Combined Effects of pH and Temperature on Listeriolysin O Production by Listeria monocytogenes SLCC 5764

Abstract

Listeria monocytogenes SLCC 5764 was propagated at 4, 25, or 37°C in tryptic soy broth (TSB) acidified with either acetic acid at pH 5.2, 5.7, or 7.0, or hydrochloric acid at pH 5.0, 5.7, or 7.0; or made alkaline with sodium hydroxide at pH 7.5, 8.5, or 9.5. These studies were undertaken to determine the combined effects of temperature and pH on the production of listeriolysin O (LLO). The LLO activity was greatest after the cells were propagated in TSB acidified by either acid to pH 7.0 at 37°C. Very little LLO activity was detected for cells propagated at 4° under acidic conditions. There were no significant differences found between the LLO produced in media acidified with either acid. The LLO activity was highest after the cells were propagated in media at pH 7.5 at 37°C.