Detection of changes in the cellular composition of Salmonella enterica serovar Typhimurium in the presence of antimicrobial compound(s) of Lactobacillus strains using Fourier transform infrared spectroscopy

It was previously established that Lactobacillus fermentum ACA-DC 179, Lactobacillus plantarum ACA-DC 287 and Lactobacillus plantarum ACA-DC 2350 exhibit antimicrobial activity against Salmonella enterica serovar Typhimurium. In order to further investigate the killing effect of these microorganisms against Salmonella cells, we employed Fourier transform infrared spectroscopy (FT-IR). Salmonella cells were incubated with different concentrated lactobacilli supernatants and their FT-IR spectra were recorded. The second derivative transformation of the original spectra revealed changes in spectral regions corresponding to absorptions of major cellular constituents (e.g. cell wall, cell membrane, and proteins of the cell) among the Salmonella cells treated with the supernatants and those treated with the control samples. Principal component analysis of the second derivative transformed spectra showed that the yet unidentified antimicrobial compound(s) produced by the lactobacilli tested clearly interfered with the fatty acids of the cell membrane, as well as the polysaccharides of the cell wall in Salmonella cells, pointing towards a dual killing mode. Our study shed light for the first time in the anti-Salmonella activity of the particular Lactobacillus strains.