Effect of ethanol stress on Lactobacilli

摘要

The aim of this work was to determine: ability of LAB to grow in the presence of ethyl alcohol, resistance of bacteria to ethanol and influence of sub-lethal pre-treatments (low alcohol concentrations) on the increase in resistance to alcohol. Additional work concerned correlation between ethanol stress and oxidative agents (H_2O_2), blocking protein synthesis (chloramfenicol) and heat treatment. Studies were performed with 19 Lactobacillus strains. The presented results indicate that from among 12 Lactobacillus strains isolated from fermentors of different distilleries in Scotland and 7 references strains, L. hilgardii 84 was the most resistant to alcohol. This strain showed the best adaptation to grow in the presence of ethanol. During the growth,the population of bacterial cells became more tolerant to alcohol, that was confirmed survival curves of population in the late logarithmic and stationary phases of growth. Bacteria in the stationary phase of growth were the most resistant and their survival increased two log cycles comparing to bacteria being in their adaptation phase. Research concerning the influence of pre-treatment of L. hilgardii 84 with different ethanol concentrations, indicates that survival of bacteria in 22% of ethanol is positively correlated with used sub-lethal concentrations of alcohol. Therefore, pre-incubation of bacteria in 15% of ethanol caused the highest enhancement of resistance to ethanol. Experiments with chloramphenicol (antibiotic inhibiting growth) showed that an increase in tolerance of bacterial cells to alcohol is possible without protein synthesis. Pre-incubation of L. hilgardii 84 in medium containing 15% of alcohol caused an increase in survival of bacteria exposed to hydrogen peroxide.