Inhibition of the growth of Salmonella typhimurium ST-10 by propionic acid and chloride salts

The ability of propionic acid and chloride salts to inhibit Salmonella typhimurium growth was determined. Brain-heart infusion (BHl) was supplemented with 0, 250, 500, or 750 mM of potassium chloride (KCL) sodium chloride (NaCl) or 0, 125, 250, or 375 mM of both KCl and NaCl. Propionic acid was added to the BHl and BHl salts to produce final concentrations of 0, 25 50, 75 mM of propionic acid. The final pH of the media was 6.5. Supplemented BHl was inoculated with 10(3) S. typhimurium ml(-1) and incubated at 37 degrees C for 48 h. Culture absorbance was measured spectrophotometrically at 625 nm, and colony forming units (cfu) ml(-1) were enumerated on plate count agar (PCA) BG sulfa agar (BGS), and bismuth sulfite agar (BS) Although propionic acid, KCl and NaCl reduced S. typhimurium growth, mixtures of propionic acid and one or both salts were more effective in inhibiting S. typhimurium growth than either substance alone. Propionic acid and chloride salts produced no injury that reduced the ability of the bacterium to grow on BGS or BS. Absorbance and cfu ml(-1) measurements detected inhibition of S. typhimurium growth by propionic acid and the salts. Findings indicate that the synergistic reaction between propionic acid and KCl or NaCl may be a useful concept to apply in the formulation of products designed to inhibit S, typhimurium growth. (C) 1999 Academic Press.