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CIDRAP - Research reveals probiotic's potential against Staph

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  • CIDRAP - Research reveals probiotic's potential against Staph


    Research reveals probiotic's potential against Staph
    Filed Under:
    Antimicrobial Stewardship
    Chris Dall | News Reporter | CIDRAP News
    | Oct 11, 2018

    New research from the National Institute of Allergy and Infectious Diseases (NIAID) indicates a type of bacteria that's commonly used in many probiotic nutritional supplements helps eliminate Staphylococcus aureus in the gut.
    In a study published yesterday in Nature, scientists from NIAID, along with colleagues in Thailand, found that among a group of volunteers from rural Thailand, individuals with Bacillus bacteria in their gut had no S aureus bacteria in their intestines or their nasal passages. Lab experiments conducted on Bacillus revealed that the bacteria prevent S aureus colonization by secreting a substance that interferes with cellular communication and the regulation of gene expression in the pathogen.
    The scientists suggest the surprising findings open the door for exploring the potential of using Bacillus as a tool to decolonize patients found to carry S aureus in their nose or their intestines, which can increase the risk for developing dangerous Staph infections. Although nasal or intestinal carriage of S aureus bacteria is not harmful on its own, S aureus infections, particularly those caused by methicillin-resistant S aureus (MRSA), can be severe and sometimes fatal.
    Gut bacteria and S aureus colonization

    The study began with the researchers collecting fecal samples from 200 healthy volunteers from rural Thailand. They were looking to see whether natural probiotic bacteria in the gut could have an impact on S aureus intestinal colonization; they chose this particular population because they theorized that rural residents would be less likely than urban residents to be affected by food sterilization and antibiotics, which can alter the intestinal microbiota.
    While S aureus is most frequently found in the nose, with studies showing persistent nasal carriage in as many as 30% of individuals, there is increasing evidence of intestinal carriage. The authors suggest this could explain why topical decolonization efforts targeted at the nose have had only partial success.
    Analysis of bacteria grown from the fecal samples found that 25 of the 200 (12.5%) volunteers carried S aureus in their intestines, and 26 out of 200 (13%) carried the bacterium in their nose. When they compared the overall gut microbiome composition of S aureus carriers with non-carriers, they found little difference.
    However, 101 of the 200 (50.5%) volunteers were found to have species of Bacillus bacteria in their intestines, mainly Bacillus subtilis. Bacillus bacteria are commonly found in soil and water, and tend to be ingested with vegetables (they can even survive the high temperatures used to cook vegetables). In addition, many Bacillus species can be found in probiotics.
    Surprisingly, none of the volunteers with B subtilis in their gut had S aureus in their intestines or their nostrils.
    Because no other substantial differences in microbiome composition were observed, that finding suggested that Bacillus might be inhibiting intestinal colonization by S aureus. But when the researchers exposed S aureus bacteria to 105 of the Bacillus isolates in lab experiments, they saw only minor growth inhibition in six of the isolates.
    Another explanation soon became clear, with experiments revealing that all of the Bacillus isolates secreted molecules that block quorum sensing—the process by which bacterial cells communicate with each other and alter gene expression in response to cell population density. The researchers identified these molecules as fengycins, a class of lipopeptides.
    The researchers then tested their theory about Bacillus in mice that had different strains of S aureus—including the USA300 MRSA strain, which causes most community-acquired MRSA infections—pumped onto their stomachs. Feeding the mice spores of B subtilis eliminated the S aureus strains in the mice intestines and feces over the course of 7 days. In a comparative test using a mutant strain of B subtilis that was engineered not to produce fengycins, S aureus colonization was not affected.
    Detailed mechanism

    "Our study presents a detailed molecular mechanism that underlines the importance of probiotic nutrition in reducing infectious disease," the authors of the study write. "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 signaling system."
    The next step for the research team will be to test whether a probiotic product containing only B subtilis can eliminate S aureus in people. In theory, using a probiotic for S aureus decolonization could reduce the risk for Staph infections and reduce the need for mupirocin, a topical antibiotic used to eliminate MRSA from the nose. The authors also suggest that fengycins could possibly play a role in fighting MRSA infections.
    Even though the findings are preliminary, NIAID Director Anthony S Fauci, MD, said the study is important because it provides scientific evidence for how probiotics may work to benefit intestinal health. To date, such evidence has been scarce. "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," Fauci said in a National Institutes of Health (NIH) press release.
    See also:
    Oct 10 Nature abstract
    Oct 10 NIH press release