What is the Difference Between Media and Medium in Microbiology

The main difference between media and medium in microbiology or any other is that the media is the plural form of medium whereas medium is the substance used to grow cells in microbiology.

Liquid media, semi-solid media, and solid media are the three types of media classified based on the physical state of media. Based on the ingredients, media can be divided into several types including simple media, complex media, synthetic media, and special media.

Key Areas Covered

1. What are Media
     – Definition, Classification, Importance
2. What is a Medium
     – Correspondence to Media
3. What is the Difference Between Media and Medium
     – Comparison of Key Differences

Key Terms

Agar, Complex Media, Medium, Simple Media, Special Media, Synthetic Media

What are Media

Media are the substances that include nutrients required by the growth of cells or microorganisms in vitro. Cell culturing is important for the identification and characterization of microorganisms. Also, microorganisms in cell cultures can be used to produce valuable biological products in the form of metabolites such as vaccines, antigens, enzymes, hormones, and, vitamins. On the other hand, culturing of microorganisms is important for the diagnosis of diseases.

The general components found in a medium are water, a carbon source, a nitrogen source, and mineral salts. In addition, it may also include special growth factors and antibiotics. Media can be classified into three based on their physical state.

Liquid media

It is also called a broth. Since they do not contain agar, these media remain as a liquid. The growth of microorganisms in these type of media will produce a turbidity. Ex: Nutrient broth

Figure 1: Thioglycollate broth

Semi-solid Media

This type of media is soft; hence, it allows the mobility of microorganisms inside the medium. This, it can be used to separate motile microorganisms from non-motile ones.

Solid Media

This type of media contains added agar in order to solidify the medium. Here, the growth of microorganisms only occurs on the top of the medium.

Secondly, these media can also be classified based on the ingredients present in it.

Simple Media

They provide the basic growth requirements for the microorganisms, allowing the non-fastidious growth. Ex: nutrient broth and nutrient agar

Figure 2: Agar Plate with Microorganisms

Complex Media

They allow the fastidious growth of microorganisms. Generally, the microorganisms used here have special growth requirements. Ex: trypticase soy agar

Synthetic/Defined Media

The preparation of these media uses pure chemical substances and the percentage of each component of the media is well-known. They are mainly used for research purposes. Ex: peptone water

Special Media

There are several types of special media including enriched media, selective media, differential media, transport media, and, anaerobic media.

• Enriched media such as blood agar contain other components added to the simple media such as blood, serum, egg or chocolate.
  

  Figure 3: Blood Agar

• Selective media contains antibiotics, which inhibit the growth of random microorganisms in the medium other than the specific strain. Other types of selective media may contain dyes, chemicals or altered pH conditions.
  

  Figure 4: Charcoal-Based Selective Medium (CSM)

• Differential media are incorporated with dyes of special metabolites, allowing the identification of bacterial strains by the developing colour on their colonies. Some examples of differential media are MacConkey agar, CLED agar, TCBS agar, and XLD agar.
  

  Figure 5: MacConkey Agar

• Transport media such as buffered glycerol saline and Stuart’s medium allow the transport of specimen.
• Anaerobic media is used for the growth of anaerobic microorganisms.

What is a Medium

Medium is the singular term for the media. It is used to describe a single type of media out of the whole types of media described above.

Difference Between Media and Medium

Definition

Media is the plural form of medium while a medium refers to the food material or substances required for the growth of microorganisms or cells in vitro.

Types

Media can be either simple, complex, synthetic or special while a medium is one type from them.

Conclusion

Media is the collection of substances used to grow cells or microorganisms in vitro while medium is the singular term for media, which defines a certain composition. Therefore, the main difference between media and medium in microbiology or any other is the terminology.

Reference:

1. “Culturing Bacteria.” Lumen, Lumen Learning, Available Here

Image Courtesy:

1. “ww325 thioglycollate broth” Byisis325 (CC BY 2.0) via Flickr
2. “Agar plate with colonies” (Public Domain) via Commons Wikimedia    
3. “Beta hemolysis on blood agar” By HansN. – Own work (CC BY-SA 3.0) via Commons Wikimedia  
4. “Campylobacter jejuni” By Kubo Michal (CC BY-SA 2.5) via Commons Wikimedia  
5. “MacConkey agar with LF and LF colonies” By Medimicro – Own work (Public Domain) via Commons Wikimedia