Streak Plate Method-Principle, Methods, Significance, Limitations
- Streak plate method is a microbiological technique used to isolate a perfect strain from a specific type of organism, often a bacterium.
- Initiated in the laboratory of Koch by Loeffler and Gaffky, the dilution or isolation through streaking technique includes carefully streaking bacteria over the agar surface in a Petri dish to form isolated colonies that would eventually expand into the quantity of cells or separated colonies.
- Streaking is a rapid and, preferably, uncomplicated isolation dilution method.
- The procedure includes decreasing the bacterial concentration, from a relatively high concentration to a lower one.
- Bacteria should have decreased, suggesting that colonies are adequately separated to induce the isolation of different types of bacteria.
- Streaking is performed using a clean implement, usually an inoculation loop or a cotton swab.
- Microbiological cultures are kept up-to-date using aseptic procedures, which also help to keep the growing media clean.
Principle of Streak Plate
- The streak plate technique is an efficient method of qualitative isolation.
- It is first necessary to minimise the number of organisms in the inoculums to employ established strategies for separating distinct colonies.
- Spreading a culture loop over the surface of an agar plate is essentially a dilution technique.
- Particular cells would be adequately separated over the surface of an agar plate medium after inoculation, resulting in the isolation of the numerous species available due to the resulting drop in the size of the population.
- In the streaking procedure, a sterile loop or swab is utilised to generate an unpolluted microbial culture. Picking colonies is the process of transferring isolated colonies from an agar plate to a new agar or gelatin plate using a sterile loop or needle.
- Then, the surface of agar is streaked with an inoculating loop or needle.
- Numerous microbes are placed on the initial section of the streak, resulting in confluent proliferation or the formation of colonies across the entire streaked surface.
- In this way, fewer germs are deposited as the streaking process advances because the loop is disinfected by heating it in the Bunsen burner’s blue flame in between streaking various portions or zones.
- The sample that was first applied to an area of the agar surface will be diluted by the streaking procedure.
Methods of Streak Plate
- A plate may be streaked using a variety of techniques. The three-sector “T streak” and four-quadrant “streak” techniques are the two most popular streak designs.
- The approach used depends on personal choice as well as the number of microorganisms found in a sample.
- The T-Streak is a three-phased pattern of streaking.
- A sterile instrument, like a cotton swab or, more often, an inoculation loop, is used to apply the streaks.
- First, a flame is used to sterilise the inoculation loop.
- A cold loop is inserted into an inoculum containing a range of bacterial species, including a broth or patient specimen.
- The inoculation loop is then dragged over the agar surface in a zigzag pattern until about 30 percent of the plate is covered.
- The plate is then turned by ninety degrees while the loop is re-sterilized.
- To continue the zigzag pattern, the loop is pushed over the region that was previously streaked two to three times.
- The process is then carried out once again, taking care not to touch the areas that had previously been streaked.
- The loop catches fewer and fewer germs until it only captures a solitary bacterial cell from which a colony may form.
- The early portion of the plate should have the highest development.
- The last portion will have the least development and the greatest number of isolated colonies. In contrast, the second part will have less development and fewer colonies.
The quadrant technique entails streaking four equal-sized sections. Continuous streaking often comprises inoculating the top half of the plate, rotating it 180 degrees, and then inoculating the bottom portion of the plate without sterilising the loop or pulling germs from the previous area.
Discontinuous Streaking Method
- By exposing the inoculating loop until the flame is red-hot, you may sterilise it in the bunsen burner. Give it time to cool.
- Select a separated colony from the agar plate growth, and then either use nearly parallel streaks to disperse it throughout the initial quadrant (about one-fourth of the plate) or insert your loop into the tube/culture bottle and extract inoculum. You don’t need a sizable portion.
- Immediate back-and-forth smearing of one-fourth of the plate with the inoculating loop.
- Fire up the loop again and let it cool. Continue the streaks into the second quarter of the plate, bringing them back to the border of area 1, where they were just completed.
- Fire up the loop again and let it cool. Stretch the streaks into the third quarter of the plate and return to the last streaked location.
- Fire up the loop again and let it cool. Expand the streaks toward the center-third of the plate, back to the most recently streaked zone.
- Once again, flame your loop.
Significance of Streak Plate Method
- The streak plate method is the most popular method for distinguishing specific bacteria from a sample having many germs.
- To remove and sample single bacterial colonies, bacteria are grown on a growth media surface using the streak plate technique.
- To identify, examine, or check the organism, samples could be obtained from the resultant isolated colonies, and a fresh microbiological culture plate could be prepared.
- The bacterial disease’s etiological agent may be found once the bacteria are separated and streaked; they are isolated.
Limitations of the Streak Plate
A technique used in microbiology labs called streak plating has two significant drawbacks.
- First off, utilising this technique won’t allow users to cultivate obligate anaerobes.
- Second, development is restricted to those organisms which were able to survive in the initial sample.
- Benson, H. J. (2005). Benson’s microbiological applications: Laboratory manual in general microbiology. Boston: McGraw-Hill Higher Education.
- James G. Cappuccino, Chad T. Welsh (2017). Microbiology: A Laboratory Manual, 11th Edition. Pearson Publications.
- Western Nevada College Biology 251 Laboratory Manual;”Three Streaks for Bacterial Isolation”; Dr. Steve Carman; 2009