Electronic count by coulter counter
This is a highly sophisticated technique for counting bacterial cells present in the culture. The method is named so after its Inventor.
The electronic device consists of tube having small orifice of about 10aua30 mm in diameter, which connects two compartments of the counter, which contain conductive medium.
The interior and exterior of the tube is connected with electrodes. The conductive medium completes the circuit.
When, bacteria pass through the small orifice, the conductivity between two compartment drops momentarily.
This is electronically recordcd in the counter. Thus as the bacteria pass through the orifice from one compartment to the other, each time they give electronic pulse to be counted. Thus the method involves a much rapid and accurate count.
The other modification of the technique is the use of a photodiode. Near the orifice, a photodiode and sensor are placed on the opposite sides.
As the organism passes through the orifice, it obstructs the path of light. This is sensed by the sensor and recorded in the counter.
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| Figure : Electronic coulter current counter method determining bacterial cell numbers. |
- Flow of the growth medium through a tube is allowed through a narrow capillary tube with a small orifice. Both ends of the tube are connected to electronic circuit through electrode.
- Through the orifice only one cell is able to pass at a time. Passage of cell through orifice causes momentary drop in conductivity, which is gives electronic pulse, to be counted.
Limitations of electronic count method
1. However, the method has got a major limitation that it cannot distinguish between dead or living organisms as well as dust particle. Every particulate matter can give rise to pulse to be counted as the organisms.
2. Many times if the organisms are larger than the diameter of the orifice, they may plug into It. Similarly clumps of bacteria cannot pass through. Hence the specimen should be initially treated to separate the clumps and then used for the count.
