Differences in Survival of Acid-stress Resistant Phenotype of Listeria monocytogenes in Quaternary Ammonium Compounds, Ethanol, NaOCl, and H2O2

Introduction: Listeria monocytogenes (Lm) has sophisticated adaptive mechanisms to various physiological and environmental stresses. There is a limited knowledge on the survival of acid-stress resistant phenotype of Lm in the presence of commonly used disinfectants.

Purpose: Conditions inducing acid-stress adaptation in Lm were investigated and the difference in survival of acid-stress resistant phenotype of Lm was determined under various lethal stresses.

Methods: Acid-stress adapted cells of Lm were prepared by pre-exposing to pH 5 for 1 h in TSB-YE. The survival of acid-stress adapted and non-adapted cells was determined under six  lethal stress conditions including, pH 3.5 lactic acid, 5-7 ppm quaternary ammonium compounds (QAC-1, QAC-2), 20% ethanol, 1000 ppm NaOCl and 1000 ppm H₂O₂ in TSB-YE.

Results: Acid-stress resistant phenotype of Lm was induced when cells were pre-exposed to pH 5.0 for 15 min for Bug 600 (serotype 1/2a) or in 30 min for Scott A (serotype 4b). Also, acid-stress resistant phenotype of Lm was readily observed in acidic whey. Such acid-stress adaptation in Lm was reversible when cells were transferred to pH 7 for 1 h at 37°C. Acid-stress resistant phenotype of Lm exhibited about 1.5-3.5 log CFU/ml greater survival in 7 ppm QAC-1, 5 ppm QAC-2 or in 20% ethanol compared to that of non-adapted cells. However, acid-stress resistant phenotype of Lm did not exhibit any greater survival in 1000 ppm NaOCl and was sensitive to 1000 ppm H₂O₂ compared to that of non-adapted cells.

Significance: Acid-stress resistant phenotype of Lm exhibits cross-resistance to QAC and ethanol but not to NaOCl or H₂O₂.