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Here are my most recent posts

31 Jan

Motility of Bacteria

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The motility of bacteria is provided by the flagella, a rigid helical structure that extends up to 10  microns out from the cell.  Flagella allow cells to move towards nutrients or away from harmful substances such as acids in a … Continue reading

17 Jan

Acid Fast Staining

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Acid fast staining is used to stain bacteria with mycolic acid in their cell walls.  The Ziehl-Neelsen staining method is used which involves mixing carbolfuchsin with phenol and heating the cells for 5 minutes.  Phenol allows the penetration of carbolfuchsin … Continue reading

03 Jan


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Bacteria such as mycobacterium have cell walls that contain a high lipid content.  One of the cell wall lipids is a waxy material called mycolic acid.  Mycolic acid is a complex lipid that is made of fatty acids and fatty … Continue reading

20 Dec

Spore Staining

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In the previous post we discussed the unique properties of endospores.  These unique properties mean that they are not easily penetrated by stains.  If endospore containing cells are stained by crystal violet, the spores appear as unstained areas in the … Continue reading

06 Dec


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When bacteria belonging to the genus Bacillus or Clostridium run out of essential nutrients, they produce endospores.  Endospores allow the bacteria to survive extreme conditions that are not optimal for growth.  If conditions become favorable, the endospore can go through … Continue reading

22 Nov

Gram Stain

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In 1884 the Danish physician Christian Gram developed a new type of stain known today as the gram stain.  He attempted to design a stain that differentiated bacterial cells from eukaryotic cells however he failed.  What resulted from his work … Continue reading

08 Nov

Capsular Staining

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Capsular staining is a technique used to stain species of bacteria that are surrounded by an extracellular slime layer called a capsule or glycolayx.  This structure provides protection for bacteria such as streptococcus pneumoniae.  The capsule prevents phagocytic white blood … Continue reading

25 Oct

Negative Staining

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Negative staining can be used to study the morphology of bacterial cells and characterize some of the external structures, such as capsules, that are associated with bacterial cells.  Negative stains are acidic and have a negatively charged chromophore that does … Continue reading

11 Oct

Simple Stain

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Using a single stain to color a bacterial cell is commonly referred to as a simple stain.  The most common dyes for this type of stain are methylene blue, fuchsin, and crystal violet.  These dyes work well because they have … Continue reading

27 Sep

Smear Preparation

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Bacterial smear preparation is an integral technique in microbiology laboratories.  There are several objectives when preparing a smear.  The first is to make sure that the cells adhere to the microscope slide so that they do not get washed off … Continue reading

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