Steak plate method for isolation of bacteria—modified for home preparation during COVID
READ THIS WHOLE DOCUMENT FIRST, BEFORE YOU BEGIN ANY WORK!
GOAL: the intention is to allow student to gain some experience and familiarity with inoculating a petri plate in order to isolate the species from a body sample. Students will use tryptic soy agar plates (college-provided) and cotton swabs (student-provided) to practice inoculating (=placing the sample on the plate) body samples collected using a cotton swab.
ABOUT THE PETRI PLATE: Petri dishes are special plastic containers that in Microbiology will be made into Petri plates when sterilized agar media are poured in and allowed to solidify. They consist of a top and bottom, the bottom being where the agar medium is poured, and the top is the lid. The lid is not tight fitting to allow for easy opening and closing during the inoculation process. The lid simply sits by gravity over the plate bottom (containing the agar) to prevent things from falling on the agar surface. If that thing is a microbe, the lid protects against growth of that unwanted introduced microbe; microbes we do not intentionally put on media for inoculation are called contaminants. You could think of contaminants like weeds in your garden–they just seem to pop up, and were not put there, and are, therefore, unwanted! Plates are always stored/placed upside down—this prevents any condensation (that forms from trapped water vapor) from falling on the agar surface. Wet agar surfaces don’t allow bacteria to grow at all, or to grow well (not in the pattern intended).
OBSERVATIONS:
How long did growth take to appear?
Is the growth typical of bacteria (smooth and paste-like) or mold (hairy and filamentous), or do you see both? if you grew mold, try to ignore it since it is not from your body!
Focusing on the bacterial colonies only, based on differences you see in relation to colony size, color, shape, surface attributes (like smooth, shiny, wrinkles, for example), determine the number of different species you have and record here.
Do you have good isolation of the different species in your sample (colonies of the different types that are not touching)? You may have some species that are well-isolated while other are not, please note any differences you see.
Using the lab manual to identify the correct terminology for colony description, describe one well-isolated colony (or, if you didn’t get good isolation then note the color and surface features only). Write NA if you did not get isolated colonies.
IF you didn’t get growth on some or all of your plates, explain what you think are the possible reasons why you didn’t get growth.
Tell us about your overall experience—
Were you successful? (how do you know?)
Were there any things you would do differently?
Did you make mistakes?
Did your agar crack?
Did you make improvements after the first plate you inoculated–what adjustments did you make?
Did you follow the steps in the right order, or did you forget anything?
Please share any final thoughts about this experience of streak plating.
You must include, along with this completed document, pictures of your labeled plates (your labels must be clear and visible in the pictures) BEFORE incubation (growing them).
You must include pictures of those same plates (your labels must be clear and visible in the pictures) AFTER incubation (growing them). Make sure that the growth is visible in the pictures if growth occurs. Include pictures of ALL plates, even the ones that did not grow any microbes.
PROPER PLATE DISPOSAL—once you make your observations and take your photographs, wrap up your plates so they cannot be opened, put in your ziplock bag and place in another bag and tape that bag shut. Place it in a secure outdoor trash bin so that no person or animal can get into them!
Figures from https://greenbioresearch.com/culture-bacteria-usin…
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