Useful Tips

Growing bacteria in a petri dish


You have an inverted biological microscope Eureka 40x-320x! You studied under it water from a ditch, water from a vase with a bouquet of flowers ... You looked at everything that could be quickly poured into a Petri dish. What now? Let's try to conduct real scientific research. You will need patience, time and imagination.

We will grow a colony of bacteria in a cup that comes with a microscope. You can purchase several cups to grow several different colonies at the same time. I think you will be struck by the variety of bacteria that surround us.

Be careful! These experiments are recommended for children over 8 years old and only under the supervision of adults! Experiments include the use of boiling water and bleach. Adult control is required!

• Agar agar powder. It is sold in grocery stores in the same department as vanillin, gelatin, cinnamon and other goodies for baking.

• 1 teaspoon of sugar.

• A small saucepan or ladle for boiling mixture.

• Incubator. We will use some kind of warm place as an incubator. In winter, it is convenient to use a place near the heater. And in the summer, when the batteries are off, you can use the place behind the refrigerator.

To begin with, do not forget to invite an adult to join our experience. We really need his help.

1. Pour water into a pan (ladle) and bring to a boil. Dissolve sugar in this water.

2. Add agar-agar powder to boiling water and mix for a minute until it is completely dissolved.

3. Cool the mixture for several minutes. Firstly, the mixture should be still hot to avoid setting the jelly directly in the pan. And secondly, we need to prevent contamination of our mixture with bacteria from the air. Our home conditions are far from sterility, but we will try to avoid unnecessary pollution.

4. Open the Petri dish. And immediately we ask the adult assistant to pour hot mixture from the saucepan on its bottom. It is not necessary to open in advance so that extra bacteria do not interfere with our experience.

5. Cover the Petri dish and put it in the refrigerator for about 4 hours. During this time, jelly will set.

6. Now it's time to collect bacteria and grow colonies on agar-agar in a Petri dish.

Note: Petri dishes with frozen agar can be stored in the refrigerator for 1-2 months before use. It is necessary to turn them over so that the condensate does not spoil the prepared nutrient medium.

7. Bacteria are not difficult to collect because they are everywhere. We take a clean cotton swab and carry it where we want to find bacteria - on dirty dishes or under the fingernails, or on the ground, or on the door handle, or on a mobile phone, or on the keyboard. Then gently draw this stick on the frozen agar in the Petri dish.

8. Close the Petri dishes with lids and seal with tape. In order not to confuse the cups, we paste stickers with inscriptions on them (where the bacteria were collected from). Turn over and remove to the incubator (warm dark place). Turn over so that the droplets that may form on the lid from evaporation do not fall on our object of study. Leave for a few days.

9. After a few days, you can observe under a microscope what is happening in the Petri dish. We will see how the colonies began to grow. Once a day or once every few days, you can check what changes are occurring.

10. Although the bacteria we have collected at home are likely to be harmless, precaution will not hurt. We will again need the help of an adult, since the plastic Petri dish needs to be thoroughly washed with a chlorine solution, and only then disposed of. If you have a glass Petri dish, then it can be reused after sterilization. Remind your adult assistant to wear rubber gloves. In no case do not work with bleach yourself!

If the experience did not work out the first time, do not despair. Ask your biology teacher at school for advice. Some types of bacteria love the animal environment, and for them you need to add a nutrient medium to the agar-agar, such as beef broth. Other bacteria multiply well in the plant environment, for them you can add a potato broth.

Why is this happening?

The bacteria are so small that they cannot be seen with the naked eye. But if they are placed on a nutrient medium and create comfortable conditions for reproduction for them, then each bacterium grows into a colony of thousands of bacteria. And now the colony can already be seen through a microscope. Growing bacteria may not be easy. Therefore, do not give up if your first attempts fail. But when the experiment is successful, count the number of colonies and pay attention to the differences in color, shape and size. Where did you find more bacteria? Try adding a drop of hand sanitizer or a toilet cleanser in the middle of a growing colony. Will there be changes in the growth and shape of the colony?

How to grow bacteria cultures in a petri dish

It works on the principle of a wiki, which means that many of our articles are written by several authors. When creating this article, 18 people (a) worked on its editing and improvement, including anonymously.

The number of sources used in this article: 9. You will find a list of them at the bottom of the page.

Have you thought about growing an entire culture of bacteria, say, science or fun for the sake of? Strange as it may seem, this is surprisingly simple. All you need is an agarized culture medium, several sterile Petri dishes, and bacteria!

Creation of all necessary conditions

First you need to prepare a nutrient broth in which the bacterium can grow and develop. To do this, you need to cook meat, preferably, boil it as long as possible to get a good fat. Then, agar is added to it: for every 60 ml of liquid - 1.2 g. Mix and heat everything until completely dissolved in the microwave. Then cool. In order to prepare a Petri dish, it will be sufficient to sterilize it with boiling water. But it is worth remembering that this is best done near the gas burner, in order to prevent the ingress of bacteria from the air. Only in such cases can it be considered that the experience will pass “purely”. The resulting liquid is poured into a sterile cup so that it only slightly covers the bottom. After that, close the container with the upper cup and carefully place it in the refrigerator, turning the bottom half upwards to avoid drops of condensation. You need to wait until the formation of a jelly-like mass. The result is a Petri dish with a nutrient medium at home.

Bacteria colonization

It is necessary to get previously prepared Petri dishes from the refrigerator and give them time to warm up to room temperature. To grow bacteria “from your own hands” you need to alternately touch your fingers with the available nutrient medium. But you need to do this very carefully, to save the whole surface. At the end, close the container very quickly with the top cup. Mark and leave in a warm place. A prerequisite is maintaining the temperature. For the development of bacteria, +37 degrees is suitable. A thermometer will help in determining the most suitable place in the house. To "colonize bacteria", you can use starch, which is in ordinary potatoes. Grate potatoes (20 g) and mix with agar (4 g), and add glucose (2 g) for the best effect. The resulting porridge is boiled in a measuring cup. The resulting liquid is poured into a Petri dish, and then left to dry. Rubbed with a sterile cotton swab to the surface where bacteria are visible, which are then transferred to the prepared nutrient medium in order to further develop them. It is possible to determine what kind of colony of microorganisms has developed in a Petri dish using numerous methods. Each distinguished culture has its own characteristics. At home, a particular colony of bacteria can be identified by shape and color.

Material recycling

At the end of the experiment, it is necessary to get rid of the grown microorganisms correctly:

  • For your protection you need to wear gloves and, if possible, a mask,
  • Pour Petri dishes with a solution of chlorine and do not touch for several minutes,
  • Pour out the contents, rinse the cups and put them in a plastic bag, throw them in the bin.

You must never forget that you need to carefully grow microorganisms on your own. In no case, you can not use any biological fluids, such as saliva and the like. Since it can cause serious health effects.

Solution features

Culture media are classified by composition, purpose, consistency. There are two main groups: production and diagnostic.

  1. Production environments are the basis for the manufacture of medical drugs, bacteria for septic tanks. Solutions allow quality control of bio-substances. In such culture media for the cultivation of bacteria cultures, there should be no harmful toxic impurities that can harm a person or affect the life processes of colonies.
  2. The following subgroups of the intended purpose are distinguished in diagnostic nutrient media:
  • to highlight certain types of bacterial cultures (differential),
  • for growing a wide range of colonies of microorganisms,
  • to isolate a specific type of pathogen, storage media (enrichment of bacteria with waste products secreted by them).

According to the consistency, they distinguish:

In dense and semi-liquid nutrient media, the main component is the liquid base, to which agar is added. This is a polysaccharide that is released in the laboratory from some varieties of seaweed.

Cultivation of culture colonies in a medium with the addition of agar can be done at home or in the laboratory, be sure to adhere to room temperature conditions. This is due to the fact that even at a temperature of + 25-30 ° C, gelatinous media melt. In a semi-liquid form, they are placed on the surface of the Petri dish until completely hardened.

The most common solid media: blood serum, eggs, colonies can also be grown on potatoes.

Popular and affordable inventory

The cultivation of microorganisms in a Petri dish is one of the most common methods for obtaining the necessary bacteria, characterized by ease of use. It is suitable for lactic acid cultures as well.

A Petri dish is a container for a laboratory and a home, which is two flat dishes with vertical, low edges. The larger dish serves as a lid.

In order to grow colonies in a nutrient medium, Petri should be prepared accordingly. For sterilization, a glass jar is poured over with dry heat using an oven. Then carefully poured onto its surface medium cooled to 55 ° C (molten), adhering to the horizontal position of the dishes. You can use any brushstrokes - from cracks in the floor or baseboards, from a table in the kitchen, even from your own skin. Gently brush a cotton swab with invisible test subjects onto the cup and close the lid. Place the cup and follow the changes daily.

It is important to know that dense nutrient media can be used in a Petri dish. This allows, in addition to cultivation, sieving, isolation of colonies of an isolated type, and evaluating the sensitivity of bacteria to antibacterial spectrum preparations.

To count the number of culture colonies at home or in the laboratory, just bring a Petri dish to a source of bright light. Availability and ease of use of this equipment greatly simplifies the process of growing bacterial colonies.

Strains for the food industry

To ensure that milk-based food production is at a high level, providing consumers with the necessary volumes of yoghurts, kefir and other lactic acid products, technologists isolate bacteria, select them and make starter cultures.

Lactic acid strains are obtained in the laboratory from whey with the addition of:

  • corn extract
  • growth stimulants
  • buffer salts.

The cultivation of lactic acid microorganisms, divided into two groups - sticks and streptococci - requires exposure to time and temperature limits.

Growing microorganisms for wastewater treatment

To achieve maximum efficiency in the filtration of wastewater, certain types of bacterial cultures are used. For owners of a septic tank, this is an indispensable substance that helps prevent the spread of unpleasant odors, and activates the mechanism for processing organic deposits at the bottom.