The omitted step in a Gram stain method that allow differentiation of Gram-positive and Gram-negative cells. Given: “Gram stain” “differentiation “and “ omitted step ” Introduction: In 1884, the Danish scientist Hans Christian Joachim Gram is discovered the Gram staining procedure to differentiate the bacteria into two groups, Gram-positive and Gram-negative. It is the preliminary step to identify the staining characteristics of bacteria based on the morphology and arrangement, which is observed under the light microscope. The main principle of Gram stain is used to differentiate based on the color retaining ability of the stain. Gram-positive bacteria retains crystal violet and appears violet or purple in color under the microscope. Since, the cell wall of Gram-positive bacteria contain thicker peptidoglycan layer. So, it retains the stain during ethanol decolonization step. Whereas in the Gram-negative with thinner peptidoglycan layer denatured during ethanol step and retains the secondary stain (safranin) and appears pink color under the microscopic examination.

Question

1. Why is it important to use a small amount of bacteria when making a smear? Give at least 2 reasons. 2. What are the two reasons for “fixing” a smear? 3. Simple staining is useful for determining what three characteristics of a bacterial cell? 4. With respect to bacteria, define morphological arrangement. Explain thoroughly!

Answer 1

Question

Chapter 3, Problem 1A

Summary Introduction

To write:

The omitted step in a Gram stain method that allow differentiation of Gram-positive and Gram-negative cells.

Given:

“Gram stain” “differentiation “and “omitted step”

Introduction:

In 1884, the Danish scientist Hans Christian Joachim Gramis discovered the Gram staining procedure to differentiate the bacteria into two groups, Gram-positive and Gram-negative. It is the preliminary step to identify the staining characteristics of bacteria based on the morphology and arrangement, which is observed under the light microscope.

The main principle of Gram stain is used to differentiate based on the color retaining ability of the stain. Gram-positive bacteria retains crystal violet and appears violet or purple in color under the microscope. Since, the cell wall of Gram-positive bacteria contain thicker peptidoglycan layer. So, it retains the stain during ethanol decolonization step. Whereas in the Gram-negative with thinner peptidoglycan layer denatured during ethanol step and retains the secondary stain (safranin) and appears pink color under the microscopic examination.

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1. Why is it important to use a small amount of bacteria when making a smear? Give at least 2 reasons. 2. What are the two reasons for “fixing” a smear? 3. Simple staining is useful for determining what three characteristics of a bacterial cell? 4. With respect to bacteria, define morphological arrangement. Explain thoroughly!

2. Explain the relationship between bacterial cell wall with gram positive and gram negative in the staining process. Please state the chemicals used and their functions.

7. Use the image to answer the following questions: (2) A student collects some of this bacteria to create a slide then performs a Gram stain as shown here: A. How many different types of bacteria are growing on the petri dish? B. How do you know (how can you tell the difference between the types of bacteria)? C. What is the Gram reaction and morphology of these cells? D. Based on the Gram stain, could this colony be used to grow pure culture? How do you know?