Salmonellosis is an infectious disease that occupies a stable place in infectious pathology and is caused by gram-negative rod-shaped bacteria of the genus Salmonella of the Enterobacteriaceae family. A feature of these microorganisms is their spreading (soil, water) and a variety of transmission factors associated with livestock and poultry products. The most frequently isolated clinical isolates of salmonella belong to Enteritidis, Typhimurium and Heidelberg serovars . In the gastrointestinal tract of a person, salmonella entering through poorly processed food or water, as well as in case of non-compliance with personal hygiene, meet with many different types of microorganisms of the intestinal microbiota (a set of microbiocenoses occupying almost all ecological niches (biotopes) on the mucous membranes of the body) The normal intestinal microbiota forms a stable community with its own internal relationships that contribute to the preservation of the viability of the microbial population. At the same time, various bacterial communities live in a certain stable ratio , lining the mucous membranes in the form of biofilms. For the effective spread in the gastrointestinal tract, Salmonella bacteria must have the ability to form biofilms and compete for nutrients with the host microbiota.
The purpose of the research: to characterize the ability of Salmonella enterica (Typhimurium serovar) to biofilm formation under conditions of interspecies interaction in a multicultural biofilm with representatives of the intestinal microbiota in an in vitro experiment.
Bacteria Salmonella enterica serovar Typhimurium strain ATCC 13311, Lactobacillus acidophilus ATCC 4356 and Lactobacillus casei ATCC 393 (manufacturer Remel Europe, Ltd, UK), Escherichia coli CECT M17 (Microgen, Russian Federation) were used in the research. The process of interspecies interaction was simulated in a mixture of LB broth with 0.85% NaCl solution in a ratio of 1:3 at an initial bacterial concentration of 103 CFU/ml (according to the turbidity standard of L. A. Tarasevich) in polystyrene Petri dishes with a diameter of 65 mm at a temperature of +37°C. The results of the experiment were evaluated on days 1, 3, 5, 7, 9, 12. The plate method was used to account for the number of viable cells in biofilms. After completion of incubation, biofilms were washed 3 times with 0.85% NaCl solution from planktonic forms, collected in a test tube, separated from the bottom of the plate, and centrifuged at 10000 g for 10 min. For inoculation on selective media (Wilson - Blair - bismuth sulfite agar, Ploskirev agar, Endo agar, lactobacillus), the sediment was used by the method of multiple dilutions. Using spectrophotometry (wavelength 595 nm), the optical density of the matrix of a biofilm stained with gentian violet was measured . To assess the tinctorial properties, bacterial samples were Gram stained. Enzymatic properties were assessed using Giss media and differential diagnostic media (Olkenitsky, medium with urea, medium for determining the mobility of bacteria). All experiments were carried out 3 times in a row. MS Excel 2010 was used for statistical data processing.Statistical processing of the results included the calculation of the mean values (x) and standard deviation (σ). The reliability of the differences between the samples was judged by the magnitude of the Student's t-test after checking the distribution for normality. Statistically significant were the indicators corresponding to the probability assessment р ≤ 0.05.