When is a biological indicator considered positive?

A biological indicator is considered positive when there is growth in the ampule after sterilization. This growth indicates that the sterilization process was ineffective, as it signifies that viable microorganisms were present after the sterilization cycle. Biological indicators are designed to challenge the sterilization process by using specific microorganisms that are resistant to the sterilization methods being evaluated. If these microorganisms survive the process, it demonstrates a failure in achieving the desired sterility.

Visible color change is often used as a preliminary indicator for the chemical indicators but does not confirm biological viability. A specific pH level does not relate directly to the effectiveness of sterilization in this context. Declaring that all spores are non-viable relates to a successful sterilization process, but simply stating that does not address the criteria for a biological indicator to be deemed positive. Thus, growth in the ampule directly correlates with failure in sterilization, confirming its status as a positive biological indicator.