Non-nutrient Agar Usually not suitable for growing bacteria. However, may be used for growing other microorganisms. Nutrient Agar Will grow the largest number of different types of microbes - fungi and bacteria. Yet, not all bacteria can grow on these. Some find it too rich, and others find it deficient. The nutrient in this is beef broth, and some extracts from yeast.
Sabouraud Agar Used for fungi and has a low pH that will kill most bacteria. It contains gentamicin, which is a aminoglycoside antibiotic. Gentamicin can also treat many different types of bacterial infections, particularly Gram-negative infection. Thayer-Martin Agar Chocolate agar designed to isolate Neisseria gonorrhoeae , also known as "gonococcus," which is a species of Gram-negative bacterium responsible for the disease gonorrhoea.
Tryptic Soy Agar A basic medium used for culturing many kinds of microorganisms. Tryptic soy agar is mainly used as an initial growth medium for the purposes of: observing colony morphology, developing a pure culture, achieving sufficient growth for further biochemical testing, and culture storage.
XLD Agar Xylose lysine deoxycholate agar. It is used for the culture of stool samples, and contains two indicators. It is formulated to inhibit Gram-positive bacteria, while the growth of Gram-negative bacilli is encouraged. The colonies of lactose fermenters appear yellow. Preparing Bottled Agar and Plates 5 Pre-experiment: Keep sterile Petri dishes closed until ready to pour agar into them.
Air-borne contaminants can easily invade an open Petri dish. Although pre-poured agar plates are available, one can make agar plates from tablet, powdered, or bottled agar by following a few simple instructions. Agar kits usually come with detailed instructions on how to prepare plates, and below are sample procedures for reference. When in doubt, be sure to clearly read the instructions and ask for help if needed either consult a teacher or call the technical help line of the agar kit supplier.
The formulation for LB Luria Bertani agar is: 9. If using tablets, dissolve 10 tablets per ml of water. For agar powders, dissolve by microwaving, 6. Stack agar plates upside down in the refrigerator. These materials supply a variety of carbon sources, nitrogen compounds in the form of amino acids, and a mixture of cofactors, such as vitamins. This basic medium can be further enriched to support the growth of more fastidious types of bacteria by the addition of carbohydrate sources, yeast extract, and materials such as plasma or blood, which provide a variety of complex nutritional factors.
A broth medium is one in which the components are simply dissolved in water. The addition of agar-agar a complex carbohydrate extracted from seaweed results in a solid medium. Agar is an ideal solidifying agent for microbiological media because of its melting properties and because it has no nutritive value for the vast majority of bacteria.
Because microbes are ubiquitously distributed in the environment, during the preparation of any culture medium, bacteria are introduced from many sources such as glassware, dry medium components, air, and so on. Related questions How does osmolarity affect bacterial growth? How do bacteria differ from a virus? How do cyanobacteria affect the planet's atmosphere? What are some examples of cyanobacteria?
What are some examples of bacteria? With this in mind, your instructor may have you watch a brief video that demonstrates the art of media making. Pre-sterilized glass or plastic graduated pipettes Figure 5 are used to transfer specific volumes of sterile liquids accurately.
It is important that you learn how to use these tools correctly, since it may be necessary to transfer sterile and sometimes contaminated liquids among various bottles and tubes. Their appropriate use will be discussed and demonstrated in lab.
Some tips to remember:. A portion of a 10 mL graduated pipette is shown in Figure 6. What is the volume of liquid in this pipette? Solid and semi-solid media. Growing cultures of bacteria on solid media agar plate or slant permits us to view and identify colonial characteristics, and also provides a way to separate bacteria in a mixed culture.
Bacteria may be grown in agar slant or stab media in tubes if the purpose is to maintain them in a longer term culture. Generally, bacteria grown on slants will remain viable for a few weeks to a few months, and sometimes longer if stored in a refrigerator. In this laboratory, you will be introduced to aseptic techniques and basic lab skills needed to grow and maintain bacteria in culture.
You will be applying these skills often, so mastery is important. Below, write the names of the two bacteria in the mixed culture and the appropriate BSL, as specified by your instructor:. The techniques needed will first be demonstrated by your instructor. Using aseptic technique, use a 10 ml graduated pipette to transfer 2 ml of broth to each tube. As demonstrated, use a flame-sterilized inoculating loop to pick up from the surface of the M. Note how the broths look immediately after you inoculate them they should still look mostly clear.
Bacterial growth in broths is indicated by the development of a cloudy appearance. If the newly inoculated broth looks cloudy at the start, you will have no way to determine if this is due to bacterial growth during the incubation period. If your broth looks cloudy, discard it and make another broth using less bacteria. Place the broth subcultures in an incubator at the temperature and time specified by your instructor.
Separation of a mixed culture into individual colonies that can be subcultured to make pure cultures depends on how well the streak plate is prepared. The goal of streak plate method is to dilute the cells by spreading them out over the surface of the agar. This is accomplished in stages, as will be demonstrated in lab before you try it yourself. Use the simulated agar surface below to practice the streak pattern using a pen or pencil.
Also write M. As demonstrated, use a sterilized inoculating loop to pick up one M. Spread the bacteria over approximately a quarter of the plate, edge to edge. Consider this step 1. Flame the loop and cool it in the agar. Overlap the step 1 streak times to pull out a reduced number of bacteria, and spread them out down the side of the plate.
Consider this step 2. Overlap the step 2 streak times and spread over the surface. Continue this process, flaming the loop in between each step, until the entire surface of the agar plate is covered. After performing this with the M. Place the streak plate subcultures in an incubator at the temperature and time specified by your instructor. Obtain one slant tube containing TSA, and label it using a small piece of tape with your name and culture name M.
Using a sterilized inoculating loop , pick up a bacterial colony or piece of a colony from the surface of the plate culture of M. Place the slant subculture in an incubator at the temperature and time specified by your instructor. Obtain one stab tube containing semisolid TSA, and label it using a small piece of tape with your name and culture name E.
Using a sterilized inoculating needle , pick up a bacterial colony or piece of a colony from the surface of the plate culture of E.
Withdraw the needle carefully and try to remove it by following the same stab line that you made pushing the needle down.
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