You are watching: What is the purpose of using a control in the gram stain
Article Summary: Bacterial controls are regularly used v differential stains as instances of common positive and an adverse stain reactions; a advantageous reference once identifying unknowns.
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Left to Right: Gram, Acid-fast & Endospore-stained slides of bacterial smears with hopeful controls on either finish of slide and unknown in center.
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The Acid-fast stain is specifically offered to determine bacteria that possess a waxy lipid in ~ the structure of their cell walls, mycolic acid. Due to the existence of this lipid, water-based stains, such as the Gram stain, perform not work-related well top top Acid-fast organisms. This protocol utilizes warm to drive the main stain right into waxy bacterial cell walls.
The Gram stain classifies almost all bacteria into one the two groups (Gram+ or Gram-), based upon characteristics the the bacterial cell wall, particularly the location and amount that the cell wall's main structural molecule, peptidoglycan.
Bacteria that have cell walls entirely made that peptidoglycan will stain Gram-positive. When prepare a Gram stain slide, a positive control would it is in a kind of bacterium the is well-known to stain Gram+, such as Staphylococcus.
Differential stains are regularly used for basic identification that bacteria, rather than identifying the precise species. Examples incorporate the Gram stain, Acid-fast stain and also Endospore staining protocols.
When act a differential stain, it is finest to use controls to help identify the stain reaction of the unknown bacteria. Controls are varieties of bacteria the are known to show a certain, details stain reaction.
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Very couple of types of bacteria can form endospores; most notably Bacillus and Clostridium. For this reason a positive regulate for the Endospore stain would be a bacterium the produces endospores; a negative control would certainly be any form of bacteria that room not endospore producers.