Correction to: Intrinsic and inducible resistance to hydrogen peroxide in Bifidobacterium species.

In the published article, the co-author Abdelmoneim Abdalla's affiliation has been published incompletely. The additional affiliation is given below.

Intrinsic and inducible resistance to hydrogen peroxide in Bifidobacterium species.

Interest in, and use of, bifidobacteria as a probiotic delivered in functional foods has increased dramatically in recent years. As a result of their anaerobic nature, oxidative stress can pose a major challenge to maintaining viability of bifidobacteria during functional food storage. To better understand the oxidative stress response in two industrially important bifidobacteria species, we examined the response of three strains of B. longum and three strains of B. animalis subsp. lactis to hydrogen peroxide (H2O2). Each strain was exposed to a range of H2O2 concentrations (0-10 mM) to evaluate and compare intrinsic resistance to H2O2. Next, strains were tested for the presence of an inducible oxidative stress response by exposure to a sublethal H2O2 concentration for 20 or 60 min followed by challenge at a lethal H2O2 concentration. Results showed B. longum subsp. infantis ATCC 15697 had the highest level of intrinsic H2O2 resistance of all strains tested and B. animalis subsp. lactis BL-04 had the highest resistance among B. lactis strains. Inducible H2O2 resistance was detected in four strains, B. longum NCC2705, B. longum D2957, B. lactis RH-1, and B. lactis BL-04. Other strains showed either no difference or increased sensitivity to H2O2 after induction treatments. These data indicate that intrinsic and inducible resistance to hydrogen peroxide is strain specific in B. longum and B. lactis and suggest that for some strains, sublethal H2O2 treatments might help increase cell resistance to oxidative damage during production and storage of probiotic-containing foods.

Transport of glucose by Bifidobacterium animalis subsp. lactis occurs via facilitated diffusion.

Two strains of Bifidobacterium animalis subsp. lactis were indistinguishable by several nucleic acid-based techniques; however, the type strain DSMZ 10140 was glucose utilization positive, while RB 4825, an industrially employed strain, was unable to grow rapidly on glucose as the principal carbon source. This difference was attributed to the presence of a low-affinity facilitated-diffusion glucose transporter identified in DSMZ 10140 but lacking in RB 4825. Uptake of D-[U-(14)C]glucose in DSMZ 10140 was stimulated by monovalent cations (ammonium, sodium, potassium, and lithium) and inhibited by divalent cations (calcium and magnesium). When competitor carbohydrates were included in the uptake assays, stereospecific inhibition was exhibited, with greater competition by methyl-beta-glucoside than methyl-alpha-glucoside. Significant inhibition (>30%) was observed with phloretin, an inhibitor of facilitated diffusion of glucose, whereas there was no inhibition by sodium fluoride, iodoacetate, sodium arsenate, sodium azide, 2,4-dinitrophenol, monensin, or valinomycin, which typically reduce energy-driven transport. Based on kinetic analyses, the mean values for K(t) and V(max) were 14.8 +/- 3.4 mM D-glucose and 0.13 +/- 0.03 micromol glucose/min/mg cell protein, respectively. Glucose uptake by several glucose-utilizing commercial strains of B. animalis subsp. lactis was also inhibited by phloretin, indicating the presence of facilitated diffusion glucose transporters in those strains. Since DSMZ 10140 has been previously reported to lack a functional glucose phosphoenolpyruvate phosphotransferase system, the glucose transporter identified here is responsible for much of the organism's glucose uptake.

Technical note: a rapid pulsed-field gel electrophoresis method for analysis of bifidobacteria.

Pulsed-field gel electrophoresis (PFGE) is a widely used and highly discriminatory molecular typing method that has been applied to bifidobacteria. However, published PFGE protocols used with bifidobacteria require between 5 and 7 d to complete. A rapid PFGE method was developed that can be completed within 24 h.

Production of an exopolysaccharide-containing whey protein concentrate by fermentation of whey.

Using whey as a fermentation medium presents the opportunity to create value-added products. Conditions were developed to partially hydrolyze whey proteins and then ferment partially hydrolyzed whey with Lactobacillus delbrueckii ssp. bulgaricus RR (RR; an EPS-producing bacterium). In preliminary experiments, pasteurized Cheddar cheese whey was treated with Flavourzyme to partially hydrolyze the protein (2 to 13% hydrolyzed). Fermentation (2 L, 38 degrees C, pH 5.0) with RR resulted in EPS levels ranging from 95 to 110 mg of EPS per liter of hydrolyzed whey. There were no significant differences in the amount of EPS produced during fermentations of whey hydrolyzed to varying degrees. Since a high level of hydrolysis was not necessary for increased EPS production, a low level of hydrolysis (2 to 4%) was selected for future work. In scale up experiments, whey was separated and pasteurized, then treated with Flavourzyme to hydrolyze 2 to 4% of the protein. Following protease inactivation, 60 L of partially hydrolyzed whey was fermented at 38 degrees C and pH 5.0. After fermentation, the broth was pasteurized, and bacterial cells were removed using a Sharples continuous centrifuge. The whey was then ultrafiltered and diafiltered to remove lactose and salts, freeze-dried, and milled to a powder. Unfermented hydrolyzed and unhydrolyzed whey controls were processed in the same manner. The EPS-WPC ingredients contained approximately 72% protein and 6% EPS, but they exhibited low protein solubility (65%, pH 7.0; 58%, pH 3.0).