News Release, National Institutes of Health

Additional studies of common supplement planned.

Woman selling vegetable snacks in a Thai market
Woman selling vegetable snacks in a Thai market – a possible source of probiotic Bacillus spores.NIAID

A new study from the National Institutes of Health scientists and their Thai colleagues shows that a “good” bacterium commonly found in probiotic digestive supplements helps eliminate Staphylococcus aureus, a type of bacteria that can cause serious antibiotic-resistant infections. The researchers, led by scientists at NIH’s National Institute of Allergy and Infectious Diseases (NIAID), unexpectedly found that Bacillus bacteria prevented S. aureus bacteria from growing in the gut and nose of healthy individuals. Then, using a mouse study model, they identified exactly how that happens. Researchers from Mahidol University and Rajamangala University of Technology in Thailand collaborated on the project.

“Probiotics frequently are recommended as dietary supplements to improve digestive health,” said NIAID Director Anthony S. Fauci, M.D. “This is one of the first studies to describe precisely how they may work to provide health benefits. The possibility that oralBacillusmight be an effective alternative to antibiotic treatment for some conditions is scientifically intriguing and definitely worthy of further exploration.”

Staphylococcusinfections cause tens of thousands of deaths worldwide each year. Methicillin-resistantStaphylococcus aureus, or MRSA, is familiar to many people as a cause of serious disease. Less well known is thatS. aureusoften can live in the nose or gut without causing any harm. However, if the skin barrier is broken, or the immune system compromised, these colonizing bacteria can cause serious infections.

One strategy to prevent Staph infections is to eliminateS. aureuscolonization. However, some decolonization strategies are controversial because they require considerable amounts of topical antibiotics and have limited success, partly because they target only the nose and bacteria quickly recolonized from the gut.

The scientists recruited 200 volunteers in rural Thailand for the study. This population, they speculated, would not be as affected by food sterilization or antibiotics as people in highly developed urban areas. The scientists first analyzed fecal samples from each of the study participants for bacteria correlated with the absence ofS. aureus.They found 101 samples positive forBacillus, primarilyB. subtilis— the type found mixed with other bacteria in many probiotic products.Bacillusbacteria form spores that can survive harsh environments and commonly are ingested naturally with vegetables, allowing them to temporarily grow in the intestine. The scientists then sampled the same 200 people forS. aureusin the gut (25 positive) and nose (26 positive). Strikingly, they found noS. aureusin any of the samples whereBacilluswere present.

In mouse studies, the scientists discovered anS. aureussensing system that must function for the bacteria to grow in the gut. Intriguingly, all of the more than 100Bacillusisolates they had recovered from the human feces efficiently inhibited that system.

Using chromatography and mass spectrometry techniques, the scientists identified fengycins, a specific class of lipopeptides — molecules that are part peptide and part lipid—as the specificBacillussubstance that inhibited theS. aureussensing system. Additional tests showed that fengycins had the same effect on several different strains ofS. aureus— including high-risk USA300 MRSA which causes most community-associated MRSA infections in the United States and is an increasingly common cause of healthcare-associated MRSA infections.

To further validate their findings, the scientists colonized the gut of mice withS. aureusand fed themB. subtilisspores to mimic probiotic intake. ProbioticBacillusgiven every two days eliminatedS. aureusin the guts of the mice. The same test usingBacilluswhere fengycin production had been removed had no effect, andS. aureusgrew as expected.

The NIAID and Thai scientists next plan to test whether a probiotic product that contains onlyB. subtiliscan eliminateS. aureusin people. They plan to enroll more Thai volunteers for the project. Michael Otto, Ph.D., the NIAID lead investigator, says, “Ultimately, we hope to determine if a simple probiotic regimen can be used to reduce MRSA infection rates in hospitals.”

NIAID conducts and supports research — at NIH, throughout the United States, and worldwide — to study the causes of infectious and immune-mediated diseases, and to develop better means of preventing, diagnosing and treating these illnesses. News releases, fact sheets and other NIAID-related materials are available on theNIAID website.