| Claims What is claimed is : 1. Semi-automatic drop plate machine with a device for aspirating and for dispensing liquid. The device comprising: A metal sample tube attached by a dropping tip (Fig.l). The body (1) is made of plastic and the dropping end (2) is made of glass tube having 0.96 millimeter outside diameter. The weight of one drop of liquid sample is 20 milligrams or 20 microliters. The metal sample tube moves down and up vertically to take up sample from sample bottle (Fig.4) and drops sample on the agar plate (Fig.5). 2. Semi-automatic drop plate machine with a micro-controller (3) to control the running of a micro-stepper motor (4) to move a micro-piston (6) up and down to take up and to drop liquid sample, 3. Semi-automatic drop plate machine according to claim 2, that takes up at least 21 microliters of liquid sample and drops 1 drop. 4. Semi-automatic drop plate machine according to claim 2, that takes up at least 41 microliters of liquid sample and drops 2 drops. 5. Semi-automatic drop plate machine according to claim 2, that takes up at least 61 microliters of liquid sample and drops 3 drops. 6. Semi-automatic drop plate machine according to claim 2, that takes up at least 201 microliters of liquid sample and drops 10 drops. |
1. Technical Field
This invention requires knowledge in mechanical engineering, electrical engineering . and computer engineering. This machine will be used in the field of microbiology for determination of viable microbial cells.
2. Background Art
The plate count methods are widely used in microbiology but the methods are not accurate until the drop plate method was improved to be the only one method that can give accurate results (Supanwong, 1972). Even so the method is not widely used because of the difficulty of the technique. The invention of drop plate machine could solve this problem.
There are 3 plate count methods.
1. The pour plate method is used with mixed culture samples. The inborn error of this method is the death of microbial cells when exposed to the hot melted agar at about 50° C.
2. The spread plate method is used with pure culture sample such as the study of microbes in the laboratory. The inborn error of this method is the attachment of varied amount of liquid sample to the glass spreader after spreading.
3. The drop plate method can be used with mixed and pure culture. There is no inborn error with this method so this method can give accurate results if performed correctly.
In 1972 a machine for performing plate counts was invented. The machine is called spiral plater. The spiral plater consists of a platform that rotates at constant speed. An agar plate is put on the center of this platform. The liquid sample is dispensed through a small tube at constant speed on to the agar plate starting at the center of the plate. While the plate is rotating, the inoculating tube is slowly moved out from the center of the agar plate creating spiral pattern on the agar surface. The more the tube moves away from the center the more the sample is diluted. In the area that discrete colonies are formed, the number of bacteria per unit volume is calculated using mathematic formula. This machine gives results similar to the pour plate and spread plate method but more convenient and economical. The spiral plate method requires 1 agar plate per one sample while the pour plate and spread plate method require at least 3 agar plates for 1 sample.
The drop plate method is considered to be free from any inborn error so it should give accurate results if perform correctly. The Pasteur pipette used in the drop plate method has 0.96 millimeter outside diameter tip. This dropping pipette gives accurate drop weighing 20 milligrams or 20 microliters if the tip is free from fatty substance and the force applied to the rubber bulb is minimal.
The invention of drop plate machine will standardize the force apply to the dropping pipette .
The result is the plate count method that gives accurate results. The method is also economical . Only one agar plate is required for one sample .
3. Disclosure of Invention
Semi-automatic drop plate machine consists of 2 motors. These 2 motors are controlled by a micro-controller.
The first motor moves one piece of metal tube up and down vertically. At the low end of this tube a dropping tip is attached. This dropping tip (Fig.l) is specifically designed for this machine. The motor moves the metal tube and the dropping tip down into a sample bottle to take up liquid sample into the dropping tip. Then the motor moves the metal tube up until the dropping tip is about 7 centimeters above the platform. The liquid sample is dropped from this height and spread over the agar surface to form a circle with diameter about 1 centimeter. The volume of one drop is
0.02 milliliter or 20 microliters.
Figure 2 shows the operation diagram of the second motor. The second motor controls the movement of a micro-piston pump to take up and dispense liquid sample, via the dropping tip, to drop on the agar surface.
Figure 3 shows general appearance of the semi-automatic drop plate machine.
There is a spot on the platform indicating the position of the drop. This spot also indicates the position that sample bottle is placed on the platform for sample take up.
The working steps of the machine are as following : Step 1. Program selection
When the machine is switched on, the screen indicates the operation step of the machine as STAND BY. The program used in previous operation is also shown as 3 DROPS. There are 3 operation programs in this machine :
1. 2 Drops Program. The machine takes up 45 microliters sample.
2. 3 Drops Program. The machine takes up 65 microliters sample.
3. 10 Drops Program. The machine takes up 205 microliters sample.
By pressing the P button the program changes in cyclic order from 2 drops to 3 drops and to 10 drops.
Step2. Take up of sample
Place the sample bottle over the circular mark on the platform and press the button T. The screen shows the TAKE UP step is in progress (Fig.4). The dropping tip moves down to bring the end of the tip to the height of 5 millimeters above the bottom of the bottle. The machine takes up 65 microliters (Program 3 Drops) and blow out. This process is repeated 3 times to mix the small amount of liquid, left from previous sample, in the tip of the glass tube with this sample. The concentration of this sample is 10 times of the previous sample. This mixing will allow the use of 1 dropping tip with 3 or even 6 dilutions starting with the highest dilution.
After the fourth take up of the liquid sample, the dropping tip moves up to bring the tip to the height of about 7 centimeters above the platform.
Step 3. Sample dropping
Remove sample bottle from the platform and replace with an agar plate. The agar plate is attached to a plastic template exhibiting 9 spots where the sample should be dropped (Fig 5.). To start the dropping process press button D. The screen shows the DROPPING step is in progress. The micro-piston pump dispenses the liquid sample slowly at 20 microliters (1 drop) in about 3 seconds. After the sample drops on one spot, the operator moves in another spot waiting for the next drop. After 3 drops, the machine returns to STAND BY step.
The sample bottle is removed touching the small amount of liquid at the end of the glass tip with the inside lip of the bottle to remove the liquid sample from the glass tip.
For the next sample steps 2 and 3 are repeated. 4. Brief Description of Drawing
Figure 1. The dropping tip body (1) is made of autoclavable plastic. The dropping end
(2) is made of glass tube having 0.96 millimeter outside diameter.
Figure 2. The operation diagram of the second motor. A micro-controller (3) controls the nmning of a micro-stepper motor (4). A micro-piston pump (5) functions according to the movement of the micro-stepper motor to move the micro- piston (6) up and down.
Figure 3. The machine has 3 control buttons. P button changes the operation program from 2 drops to drops, from 3 drops to 10 drops and form 10 drops to 2 drops. Figure 4. The take up of liquid sample step.
Figure 5. The dropping of liquid sample step.
5. Best Mode for Carrying out the Invention.
As described in Disclosure of Invention.
6. Industrial Applicability.
This machine will be used in all education and research institutes in microbiology.
The plate count will not be a tedious work anymore. The machine can also be used in Food industry where pure cultures of bacteria or yeasts are used in the process.
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