stearothermophilus

Geobacillus stearothermophilus, formerly known as Bacillus stearothermophilus, is a Gram-positive, rod-shaped, endospore-forming bacterium. It is a thermophile, with an optimum growth temperature around 55 to 65°C and the ability to grow at higher temperatures, up to about 75–80°C. The organism is typically aerobic or facultatively anaerobic and produces highly heat-resistant spores.

Taxonomy and identification have shifted with advances in molecular analysis, leading to its current placement in the genus Geobacillus. The name stearothermophilus reflects its association with fats (stearo-) and its heat-loving nature.

Ecology and physiology: G. stearothermophilus is commonly found in soil and other hot environments. It is widely distributed in nature and is not considered a human pathogen under normal circumstances. Like other Bacilli and Geobacilli, it forms endospores that can survive harsh conditions, including certain sterilization processes.

Applications: The heat-resistant spores of G. stearothermophilus are used as biological indicators to validate steam sterilization processes in healthcare and industry. Spore strips or vials containing the organism are exposed to sterilization cycles and subsequently incubated to check for growth, providing a readout of process effectiveness. The species also contributes thermostable enzymes, such as amylases and proteases, that are exploited in various industrial processes.

Safety considerations: G. stearothermophilus is generally nonpathogenic to humans. As a spore-former, it poses contamination risks in sterile products, so proper biosafety and aseptic practices are followed in laboratory and manufacturing settings.

See also: Bacillus stearothermophilus; Geobacillus; sterilization indicators.