Effect of Sub-Lethal Environmental Stresses on the Cell Survival and Antibacterial Susceptibility of Listeria monocytogenes PTCC1297

Background: Listeria monocytogenes is slowly becoming drug resistant, study on resistance of this pathogen is important to ensure effective treatment of human listeriosis. The aim of this work was evaluating the changes in susceptibility to antibiotics and cell survival of L. monocytogenes PTCC1297 (serotype 4a) after exposure to some stresses. Materials and Methods: In this descriptive-analytic study L. monocytogenes PTCC1297 subjected to sub-lethal environmental stresses including ethanol (5% v/v), sodium chloride (7% w/v), acid (HCl, pH=5.0), hydrogen peroxide (600 ppm) and heat (45?C). After the stress treatments, antibacterial susceptibility and cell survival were determined. Results: Exposing to hydrogen peroxide (600 ppm) and heat (45?C) significantly (p < 0.05) increased resistance to all selective antibiotics. But treating to stresses such as hydrochloric acid (pH=5.0), sodium chloride (7% w/v) and ethanol (5% v/v) decreased resistance (p < 0.05) to antibiotics. L. monocytogenes PTCC1297 cell survival was decreased at 60?C which is considered as lethal condition. Exposing to sub-lethal acid stress increased survival to high acidic conditions (pH=3.0). But upon increasing hydrogen peroxide the viability of cell decreased. Treating the cells with ethanol (14% v/v) and NaCl (20% w/v) increased cell survival. Conclusion: Adaptation to some stresses including hydrogen peroxide and heat increase resistance to antibiotics. Stresses such as ethanol, hydrochloric acid and sodium chloride act in adverse. Exposing to some sub-lethal stresses increased cell survival when lethal doses of the same stress such as acid, ethanol and sodium chloride were used. But, when we treating the cells to sublethal doses of H2O2 and heat the cell survival decreased.