Difference Between Streak Plate and Spread Plate

The key difference between streak plate and spread plate is that the streak plate is used to isolate and purify a particular bacterial species from a mixture of bacteria while the spread plate is used to enumerate and quantify bacteria in a sample. 

Apart from the above difference, there are many other differences between streak plate and spread plate. In streak plate, inoculum introduces into the fresh medium using an inoculation loop or a cotton swab while in spread plate, inoculum draws using a sterile micro-pipette. Furthermore, in streak plate, zig-zag pattern lines are drawn on the surface of the fresh medium while in spread plate, the inoculum is spread evenly on the surface of the medium. Streak plate and Spread plate are two microbial techniques to isolate, purify and enumerate bacteria. There are differences as well as similarities between streak plate and spread plate. Further, both methods are commonly and routinely used in bacterial studies.

CONTENTS

1. Overview and Key Difference
2. What is a Streak Plate
3. What is a Spread Plate
4. Similarities Between Streak Plate and Spread Plate
5. Side by Side Comparison – Streak Plate vs Spread Plate in Tabular Form
6. Summary

What is a Streak Plate?

Streak plate is a technique that allows isolating and purify bacterial species in a sample. Therefore, it is a simple and easy method to perform in a lab. We can dilute the sample before introducing into the fresh growth medium. However, few materials are necessary to perform this technique. They are an inoculating loop or a cotton swab, solidified agar plates, bunsen burner, and a laminar air flow. A loopful of inoculum has to be taken from the sample and drawn zig-zag zag pattern lines on the surface of the fresh medium under the sterile environment (often inside a laminar air flow).

Figure 01: Streak Plate

Inoculated plates are incubated at a suitable temperature. Separated bacterial colonies will grow on the lines drawn. Furthermore, interested or expected single colony can be further purified by adopting the same method until you get a purified bacterial species. Hence, this method is suitable for separating bacteria into single colonies and picking and purifying your desired bacterium.

What is a Spread Plate?

A spread plate is another microbial technique that allows enumerating bacteria in a sample, hence it facilitates the accurate quantification of bacteria. It provides information regarding the number of bacteria present in the sample. In this technique also it is necessary to dilute the sample before inoculating into fresh medium.

Figure 02: Spread Plate

Moreover, micropipette and a sterilized spreader are the main materials necessary to perform this technique. A suitable aliquot (often 0.1 ml or 1 ml) is drawn out from the sample by a micropipette and transferred into fresh agar plate. Using a spreader, the inoculum spreads evenly throughout the surface and incubates at a suitable temperature. Aerobic bacteria will grow on the surface of the medium as separate colonies. Therefore, enumeration will be easy in this technique if the dilution is correct. According to the recommendation, the plates which have 30 to 300 colonies are selected for enumeration. Using an equation, we can do the correct quantification after enumeration.

What are the Similarities Between Streak Plate and Spread Plate?

• Streak plate and spread plate are two microbial techniques that we use in bacteriology.
• Both methods are in use to isolate or separate bacteria from a mixture.
• In both techniques, we can dilute the sample prior to inoculation.
• Both methods require solidified agar plates.
• Bacteria grow on the surface of the medium in both methods.
• In both techniques, aerobic bacteria grow on the surface of the medium.
• We use a Sterilized inoculating tool to introduce the inoculum into fresh medium in both techniques.
• A sterile environment is necessary to perform both techniques.

What is the Difference Between Streak Plate and Spread Plate?

Streak plate technique allows you to isolate and purify bacteria. On the other hand, spread plate technique allows you to enumerate bacteria. This is the key difference between streak plate and spread plate. Furthermore, we can use an inoculating loop or cotton swab as an inoculating tool in streak plate while we need a spreader for spread plate technique. A loopful of the sample is the quantity that draws from the sample in the first technique while 0.1 ml or 1 ml are the quantities of second technique. Inoculum introduces into a fresh medium by drawing zig-zag pattern lines in streak plate while the inoculum spreads evenly throughout the surface in the spread plate.

Summary – Streak Plate vs Spread Plate

Streak plate and spread plate are two microbial techniques perform in bacteriology. Streak plate facilitates isolation and purification of a specific bacterium while spread plate facilitates enumeration of bacteria in a sample. Both methods are highly useful for bacterial studies, especially for aerobic bacteria. Streaks in a zig-zag pattern are done in a streak plate while the inoculum is evenly spread on the surface of the medium in spread plate. This is the difference between streak plate and spread plate.

Reference:

1.“Streaking (Microbiology).” Wikipedia, Wikimedia Foundation, 14 July 2018. Available here 
2.“Spread Plate Technique: Principle, Procedure and Results -.” Home -, 27 July 2017. Available here 

Image Courtesy:

1.’Legionella Plate 01’By CDC/James Gathany – CDC Public Health Image Library, (Public Domain) vis Commons Wikimedia
2.’33934804403’by R6, State & Private Forestry, Forest Health Protection’s photostream (Public Domain) via Flickr

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