Minimal water activity for growth of Listeria monocytogenes as affected by solute and temperature

Two strains of Listeria monocytogenes, Scott A (serotype 4b) and Brie 1 (serotype 1b) were characterized in terms of minimum aw requirements for growth at 4 and 30 degrees C, using NaCl, glycerol and sucrose as test solutes. Both strains grew well at 30 degrees C in glycerol-supplemented tryptic soy broth (TSB), but not in NaCl- and sucrose-supplemented TSB at aw 0.90. Sucrose was more inhibitory than NaCl and glycerol. The Brie 1 strain was less tolerant to sucrose compared to the strain Scott A at both 4 and 30 degrees C. The effects of all three solutes were magnified at 4 degrees C, where tolerance to low aw was markedly less than at 30 degrees C. Results confirm that the type of solute as well as the osmotic conditions created by the solute affects the ability of Listeria monocytogenes to grow at 4 and 30 degrees C.