Acid-Injury of Listeria monocytogenes.

Acid injury Listeria monocytogenes in solutions of 0.3 and 0.5% acetic, citric and lactic acid at 13 and 35°C was determined. Acetic acid caused greatest inactivation, but generally, citric acid caused the greatest degree of injury followed in order by lactic and acetic acid. Acid-injured L. monocytogenes failed to grow on tryptose agar with 6% added NaCl. Incubation at 13°C did not cause a significant increase in lethality or acid injury over that observed at 35°C, Both injured and uninjured organisms remained viable for a relatively long time at the low temperature (about nine times longer at 13°C than at 35°C), indicating the potential for a health hazard should the pathogen not be detected.