Bacterial Morphology and Staining Techniques
Exercise 1: Direct and Negative Stains
Questions -
A. What is the purpose of heat fixing? Why did the slides need to be heat fixed during the direct stain but not during the negative stain? Heat fixing kills bacterial which allows them to adhere to the slide, it coagulates cytoplasmic proteins to make them more visible. Moreover, the slides needed to be heat fixed during direct stain and not during negative stain because these bacteria are too fragile for heat-fixing and disrupt specimen.
B. Define the three major types of bacterial shapes. Which of these did you observe in the exercise? Coccus- spherical in shape, Bacillus- rod shaped and spiral -twisted in shape.
C. Is Crystal Violet a basic substance or an acidic substance? Is Congo red a basic or an acidic substance? Describe how you were able to arrive at this conclusion and relate your findings to your experimental observations. Crystal violet, a dark purple dye also called methyl violet 10B which like many staining dyes, is acidic.
Exercise 2: Differential Stains
Questions
A. Describe the difference between Gram-negative and Gram-positive bacteria. Which type of bacteria are most often treatable with antibiotics and why?
B. List the steps of the Gram stain technique and describe the purpose of each. Be sure to include a description of what color the bacteria appear during each step.
C. What is the major advantage of a differential stain, such as the Gram stain, over a simple stain? Was this observed in your experiment?
Attachment:- Assignment.rar