Unit 4: Microbial Characteristics and Identification
In this unit, we will examine the different shapes and arrangements of bacteria and compare and contrast bacteria with other microorganisms. We will also survey some of the methods (such as plating and staining) used to distinguish between organisms in order to diagnose the causes of infection. When a sample reaches the clinical lab, differential staining enables technicians to identify the shape, arrangement, and gram stain of the organism that the sample contains. This preliminary information, along with cultures, can be used to identify pathogenic microorganisms and isolate them from normal flora.
Completing this unit should take you approximately 3 hours.
Upon successful completion of this unit, you will be able to:
- identify different bacterial shapes and arrangements;
- identify gram positive and gram negative organisms of various shapes and arrangements;
- compare and contrast the sizes of various microorganisms; and
- describe how plating and staining are used to identify different types of microorganisms.
4.1: Characteristics of Microorganisms
4.1.1: Prokaryote Shapes
Read this page. Click on every embedded hyperlink, and explore the linked contents. Finally, click on "Quiz Yourself on This Section" to test your knowledge.
4.1.2: Size of Microorganisms
Read this article, which provides some generalized information on the sizes of various microbes.
4.1.3: Morphological Characteristics
Read this article on distinguishing between the different patterns of bacterial growth for cultures grown on plates.
4.2: Identifying Microorganisms
4.2.1: Plating and Culturing
Read this article, which describes how media can be used to grow microorganisms, such as bacteria and fungi. Media is prepared using various agents that will either enhance or inhibit the growth of certain organisms.
4.2.2: Differential Staining
4.2.2.1: Gram Staining
Read these lecture slides for a demonstration of the gram staining procedure.
4.2.2.2: Acid Fast Staining
Study this short demonstration of the acid-fast staining procedure. Acid-fast staining is used to differentiate between organisms like the acid-fast positive "Mycobacterium tuberculosis" and other acid-fast negative organisms. Complete the two short review activities to evaluate how much you have learned. You will only be able to access the second activity after completing the first matching activity on the last slide of the presentation.
- Community College of Baltimore County: Gary E. Kaiser's "Lab 5: Direct Stain and Indirect Stain" URL
Complete this quiz. After clicking on the link above, scroll down to "Self-Quiz" at the bottom of the page. After completing the quiz return to the first page and click on "Answers" to see the correct answers. There is a detailed introduction to this assessment above the "Self-Quiz." Be sure to visit the "Results" section, also note that clicking on the links under the empty frames brings you to annotated micrographs.
Complete this quiz. After clicking on the link above, scroll down to "Self-Quiz" at the bottom of the page. After completing the quiz return to the first page and click on "Answers" to see the correct answers. There is a detailed introduction to this assessment above the "Self-Quiz." Be sure to visit the "Results" section, also note that clicking on the links under the empty frames brings you to annotated micrographs.