What is colony counter?
Colony counter is a digital display type automatic bacterial testing instrument. It consists of a counter, probe pen, counting pool, and other parts. The counter is carefully designed with a CMOS integrated circuit, LED digital tube display, word height 13mm, clear and bright, with special probe pen, counting sensitive and accurate. With fluorescent light illumination in the black background type counting pool, the contrast of bacterial colonies is clear and easy to observe. This instrument can reduce the labor intensity of laboratory personnel, improve work efficiency, improve the quality of work, widely used in food, beverage, drugs, biological products, cosmetics, hygiene products, drinking water, domestic sewage, industrial wastewater, clinical specimens in the number of a bacteria test.
It is a necessary instrument for laboratories of grand epidemic prevention stations, environmental monitoring stations, food hygiene supervision, and inspection institutes, hospitals, biological products institutes, drug inspection institutes, commodity inspection bureaus, food factories, beverage factories, cosmetic factories, daily chemical factories and universities, and scientific research units at all levels.
What is colony count?
A colony is a growth that can be recognized by the naked eye as a collection of tens of thousands of identical bacteria that grow and multiply on solid media. When the sample is diluted to a certain level and mixed with the medium, under certain incubation conditions, each bacterial cell that can grow and multiply can form a visible colony on the plate. The total number of colonies is the total number of bacterial colonies per gram (per milliliter) of the sample grown under certain conditions (such as aerobic conditions, nutritional conditions, pH, incubation temperature and time, etc.). According to the national standard method, that is, in the aerobic condition, 37 ℃ culture 48h, can grow in the ordinary nutrient agar plate of the total number of bacterial colonies, so anaerobic or microaerobic bacteria, special nutritional requirements, and non- mesophilic bacteria, because the existing conditions cannot meet its physiological needs, it is difficult to reproduce and grow. Therefore, the total number of colonies does not indicate the actual total number of all bacteria, and the total number of colonies does not distinguish the types of bacteria in it.
Colony determination is an important indicator in the microbiological determination of food safety. The total colony count is used to determine the degree of bacterial contamination and the hygienic quality of the food, which reflects whether the food meets the hygienic requirements in the production process, to make an appropriate hygienic evaluation of the samples examined. The amount of the total number of colonies to a certain degree marks the quality of food hygiene.
Working principle of colony count
Colony counting is generally used as the plate colony counting method, which is an effective method to count the number of bacteria in the items. After the sample to be tested is properly diluted, the microorganisms are fully dispersed into individual cells, a certain amount of diluted sample solution is taken and applied to the plate, and after incubation, every single cell grows and multiplies to form a colony visible to the naked eye, i.e. a single colony should represent a single cell in the original sample; the number of colonies is counted, and the number of bacteria in the sample can be converted according to its dilution multiple and the inoculation amount of the sample.
Types of colony counter
The colony counter is an effective method to count the number of bacteria in articles because the colony counter can reduce the labor intensity of laboratory personnel, and improve the efficiency and quality of work. The product is widely used in food, beverage, medicine, biological products, hygiene products, drinking water, industrial wastewater, and clinical specimens in several tests. The colony counter is divided into an automatic colony counter, semi-automatic colony counter, and manual colony counter.
Automatic colony counter
Automatic colony counter can be used with a computer. The operator can put the petri dish on top of the instrument and the system software in the computer can recognize it. Counting can be counted by mouse click and other ways. After counting, the data report can be issued. Automatic colony counters also have the function of detecting inhibition circles and E. coli and spiral analysis at the same time. If you need data report analysis or need to carry out other measurements, such as inhibition circle measurement and E. coli measurement, you can use the automatic colony counter.
Semi-automatic colony counter
Semi-automatic colony counter is a kind of laboratory instrument with no special stylus and a simple, easy, fast, and reliable counting operation. It can replace the traditional microbial counting method, reduce the work intensity of the inspector and improve the counting efficiency. The use of flexible arm magnification to increase the accuracy of the count, direct lighting, and indirect lighting to expand the instrument does not mean the applicable function of the culture medium.
Manual colony counter
Manual colony counter is composed of a counter, probe, counting cell, and other parts. If the use of unit counting is not very frequent as well as the culture of bacteria not more than 3 digits, you can use the manual colony counter. The principle of manual colony counters is to place the petri dish on a base with a lower light source, and the operator observes the petri dish through a magnifying glass and light source. Click on the petri dish with the counting pen, and count each click by the pressure touch device.
Use of colony counter
a. Insert the power plug into the 220V power outlet. Insert the probe pen into the probe pen jack on the instrument.
b. Turn the power switch “ON” and the light in the counting cell lights up. At the same time, the display window shows bright, indicating that counting is allowed.
c. Place the petri dish to be examined bottom side up in the counting cell. Use the probe pen to count all the colonies one by one on the bottom of the petri dish. At this time, the colony is marked with color, and the numbers in the display window are automatically added up.
d. Check carefully with a magnifying glass and make sure there are no missing points, and the counting is finished.
e. The number in the display window is the number of colonies in the petri dish.
f. Record the number and remove the Petri dish. Press the reset button, and the display will be restored and ready for another petri dish to be counted.
Precaution of colony count
a. When the specified incubation time is reached, the count should be done immediately. If the bacteria cannot be counted immediately, the plate should be placed at 0-4 ℃, but not more than 24h.
b. Counting should be selected when the number of colonies is between 30-300 CFU plates. If there are two dilutions between 30-300 CFU, should be decided by the ratio of the two. The ratio is less than or equal to 2 to take the average, if the ratio is greater than 2 then it’s a smaller number (if there are provisions that do not consider the size of its ratio, are reported as the average).
c. If all dilutions are not in the counting interval, the analysis should be performed as appropriate. If they are greater than 300 CFU, the highest dilution of the average number of colonies is multiplied by the number of dilutions reported. If they are less than 30 CFU, the average number of colonies at the lowest dilution is multiplied by the number of dilutions reported. If the number of colonies is greater than 300 CFU, and some are less than 30 CFU but are not between 30-300 CFU, then the average number of colonies closest to 300 CFU or 30 CFU is multiplied by the number of dilutions reported. If all dilutions are no colony growth, should be less than 1 multiplied by the lowest dilution reported. Some of the provisions of the above-mentioned cases are calculated by the estimated number of colonies reported.
d. Different dilution of the colony number should be inversely proportional to the dilution (the same dilution of the two plates of the colony number should be close), that is, the higher the dilution of the colony number is, the lower the dilution of the colony number is more. If the inverse phenomenon should be regarded as the error in the test (some food sometimes may appear inverse phenomenon, such as acidic beverages), should not be used as the basis for the sample count report.
e. When chain colonies are growing on the plate, such as chain growth of colonies without any obvious boundaries between them, should be counted as a colony, such as the existence of several different sources of the chain, each chain should be counted as a colony, do not count each colony growing on the chain separately. If there is lamellar colony growth, the plate is generally not suitable, such as lamellar colonies are less than half of the plate, and the other half is evenly distributed, the number of colonies can be half of the plate multiplied by 2 on behalf of the whole plate of the number of colonies.
f. When the number of colonies in the counting plate is too many (i.e. when all dilutions are greater than 300 CFU), but the distribution is very uniform, half or 1/4 of the plate can be counted. Then multiply the corresponding dilution times by the number of colonies of the plate.
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