Bacillus stearothermophilus is an apathogenic and rod-shaped species of bacteria belonging to the family Bacillaceae and division Firmicutes. The bacterial species belongs to the so-called spore-formers, i.e. it forms resistant endospores under unfavorable conditions. For humans, the bacterial species is important mainly as a test germ, for example, for the control of thermal equipment for sterilization.
What is Bacillus stearothermophilus?
Bacillus stearothermophilus is a bacterial species of the family Bacillaceae, of which about 50 genera are known. The species belongs to the genus Bacillus, which belongs to the division Firmicutes. Among them, the bacterial species falls into the class Bacilli and is included in the order Bacillales. Like all bacteria from the order Bacillales, Bacillus stearothermophilus is a gram-positive bacterium with a rod shape. Many members of the Bacillales can form endospores under unfavorable conditions such as lack of food and extreme temperature. This is also true for Bacillus stearothermophilus, so that the species is classified together with the Clostridia in the group of spore-formers. Individuals of the species Bacillus stearothermophilus are thermophilic organisms and grow up to ten µm in length. The bacterial species does not cause disease and shows gram-positive staining behavior. The apathogenic bacteria are used in biotechnology, for example for sterilization processes. The species plays a role in molecular biology in that it possesses the enzyme polymerase. Polymerase can be used to cleave DNA strands. Polymerase plays a role in the polymerase chain reaction and in other methods of DNA amplification or DNA modification.
Occurrence, distribution, and properties
Bacilli of the bacterial species Bacillus stearothermophilus occur ubiquitously and enter a spore stage under poor propagation conditions. This process gives the individuals a higher resistance to certain environmental conditions. The bacterial species can even survive in 70 percent alcohol in this way. To fulfill disinfection purposes and thus kill the bacteria, the alcohol used must be sterile-filtered. The bacterial species lives obligately aerobic. This means that the individuals can survive in an oxygen-rich environment. Their metabolism is oriented toward oxygen. Under complete oxygen exclusion, unlike many other bacteria, they cannot survive. The preferred environment of Bacillus stearothermophilus is humus-rich soil. Strains of the bacterial species are also found in hot springs, in desert sand, in compost or in food. The same is true for Arctic waters and ocean floors. Due to its ability to form spores, the species is extremely heat-stable and resistant to environmental influences. Germination occurs exclusively under favorable environmental conditions. The bacteria possess DNA polymerase, a multifunctional enzyme that catalyzes the polymerization of single nucleotides into a long chain. In DNA replication, it catalyzes DNA synthesis from single deoxyribonucleotides.
Importance and function
Together with Bacillus subtilis, Bacillus stearothermophilus has high utility for humans, most notably as a test germ in the biological control of various sterilization devices. When checking autoclaves or hot air sterilizers, bacterial strains of the species are used as bioindicators and serve to determine the die-off kinetics. This is the time interval in which bacteria are killed by a setrilization device. By means of the die-off kinetics, the success of sterilization processes can thus be measured. Bacillus stearothermophilus is highly thermostable. Therefore, the test germ is mainly used in thermal sterilization to determine efficiency. The germ is placed in glass ampoules filled with a liquid nutrient medium and a color indicator. The individual ampoules are autoclaved and then incubated together with a control ampoule at 60 degrees Celsius for several days. The color change of the indicator shows the metabolic activity of the individual cells. This means that in successfully sterilized ampoules the coloration does not change. Sterilization testing using Bacillus stearothermophilus can also be performed in the form of spore strips. Strips of filter paper to which endospores of the bacterium are applied are known as spore strips.This application also usually takes place in connection with steam sterilization testing. For this purpose, the test germ is placed in spore strips in an autoclave, then placed in a nutrient solution and finally incubated. Growth does not occur if sterilization is successful. Beyond these applications, Bacillus stearothermophilus plays a role in the production of enzymes such as BstBI.
Diseases and ailments
The bacterial species Bacillus stearothermophilus is not pathogenic to humans or animals. Thus, the individual strains of the species are not pathogens. This is not unusual for bacteria from the order Bacillales and the family Bacillaceae. The family includes various apathogenic species, but on the other hand also contains facultative pathogens and obligate pathogens. Bacillus subtilis, for example, is a facultative pathogen of the family that causes disease only under certain conditions. Bacillus anthracis, on the other hand, is an obligate pathogen that necessarily causes the so-called anthrax. Unlike facultative and obligate pathogenic species, the apathogenic Bacillaceae species Bacillus stearothermophilus is not expected to cause disease under any circumstances if the bacteria come into contact with humans. Inhalation of spores of the species is also not associated with disease potential. The immune status of patients does not play a role in this regard. Whereas facultative pathogenic germs are mostly opportunistic pathogens and thus can cause disease in people with a below-average immunologic constitution, apathogenic germs such as Bacillus stearothermophilus are harmless even to immunocompromised individuals.
