeruginosa, with the following main results: (a) Upon the addition of the binary polycomplex, 30% or more of the cells survived after 20 h. (b) The ternary complex killed S. aureus bacteria but was ineffective against P. aeruginosa bacteria. (c) When the ternary complex with Ag nanoparticles was added, the percentage of surviving cells of both types did not exceed 0.03%. The obtained results are valuable for the development of antibacterial formulations.

The study aimed to investigate the prevalence of Campylobacter spp. in different stages of poultry and pork processing in the Central region of Russia. A total of 47 Campylobacter isolates were obtained from 107 samples from poultry processing plants (40.2%): 87.2% were identified as Campylobacter jejuni, whereas 12.8% were identified as Campylobacter coli. The prevalence of Campylobacter was significantly (p <0.05) higher after evisceration in the poultry processing plant. Campylobacter spp.was detected in 62.7% of the equipment and environmental samples. From positive samples of Campylobacter spp., 84.3% of Campylobacter jejuni and 15.7% Campylobacter coli were observed. A total of nine Campylobacter isolates were obtained from 116 samples from pork processing plants (7.8%): 33.3% of them were identified as Campylobacter jejuni whereas 66.7% were identified as Campylobacter coli. Splitting and evisceration were also critical in Campylobacter contamination. Almost all pork carcasses were Campylobacter positive, and all of them were identified as Campylobacter coli. The prevalence of positive Campylobacter samples in poultry processing plants was significantly (p < 0.05) higher than in pork processing plants.

Determination of eukaryotic cell viability using flow cytometry is widespread and based on the use of fluorescent dyes such as SYTO, DAPI, SYBR, PI, and SYTOX. For many years, traditional microbiological methods have been used to successfully analyze prokaryotic cells, but the application of flow cytometry should be considered because it provides an opportunity for quantitative assessment. A combination of SYTO 9 or SYBR green and PI has been used successfully. DNA-binding dyes such as SYTO 9, SYBR green, and EvaGreen are used in qPCR. The aim of this study was to assess the feasibility of EvaGreen to determine the viability of Listeria monocytogenes АТСС 13932 cells using flow cytometry. RNA from Escherichia coli ATCC 25922 was isolated using the MagNA Pure LC RNA Isolation Kit-High Performance (Roche, Germany) according to the kit instructions on MagNA Pure LC® 2.0 (Roche, Switzerland). Chicken DNA was isolated using the Sorb-GMO-B kit (Syntol CJSC, Russia) according to the kit instructions. RNA from E. coli ATCC 25922, chicken DNA, a positive control, and a negative control of L. monocytogenes АТСС 13932 were stained with EvaGreen and analyzed on the Guava EasyCyte flow cytometer (Merck Millipore, Germany). Chicken DNA demonstrated both green and red fluorescence, while E. coli RNA displayed only red fluorescence. While the positive L. monocytogenes АТСС 13932 control and chicken DNA demonstrated similar fluorescence properties, the negative control showed a localization similar to that observed with E. coli RNA. Degraded ssDNA and RNA stained with EvaGreen demonstrated red fluorescence. Although EvaGreen is a class III dye, we observed fluorescence of live L. monocytogenes АТСС 13932 cells in the positive control stained with EvaGreen. The observed phenomenon was linked to the solution composition. It is necessary to repeat this analysis with various solution compositions as well as a wide range of both Gram-positive and Gram-negative bacteria to determine the effects on cell envelope permeability of EvaGreen.

Biofilm formation on equipment surfaces is a potential food safety hazard, providing increased resistance and persistence of pathogens and spoilage microorganisms in food production environments. The issue of preventing the biofilm formation is extremely important, since a wide range of disinfectants does not always provide the proper effect. The article discusses the antimicrobial effectiveness of disinfectants with various active ingredients (based on active chlorine, peracetic acid and quaternary ammonium compounds (QAC) with enzymatic substances) on binary biofilms. The objects of the study were the strains of pathogenic and opportunistic microorganisms isolated from abiotic surfaces of food production environments and food products. Different effects of disinfectants on biofilms formed by bacteria have been established. Disinfectant based on peracetic acid and chlorine had the greatest effect on binary biofilms of Brochothrix thermosphacta/Salmonella spp. and Staphylococcus equorum/Salmonella spp. The greatest antimicrobial effect on biofilm of Listeria monocytogenes 12/Pseudomonas azotoformans 6 was shown by a chlorine-based disinfectant. Disinfectants based on chlorine and QAC with enzymatic substances were most effective against the binary biofilm of L. monocytogenes 12/Salmonella spp. 14. However, none of the disinfectants had absolute antimicrobial effectiveness against the studied binary biofilms. Biofilm-forming microorganisms have shown resistance to the recommended concentrations of disinfectants. Therefore, currently, it is extremely important to revise approaches to hygiene at enterprises by finding working concentrations of new antimicrobial agents and new procedure that are effective for destroying biofilms.