Final answer:
Biological Indicators are used to directly determine the concentration of the most resistant microorganisms during sterilization efficacy assessments, by using endospores of microorganisms such as Geobacillus stearothermophilus.
Step-by-step explanation:
Among the methods of assessing the efficacy of sterilization, Biological Indicators directly determine the concentration of the most resistant microorganisms. This method involves the use of endospores of highly resistant microorganisms such as Geobacillus stearothermophilus. After undergoing the sterilization process, these biological indicators are incubated to ensure no viable endospores remain. The absence of bacterial growth is an indication that the sterilization method was effective.
Other methods like Chemical Indicators, Mechanical Indicators, and Physical Indicators are also used for validating sterilization processes, but they do not directly measure the resistance of specific microorganisms in the same way that biological indicators do.