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2021-05-14

How do you kill bacteria in a petri dish?

How do you kill bacteria in a petri dish?

Measure and compare the size of the kill zone to determine effectiveness of each antibacterial agent. Before disposing of dishes in the trash the bacteria should be destroyed. Pour a small amount of household bleach over the colonies while holding dish over sink.

How do bacteria grow experiment?

Once the culture dish is prepared, use a sterile cotton swab or inoculating needle and swab the inside of your cheek. Very gently rub the swab over the agar in a few zigzag strokes and replace the lid on the dish. You’ll need to let the dish sit in a warm area for 3-7 days before bacteria growth appears.

How do you plate bacteria on a petri dish with agar?

Open the lid of the Petri dish containing your sample and pour the agar in carefully (Panel B of Figure 4). Close the lid then mix the sample with the agar by gently swirling the plate. Allow the agar to thoroughly solidify before inverting the plate for incubation.

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How do you inoculate agar plates with bacteria?

Use of aseptic techniques to avoid contamination

  1. An inoculating loop can be used to transfer bacteria.
  2. To inoculate the agar, lift the lid of the Petri dish and tilt.
  3. Following inoculation, the lid of the Petri dish should be secured in place by strips of adhesive tape for safety reasons.

What happens if you incubate bacteria too long?

If a bacterial culture is left in the same media for too long, the cells use up the available nutrients, excrete toxic metabolites, and eventually the entire population will die. Thus bacterial cultures must be periodically transferred, or subcultured, to new media to keep the bacterial population growing.

What is the advantage of pour plate method?

The most common method for determining the total viable count is the pour-plate method. The pour plate technique can be used to determine the number of microbes/ mL in a specimen. It has the advantage of not requiring previously prepared plates and is often used to assay bacterial contamination of foodstuffs.

What are the disadvantages of pour plate method?

Disadvantages of Pour plate method

  • Preparation for pour plate method is time consuming compared with streak plate/and or spread plate technique.
  • Loss of viability of heat-sensitive organisms coming into contact with hot agar.
  • Embedded colonies are much smaller than those which happen to be on the surface.

What is the difference between pour plate and spread plate method?

The main difference between pour plate and spread plate is that the molten agar is poured on to the inoculum during the preparation of the pour plate whereas inoculum is spread on the surface of the solidified agar during the preparation of the spread plate.

What advantage S does the pour plate method have over the streak plate method?

What advantage does the pour-plate method have over the streak plate method? The pour plate method requires less skill, has optimization built in, and will more likely produce the desired result.

What would happen if you forgot to sterilize your loop in between each quadrant streak?

What is a bacterial colony? What would happen if you forgot to sterilize your loop in between each quadrant streak? You would spread a lot of bacteria back into quadrant one and probably not see isolated colonies.

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Will isolated colonies always be in fourth sector?

Will the isolated colonies always be in the fourth sector on the streak plate? No, sometimes you might get them in the third but usually not the fourth because they’re all so clumped together.

What are the advantages and disadvantages of streak plate method?

Streak plating is a microbiology laboratory method that has two major disadvantages. Firstly, users will not be able to grow obligate anaerobes using this method. Secondly, only organisms that were viable in the original sample are able to be grown.

Why do we Flame the loop between streaks?

Flaming the loop between streaks ensures that the loop starts clean and that only this small amount of bacteria is used to inoculate the next quadrant.

What is the most important reason to streak for isolation?

As you might guess, the purpose of streaking for isolation is to produce isolated colonies of an organism on an agar plate. This is useful when you need to separate organisms in a mixed culture or when you need to study the colony morphology of an organism.

What is the purpose of creating a streak plate?

In microbiology, streaking is a technique used to isolate a pure strain from a single species of microorganism, often bacteria. Samples can then be taken from the resulting colonies and a microbiological culture can be grown on a new plate so that the organism can be identified, studied, or tested.

How can a streak plate become contaminated?

How can a streak plate become contaminated? If the loop is not sterilized. If you drop the plate. If lid isn’t on.

In which quadrant will we find the most bacteria?

first quadrant

How do you describe a streak plate?

Streak plate technique is used for the isolation into a pure culture of the organisms (mostly bacteria), from a mixed population. The inoculum is streaked over the agar surface in such a way that it “thins out” the bacteria. Some individual bacterial cells are separated and well-spaced from each other.

What is a pour plate?

: a plate prepared by mixing the inoculum with the cooled but still fluid medium before pouring the latter into the petri dish.

How do you streak a bacterial culture?

Streak the loop containing the bacteria at the top end of the agar plate moving in a zig-zag horizontal pattern until 1/3 of the plate is covered. Sterilize the loop again in the flame and cool it at the edge of the agar away from the bacteria in the plate that you just streaked.

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What must be done between each phase in a streak plate?

What must be done between each phase in a streak plate? Examine the plate macroscopically for difference in colony characteristics. The medium clears around the colony from opaque to transparent. Gamma-hemolysis: no hemolysis.

What is the difference between selective and differential media?

Selective and differential media are used to isolate or identify particular organisms. Selective media allow certain types of organisms to grow, and inhibit the growth of other organisms. Differential media are used to differentiate closely related organisms or groups of organisms.

Why is the isolation of a single colony important?

Since all of the cells in a colony derive from a single original cell through repeated binary fission; all of the cells in that colony should be genetically identical. Therefore an ISOLATED colony represents a pure source of an organism from which a pure culture can be started.

How do you revive a bacterial culture?

Bacteria. For frozen cultures, thaw the bacterial strain using gentle agitation in a water bath that is set to 25°C to 30°C. Thawing will be rapid; approximately 2 minutes or until all ice crystals have melted.

Why is it important to isolate bacterial colonies?

A pure, isolated colony is what scientists want to start with before beginning an experiment; it allows for consistency and assurance that your sample isn’t contaminated with any other strains of bacteria.

Why are agar plates incubated upside down?

Petri dishes need to be incubated upside-down to lessen contamination risks from airborne particles landing on them and to prevent the accumulation of water condensation that could disturb or compromise a culture.

How is an inoculating loop or needle sterilized prior to use?

How is an inoculating loop or needle sterilized prior to use? Inoculating loops and needles are typically sterilized by holding in the flame of a Bunsen burner until red-hot.

How long do you hold the loop in the incinerator to sterilize it?

Place your loop in the mouth of the incinerator briefly for 2-4 seconds to sterilize it. Do not leave your loop in the incinerator for more than 10 seconds, you will destroy the loop!