What is the Difference Between Streak Plate and Pour Plate

The main difference between streak plate and pour plate is that in streak plate, the first to be added is the melted nutrient agar and the second to be added is a loop of bacteria from a slant, whereas the first to be added in pour plate is the bacterial broth and the second to be added is the nutrient agar. Furthermore, the volume of inoculum in the streak plate is only a loopful from a bacterial slant while the volume of inoculum in pour plate is 1.0 to 0.1 mL. Moreover, streak plate is for the isolation of colonies while the pour plate is for counting the number of colonies. 

Streak plate and pour plate are two techniques in microbiology to grow mainly bacteria and fungi in Petri dishes with nutrient agar. 

Key Areas Covered 

1. What is Streak Plate
     – Definition, Method, Importance
2. What is Pour Plate
     – Definition, Method, Importance
3. What are the Similarities Between Streak Plate and Pour Plate
     – Outline of Common Features
4. What is the Difference Between Streak Plate and Pour Plate
     – Comparison of Key Differences

Key Terms 

Bacterial Broth, Colony Counting, Isolation of Colonies, Nutrient Agar, Pour Plate, Streak Plate

What is Streak Plate 

Streak plate is the technique in microbiology to isolate pure strain from a single species of microorganisms. Moreover, the resulting colonies can be further studied through isolation. However, the main importance of this technique is to dilute a comparatively large concentration to a smaller concentration. 

Figure 1: Streak Plate

Generally, the inoculation loop is the main equipment for streaking. Usually, the sterile inoculation loop is dipped in the inoculation of microorganisms and then is dragged across the surface of the agar back and forth in a zigzag motion. When 30% of the surface area is covered, the plate is turned 90 degrees. Moreover, the inoculation loop has to be sterilized. Then, the streaking continues, starting from the previous section in the zigzag motion, until it covers all the surfaces of the plate is the T-streak method. 

What is Pour Plate 

Pour plate is another technique in microbiology important for counting the number of colony-forming bacteria in a liquid specimen. Generally, in this method, around 1 mL of the liquid broth is placed on the sterile Petri dish using a pipette. Then, pouring the melted nutrient agar and well-mixing is the second step. 

Figure 2: Colony Counting

Furthermore, in the pour plate, microorganisms grow on the surface as well as within the medium. However, the faster growth of colonies occurs on the surface. Each colony represents a colony-forming unit. Therefore, we can use their counting to determine the number of microorganisms in the sample by the following formula. 

CFU/mL= CFU * dilution factor * 1/aliquot  

Similarities Between Streak Plate and Pour Plate 

• Streak plate and pour plate are two techniques in microbiology to grow bacteria and fungi. 
• Both require a Petri dish, melted nutrient agar, and an alcohol lamp. 
• Also, after inoculation, we have to incubate the Petri dishes for the microbial growth at their optimal temperature. 
• Moreover, keeping aseptic conditions is important to avoid contamination in microbial cultures. 

Difference Between Streak Plate and Pour Plate 

Definition 

Streak plate refers to a rapid qualitative isolation method for obtaining discrete colonies from a mixed population while pour plate refers to the method of choice for counting the number of colony-forming bacteria present in a liquid specimen. Thus, this explains the fundamental difference between the streak plate and pour plate.

First to Add

The first thing we add in a streak plate is the melted nutrient agar, while the first thing we add in a pour plate is the bacterial broth. 

Second to Add

In contrast to the above, the second thing we add to the streak plate is a loopful of bacteria from a slant, while the second thing we add to the pour plate is the melted nutrient agar. 

The Volume of the Inoculum 

The volume of inoculum in the streak plate is only a loopful from a bacterial slant while the volume of inoculum in pour plate is 1.0 to 0.1 mL. 

Purpose 

Another major difference between the streak plate and pour plate is that streak plate is for the isolation of colonies while the pour plate is for counting the number of colonies. 

Equipment 

Streak plate method requires a Petri dish, alcohol lamp, and a wire loop while the pour plate method requires a Petri dish, alcohol lamp, pipet, test tubes, and a glass rod. 

Type of Colonies 

Streak plate produces surface colonies while the pour plate produces both surface and subsurface colonies. 

Advantages 

Moreover, streak plate is important for the isolation of bacterial cultures by preparing distinct colonies while the pour plate is important for the quantification of colonies in a solid medium. 

Disadvantages 

The main disadvantage of streak plate is the higher probability of contamination while the main disadvantage of pour plate is microbes have to withstand the temperature of the melted nutrient broth during preparation. 

Conclusion 

Streak plate is a technique in microbiology used to isolate colonies from a culture. In this technique, a loopful from the bacterial slant is systematically streaked on a nutrient broth. Therefore, it produces surface colonies. Also, this method is important to isolate pure species from a mixture. On the other hand, pour plate is another technique in microbiology used to count colonies. Here, the sample of bacteria is suspended in a Petri dish using melted nutrient agar. Therefore, it produces both surface and subsurface colonies. Moreover, it is important to quantify the colony-forming bacteria. However, the main difference between streak plate and pour plate is the method and importance. 

References:

1. “Streaking (Microbiology).” Wikipedia, Wikimedia Foundation, 28 May 2019, Available Here.
2. tankeshwar. “Pour Plate Method: Principle, Procedure, Uses, and (Dis) Advantages.” Microbeonline, 16 Oct. 2016, Available Here.

Image Courtesy:

1. “Legionella Plate 01” By CDC/James Gathany – CDC Public Health Image Library (ID#: 7925) (Public Domain)via Commons Wikimedia   
2. “Manual CFU counting” By Quentin Geissmann – Own work (CC BY-SA 3.0) via Commons Wikimedia