Why is it permissible to use same tip when plating out from highest to lowest dilution?

Using the same tip when plating samples from highest to lowest dilution is permissible because it minimizes the risk of cross-contamination between samples at different dilution levels. Since the highest dilution contains the fewest cells, any residual sample on the tip is less likely to affect the lower dilutions significantly. This practice can increase efficiency and reduce waste while still providing reliable results, as long as proper sterile techniques are followed. However, it’s crucial to ensure that the tips are changed after the lowest dilution to prevent any carryover effects in subsequent experiments.