Difference Between Acid Fast and Non Acid Fast Bacteria

Main Difference – Acid Fast vs Non Acid Fast Bacteria

Acid fastness is a physical character of bacteria, which can be described as the resistance to decolorization by acids during staining procedures such as Gram staining. The acid-fast staining is used to differentiate bacteria as acid fast and non acid fast bacteria. The most commonly used acid-fast staining technique is Ziehl-Neelsen stain. Three different reagents are used in acid-fast staining. They are carbol-fuchsin as the primary stain, acid-alcohol as decolorizing agent, and methylene blue as the counterstain. A few genera of bacteria such as Mycobacterium can only be visualized by acid-fast staining. Some protozoa also exhibit acid fastness. The main difference between acid fast and non acid fast bacteria is that acid fast bacteria resist decolorizing by acid after accepting a stain whereas non acid fast bacteria are readily decolorized by acid after staining.    

Key Areas Covered

1. What are Acid Fast Bacteria
      – Definition, Features, Examples
2. What are Non Acid Fast Bacteria
      – Definition, Features, Examples
3. What are the Similarities Between Acid Fast and Non Acid Fast Bacteria
      – Outline Of Common Features
4. What is the Difference Between Acid Fast and Non Acid Fast Bacteria
      – Comparison of Key Differences

Key Terms: Acid Fast Bacteria, Acid Fast Staining, Carbol-fuchsin, Mycobacterium Tuberculosis, Mycolic Acid, Non Acid Fast Bacteria

What are Acid Fast Bacteria

The acid fast bacteria are a type of bacteria that resist decolorizing by acid after staining. Acid fastness is a physical property of bacteria, which rely on the structure of the bacterial cell wall. Typically, the cell wall of bacteria is made up of proteins, carbohydrates, and lipids. Acid fast bacteria comprise a thin layer of peptidoglycans. The mycolic acid is a long chain of fatty acids, attached to the peptidoglycans. Once the primary stain, carbol-fuchsin is added to the slide containing bacteria, the mycolic acid is attached to carbol-fuchsin. This makes the acid fast bacteria to stain in pink even after decolorization.

Figure 1: Acid Fast Bacteria

Mycobacteria is a common type of bacteria, which grows slowly; hence, they are composed of a thick layer of mycolic acid. In addition to mycolic acid, acid fast bacteria consist of a large amount of fatty acids, complex lipids, and waxes. Due to the presence of thick bacterial cell wall, acid fast bacteria are highly resistant to disinfectants as well as dry conditions. The cell wall structure and the staining of acid fast bacteria are shown in figure 1. 

What are Non Acid Fast Bacteria

The non acid fast bacteria are a type of bacteria that are readily decolorized by acid after staining. During the decolorizing, when the microscopic slide with bacteria is washed from a strong decolorizer, all the carbol-fuchsin is washed away from the bacterial smear. Then the counterstain is taken up by the non acid fast bacteria and this shows a blue color under the microscope.

Figure 2: Ziehl-Neelsen Staining Procedure

Since carbol-fuchsin stain is incapable of penetrating the cell wall of the non acid fast bacteria, the cell wall of the non acid fast bacteria does not keep the stain. The basic steps of the Ziehl-Neelsen staining procedure are shown in figure 2. 

Similarities Between Acid Fast and Non Acid Fast Bacteria

• Acid fast bacteria and non acid fast bacteria can be differentiated by acid –fast staining techniques.
• The cell wall structure of bacteria is involved in the differentiation of both acid fast and non acid fast bacteria.

Difference Between Acid Fast and Non Acid Fast Bacteria

Definition

Acid Fast Bacteria: The acid fast bacteria are a type of bacteria that resist decolorizing by acid after staining.

Non Acid Fast Bacteria: The non acid fast bacteria are a type of bacteria that are readily decolorized by acid after staining.

Final color

Acid Fast Bacteria: The final color of the acid fast bacteria is pink or red.

Non Acid Fast Bacteria: The final color of the non acid fast bacteria is blue.

Significance

Acid Fast Bacteria: Acid fast bacteria are stained with the primary stain.

Non Acid Fast Bacteria: Non acid fast bacteria are stained with the counter stain.

Mycolic Acid

Acid Fast Bacteria: Acid fast bacteria consist of mycolic acid in their cell wall.

Non Acid Fast Bacteria: Non acid fast bacteria lack mycolic acid.

Examples

Acid Fast Bacteria: Mycobacterium is an example of acid fast bacteria.

Non Acid Fast Bacteria: Escherichia coli is an example of acid fast bacteria.

Conclusion

Acid fast and non acid fast bacteria are two types of bacteria, which can be differentiated based on the presence of mycolic acid in the cell wall of the bacteria. Acid-fast staining is the technique used in discriminating the two types of bacteria. Acid fast bacteria are composed of mycolic acid in their cell wall; hence, they are stained in pink by the primary stain, carbol-fuchsin. Since non acid fast bacteria lack mycolic acid in their cell wall, they are incapable of retaining the primary stain. Thus, the main difference between acid fast bacteria and non acid fast bacteria is the differential staining of each type of bacteria in the acid-fast staining technique.

Reference:

1.”Acid-Fast Bacteria: Definition & Examples.” Study.com. N.p., n.d. Web. Available here. 10 July 2017. 
2. “Acid Fast Stain.” Welcome to Microbugz. N.p., n.d. Web. Available here. 10 July 2017. 

Image Courtesy:

1. “OSC Microbio 03 03 acidfast” By CNX OpenStax – (CC BY 4.0) via Commons Wikimedia
“Acid Fast Stain” by Elizabeth Gray (CC BY-SA 4.0) via Commons Wikimedia