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28 Mar


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Bacteria can be classified into two groups based on their oxygen needs.  Obligate aerobes and anaerobes.  Aerobes require oxygen for growth because they perform respiratory metabolism which utilizes oxygen as a final electron acceptor.  Anaerobes can be further divided into … Continue reading

14 Mar

Differential and Selective Media

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Media can be made with different components that will promote the growth of certain bacteria while inhibiting the growth of others.  This medium is known as a selective medium.  Antibiotics, dyes, and various inhibitory compounds are often incorporated into media … Continue reading

28 Feb

Nutritional Requirements of Bacteria

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Bacteria can be divided into groups based on their nutritional requirements and how they obtain nutrients.  Organisms can be divided into two groups based on their carbon requirements: heterotrophs and autotrophs.  Heterotrophs obtain their carbon from organic compounds like lipids, … Continue reading

14 Feb

Motility Determination

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The motility of bacteria can be determined by several methods.  It can be determined microscopically by observing cells in a wet mount.  In this method a drop of cells is placed on a microscope slide and covered with a cover … Continue reading

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

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