Final answer:
Biological indicator spore tests using spores from Geobacillus stearothermophilus placed in the center of a pack are the best indicators for confirming effective autoclave sterilization, as they test for the destruction of highly resistant spores and provide data on temperature and exposure time.
Step-by-step explanation:
The best indicators of proper sterilization in an autoclave when placed in the center of a large pack are biological indicator spore tests that utilize highly heat-resistant spores, such as those from Geobacillus stearothermophilus. These tests are considered the gold standard because they can definitively determine whether the sterilization process has been successful, by confirming the destruction of even the most resistant forms of bacterial life. In addition to spore tests, temperature-sensitive pellet indicators like the Diack tube can be used, which contain a pellet that melts at the appropriate sterilization temperature. However, unlike heat-sensitive tape, these tests provide information about both temperature reached and duration of exposure, ensuring complete sterilization.