Staphylococcus aureus (S.aureus), a bacterium present on human skin and mucous membranes, is typically harmless but can cause a multitude of serious and often fatal infections. Complicating treatment is pervasive antibiotic resistance, such as in methicillin-resistant S. aureus (MRSA) which has led to rising death tolls globally. A search for alternative therapies has involved the recognition of interactions between S. aureus and the gut microbiota. This blog explores the research regarding the interface between S. aureus infections and gut microbiota as well as the potential of modification of gut microbiota through oral probiotics to reduce infection or its harms.
S. aureus, in brief
An opportunistic pathogen, S. aureus colonizes the skin, nasal cavities, and intestines of many people who show no symptoms or infections.
But trouble arises with compromising conditions such as type 1 diabetes, immunodeficiency, and undergoing hemodialysis or surgery. Infections can range from minor skin and soft-tissue infections to severe forms such as sepsis, endocarditis, pneumonia, and more.
S. aureus has earned a prominent place on the unenviable ESKAPE list of nosocomial (hospital-acquired) pathogens, which cause life-threatening infections and are often resistant to antibiotic medications. MRSA is a significant contributor to the millions of deaths attributed to antibiotic resistance annually across the world.
Since S. aureus infections often stem from asymptomatic colonization, decolonization with antibiotics has been the primary approach to therapy. Yet, in addition to increasing antibiotic resistance, these medications can also disrupt the healthy microbiota.
New avenues to enhance decolonization are needed. Researchers are exploring the foundations of S. aureus‘s impact on the microbiota and suggesting new avenues to decolonize effectively.
S.aureus and the gut microbiota
Studies have shown that S. aureus infections, whether in cows, mice, or humans, lead to changes in the intestinal microbiota, such as increased pathogenic bacteria and decreased beneficial SCFA-producing bacteria. For example, S. aureus can adhere to human intestinal mucus and impact gut microbial homeostasis. Dysbiosis involving S. aureus may disturb the intestinal immune system, affecting overall immune status or enabling bacterial translocation through the blood to other tissues and organs in the body.
Additionally, gastrointestinal colonization by S. aureus and MRSA in particular increases the risk of invasive infections and environmental contamination through fecal shedding, highlighting the importance of maintaining a balanced gut microbiota to prevent MRSA overgrowth.
Probiotics and S. aureus decolonization
Preventing infection and lessening severe outcomes through pathogen reduction demands newer therapies beyond antibiotics. Methods to decolonize and maintain gut microbial homeostasis include probiotics, which have been used to enhance the immune system function, improve digestive system health, and prevent/treat multiple diseases.
Animals
Research has shown that treating mice with a combination of lactic acid bacteria can prevent S. aureus infection and restore the intestinal microbiota structure disrupted by the infection.
Humans
In humans, one study found a “complete correlation” between Bacillus colonization and the absence of S. aureus colonization, based on the analysis of fecal CFU. The researchers said, “Most strains of Bacillus spp. that we studied, including most strains of B. subtilis, secrete molecules that specifically inhibit S. aureus quorum-sensing, a mechanism we demonstrated is essential for S. aureus intestinal colonization.”
A study conducted in Thailand tested an oral dose of B. subtilis in this regard. Healthy participants (84 with intestinal and 50 with nasal S. aureus colonization) received 250 mg of a specific strain of probiotic B. subtilis or placebo once daily for 30 days and S. aureus colonization was ascertained after the last dose. In the probiotic group, there was a significant reduction of S. aureus in the stool (96.8%) and nose (65.4%) compared to the placebo group without significant changes to the broader composition and diversity of the intestinal microbiota. Notably, the researchers conjectured that the results suggested that decolonization efforts should primarily target the intestinal site, or at least include it alongside nasal colonization.
Takeaway
Staphylococcus aureus can cause serious infections, particularly in individuals with compromised health, and its treatment is complicated by antibiotic resistance as with MRSA. Recent research indicates that modifying gut microbiota through oral probiotics, such as B. subtilis, can reduce S. aureus colonization. One study showed a reduction of a large portion (> 95%) of the total number of S. aureus colonizing humans without an increase in reported adverse side effects. Probiotic therapy may be a promising alternative or supplement to traditional antibiotic therapies—which may trigger resistance— especially in sites with numerous S. aureus infections, such as long-term care facilities or surgical units.
Image by PublicDomainPictures from Pixabay
Key references
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