Batch culture growth response of a poultry Salmonella typhimurium isolate to ammonium salts

High ammonium levels have often been associated with poultry waste. In this study we chose to examine the effect of ammonium salt on growth of salmonellae. A nalidixic acid, novobiocin, resistant primary poultry Salmonella typhimurium isolate was grown at 37°C in bicarbonate buffered (60 m ) tryptic-soy broth containing either NH4Cl, NaCl, KCl, (NH4)2SO4, ammonium oxalate, ammonium acetate or NH4OH. Concentrations tested ranged from 0 to 600 m ammonium-nitrogen and growth response was measured at 37°C as batch culture maximum growth rate. NH4OH was the most inhibitory ammonium salt with a minimum inhibitory concentration of 50 m ammonium-nitrogen while the other ammonium salts were much less inhibitory. Based on comparison of the inhibition constant (Ki) calculated from growth rates of bacteria grown on the respective salt, S. typhimurium was least sensitive to (NH4)2SO4 and most sensitive to NH4OH when compared to all other growth and salt conditions. Salmonella typhimurium was equally sensitive to nonbuffered NH4Cl, KCl and NaCl containing media. However, cells that were initially exposed to ammonium oxalate, ammonium acetate or cells exposed to NH4Cl and either adapted (at least 10 transfers in the same basal medium), unadapted (less than four transfers), or grown anaerobically were more inhibited. It appears that the initial inhibition of Salmonella growth by ammonium is dependent on extracellular pH and type of ion forming the ammonium salt, but some adaptation over time to higher concentrations may also occur.