Entry 16
Probiotic science page
Uses cell wall polysaccharides to modulate immunity and reduce IBS symptoms, with RCT evidence.
Overview
Levilactobacillus brevis KB290 is a probiotic strain. It was isolated from Japanese traditional fermented pickles called suguki [6]. It stands out because it produces exopolysaccharide (EPS, a slimy sugar coating) from genes on a plasmid. This coating makes the cells clump together, resist bile, and form wrinkled colonies [4,5]. KB290 has been tested in human randomized controlled trials for irritable bowel syndrome (IBS) symptoms and flu prevention. It has also been tested in animal models for gut inflammation, belly fat buildup, and antiviral immunity [1–3,6]. Both live and heat-killed forms show biological activity [1,6]. In the 2020 reclassification, this species was moved to the new genus Levilactobacillus [7].
Mechanism
KB290 produces a cell-bound exopolysaccharide (EPS). A three-gene unit (gtf27, gtf28, orf29) on the 42.4-kb plasmid pKB290-1 encodes it [4]. The predicted products of gtf27 and gtf28 are membrane-bound sugar-adding enzymes (glycosyltransferases). orf29 encodes an ABC transporter [4]. Researchers removed the plasmid from the bacteria. The plasmid-free bacteria lost EPS production, cell clumping, and bile resistance. This proved these genes are both necessary and enough for these traits. The EPS is made of glucose and N-acetylglucosamine [4]. EPS production is controlled by the carbon source. It drops sharply when the bacteria grow on arabinose or xylose instead of glucose [4]. The wrinkled colony look of KB290 comes directly from cell-bound EPS made by these same plasmid genes [5].
Bile resistance is critical for surviving the gut. KB290 grows in the presence of bile. The EPS layer probably shields cells from the detergent-like effects of bile acids [4,6]. The anti-inflammatory mechanism involves changing immune cell populations in the gut. KB290 given with vitamin A raised the ratio of CD11c+ macrophages to CD103− dendritic cells in a mouse colitis model. This promoted a calming immune environment [3]. In a belly fat model, heat-killed KB290 changed the gut microbiome. It also raised adiponectin and β3-adrenergic receptor levels in fat tissue. This suppressed diet-driven metabolic problems [6].
Health Benefits
Human RCT (influenza): A randomized, double-blind, placebo-controlled parallel-group trial enrolled healthy Japanese adults aged 20 to 59. They took heat-killed KB290 plus beta-carotene. The treatment showed a trend toward fewer flu cases. A closer look at subgroups found a real benefit in people under 40. Incidence was 1.9% in the treatment group versus 3.9% in the placebo group [1]. (Evidence level: human RCT, subgroup finding)
Human RCT (IBS): A randomized, double-blind, placebo-controlled, parallel-group trial tested KB290 plus beta-carotene for 12 weeks. It improved the intensity of abdominal pain and stool frequency in healthy people with mild IBS-D-like symptoms. It also raised serum IL-10 [2]. (Evidence level: human RCT)
Murine colitis: KB290 plus vitamin A eased intestinal inflammation. This was linked to an increased ratio of CD11c+ macrophages to CD103− dendritic cells [3]. (Evidence level: animal model)
Murine visceral fat: Heat-killed KB290 reduced belly fat buildup. It also improved metabolic markers (glucose, insulin, HOMA-IR) in mice fed a high-fat diet [6]. (Evidence level: animal model)
Biology
Plasmid biology: The 42.4-kb plasmid pKB290-1 carries the EPS production unit (gtf27-gtf28-orf29). Bacteria with the plasmid removed lose EPS production, clumping, and bile resistance [4].
Colony morphology: Wrinkled colony appearance is tied to cell-bound EPS. Smooth variants come from reduced EPS expression [5].
Bile adaptation: KB290 grows in bile-containing media. Bile resistance depends on EPS [4,6].
Taxonomy: L. brevis was reclassified as Levilactobacillus brevis in the 2020 reclassification [7].
Bibliography
[1] Satomi S, Waki N, Arakawa C, Fujisawa K, Suzuki S, Suganuma H. (2021). “Effects of Heat-Killed Levilactobacillus brevis KB290 in Combination with β-Carotene on Influenza Virus Infection in Healthy Adults: A Randomized Controlled Trial.” Nutrients. 13(9). PMID: 34578917
[2] Fuke N, Aizawa K, Suganuma H, Takagi T, Naito Y. (2017). “Effect of combined consumption of Lactobacillus brevis KB290 and β-carotene on minor diarrhoea-predominant irritable bowel syndrome-like symptoms in healthy subjects: a randomised, double-blind, placebo-controlled, parallel-group trial.” Int J Food Sci Nutr. 68(8):973–986. PMID: 28391736
[3] Fuke N, et al. (2018). “Lactobacillus brevis KB290 With Vitamin A Ameliorates Murine Intestinal Inflammation Associated With the Increase of CD11c+ Macrophage/CD103− Dendritic Cell Ratio.” Inflamm Bowel Dis. 24(2):317–331. PMID: 29361084
[4] Fukao M, et al. (2019). “Plasmid-encoded glycosyltransferase operon is responsible for exopolysaccharide production, cell aggregation, and bile resistance in a probiotic strain, Lactobacillus brevis KB290.” J Biosci Bioeng. 128(4):391–397. PMID: 31126721
[5] Fukao M, et al. (2019). “Relation between cell-bound exopolysaccharide production via plasmid-encoded genes and rugose colony morphology in the probiotic Lactobacillus brevis KB290.” Anim Sci J. 90(12):1575–1580. PMID: 31593351
[6] Watanabe J, et al. (2021). “Heat-killed Lactobacillus brevis KB290 attenuates visceral fat accumulation induced by high-fat diet in mice.” J Appl Microbiol. 131(4):1998–2009. PMID: 33742756
[7] Zheng J, et al. (2020). “A taxonomic note on the genus Lactobacillus: Description of 23 novel genera, emended description of the genus Lactobacillus Beijerinck 1901, and union of Lactobacillaceae and Leuconostocaceae.” Int J Syst Evol Microbiol. 70(4):2782–2858. PMID: 32293557
Available Products
KB290 is used as a functional food ingredient in Japan. It comes in both live and heat-killed forms in dietary supplements and functional drinks. The strain is licensed from research institutions. It is included in commercial probiotic products in the Japanese market.