Probiotic Bacteria Keep Staphylococcus At Bay

Bacillus, a type of bacteria commonly found in probiotics, prevents Staphylococcus aureus colonization of the gut and nose, according to scientists in Thailand and the US.

AsianScientist (Nov. 1, 2018) – A team of researchers in Thailand and the US have found that good bacteria commonly found in probiotic digestive supplements help prevent the colonization of the gut and nose by Staphylococcus aureus, a type of bacteria that can cause serious antibiotic-resistant infections. They published their findings in the journal Nature.

Staphylococcus infections cause tens of thousands of deaths worldwide each year. Methicillin-resistant Staphylococcus aureus, or MRSA, is becoming a major threat in hospitals across the globe.

Less well known is that S. aureus can often live in the human 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.

In this study, researchers at Mahidol University, Thailand, and the National Institutes of Health, USA, have demonstrated that Bacillus bacteria commonly found in probiotic supplements can suppress the growth of pathogenic S. aureus in the gut and nose of healthy individuals.

The scientists recruited 200 volunteers in rural Thailand for the study. This population, they hypothesized, 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 of S. aureus.

They found 101 samples positive for Bacillus, primarily Bacillus subtilis—the type found mixed with other bacteria in many probiotic products. B. subtilis forms spores that can survive harsh environments and are ingested naturally with vegetables, allowing them to temporarily grow in the intestine.

The scientists then sampled the same 200 people for S. aureus in the gut and nose. Strikingly, they found no S. aureus in any of the samples where Bacillus was present.

In studies done in mice, the scientists discovered a sensing system in S. aureus that must function for the bacteria to grow in the gut. Intriguingly, all of the more than 100 Bacillus isolates they had recovered from human fecal samples efficiently inhibited the S. aureus sensing 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 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 and is an increasingly common cause of healthcare-associated MRSA infections.

To further validate their findings, the scientists colonized the gut of mice with S. aureus and fed them B. subtilis spores to mimic a probiotic. Probiotic Bacillus given every two days eliminated S. aureus in the guts of the mice. The same test using Bacillus that did not produce fengycin had no effect on S. aureus growth, suggesting that fengycin was necessary to eliminate S. aureus.

The scientists plan to test whether a probiotic product that contains only B. subtilis can eliminate S. aureus in people. They intend to enroll more Thai volunteers for the project.

“Ultimately, we hope to determine if a simple probiotic regimen can be used to reduce MRSA infection rates in hospitals,” said Professor Michael Otto of the National Institutes of Health.

The article can be found at: Piewngam et al. (2018) Pathogen Elimination by Probiotic Bacillus via Signalling Interference.


Source: US National Institute of Allergy and Infectious Diseases; Photo: Shutterstock.
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