Pathogen elimination by probiotic Bacillus via signalling interference.

Probiotic nutrition is frequently claimed to improve human health. In particular, live probiotic bacteria obtained with food are thought to reduce intestinal colonization by pathogens, and thus to reduce susceptibility to infection. However, the mechanisms that underlie these effects remain poorly understood. Here we report that the consumption of probiotic Bacillus bacteria comprehensively abolished colonization by the dangerous pathogen Staphylococcus aureus in a rural Thai population. We show that a widespread class of Bacillus lipopeptides, the fengycins, eliminates S. aureus by inhibiting S. aureus quorum sensing-a process through which bacteria respond to their population density by altering gene regulation. Our study presents a detailed molecular mechanism that underlines the importance of probiotic nutrition in reducing infectious disease. We also provide evidence that supports the biological significance of probiotic bacterial interference in humans, and show that such interference can be achieved by blocking a pathogen's signalling system. Furthermore, our findings suggest a probiotic-based method for S. aureus decolonization and new ways to fight S. aureus infections.

Probiotic for pathogen-specific Staphylococcus aureus decolonisation in Thailand: a phase 2, double-blind, randomised, placebo-controlled trial.

BACKGROUND: Decolonisation is considered a valuable means to reduce Staphylococcus aureus infection rates. However, previous topical strategies targeting the nose or skin had little success, and oral antibiotic-based decolonisation is ill advised because of eradication of the microbiota and development of antibiotic resistance. We previously showed that the probiotic Bacillus subtilis significantly diminished S aureus at the main intestinal colonisation site via specific bacterial interaction in mice; in this study, we tested this probiotic approach to control S aureus colonisation in humans. METHODS: We did a single-centre, phase 2, double-blind, randomised, placebo-controlled trial in adults from the Songkhla region of Thailand who were colonised by S aureus. Eligible participants were adults (aged ≥18 years) without history of intestinal disease, antibiotic treatment, or hospital admission within the previous 90 days. Participants were excluded if they were pregnant, breastfeeding, taking probiotics, or had diarrhoea. Participants were allocated (1:1) to groups by computer randomisation in blocks of four, and research coordinators were masked to group allocation. Participants received 250 mg of probiotic B subtilis MB40 or placebo once per day for 30 days and S aureus colonisation was determined after the last dose was received. The primary outcome was colonisation by S aureus (continuous, mean decrease in colony-forming-unit count) in the intestine (by faecal counts) and nares (by nasal swabs) after intervention (30-day regimen of B subtilis probiotic). This trial is registered with the Thai Clinical Trials Registry, TCTR20210128003. FINDINGS: The trial was done between Jan 29 and June 30, 2021, with enrolment taking place from Jan 29 to April 6, 2021. 115 participants were colonised by S aureus, either in the intestine (n=84), nose (n=50), or both (n=19), and were randomly assigned to treatment (n=55) and placebo groups (n=60). Oral probiotic B subtilis resulted in significant reduction of S aureus in stool (96·8%; p<0·0001) and nose (65·4%; p=0·0002). There were no differences in adverse effects or significant microbiome changes between the intervention and placebo groups. INTERPRETATION: B subtilis probiotic eliminated more than 95% of the total S aureus colonising the human body without altering the microbiota. This probiotic strategy offers several key advantages over presently used decolonisation strategies for potential use in people with chronic or long-term risk of S aureus infection. Furthermore, by establishing a defining role of the intestinal colonisation site, our findings call for revisiting fundamental notions about S aureus colonisation. FUNDING: National Research Council of Thailand and US National Institutes of Health.

Characterization and immunomodulatory activity of sulfated galactan from the red seaweed Gracilaria fisheri.

Polysaccharides from the red seaweed Gracilaria fisheri possess many functions, which include antioxidant, antiviral, and antibacterial activities. However, detailed data on their immunomodulatory activities are scarce. Here, we isolated sulfated galactans (SG) from G. fisheri. We found that the predominant SG from G. fisheri, termed SG-1, had an estimated molecular mass of 100 kDa and activated murine J774A.1 macrophages via the dectin-1 signaling pathway. Furthermore, we observed enhancement of nitric oxide (NO) secretion, increased expression of inducible nitric oxide synthase (iNOS) mRNA, and increased mRNA levels of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukins IL-1ß and IL-6 by SG-1 in macrophages. Moreover, there was higher expression of intercellular adhesion molecule 1 (ICAM-1) and co-stimulatory molecules (B7-1 and B7-2) mRNA. Treatment with G. fisheri SG-1 at 50 µg/mL generally achieved or exceeded the pro-inflammatory activities of 100 ng/mL lipopolysaccharide. Our study demonstrates immune-stimulatory activities of G. fisheri SG that may be of value for immune-potentiating treatment in humans or livestock.