Staphylococcus aureus is recognized as one of the most important bacteria that cause disease in humans. It is the leading cause of skin and soft tissue infections. Infections caused by this pathogen are common in community-acquired and hospital-acquired settings. Treatments can be challenging due to multi-drug resistant strains such as MRSA (Methicillin-Resistant Staphylococcus aureus). Now, a new study by researchers at the National Institutes of Health (NIH) led by Michael Otto, PhD, an NIH senior investigator at the National Institute of Allergy and Infectious Diseases (NIAID), demonstrates using a probiotic to control S. aureus instead of antibiotics—was safe and highly effective in a Phase II clinical trial.

The study is published in the Lancet Microbe in an article titled, “Probiotic for pathogen-specific Staphylococcus aureus decolonization in Thailand: a Phase II, double-blind, randomized, placebo-controlled trial.”

“Decolonization is considered a valuable means to reduce S. aureus infection rates,” wrote the researchers. “However, previous topical strategies targeting the nose or skin had little success, and oral antibiotic-based decolonization 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 colonization site via specific bacterial interaction in mice; in this study, we tested this probiotic approach to control S. aureus colonization in humans.”

In the clinical trial, conducted in Thailand, the research team tested whether this approach works in people. They enrolled 115 healthy participants, all of whom were colonized naturally with S. aureus. A group of 55 people received B. subtilis probiotic once daily for four weeks; a control group of 60 people received a placebo. After four weeks researchers evaluated the participants’ S. aureus levels in the gut and nose. They found no changes in the control group, but in the probiotic group they observed a 96.8% S. aureus reduction in the stool and a 65.4% reduction in the nose.

“The probiotic we use does not ‘kill’ S. aureus, but it specifically and strongly diminishes its capacity to colonize,” Otto said. “We think we can target the ‘bad’ S. aureus while leaving the composition of the microbiota intact.”

The researchers also observed that levels of S. aureus bacteria in the gut exceeded S. aureus in the nose, which has been the focus of staph infection prevention research. This finding adds to the potential importance of S. aureus reduction in the gut.

“Intestinal S. aureus colonization has been evident for decades, but mostly neglected by researchers because it was not a viable target for antibiotics,” Otto said. “Our results suggest a way to safely and effectively reduce the total number of colonizing S. aureus and also call for a categorical rethinking of what we learned in textbooks about S. aureus colonization of the human body.”

Looking toward the future, the researchers plan to continue their work by testing the probiotic in a larger and longer trial. They noted that their approach probably does not work as quickly as antibiotics, but can be used for long periods because the probiotic as used in the clinical trial does not cause harm.