TABLE 4.
Overview of short sublethal stress treatments of Bifidobacterium strains that resulted in improved survival of the strains to elevated lethal stress
| Stress treatment and strain | Sublethal stress | Improved tolerance | Remarks | Reference(s) |
|---|---|---|---|---|
| Homologous | ||||
| B. longum D2957 | H2O2 (1.25 mM, 20 min) | H2O2 (2.55 mM) | Species- and strain-dependent intrinsic and inducible resistance to H2O2. The result depended on the combination of duration of sublethal treatment and subsequent level of lethal stress treatment applied. | 143 |
| B. longum NCC2705 | H2O2 (1.25 mM, 60 min or 20 min) | H2O2 (5.25 mM and 2.55 mM after 60 min pretreatment and 2.55 mM after 20 min) | Species- and strain-dependent intrinsic and inducible resistance to H2O2. The result depended on the combination of duration of sublethal treatment and subsequent level of lethal stress treatment applied. | 143 |
| B. animalis subsp. lactis RH-1 and B. animalis subsp. lactis BL-04 | H2O2 (1.25 mM, 20 min) | H2O2 (5.25 mM) | Species- and strain-dependent intrinsic and inducible resistance to H2O2. The result depended on the combination of duration of sublethal treatment and subsequent level of lethal stress treatment applied. | 143 |
| B. adolescentis NCC251 | Bile (0.1%, oxgall) | Bile (0.3 and 0.4% bile salts, oxgall) | Mechanism that prevents solubilization of membrane proteins might be induced. Effect is stronger in exponentially growing cells. Improved tolerance might be due to the induction of chaperones (e.g., DnaK) by sublethal stress treatment. | 65 |
| B. adolescentis NCC251 | Heat (45°C, 30 min, or 47°C, 15 min) | Heat (55°C) | Improved tolerance might be due to the induction of chaperones (e.g., DnaK) by sublethal stress treatment. | 65 |
| B. longum NCC2705 | Heat (47°C) | Heat (50°C, 5 min) | Results varied slightly depending on the operation mode applied for fermentation in which the effect of sublethal stress treatment was tested (batch vs continuous mode). | 246 |
| B. longum E-011884 (E1884) | Heat (47°C, 1 h) | Heat (55°C, 1 h) | Only slightly improved tolerance observed after sublethal stress treatment | 285 |
| B. longum BBMN68 | Acid (pH 4.5) | Acid (pH 3.5) | Improved tolerance might be due to global metabolic adaptation to acid stress. | 157, 163 |
| B. animalis subsp. lactis (Degussa BioActive) | Decrease of medium from pH 6 to pH 5.2, tested in multiadaptation treatments | Acid (synthetic gastric fluid, pH 3.5) | Decreased pH might induce changes in membrane fatty acid composition or induce production of acid shock proteins. | 284 |
| Heterologous | ||||
| B. adolescentis NCC251 | Salt (1.5% NaCl, 1 h, or 2% NaCl, 1 h) | Heat (55°C) | Improved tolerance might be due to the induction of chaperones (e.g., DnaK) by sublethal stress treatment. | 65 |
| B. adolescentis NCC251 | Salt (2 % NaCl, 1 h) | Freeze-thawing cycles | Improved tolerance might be due to the production by an intrinsic osmoprotectant. | 65 |
| B. longum NCC2705 | Osmotic stress (10% NaCl) | Freeze-drying | Improved survival has been observed in continuous setup but not in batch mode. | 246 |
| B. longum NCC2705 | Acid, pH 4 | Gastric juice (0.5% (wt/vol) NaCl, 0.3% (wt/vol) pepsin at pH 2.8, 15 min), bile salts (1.5% [wt/vol] porcine bile extract, 10 min), and osmotic stress (27% [wt/vol] NaCl, 2 h) | Treatment at pH 4 caused high loss of viable-cell count and can therefore not be considered sublethal. | 246 |
| B. animalis subsp. lactis E-012010 (E2010/BB-12) | Acid (pH 3.5) | Bile (1.5% bile extract, 3 h) | Slightly improved survival observed after sublethal stress treatment; impaired acid tolerance of B. longum E1884 | 285 |
| B. animalis subsp. lactis E-012010 (E2010/BB-12) | Heat (47°C, 1 h) | Bile (1.5% bile extract, 3 h) | Slightly improved tolerance observed after sublethal stress treatment in laboratory scale (3–4 mL) but only minor effect at fermentation scale (7 L) | 285 |
| B. longum ATCC 15707 | Starvation (30–60 min), tested in multiadaptation treatments | Cold (6°C) | Starvation might induce regulators of stress response or changes in the membrane fatty acid composition (increased cyclic fatty acids). No effect on −80°C survival. | 284 |