Final answer:
For a blood culture, isopropyl alcohol should be used to disinfect the site by rubbing it for 30 seconds to a minute to prevent contamination.
Step-by-step explanation:
When preparing for a blood culture, it is critical to disinfect the site thoroughly to prevent contamination. Use isopropyl alcohol to rub the chosen area for at least 30 seconds to a minute, ensuring that the entire area is covered effectively. This action helps in reducing the potential contaminants on the skin surface which can lead to false positive results in the culture.