SALACID

Short-chain carboxylic acids (SCCA) and alcohols (SCALC) that are produced by plants and microbial fermentative systems support the protection against invading pathogens. This study investigated the effects of structurally different SCCA/SCALC with 3-carbon chain (propionic acid, PA; 3-phenylpropionic acid, 3PP; 3-phenylpropanol, 3PPol), and 3-carbon chain with an additional hydroxyl group (lactic acid, LA; 3-phenyllactic acid, 3PL; 1-phenylpropanol, 1PPol) on the fitness, metabolic activity and gene expression of Salmonella enterica at pH 4.5, which is common in fermented food. SCCA inhibited Salmonella at lower concentrations than SCALC with the exception of LA, which was partly consumed. The presence of the phenyl group enhanced antimicrobial activity. SCCA but not SCALC increased the lag phase and in general, acetate was formed when the cell growth was reduced by 20%. Principal component analysis and hierarchical clustering indicated distinct gene expression profiles in the response to SCCA and SCALC. In the presence of SCCA/SCALC, S. enterica activated genes related to glutamate and arginine metabolism. PA and 3PP induced higher expression of eut and pdu genes that are linked to microcompartment formation and the metabolism of 1,2-propanediol and ethanolamine, and concurrently produced more propionate. SCCA and SCALC activated different flg and fli genes that are linked to flagellar assembly.