Short communication 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 Georgia Zoumpopoulou a,b , Konstantinos Papadimitriou a , Moschos G. Polissiou b , Petros A. Tarantilis b, ⁎, Effie Tsakalidou a a Laboratory of Dairy Research, Department of Food Science and Technology, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece b Laboratory of Chemistry, Department of Science, Agricultural University of Athens, Iera Odos 75, 11855 Athens, Greece abstract article info Article history: Received 6 July 2010 Received in revised form 20 September 2010 Accepted 24 September 2010 Keywords: Salmonella enterica Lactobacillus Antimicrobial activity FT-IR 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. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Lactic acid bacteria (LAB) have been used for centuries in the fermentation of foods, not only for flavor and texture development, but also because of their ability to produce antimicrobial compounds which prevent the growth of spoilage and pathogenic microorgan- isms. The main antimicrobial compounds of LAB include weak organic acids, such as lactic acid and acetic acid (Servin, 2004), and bacteriocins (De Vuyst and Vandamme, 1994). Moreover, LAB metabolic products, such as hydrogen peroxide, pyroglutamic acid, phenyllactic acid, benzoic acid, methylhydantoin, mevalonolactone, reuterin and reutericyclin are known to exhibit antimicrobial activity as well (Servin, 2004). Finally, in some cases the nature of the LAB antimicrobial compounds has not been elucidated (Servin, 2004) or the antimicrobial activity has been attributed to a mixture of compounds rather than to a single molecule (Bernet-Camard et al., 1997; Milette et al., 2007). The effect of the antimicrobial compounds on the target micro- organisms varies from the decrease of the intracellular pH by the organic acids to pore formation on the cell membrane or inhibition of cell wall biosynthesis in the case of bacteriocins (Brul and Coote, 1999; Deegan et al., 2006). Fourier transform infrared (FT-IR) spectroscopy is known to offer the potential for studying the total molecular composition of cells (Helm and Naumann, 1995), since all the functional groups of organic (bio)molecules specifically absorb infrared (IR) light. Thus, valuable information on the chemical composition of the cells can be obtained (Oust et al., 2006). So far, FT-IR spectroscopy has been often used for taxonomy studies (Mariey et al., 2001). However, there are several reports on the application of this technique to detect changes at the cellular level after exposure of cells to different stress factors (Kamnev, 2008). The discrimination of intact and sonication-injured cells of Listeria monocytogenes (Lin et al., 2004), the cell damage of a Lactobacillus helveticus strain during vacuum drying (Santivarangkna et al., 2007), and the heat-induced lethal and sublethal injury of Lactococcus lactis (Kilimann et al., 2006) have been studied using FT-IR spectroscopy. FT-IR spectros- copy was also used to analyze the impact of sodium chloride and potassium chloride on Desulfovibrio vulgaris cells (Mukhopadhyay et al., 2006) and the impact of ethanol, sodium hypochlorite, sodium chloride and sulfur dioxide on yeasts (Corte et al., 2010). Additionally, structural changes in bacterial cells under different International Journal of Food Microbiology 144 (2010) 202–207 ⁎ Corresponding author. Tel.: + 30 210 5294262; fax: + 30 210 5294265. E-mail address: ptara@aua.gr (P.A. Tarantilis). 0168-1605/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ijfoodmicro.2010.09.023 Contents lists available at ScienceDirect International Journal of Food Microbiology journal homepage: www.elsevier.com/locate/ijfoodmicro