Bacterial Staining: After participating in this topic, students will be able to perform simple stains and several differential staining techniques that are used to observe unique molecules and structures found in various bacterial genera. The Gram stain, which aids in differentiating bacterial cell wall structure, the acid-fast stain, which detects mycobacteria, and the endospore stain, which detects endospore-forming bacteria, are useful for identification of these unique microorganisms. (Online) Manipulation of Microorganisms - Methods of Culture Transfer, Pure Culture Isolation, and Antimicrobial Testing: After participating in this lab, students will be able to use aseptic technique to transfer bacteria from one medium to another, use the streak-plate method to isolate bacterial colonies, and use the Kirby-Bauer disk diffusion assay to test for bacterial sensitivity to antibiotics, antiseptics, and disinfectants. The results of antimicrobial testing can help determine if a bacterial isolate is susceptible or resistant to various antibiotics, and may help direct a clinician to an effective treatment.
Objectives:
- Describe the rationale for the steps required to prepare a bacterial smear.
- Compare and contrast the staining characteristics of three species of bacteria using positive and negative staining techniques.
- Name four positive stains and two negative stains, and explain how their chemical charge affects staining of bacteria.
- Describe the morphology and cellular arrangement of two species of bacteria.
- Describe the steps of a Gram stain, and illustrate the type of cell wall structure present in Gram-negative and Gram-positive bacterial cell walls.
- Identify two acid-fast positive and two acid-fast negative bacteria, and describe the method and steps used in an acid-fast stain.
- Explain why the unique molecule found in the cell wall of an acid-fast positive bacterium causes this bacterial genus to be difficult to stain.
- Describe the method and steps of an endospore stain, and illustrate the staining characteristics of endospores and vegetative cells.
- Identify three bacterial species that form endospores and describe the disease caused by each one.
- Identify the distinguishing chemical found in the coat of endospores and explain its significance in the resistance of endospores to various chemicals/treatments.
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