A mode of action (MoA) describes a functional or anatomical change, resulting from the exposure of a living organism to a substance. In comparison, a mechanism of action (MOA) describes such changes at the molecular level.
A mode of action is important in classifying chemicals, as it represents an intermediate level of complexity in between molecular mechanisms and physiological outcomes, especially when the exact molecular target has not yet been elucidated or is subject to debate. A mechanism of action of a chemical could be "binding to DNA" while its broader mode of action would be "transcriptional regulation". However, there is no clear consensus and the term mode of action is also often used, especially in the study of pesticides, to describe molecular mechanisms such as action on specific nuclear receptors or enzymes.
Disinfectants are commonly used in order to eliminate microorganisms. The effectiveness of a disinfectant is dependent on both the chemical composition of the product as well as the contact time between the microorganism and the disinfectant. There are two main modes of action for disinfectants: growth inhibition and lethal action. In terms of mode of action, disinfectants can act on external bacterial membranes, cytoplasmic membranes, nuclei, and spores. The most common type of disinfectant is chlorine, which acts by inhibiting respiratory enzymes in bacteria. Hydrogen peroxide is another popular disinfectant that works by causing oxidative stress in cells. Quaternary ammonium compounds are often used as surface disinfectants since they can kill a variety of microorganisms including bacteria, fungi, and viruses. Phenolic compounds are also effective against a wide range of microorganisms; however, they are corrosive and can cause damage to surfaces. In general, it is important to select a disinfectant that is effective against the specific type of microorganism present as well as taking into account the potential for damage to surfaces.