Module 8: Lab 8 Acid-Fast Staining (Ziehl–Neelsen Method)

Acid-fast staining is a specialized differential staining technique used to identify bacteria with unique cell walls that contain high concentrations of waxy lipids, particularly mycolic acids. These lipids make the cells resistant to conventional staining methods and allow them to retain the primary stain even after treatment with strong decolorizing agents. This characteristic is especially important for the identification of clinically significant organisms, such as species of Mycobacterium. In this module, students will examine the structural basis of acid-fastness, learn the principles behind the acid-fast staining procedure, and practice performing and interpreting an acid-fast stain to distinguish acid-fast bacteria from non–acid-fast organisms using the microscope.

Slide made by Fletcher Technical Community College student Nicola Ladner. Image captured by Professor Erica A. Burns

Course Learning Objectives

1. Explain the purpose of the acid-fast stain. (CO#2)
2. Identify the cell wall substance unique to acid-fast bacteria that allows them to retain the carbolfuchsin stain. (CO#2)
3. Identify the decolorizer used in the acid-fast staining procedures. (CO#2)
4. List groups of pathogenic organisms that stain acid-fast. (CO#5)
5. Perform a Ziehl–Neelsen acid-fast stain. (CO#2,3,4)
6. Distinguish acid-fast (positive) from non-acid-fast (negative) bacteria on a slide using a microscope. (CO#4,6)

To achieve these objectives:

1. Read the Module # Introduction 
   
2. Read and view the materials in the Module #8, Acid-Fast Staining PowerPoint, and Pressbooks book chapter
   
3. Read Lab 8 in Medical Microbiology for Nursing and Allied Health Lab Manual
   
4. Complete the Lab 8 Acid-Fast Post Lab Questions Quiz

Module Pressbooks Resources and Activities