Geobacillus stearothermophilus

Geobacillus stearothermophilus
Scientific classification
Domain:	Bacteria
Phylum:	Bacillota
Class:	Bacilli
Order:	Bacillales
Family:	Bacillaceae
Genus:	Geobacillus
Species:	G. stearothermophilus
Binomial name
Geobacillus stearothermophilus (Donk 1920) Nazina et al. 2001

Geobacillus stearothermophilus (previously Bacillus stearothermophilus)^[1][2] is a rod-shaped, Gram-positive bacterium and a member of the phylum Bacillota. The bacterium is a thermophile and is widely distributed in soil, hot springs, ocean sediment, and is a cause of spoilage in food products. It will grow within a temperature range of 30–75 °C. Some strains are capable of oxidizing carbon monoxide aerobically. It is commonly used as a challenge organism for sterilization validation studies and periodic check of sterilization cycles. The biological indicator contains spores of the organism on filter paper inside a vial. After sterilizing, the cap is closed, an ampule of growth medium inside of the vial is crushed and the whole vial is incubated. A color and/or turbidity change indicates the results of the sterilization process; no change indicates that the sterilization conditions were achieved, otherwise the growth of the spores indicates that the sterilization process has not been met. Fluorescent-tagged strains, known as rapid-read BIs,^[3] are becoming more common to verify sterilization, since the visible fluorescence appears in about one-tenth the time needed for pH-indicator color change and an inexpensive light sensor can detect the growing colonies.

It was first described in 1920 as Bacillus stearothermophilus,^[4] but, together with Bacillus thermoglucosidasius, it was reclassified as a member of the genus Geobacillus in 2001.^[5]