3Tues_Spore and capsule stains

3Tues_Spore and capsule stains - Lab Exercise 9: Special...

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Lab Exercise 9: Special stains for cell structures: spore and capsule stains OBJECTIVES 1. Understand the chemical basis for the spore and capsule stains. 2. Perform a successful spore stain to differentiate between bacterial spores and vegetative cells. 3. Perform a successful capsule stain to distinguish capsular material from the bacterial cell. INTRODUCTION The spore stain Certain bacterial species, most commonly gram-positive bacilli such as those of the genera Bacillus and Clostridium , undergo a complex developmental cycle that produces a resting endospore when faced with environmental adversity. The process of sporulation allows the bacteria to survive in harsh environmental conditions such as low nutrients, high temperatures, UV radiation, acids and toxic chemicals. If conditions improve, the spore may germinate to form a new vegetative cell and growth will resume. Endospores are very dehydrated structures that are not metabolically active. They possess a protein coat, called an exosporium , that forms a barrier around the spore. Since endospores are not easily destroyed by heat or chemicals, they define the conditions necessary to extablish sterility. For example, to destroy endospores by heating, they must be exposed for 15-20 minutes to steam under pressure, which generates temperatures of 121° C. Such conditions are produced in an autoclave , discussed in Lab Exercise 3. These resistant properties also mean they are not easily penetrated by stains.
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3Tues_Spore and capsule stains - Lab Exercise 9: Special...

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