Bacillus subtilis is a bacterium commonly found in soil, water, and the gastrointestinal tracts of humans and animals. This organism is highly regarded for its widespread use in consumer products and industrial applications due to its robust nature. Given its prevalence, many people question the safety of B. subtilis for human consumption and interaction. This article examines the safety profile of this organism and explores the rare instances where it might pose a risk.
What Bacillus Subtilis Is
Bacillus subtilis is a rod-shaped, Gram-positive bacterium belonging to the genus Bacillus. It is historically known by common names such as the hay bacillus or grass bacillus. Its natural habitat is the upper layers of the soil, where it is found in high concentrations, and it is also a common microbe in the human gut.
A key feature of B. subtilis is its ability to form a tough, protective endospore when environmental conditions become unfavorable, such as during heat or desiccation. This spore formation allows the bacterium to survive extreme conditions, like heat and stomach acid, making it highly resilient. Due to its long history of safe use and lack of disease-causing traits, the U.S. Food and Drug Administration (FDA) often recognizes various strains of B. subtilis as Generally Recognized as Safe (GRAS) for use in food products.
Uses in Human Health and Industry
The resilience of B. subtilis spores makes it valuable across a wide range of human health and industrial applications. This characteristic is beneficial in the probiotic supplement market, where spore-based strains are favored for their ability to survive the acidic environment of the stomach. Once in the intestine, the spores germinate, and the bacteria may help modulate the gut microbiome, potentially promoting the growth of beneficial bacteria.
Specific strains of the bacterium are also integral to traditional food fermentation processes. The Japanese food natto and the Korean food cheonggukjang, both fermented soybean products, rely on B. subtilis var. natto to achieve their characteristic textures and flavors. This long history of consumption in fermented foods supports its general safety profile.
Beyond direct consumption, B. subtilis is one of the most widely utilized microorganisms on an industrial scale for its capability to produce and secrete enzymes. Biotechnology companies use it as a microbial cell factory to produce enzymes like amylases and proteases, which are then integrated into products such as laundry detergents and specialty chemicals.
Addressing the Potential for Harm
While B. subtilis is overwhelmingly considered safe for the general population and is a common ingredient in health and food products, rare instances of harm have been documented. The organism is not considered a primary pathogen, meaning it does not possess inherent virulence factors designed to cause disease in healthy individuals. However, it can act as an opportunistic pathogen in specific, compromised hosts.
Infections attributed to B. subtilis, such as bacteremia, endocarditis, pneumonia, and septicemia, are almost exclusively found in patients with severely compromised immune systems. These infections typically require a weakened host and a high bacterial load, often occurring in hospital settings. The bacteria can be directly introduced through medical devices or procedures.
There have also been associations between B. subtilis and cases of food poisoning, which are a separate concern from infection. In these instances, the illness is not caused by the live bacteria infecting the person, but by heat-stable toxins produced by certain strains of the Bacillus group in contaminated food. One such toxin is amylosin, which is produced by some foodborne strains of B. subtilis when they grow in improperly stored food. These food poisoning incidents are related to poor food handling that allows for bacterial growth and toxin production, rather than the consumption of approved probiotic or fermented strains.