Studies Of Adaptation Of Bifidobacteria To Hydrogen Peroxide

Recently, the concept of probiotics is fast gaining popularity worldwide, because these bacteria can enhance the population of beneficial bacteria in the human gut, suppress pathogens, and build up resistance against intestinal diseases. Bifidobacterium spp. have gained recognition as probiotic bacteria due to their various therapeutic health benefits such as prevention of diarrhea, alleviating lactose intolerance and lowering of serum cholesterol. However, Bifidobacteria are oxygen-sensitive bacteria. In the presence of oxygen, bifidobacteria can't convert reactive oxygen into nontoxic molecules, these compounds will accumulate in the cell and cause cell death from oxidative damage. In order to protect Bifidobacterium spp. from oxygen toxicity in probiotic products, many techniques were applied in the production of probiotic products. Among the protective techniques, Oxidative stress adaptation seems to be a promising tool to incorporate robust oxygenresistant probiotic strains in the product and thereby prevent cell loss during shelf-life, because this method is economic and is easiliy operated.It is well known that exposing microorganisms to sublethal or gradually increasing doses of stress can induce an adaptive cellular response that enables them to better resist lethal doses of stress. Under certain circumstances, the concentration of active oxygen rises to a level that overwhelms the basal level of the scavenging capacity of the cell, giving rise to an oxidative stress condition. Artificially, oxidative stress can be brought about by addition of H₂O₂ or superoxide radical generators such as paraquat and plumbagin or by raising the partial pressure of oxygen by bubbling pure oxygen through a culture. It has been reported that the oxygen-adapted cells of Bifidobacterium by raising the partial pressure of oxygen by bubbling pure oxygen into a culture.were found to be capable of withstanding elevated concentrations of dissolved oxygen in culture. However, it has not been reported that the oxygen-adapted cells of Bifidobacterium by addition of H₂O₂ or superoxide radical generators were found to be capable of withstanding elevated concentrations of H₂O₂ or O₂^- in culture. In many studies, it was showed that H₂O₂ is mainly responsible to oxygen toxicity. Therefore, the oxidative stress adaptation of Bifidobacterium by addition of H₂O₂ was studied in the article.Firstly, the test strain whose hydrophobicity and cholesterol removal ability are high was selected from 7 Bifidobacterium in the stduy. Secondly, the concentration of hydrogen peroxide to adapt to the test strain was selected by assay of sensitivity of the test strain to hydrogen peroxide. Thirdly, adaptive response of the test strain to hydrogen peroxide was assayed. Finally, its influence on growth, hydrophobicity and cholesterol removal ability, cross-protection and hereditary stability of hydrogen peroxide stress adaptation was assayed in the test strain.The results were as follows.(1) Selection of Test Strain Among 7 Bifidobacterium, both hydrophobicity and cholesterol removal ability of B. bifidum KLDS2.0613 were highest, respectively 90.71%±3.07% and 15.96±0.51μg/mL. Therefore, B. bifidum KLDS2.0613 was selected as test strain.(2) Adaptive Responses of Test Strain to Hydrogen PeroxideAdaptive response of B. bifidum KLDS2.0613 to hydrogen peroxide appear to depend on the concentration of hydrogen peroxide that cells are being adapted for. For example, pre-exposure of mid-log phase B. bifidum KLDS2.0613 at 3 mg/L hydrogen peroxide provided superior protection against a lethal hydrogen peroxide challenge at 120 mg/L hydrogen peroxide compared to 0.3 mg/L hydrogen peroxide.(3) Influence of Hydrogen Peroxide Stress Adaptation on Test StrainBoth the growth and the cholesterol removal ability of B. bifidum KLDS2.0613 were not altered after the pre-exposure of mid-log phase B. bifidum KLDS2.0613 at 3 mg/L hydrogen peroxide. In contrast, the hydrophobicity of B. bifidum KLDS2.0613 was altered. However, the hydrophobicity of B. bifidum KLDS2.0613 was recovered after incubation of at 37℃anaerobic conditions for 18h.(4) Cross-Protection of Hydrogen Peroxide Stress Adaptation in Test StrainBoth hydrogen peroxide-adapted cells showed cross-protection against heat and acid stresses. Heat tolerance and acid tolerance were enhanced about 30.80 and 1.92 times respectively in hydrogen peroxide-adapted B. bifidum KLDS2.0613 cells.(5) Hereditary Stability of Hydrogen Peroxide Stress Adaptation in Test StrainAdaptive response of B. bifidum KLDS2.0613 to 3 mg/L hydrogen peroxide. was transient and protected these strains for the short term only. For example, the survival ratio of hydrogen peroxide adapted cells of B. bifidum KLDS2.0613 is 46.88±6.62%. However, the survival ratio of hydrogen peroxide adapted cells is only 0.40±0.03% after incubation of at 37℃anaerobic conditions for 5h.