Petri dish lids
prevent dust from falling directly onto plates but allow diffusion of air around the edges
. There are no direct air currents into the plate, and to enter, dust particles would have to rise vertically more than a centimeter. This does not often occur because of the density of the particles.
Why is it important to keep the lid on petri plates and the cap on test tubes containing growth medium?
After the culture medium is set, and streaked with the required microbe/stock, the lid is put on and the
petri dish is incubated upside down to minimize contamination
. So, it is easier to read the label on the bottom. … agar plates must be kept with lid on to avoid contamination when not being used.
Why should you hold the lid over the plate while streaking?
Lift
the lid slightly ajar and hold it at an angle
, while you are streaking the plate. While this prevents contaminated dust from falling on plate, it may be difficult to see what you are doing.
Why is the cover of the petri dish slightly opened during inoculation of the plate?
Reason –
The lid stops additional unwanted bacteria in the air contaminating the plate
. Do not fully seal the lid, as this will stop oxygen reaching the bacterium, and this may encourage harmful anaerobic bacteria to grow.
Why is it important to close the lid of the petri dish immediately after transferring the bacterial sample to the medium?
The most exasperating problem confronting attempts to cultivate moulds is contamination by other moulds. Most mould spores are very light and easily transported by air. Even opening the lid of a Petri dish for a few seconds may allow the
entry
of contaminating organisms.
How does keeping the lids closed on tubes and petri dishes keep things from getting contaminated?
Petri dish lids prevent dust from falling directly onto plates but
allow diffusion of air around the edges
. There are no direct air currents into the plate, and to enter, dust particles would have to rise vertically more than a centimeter. This does not often occur because of the density of the particles.
What is the purpose of the spread plate technique?
The spread plate method is a
technique to plate a liquid sample containing bacteria so that the bacteria are easy to count and isolate
. A successful spread plate will have a countable number of isolated bacterial colonies evenly distributed on the plate.
What is the purpose of flaming the loop between streaks areas?
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 purpose of keeping the inoculated media in the incubator with 37 C temperature?
To do this, a sample was harvested and placed onto a sterile dish and into the incubator. The air in the incubator was kept at 37 degrees Celsius, the same temperature as the human body, and the incubator
maintained the atmospheric carbon dioxide and nitrogen levels necessary to promote cell growth
.
Why is the lid only partially removed during streaking?
the lid should
partially cover the plate while the student is removing inoculum
, as shown in this photograph. This technique prevents airborne microbes from contaminating the surface of the agar.
What is the purpose of transferring the cultures to the refrigerator after the incubation period?
If you cannot return to lab during an “open lab” period, then incubate them at room temperature, or arrange to have your cultures transferred to a refrigerator after they grow, so
that the culture won’t die out before you can finish your experiments
.
Why should you keep test tube lids on your inoculated cultures for incubation screwed on loosely?
Leave the lid
loose on your slant so that the bacteria have access to oxygen
.
Are petri dishes airtight?
No,
our petri dishes are not air tight
. … Most petri dishes are going to be loose so that the germs inside, when applied, can breathe and survive. Most experiments require you to tape the two lids together but that might not be something that works for you.
What is the importance of petri dish?
Petri dish is majorly
used as laboratory equipment in the field of biology & chemistry
. The dish is used to culture cells by providing storage space and preventing them from getting contaminated. Since the dish is transparent, it is easy to observe the growth stages of microorganisms clearly.
Why should petri dish not be left open?
Petri dishes should not be kept open to
reduce the risk of contamination by air microbes
. Cross contamination can occur as a result. If a petri plate becomes contaminated by microbes, it will interfere with the growth of the target microbes within the plates, and it will hamper the cell culture process.
What is the purpose of the slanted surface in an agar slant?
Slanting the surface of the agar
gives the bacteria a greater surface area on which to grow in a test tube
. Furthermore, slants are created in test tubes that can be capped, which minimizes water loss. This is important because of the high moisture content of agar media.
Why is it important to hold open culture tubes in a nearly horizontal position?
Why is it important to hold open culture tubes in a near-horizontal position?
So that microbes don’t fall off/out
.
What is the purpose of spread plating and streak plating in isolating cultures?
Colony streaking leads to to the isolation of individual colonies, which are a group of microbes that came from one single progenitor mircrobe. Spread plates
allow for the even spreading of bacteria onto a petri dish
; allowing for the isolation of individual colonies, for counting or further experiments.
Where should lids be placed while doing an experiment?
Do not place the lid face down on the bench top
; avoid placing it on the bench all together. Do not leave plates uncovered. Do not walk around the room with an open plate. When working with cultures in test tubes, work diligently and as fast as possible.
How do Petri dishes work?
The agar and other ingredients are dissolved in warm water and poured into the
dish
and left to cool down. Once the medium solidifies, a sample of the organism is inoculated (“plated”). The dishes are then left undisturbed for hours or days while the organism grows, possibly in an incubator.
What is the advantage of spread plate over pour plate?
Heat sensitive microbes are not affected. No subsurface colonies appear in spread plate so
isolation of the organism is easy
.
What is the purpose of ethanol in the spread plate technique?
What is the purpose of the ethanol in the spread-plate technique?
Kills off bugs on “L” shaped spreader before putting it into contact with the spread plate.
Why is flaming the inoculating loop important?
Significance of Flaming:
Flaming the loop:
Holding the loop in the flame of the Bunsen burner kills all contaminating organisms, thus sterilizing the loop
.
Why is it important to use a sterilized loop between streaks when preparing a streak plate?
Don’t forget to sterilize.
Flame the loop or use a new disposable loop after you streak each quadrant. Using a new or sterilized loop
allows you to effectively dilute the inoculum on the plate and obtain isolated colonies by spreading the inoculum thinner and more evenly
.
What is the purpose of flaming the bacterial loop before use and after use?
The purpose of flaming the inoculating loop is
to sterilize it to make sure that there is no unwanted bacteria left on the inoculating loop
. You should sterilize the inoculating lopp before and after you use it. what would happen if the loop was not flamed?
What is the purpose of incubation in microbiology?
Incubating the plates
to promote growth of microbes
is an essential part of any microbiology investigation. Incubating in aerobic conditions, and below human body temperature, reduce the risk of encouraging microorganisms (particularly bacteria) that could be pathogenic to humans.
Why is the cover of the petri plate removed before exposing the plate to UV radiation?
Why do you remove the cover prior to exposing the dish to UV light?
UV light does not penetrate well, and can not penetrate the plastic
.
When streaking a plate the lid should be?
Open the lid of the plate sufficiently (
45 degrees
) to introduce an inoculation loop and only for the time it takes to obtain inoculums. Rotate the plate counter clockwise 90 degrees and cross the prior streaks to pick up some bacteria and spread them into the next quadrant (Repeat in all the four quadrants).
How is streaking done?
The streaking is done using
a sterile tool
, such as a cotton swab or commonly an inoculation loop. The inoculation loop is first sterilized by passing it through a flame. When the loop is cool, it is dipped into an inoculum such as a broth or patient specimen containing many species of bacteria.
Why is it important to keep the culture at the correct incubation temperature?
The primary reason for incubating bacterial cultures at different temperatures is
that specific bacteria are adapted to grow best at different temperatures
. … Lastly, bacteria adapted for freezing conditions are known as psychrophiles, and can survive down to -4 C (25 F).
What is the importance of the uninoculated and inoculated conditions?
b) Its main purpose is
to verify that the hydrogen peroxide hasn’t deteriorated into oxygen and water
. To a lesser extent, it shows novice microbiologists what “bubbling” looks like. Consider the step in the tube test where hydrogen peroxide is added to the uninoculated tube.
What do we use to seal Petri dishes?
Parafilm
is a flexible film, available in several different lengths and widths. It is commonly used for sealing or protecting containers, like our Petri dishes.
What do we use to seal Petri dishes after inoculation?
Your Petri dishes should be sealed with
tape
and kept in sealed plastic bags since you are working with unknown organisms.
How do you seal agar plates?
The best option is to use
3M Micropore tape
that can be bought from medical stores It is highly porous and highly effective in blocking particles the size of bacteria and above. You can use cleanwrap of cling film for sealing the plates. You can also use surgical tape. You can use PVC film.
Why is it necessary for cultures intended for further use be stored in the refrigerator 40c?
Cultures stored at 4°C
are sensitive to more rapid die off than frozen or freeze dried bacteria
. Often researchers store cultures on plates which are very susceptible to fungal contamination and drying. Consequently, refrigerated bacterial stocks are best stored in small vials containing agar media.
Why do you have to keep cultures inside the refrigerator?
The goal of preserving the cultures is
to slow that death rate
so that when the culture is revisited, some of the cells are still viable and available for culturing. The reasons the cells die can be numerous, but in every instance are based on the inherent chemistry of the cells and their environment.
What is the purpose of preparing a stock culture?
Stock cultures are microorganisms maintained for the purpose of
keeping the microorganisms viable
. Maintaining cultures internally may seem like the most cost-effective solution.
What is the purpose of keeping the inoculated media in the incubator with 37 C temperature?
To do this, a sample was harvested and placed onto a sterile dish and into the incubator. The air in the incubator was kept at 37 degrees Celsius, the same temperature as the human body, and the incubator
maintained the atmospheric carbon dioxide and nitrogen levels necessary to promote cell growth
.
Why should you never set the lid of the petri dish or the test tube cap on the bench top?
Never set them on the table,
as they could pick up contaminants
. … Also, keep the lid over a plate when removing inoculum, as this will help prevent environmental contamination. Always flame the lip of a culture tube when you open it and before you replace the cap.
What should be done with tube caps when using proper aseptic technique?
If you remove a cap or cover, and have to put it down on the work surface,
place the cap with opening facing down
. Use only sterile glassware and other equipment. Be careful not to talk, sing, or whistle while performing sterile procedures. Perform experiments as rapidly as possible to minimize contamination.
What is the purpose of agar?
Agar is commonly used in the laboratory to
help feed and grow bacteria and other microorganisms
. It acts as a culture that provides nutrients and a place for these items to grow, but since it is indigestible to the microorganisms, they cannot eat and destroy it.
Why are plated media stored in an inverted position?
Plates should be stored in the inverted position
to prevent moisture from contacting the surface of the media
. Media should never be exposed to sunlight or UV light, since many ingredients, especially dyes and indicators, are not stable upon light or heat exposure.
