Metabolic and biochemical responses of probiotic bacteria to oxygen.

The interaction between oxygen and probiotic bacteria was studied by growing Lactobacillus acidophilus and Bifidobacterium spp. in 0, 5, 10, 15, and 21% oxygen in a hypoxic glove box. The metabolic responses of each probiotic strain in the different oxygen environments were monitored by measuring the levels of lactic acid and determining the lactate-to-acetate ratio. Biochemical changes induced by oxygen were examined by monitoring the specific activities of NADH oxidase, NADH peroxidase, and superoxide dismutase. In addition, the ability to decompose hydrogen peroxide and the sensitivity of each strain to hydrogen peroxide was also determined. With an increase in oxygen percentage, levels of lactic acid in L. acidophilus strains decreased, whereas the lactate-to-acetate ratio reduced in all the bifidobacteria tested. At 21% oxygen, the specific activities of NADH oxidase and NADH peroxidase, and the hydrogen peroxide decomposing ability of five probiotic strains was significantly higher than at 0% oxygen. The sensitivity of the probiotic strains to hydrogen peroxide however, remained unaffected in all the different oxygen percentages. Superoxide dismutase levels did not reveal any conclusive trend. In both L. acidophilus and Bifidobacterium spp., NADH oxidase and NADH peroxidase functioned optimally at pH 5. Growth in the various oxygen environments did not change this optimum pH.