Comparative analysis of susceptibility to high temperatures of salmonella strains

Abstract

Introduction. Today in the world there is a tendency towards an increase in the incidence of salmonellosis. As well as an increase in the proportion of antibiotic-resistant and various temperature regimes of the pathogen strains. This justifies the urgency of studying this problem, because bacteria of the genus Salmonella are the causative agents of acute infectious intestinal disease – salmonellosis.

The aim of the study. To give a comparative characteristic of the sensitivity of a number of Salmonella strains to the action of high temperatures of Salmonella strains. To study the degree of thermal resistance of Salmonella strains at different temperature conditions and exposure periods. One of the components of observations of the circulation of zoonotic Salmonella is the study of changes in their biological properties. One of such properties is the ability to evolve in the environment and the ability to adapt to its adverse conditions by changing the sensitivity of bacteria to temperature and the ability to acquire heat-resistant signs. One of these properties is high stability in the external environment and the ability to adapt to its unfavorable conditions and the sensitivity of bacteria to the action of high temperature conditions, and the ability to acquire thermoresistant signs.

Research objectives. Objectives of the study. To determine the ability of current and archival strains of salmonella to the action of the temperature factor and to compare their thermal sensitivity spectra.

Materials and methods. Materials and methods. The object of the study were 136 strains of salmonella obtained from the Museum of Pathogenic Microorganisms of the Laboratory of Medical Microbiology of the Institute of Epidemiology and Infectious Diseases LV Gromashevsky NAMS of Ukraine". Research methods: microbiological research methods, as well as statistical analysis of the results.

Results. The research results were processed using the licensed program «GraphPad Prism 6» and statistical methods 2-way ANOVA. The data were presented graphically. The significance of the changes was denoted by the symbol ″ * ″ – the probable difference at p ≤ 0.05. It was found that the control strain of Escherichia coli ATCC 25922 was sensitive to all temperature conditions. The results of the study of susceptibility of S. typhimurium strains to the action of temperature in 70ºC showed that on average 75 % of archival strains survived at one-minute exposure, 33,00 % – at 3 minutes of exposure 70ºC, and up to 8,00 % at exposure of 10 minutes. The obtained results indicate an increase in heat resistance among S. Тyphimurium strains isolated in 2006–2012 compared to those isolated in 1996–2005 due to increased adaptive potential of microorganisms and increased chances of survival of bacteria in adverse conditions. The change of sensitivity to the action of high temperatures of Salmonella due to the accumulation of a significant number of heat-resistant strains in the population has been established. An increase in the percentage of moderately sensitive to high temperature actual strains of S. Тyphimurium and S. Еnteritidis in comparison with archival strains is shown. Increased adaptability to high temperatures was found in both S. Еnteritidis strains isolated from sick people and in salmonella strains of rare groups isolated from the environment. Topical strains of S. Еnteritidis and salmonella strains of rare groups were the most heat-resistant. In the course of the study, the author showed an increase in the percentage of moderately sensitive to high temperature actual strains of S. Тyphimurium and S. Еnteritidis in comparison with archival strains. Current strains of S. Еnteritidis and salmonella strains of rare groups were the most heat-resistant.

Conclusions. The change of the biological properties of salmonella due to the accumulation of a significant number of heat-resistant strains in the circulating population has been established. An increase in the proportion of moderately sensitive to high temperature actual strains of S. Тyphymurium and S. Еnteritidis in comparison with archival strains is shown. Increased adaptability to the action of high temperatures was found in both S. Enteritidis strains isolated from sick people and in Salmonella strains of rare groups isolated from the environment. Topical strains of S. Еnteritidis and salmonella strains of rare groups turned out to be the most heat-resistant. The results of studies to assess the sensitivity of Salmonella to high temperatures indicate changes in the genotype of bacteria and as the result of evolutionary changes aimed at preserving the genus.