What indicates that growth has occurred during a sterility test with Bacillus stearothermophilus?

The correct indication that growth has occurred during a sterility test with Bacillus stearothermophilus is a color change in the growth medium. This bacterium is commonly used in sterility testing due to its heat resistance, which makes it an excellent challenge organism for validating sterilization processes.

When Bacillus stearothermophilus is introduced into a culture medium that contains specific indicators, the metabolic activity of the growing bacteria causes a change in the pH of the medium. This pH change will typically result in a visible color shift, which serves as a clear visual cue that microbial growth has taken place.

In contrast, no change in the growth medium would indicate that no microbial growth occurred, suggesting that the sterilization process was effective. Increased temperature in the vial might suggest metabolic activity, but it is not a direct indicator of growth. Decreased pressure in the vial does not typically relate to the growth of Bacillus stearothermophilus during a sterility test and would not be a reliable measure for assessing microbial viability. Thus, observing a color change provides the most definitive evidence of bacterial growth in this context.