Spread plate technique is the method of isolation and enumeration of microorganisms in a mixed culture and distributing it evenly. The technique makes it easier to quantify bacteria in a solution.
Principle of Spread Plate Technique
The spread plate technique involves using a sterilized spreader with a smooth surface made of metal or glass to apply a small amount of bacteria suspended in a solution over a plate. The plate needs to be dry and at room temperature so that the agar can absorb the bacteria more readily. A successful spread plate will have a countable number of isolated bacterial colonies evenly distributed on the plate.
Procedure of Spread Plate Technique
- Make a dilution series from a sample.
- Pipette out 0.1 ml from the appropriate desired dilution series onto the center of the surface of an agar plate.
- Dip the L-shaped glass spreader into alcohol.
- Flame the glass spreader (hockey stick) over a Bunsen burner.
- Spread the sample evenly over the surface of agar using the sterile glass spreader, carefully rotating the Petridish underneath at the same time.
- Incubate the plate at 37°C for 24 hours.
- Calculate the CFU value of the sample. Once you count the colonies, multiply by the appropriate dilution factor to determine the number of CFU/mL in the original sample.
Uses of Spread Plate Technique
- It is used for viable plate counts, in which the total number of colony forming units on a single plate is enumerated.
- It is used to calculate the concentration of cells in the tube from which the sample was plated.
- Spread plating is routinely used in enrichment, selection, and screening experiments.
Limitations of Spread Plate Technique
- Strick aerobes are favored while microaerophilic tends to glow slower.
- Crowding of the colonies makes the enumeration difficult.
- M. J. Pelczar
- Mackie and McCartney. Practical Medical Microbiology
- Bailey & Scott’s Diagnostic Microbiology.
- Practical Microbiology. Pradeep Kumar Sharma.