Abstract
BackgroundLactobacillus rhamnosus GG (LGG) is the most widely used probiotic, but the mechanisms underlying its beneficial effects remain unresolved. Previous studies typically inoculated LGG in hosts with established gut microbiota, limiting the understanding of specific impacts of LGG on host due to numerous interactions among LGG, commensal microbes, and the host. There has been a scarcity of studies that used gnotobiotic animals to elucidate LGG-host interaction, in particular for gaining specific insights about how it modifies the metabolome. To evaluate whether LGG affects the metabolite output of pathobionts, we inoculated with LGG gnotobiotic mice containing Propionibacterium acnes, Turicibacter sanguinis, and Staphylococcus aureus (PTS).Results16S rRNA sequencing of fecal samples by Ion Torrent and MinION platforms showed colonization of germ-free mice by PTS or by PTS plus LGG (LTS). Although the body weights and feeding rates of mice remained similar between PTS and LTS groups, co-associating LGG with PTS led to a pronounced reduction in abundance of P. acnes in the gut. Addition of LGG or its secretome inhibited P. acnes growth in culture. After optimizing procedures for fecal metabolite extraction and metabolomic liquid chromatography-mass spectrometry analysis, unsupervised and supervised multivariate analyses revealed a distinct separation among fecal metabolites of PTS, LTS, and germ-free groups. Variables-important-in-projection scores showed that LGG colonization robustly diminished guanine, ornitihine, and sorbitol while significantly elevating acetylated amino acids, ribitol, indolelactic acid, and histamine. In addition, carnitine, betaine, and glutamate increased while thymidine, quinic acid and biotin were reduced in both PTS and LTS groups. Furthermore, LGG association reduced intestinal mucosal expression levels of inflammatory cytokines, such as IL-1α, IL-1β and TNF-α.ConclusionsLGG co-association had a negative impact on colonization of P. acnes, and markedly altered the metabolic output and inflammatory response elicited by pathobionts.
Highlights
Lactobacillus rhamnosus GG (LGG) is the most widely used probiotic, but the mechanisms underlying its beneficial effects remain unresolved
Previous studies have shown that extraction of mouse feces and subsequent normalization played a role in determining the quality of analysis [41, 42]
(See figure on previous page.) Fig. 4 Patterns of regulation of identified metabolites in GF, Propionibacterium acnes (PTS) and Lactobacillus rhamnosus GG plus Propionibacterium acnes (LTS) mice. a Box-whisker plots of representative upregulated metabolites in LTS and PTS mice compared to GF. b Box-whisker plots of representative downregulated metabolites in LTS and PTS mice compared to GF. c Box-whisker plots of representative downregulated metabolites in LTS compared to PTS and/or GF mice. d Box-whisker plots of representative upregulated metabolites in LTS compared to PTS and/or GF mice. * P < 0.05; ** P < 0.025; *** P < 0.001; NS = not significant, P > 0.05 levulinic acid, a potent anti-bacterial agent targeting mainly pathobionts as it inactivates Salmonella and verotoxigenic E. coli O157:H7 [53]
Summary
Lactobacillus rhamnosus GG (LGG) is the most widely used probiotic, but the mechanisms underlying its beneficial effects remain unresolved. Lactobacillus rhamnosus GG (LGG) is a Gram-positive facultative anaerobic bacterium of the phylum Firmicutes typically associated, as are many other Lactobacillus spp., with the treatment and prevention of intestinal inflammatory disorders [1,2,3]. Heat-killed Lactobacillus bulgaricus and cell-surface modified LGG attenuate dextran sulfate sodium (DSS)-induced colitis in mice [8, 9], suggesting that cell surface characteristics underlie at least some of their probiotic properties. There has been a scarcity of studies investigating LGG-associated gut microbial metabolites. This is unfortunate, as Lactobacillus spp. may produce metabolites that can act as anti-inflammatory mediators. Aryl Hydrocarbon Receptor (AHR) ligands from dietary and Lactobacilli-metabolized tryptophan utilized AHR signaling to mediate their beneficial effects, including exclusion of pathobiont species and mucosal protection from inflammation [14, 15]
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