page_title: Mechanism of action
section_title: Microscopy-based methods
hierarchical_section_title: Mechanism of action / How mechanism of action is determined / Microscopy-based methods
caption_attribution_description: English: A Bacillus cereus cell that has undergone filamentation following antibacterial treatment
context_page_description: In pharmacology, the term mechanism of action refers to the specific biochemical interaction through which a drug substance produces its pharmacological effect. A mechanism of action usually includes mention of the specific molecular targets to which the drug binds, such as an enzyme or receptor. Receptor sites have specific affinities for drugs based on the chemical structure of the drug, as well as the specific action that occurs there.
  Drugs that do not bind to receptors produce their corresponding therapeutic effect by simply interacting with chemical or physical properties in the body. Common examples of drugs that work in this way are antacids and laxatives.
  In contrast, a mode of action describes functional or anatomical changes, at the cellular level, resulting from the exposure of a living organism to a substance.
context_section_description: Bioactive compounds induce phenotypic changes in target cells, changes that are observable by microscopy, and which can give insight into the mechanism of action of the compound.
  With antibacterial agents, the conversion of target cells to spheroplasts can be an indication that peptidoglycan synthesis is being inhibited, and filamentation of target cells can be an indication that PBP3, FtsZ or DNA synthesis is being inhibited.  Other antibacterial agent-induced changes include ovoid cell formation, pseudomulticellular forms, localized swelling, bulge formation, blebbing and peptidoglycan thickening.  In the case of anticancer agents, bleb formation can be an indication that the compound is disrupting the plasma membrane.
  A current limitation of this approach is the time required to manually generate and interpret data, but advances in automated microscopy and image analysis software may help resolve this.
caption: Filamentation (top right) can indicate that an antibacterial agent is targeting PBP3, FtsZ or DNA.[4]
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