Bacillus stearothermophilus (or Geobacillus stearothermophilus)^[1] is a rod-shaped, Gram-positive bacterium and a member of the division Firmicutes. The bacteria is a thermophile and is widely distributed in soil, hot springs, ocean sediment, and is a cause of spoilage in food products. 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 in indicates sterilization conditions were achieved, otherwise the growth of the spores indicates that the sterilization process has not been met.

Examples of this type of Biological Indicator (BI) using this bacillus are Getinge's Biosign Steam-24. BIs are used in conjunction with Chemical Indicators (CI) and Process Indicators (PI) to validate sterilization processes.

Molecular Biology

Recently, a DNA polymerase, Bst polymerase, derived from these bacteria has become important in molecular biology applications.

Bst DNA Polymerase has a helicase-like activity making it able to unwind DNA strands. Its optimum functional temperature is between 60-65°C and is denatured at temperatures above 70ºC These features make it useful in isothermal nucleic acid amplification ^[2]. Isothermal amplification is similar to PCR but does not require the high temperature (96°C) step required to denature DNA.

References

1. ↑ http://ijs.sgmjournals.org/cgi/reprint/51/3/795.pdf
2. ↑ http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1373654