Table 1.

Summary of studies evaluating in animal models the effects of gut bacterial species on the mucus layer.

Bacterial Strain	Animal Model	Experimental Administration	Study Period	Outcomes and Mechanisms of Action	Reference
Lactobacillus rhamnosus CNCM I-3690 and L. paracasei CNCM I-3689	DNBS-induced colitis in C57BL/6J mice	Intragastric administration with 1 × 109 CFU/mL	10 days	−Restoration of the induced increase of the colonic permeability by L. rhamnosus CNCM I-3690 but not L. paracasei CNCM I-3689. −Reinforcement of the intestinal barrier by modulation of the expression of epithelial tight junction proteins and reduced colonic levels of IL-4, IL-6 and IFN-γ cytokines.	[66]
Lactobacillus rhamnosus CNCM I-3690	DNBS-induced colitis in C57BL/6J mice	Intragastric administration with 5 × 109 CFU/mL	10 days	−Improvement of colonic macroscopic scores, colonic cytokine levels, colon and ileum myeloperoxidase activity and intestinal permeability. −Increase in the contents of acid and neutral mucopolysaccharides in goblet cells and MUC2 staining in the mucus layer. −Induction of an anti-inflammatory response in the spleen and mesenteric lymph nodes. −Upregulation of genes involved in gut health and protective functions against permeability, analyzed by colonic transcriptome analysis.	[73]
Lactobacillus reuteri R2LC and Lactobacillus reuteri 4659	DSS-induced colitis in C57BL/6J mice	Oral gavage with 1 × 108 live bacteria	14 days	−Reduction of colitis clinical and histological severity indexes. −Reduction of the pro-inflammatory markers myeloperoxidase, IL-1β, IL-6 and mouse keratinocyte chemoattractant. −Induction of adherent mucus thickness and expression of tight junction proteins occludin and ZO-1 in the colonic crypts.	[74]
Bacillus subtilis JNFE0126	DSS-induced colitis in C57BL/6J mice	B. subtilis-fermented milk oral gavage (6 × 108 CFU/mL)	21 days	−Prevention and alleviation effects against intestinal inflammation in both the active and recovery phases. −Reduction of disease activity index and pathological changes in the small intestine and colon. −Amelioration of neutrophil infiltration and mucosal pro-inflammatory cytokines. −Promotion of the proliferation of intestinal stem cells (Lgr5), epithelial cells (CDx2) and mucosal barrier (Mucin2, Zo-1, Villin). −Increase of microbiota diversity and restoration of gut balance.	[75]
Escherichia coli strain Nissle 1917	DSS-induced colitis in BALB/c mice	Intragastric administration with 1 × 109 CFU/mL	17 days	−Protection against induced clinical and histopathological colitis and preservation of intestinal permeability. −Reduction of mucosal infiltration of neutrophils and eosinophils, myeloperoxidase activity and IL-1β and CXCL1/KC levels. −Expansion of regulatory T-cells in the Peyer´s patches	[76]
Bifidobacterium longum NCC 2705	Western style diet-induced obesity in C57BL/6J mice	Supplementation of the drinking water with 2 × 106 CFU/mL	4 weeks	−Alteration of gut microbiota composition with loss of Bifidobacterium taxa and reduced growth rate and higher penetrability of the colonic mucus by the Wester style diet. −Prevention of mucus growth defects in the probiotic-supplemented group.	[77]
Bifidobacterium dentium ATCC 27678	Swiss Webster germfree mice	Oral gavage with 2 × 108 CFU/mL	1–2 weeks	−Microbial colonization of the colon mucus layer in gnotobiotic mice. −Increase in the number of filled intestinal goblet cells and modulation of mucus glycosylation. −Promotion of cell maturation and function with increased expression of Muc2, Krüppel-like family of zinc-finger transcription factor 4 (Klf4), resistin-like molecule-β (Relm-β) and trefoil factor 3 (Tff3), without corresponding changes in mucin-modulating cytokines.	[69]
Lactobacillus reuteri LR6	Protein and energy malnutrition in Swiss mice	Diet with fermented product or bacterial suspension at 1 × 109 CFU/day	1 week	−Reinforcement of intestinal health. −Expansion of the intact morphology of colonic crypts and lamina propria, normal goblet cells, while lessening of inflammation in large intestine and spleen and absence of fibrosis. −Stimulation of secretory IgA+ cells and the counts of phagocytic macrophages and bone marrow derived dendritic cells.	[78]
Akkermansia muciniphila MucT BAA-835	Accelerated aging Ercc1-/Δ7 mice	Oral gavage with 2 × 108 CFU/200 µL	10 weeks	−Expansion of colonic mucus thickness. −Decrease in the expression of colonic and ileal genes related to inflammation and immune and metabolic functions. −Lower presence of B cells in colon, decreased frequencies of activated CD80+CD273− B cells in Peyer’s patches and Ly6Cint monocytes in spleen and mesenteric lymph nodes. −Expansion of mature and immature B cells in bone marrow and peritoneal resident macrophages.	[71]
VSL#3 probiotic mixture	DSS-induced colitis in Muc2−/− mice	Oral gavage with 2.25 × 109 CFU/day	2 weeks	−Improvement of compromised intestinal barrier without significant protection against colitis progression. −Attenuation of basal pro-inflammatory cytokine levels and induced production of innate cytokines and reactive oxygen species. −Enhancement of tissue regeneration growth factors, antimicrobial peptides and abundance of bacterial gut commensals. −Enhanced production of SCFAs, mainly acetate.	[79]
VSL#3 probiotic mixture	DSS-induced colitis in C57BL/6J mice	Oral gavage with 3 × 109 live bacteria	60 days	−Anti-inflammatory effect with reduced scores of disease activity index, histological activity index and myeloperoxidase activity. −Reduction in IgM, IgG and IgA levels in colon mucus and the number of T follicular helper cells in mesenteric lymph nodes.	[80]
Lactobacillus johnsonii IDCC9203, Lactobacillus plantarum IDCC3501 and Bifidobacterium animalis subspecies lactis IDCC4301 (ID-JPL934 probiotic mixture)	DSS-induced colitis in BALB/c mice	Oral gavage with probiotic mixture (1 × 106–1 × 109 CFU/day)	8 days	−Dose-dependent reduction of colitis symptoms including body weight loss, diarrhea and bloody feces and colon length contraction. −Similar effects to sulfasalazine at 500 mg per kg per day. −Suppression of the infiltration of immune cells into mucosa and submucosa, crypt damage, expression of pro-inflammatory TNFα, IL-1β and IL-6. −Restoration of physiological epithelial cells and goblet cells histology.	[81]
Lactobacillus rhamnosus, L. acidophilus and Bifidobacterium bifidumi	High fat diet-induced obesity in Swiss mice	Oral gavage with probiotic mixture (6 × 108 CFU of each strain; final concentration of 1.8 × 109 CFU of bacteria)	5 weeks	−Induction of gut microbiota alterations, intestinal permeability, LPS translocation and systemic low-grade inflammation, reverted by the probiotic mixture. −Endorsement of glucose tolerance, hyperphagic behavior, hypothalamic insulin and leptin resistance.	[82]

DNBS: dinitrobenzene sulfonic acid; DSS: dextran sulfate sodium; CFU: colony-forming units; SCFAs: short-chain fatty acids; LPS: lipopolysaccharide.