Welcome to the Microbiology Information

Bacillus stearothermophilus or Geobacillus stearothermophilus is one of the most common spoilage bacterium in commercially sterile heat processed foods. Although most bacterium cannot survive the high temperature, Bacillus stearothermophilus has a highly heat resistant spores that has enabled this bacterium to spoil canned foods, UHT milk, and other commercially sterile foods.

So what temperature is required to kill this bacterium? How long must it be held at this temperature?

A measure used to determine the effective kill rate is called the D or D’ Value. Basically, the D Value measures the time in minutes required at a given temperature for destruction of 90% of the cells.

Although it sounds simple, it’s not. It also depends on the nature of the food product, the pH, the salt level and so forth. For example, the lower the pH, the lower the temperature required. The higher the pH or close to a neutral pH of 7, the higher the temperature is required to kill this bacterium.

Below is a graph showing the thermal inactivation of Bacillus stearothermophilus spores (ATCC 12980).

For more detailed information you can download the pdf file here on the Thermal Inactivation and Injury of Bacillus Stearothermophilus Spores.