Tolerance of Lactobacillus sakei to Osmotic Stress

Abstract

Introduction. The development of new technologies of bacterial cultures for fish products is an important area of re-search. Sodium chloride (NaCl) has an inhibitory effect on most microorganisms and is often used in fish industry. The present research objective was to study the effect of NaCl on the growth of lactic acid bacteria of the species Lactoba-cillus sakei. Study objects and methods. The research featured strains of lactic acid bacteria L. sakei (L. sakei LSK-45 and L. sakei DSM 20017). The bacteria were cultivated in a semi-liquid MRS medium supplemented with sodium chloride at vari-ous concentrations. The optical density (OD) of the medium and the viable cell counts served as indicators of bacterial growth. The morphology of bacterial cells was studied by microscopic examination of Gram-stained bacteria. Results and discussion. Both L. sakei strains proved tolerant to NaCl concentrations up to 6% as proved by the high density of the cell population – 109 CFU/cm3. When NaCl concentration reached 10%, L. sakei LSK-45 demonstrated the highest resistance to osmotic stress. At the end of cultivation, the population density dropped to 108 CFU/cm3, and the survival rate was 92%. The number of viable cells of L. sakei DSM 20017 decreased to 106 CFU/cm3, and the sur-vival rate reached 62%. The high resistance of L. sakei LSK-45 to osmotic stress was caused by cell cohesion, which increased with the growing NaCl concentration and was regulated by the quorum sensing system. Conclusion. L. sakei showed a flexible response to the changes in NaCl concentration. L. sakei LSK-45 strain had the highest resistance to osmotic stress.