Quaternary ammonium compounds are ineffective when they come in contact with:

Quaternary ammonium compounds, commonly known as quats, are surface disinfectants widely used in various settings, including healthcare. However, their effectiveness can be compromised when they come into contact with specific substances.

When quaternary ammonium compounds are mixed with bleach (a strong oxidizing agent), they can undergo a chemical reaction that neutralizes their disinfecting properties. Bleach can destroy the active ingredients in quats, rendering them ineffective as disinfectants.

Similarly, when quats come into contact with enzymes, particularly those used in cleaning agents, they can be inhibited. Enzymes are biological catalysts that break down organic materials, but their interaction with the charged molecules in quaternary ammonium compounds can lead to a loss of efficacy in disinfecting.

Thus, the combination of these two substances—enzymes and bleach—can significantly reduce the functionality of quaternary ammonium compounds. Therefore, the correct answer highlights that quaternary ammonium compounds are indeed ineffective when they encounter both enzymes and bleach, confirming that proper knowledge of their interactions with other chemicals is crucial for effective sterile processing practices.