The value of exogenously supplied live bacteria for the maintenance of health in humans has been recognized both scientifically in the published literature and commercially in the availability of probiotic products. Although many bacteria characterized as probiotics are strains of Lactobacillus or Bifidobacterium , sporeforming bacteria, primarily of the genus Bacillus and related genera, have also been studied and commercialized as probiotics. This article reviews the characterization, efficacy, and safety of sporeformers used as probiotics.

Afifa Ait-Belgnaoui, Isabelle Payard, Claire Rolland, Cherryl Harkat, Viorica Braniste, Vassillia Théodorou, and Thomas A Tompkins. J Neurogastroenterol Motil 2018;24:138-46. https://doi.org/10.5056/jnm16167

The fungus Candida albicans is an opportunistic pathogen that can exploit imbalances in microbiome composition to invade its human host, causing pathologies ranging from vaginal candidiasis to fungal sepsis. Bacteria of the genus Lactobacillus are colonizers of human mucosa and can produce compounds with bioactivity against C. albicans. Here, we show that some Lactobacillus species produce a small molecule under laboratory conditions that blocks the C. albicans yeast-to-filament transition, an important virulence trait. It remains unexplored whether the compound is produced in the context of the human host. Bioassay-guided fractionation of Lactobacillus-conditioned medium linked this activity to 1-acetyl-β-carboline (1-ABC). We use genetic approaches to show that filamentation inhibition by 1-ABC requires Yak1, a DYRK1-family kinase. Additional biochemical characterization of structurally related 1-ethoxycarbonyl-β-carboline confirms that it inhibits Yak1 and blocks C. albicans biofilm formation. Thus, our findings reveal Lactobacillus-produced 1-ABC can prevent the yeast-to-filament transition in C. albicans through inhibition of Yak1.

Lactobacillus helveticus CNRZ 32 is recognized for its ability to decrease bitterness and accelerate flavor development in cheese, and has also been shown to release bioactive peptides in milk. Similar capabilities have been documented in other strains of Lb. helveticus, but the ability of different strains to affect these characteristics can vary widely. Because these attributes are associated with enzymes involved in proteolysis or AA catabolism, we performed comparative genome hybridizations to a CNRZ 32 microarray to explore the distribution of genes encoding such enzymes across a bank of 38 Lb. helveticus strains, including 2 archival samples of CNRZ 32. Genes for peptidases and AA metabolism were highly conserved across the species, whereas those for cell envelope-associated proteinases varied widely. Some of the genetic differences that were detected may help explain the variability that has been noted among Lb. helveticus strains in regard to their functionality in cheese and fermented milk.

Clinical effects of antimicrobials and probiotics in combination have been reported, however, little is known about their impact on gut microbiota and its resistome. In this study 16S rRNA gene amplicon, shotgun metagenomics sequencing and antibiotic resistance (ABR) microarray were used on fecal samples of 70 healthy participants, taken at four time points in probiotic (Lactobacillus rhamnosus R0011 and Lactobacillus helveticus R0052) and placebo groups to profile the gut bacterial microbiota and its resistome following administration of amoxicillin-clavulanic acid for one week. Significant shifts in microbiota family composition caused by the antimicrobial in both groups that included decreases in the proportion of Lachnospiraceae, Coriobacteriaceae and unidentified Clostridiales; and notable increases for the proportion of Enterobacteriaceae, Bacteroidaceae and Porphyromonadaceae compared to baseline levels. Resistome showed a corresponding enrichment of ABR genes compared to baseline from such classes as aminoglycosides and beta-lactams that were linked, by in silico inference, to the enrichment of the family Enterobacteriaceae. Despite perturbations caused by short-term antibiotic treatment, both gut microbiota and resistome showed prompt recovery to baseline levels one week after cessation of the antimicrobial. This rapid recovery may be explained by the hypothesis of community resilience.

The HT29MTXE12 (E12) cell line harbors an adherent mucus layer, providing a novel technique to model mucosal infection in vitro . In this study, we have characterized the interaction of Campylobacter jejuni with the E12 cell line and exploited its unique mucus layer to examine the potential efficacy of probiotic treatment to attenuate C. jejuni virulence properties. C. jejuni 81-176 colonized and reproduced in E12 mucus. Adhesion to and internalization of C. jejuni were enhanced in E12 cells harboring mucus compared to parental cells without mucus. Translocation of C. jejuni occurred at early time points following infection. C. jejuni aligned with tight junctions and colocalized with the tight junction protein occludin, suggesting a paracellular route of translocation. Probiotic strains Lactobacillus rhamnosus R0011, Lactobacillus helveticus R0052, Lactobacillus salivarius AH102, Bifidobacterium longum AH1205, a commercial combination of L. rhamnosus R0011 and L. helveticus R0052 (Lacidofil), and a cocktail consisting of L. rhamnosus , L. helveticus , and L. salivarius (RhHeSa) colonized E12 mucus and bound to underlying cells. Probiotics attenuated C. jejuni association with and internalization into E12 cells and translocation to the basolateral medium of transwells. Live bacteria and prolonged precolonization of E12 cells with probiotics were necessary for probiotic action. These results demonstrate the potential for E12 cells as a model of mucosal pathogenesis and provide a rationale for the further investigation of probiotics as prophylaxis against human campylobacteriosis.