Researchers, led by scientists at US National Institutes of Health’s (NIH) National Institute of Allergy and Infectious Diseases (NIAID), found certain strains of Bacillus bacteria, commonly found in probiotics, prevent the growth of Staphylococcus aureus bacteria – the cause of fatal infections such as MRSA that kill tens of thousands each year.
NIAID director Anthony S. Fauci, M.D., said: “Probiotics frequently are recommended as dietary supplements to improve digestive health. This is one of the first studies to describe precisely how they may work to provide health benefits. The possibility that oral Bacillus might be an effective alternative to antibiotic treatment for some conditions is scientifically intriguing and definitely worthy of further exploration.”
One strategy to prevent Staph infections is to eliminate S. aureus. But decolonisation strategies are controversial because they require large amounts of antibiotics and have limited success, partly because they target only the nose and bacteria quickly recolonise from the gut.
Researchers from Mahidol University and Rajamangala University of Technology in Thailand recruited 200 volunteers in rural Thailand who they thought would not be as affected by food sterilisation or antibiotics than people in highly developed urban areas.
The team analysed faecal samples and found 101 samples positive for Bacillus, primarily B. subtilis — a strain found in many probiotic products. The scientists then checked the volunteers for S. aureus, but found none in any of the samples where Bacillus were present.
In a separate mouse study, the researchers discovered a S. aureus sensing system that must function for the bacteria to grow in the gut. Intriguingly, all of the Bacillus isolates they recovered from the human faeces efficiently blocked that system.
On further analysis, the scientists identified fengycins, a class of lipopeptides — molecules that are part peptide and part lipid—as the specific Bacillus substance that inhibited the S. aureus sensing system.
Additional tests showed that fengycins had the same effect on several different strains of S. aureus — including high-risk USA300 MRSA which causes most community-associated MRSA infections in the US.
To validate their findings, the scientists colonised the gut of mice with S. aureus and fed them B. subtilis spores to mimic probiotic intake. Giving them probiotic eliminated S. aureus in the guts of the mice.
The test was then repeated, but this time they blocked fengycin production. In this case B. subtilis had no effect and S. aureus grew as expected.
The NIAID and Thai scientists next plan to test whether a probiotic product containing only B. subtilis can eliminate S. aureus in people by enrolling more Thai volunteers.
“Ultimately, we hope to determine if a simple probiotic regimen can be used to reduce MRSA infection rates in hospitals,” said lead investigator Michael Otto, Ph.D.
Source: International Journal of Science
Published online ahead of print: 10th October 2018 doi.org/10.1038/s41586-018-0616-y
“Pathogen elimination by probiotic Bacillusvia signalling interference”
Authors: Pipat Piewngam, et al