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The Spiral plating technique
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The principle of Spiral exponential plating
The Spiral plating technique is a standardised method of enumeration via plating that standardises the Pasteurian method.
A sample is deposited on the surface of a rotating Petri dish by a high-precision syringe in a logarithmically decreasing Archimedean spiral from the centre of the dish to its periphery.
It allows four dilution log on the same dish, providing a spread by exhaustion. The volume is calibrated and known on all points of the Petri dish.
In the reference method, four successive dilutions are made and the 4th dilution is plated to obtain a Petri dish that is interpretable. The spiral technique here allows us to inoculate the mother sample directly.
Manual plating is a method with repetitive actions: at least 4 dilutions and 4 consecutive plating to obtain only 1 interpretable Petri dish.
With this method, make your analysis using only 1 single Petri dish!
Comparison between the classical method and the Spiral plating technique
The Spiral technique is a surface plating mode. It is similar to the horizontal methods commonly used in laboratories. Compare to the reference methods, interlaboratory tests such as RAEMA show that there is no statistically significant differences between both methods.
Here is a comparative study between the reference method and the Spiral plating technique:
Aim: To study the reliability of the easySpiral/easySpiral Pro plating in decreasing exponential mode (called Spiral plating technique) by carrying out a comparative study with the reference method "manual surface plating" (called classical method).
Conclusion: Our results show that there is a strong correlation (R2 = 0.989) between the Spiral plating technique perfomed by the easySpiral and the classical method. Also the average difference in log CFU/mL between the two methods is 12 times lower than the maximum difference, thus not significant.
Correlation line between the (Escherichia coli count (in Log CFU/mL) obtained by plating with the Spiral and conventional methods
Example of different concentrations of Escherichia coli, plated onto MacConkey medium, using the Spiral plating technique
2.6 x 103
1.3 x 104
2.6 x 104
1.3 x 105
2.6 x 105
Is the Spiral plating technique standardized?
Yes, it is a standard technique mentioned under ISO 7218 or ISO 4833-2 for the enumeration of total mesophilic flora. Moreover, it is also present in the American market in the FDA and AOAC.
From ISO 4833-2 : "This annex specifies a method for the enumeration of microorganisms in food, feed, and environmental samples using a spiral plating device."
From FDA - BAM : "The spiral plate count (SPLC) method for microorganisms in milk, foods, and cosmetics is an official method of the APHA and the AOAC."
How to count?
The bacterial concentration is determined by dividing the number of counted colonies by the plated volume per sector. CFUs can be counted either manually (utilizing an abacus or any manual colony counter), or automatically using any automatic colony counter Scan.
Manual method
The reading of the Spiral plating technique requires an Abacus supplied with the easySpiral plater.
This abacus is divided into 4 quadrants: A | A | B | B. Each quadrant is subdivided into 6 sectors.
Count 20 colonies starting from sector 1 (most diluted sector), then continue counting until at least 20 colonies are reached and finish to count all colonies at this sector.
Complete the count of the sector containing the 20th colony.
Count the colonies in the same sectors of the opposite quadrant.
Add up the number of colonies of these two dials: (n1 + n2) = N
Divide N by the volume of sectors read and counted: V (cumulative volumes provided by the supplier).
Multiply by a dilution factor if necessary: D
Convert µL to mL by multiplying by a factor of 1000.
Bacterial concentration: C in CFU/mL.
Alternative method
Instead of using the Spiral counting formula, refer to the appendices of the user manual.
Results table
Automatic method
Interscience offers a range of colony counters that allow to enumerate the Spiral technique in an automated way.
Incubation and counting in real time
ScanStation 100 | ScanStation 200 | ScanStation 300
Spiral plating technique: 45 years of experience
For 45 years, Interscience automatic Spiral platers have been a reference for food, medical, research, cosmetic, pharmaceutical and probiotic laboratories worldwide.
1973
The Spiral plating technique of sample plating was invented by Dr. Ed Campbell, a researcher at the FDA (Food and Drug Administration) in Cincinnati, USA.
1979
Launching of the Spiral DS plater
1992
Dr. Ed. Campbell and François Jalenques, founder of Interscience, jointly patent an updated version of the Spiral plating technique.
1996
Launching of the Spiral DS + plating machine
2010
Interscience launches easySpiral and easySpiral Pro with a brand new architecture: faster, easier to use
Frequently Asked Questions
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Do I need to change my media supplier?
The consumables are not captive, so there is no obligation to change media suppliers. However, the media should contain between 12 and 15 grams per litre of agar. The Interscience easySpiral has a counterweight on the turret holding the stylus which allows it to be adapted to all agar, even those poured by hand.
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Do I have to work in a sterile environment?
With the Spiral plating technique, it is recommended to work in a sterile environment, under a microbiological safety cabinet (BSC) or in a laminar flow hood. For laboratories that do not have the possibility to work under these conditions, we recommend to place the automat near a Bunsen burner. Interscience also offers a housing protection that can be placed on the easySpiral to prevent air flow on the work platform.
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What microorganisms can be plated?
All microorganisms usually plated on the surface can be plated with the Spiral plating technique after validation by the laboratory.
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How many dilutions are taken into account and visualized with the Spiral plating technique?
The Spiral plating technique allows the equivalent of 4 dilution logs on the same Petri dish: the mother sample and three consecutive dilutions of this sample. The Spiral dilutions are visualized via spreading a linearly decreasing volume of the inoculum in an Archimedes’ spiral, which is highly concentrated in the center and much less on the edge.
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What are the areas of application of the Spiral plating technique?
The Spiral plating technique can be used in various fields of application such as food processing for the enumeration of quality criteria of all matrices even coloured ones or milk as a raw material. It can also be used to perform bacterial kinetic studies. The Spiral plating technique can be used in the field of pharmacology or cosmetology for challenging tests, R&D, Quality Control and fertility/sterility tests.
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What are the benefits of the Spiral plating technique?
The Spiral plating technique has several interests:
- Standardization of the Pasteurian method
- Controlling the cost of purchasing non-captive media/consumables
- Reduction of stocks of immobilized media
- Maintenance of scientific expertise in the laboratory
- Freedom to validate any parameter in the laboratory with the Spiral plating technique
- Compatible with any type of sample, even coloured ones
- Faster sample processing in less time.
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What hygiene criteria can we look for with the Spiral plating technique?
The criteria accepted with the Spiral plating technique depend on the detection thresholds. Any criterium above 100 CFU can be used (subject to validation by the laboratory) except for strict anaerobes which must be inoculated in double layers. Scientific studies value and approve the Spiral plating technique within the laboratory..
