Tolerance of Salmonella enterica serovar Typhimurium to nisin combined with EDTA is accompanied by changes in cellular composition

Nisin has been widely used in many countries, as a food additive for dairy products and canned vegetables and fruits. Although Gram-negative bacteria have natural resistance to nisin due to the presence of the outer membrane, the use of chelating agents, such as EDTA, allows for their sensitization. However, Salmonella can alter the composition and the structure of their lipopolysaccharide layer (LPS) in response to changes in environmental conditions, and thus mitigate their sensitivity to bacteriocins, such as nisin. In this study, we demonstrated and characterized tolerance to nisin combined with EDTA in Salmonella Typhimurium cultured under specific conditions of temperature and pH by means of assays of growth, viability, leakage of intracellular content and Fourier transform infrared spectroscopy (FT-IR). The modifications related to the tolerance phenotype to nisin combined with EDTA possibly involve changes in the phospholipid acyl chains, in the sugar content of LPS and in the peptidoglycan present in the cell wall. These findings demonstrate the importance of better understanding the behavior of the cells treated with nisin and EDTA, especially due to widespread use of this bacteriocin in food preservation.