fungus on a hard surface

[vice]

How can you test for fungal growth and bacterial growth on a hard surface? It would need to be tested for repeated days on a small plastic test surface. Vice

[donnahardy2]

Hi,

There are two basic methods for microbial testing on sold surfaces. One method involves swabbing a sterile swab using a defined surface area, and the second method is by contact plates that are pressed onto the surface. The basic methods including the advantages and disadvantages are described in the following website:

http://faculty.weber.edu/coberg/3853%20 ... edures.htm

Here is information from the Science Buddies website on microbial testing:

https://www.sciencebuddies.org/science- ... ques.shtml

Be sure to check out the Science Buddies safety guide on microbial testing.

https://www.sciencebuddies.org/science- ... fety.shtml

If you are interested in both bacteria and fungi, you will need two different types of culture media. Do you know what media you will be using for the two groups of microbes? What is the purpose of your project?

Donna Hardy

[vice]

Actually I will be testing a cleaning solution over many days and not actually the plastic like I originally thought. I want to test for both fungus and bacteria. Would I dip a swab in the solution and then swab an agar like plate? Is there one for fungus? Would I keep adding to the same plate over the days? or do different plates for different days? Vice

[lilyc]

Hi Vice,
Both bacteria and fungi will grow on agar plates (wikipedia has a good overview: http://en.wikipedia.org/wiki/Agar_plate) -- actually, mold that sometimes contaminates bacterial plates in labs are all fungi.

From what you have posted, it appears that you want to test the efficacy of some type of cleaning solution designed for plastic surface-- is this correct?

Before you begin, however, you should consider a few factors, such as:
1) What kind of mold and/or bacteria am I interested in growing? Where may I find sources of these bacteria/mold?
2) What chemicals are in my cleaning solution, and what effects are they predicted to have on certain types of bacteria and mold?
3) What factors will I be holding constant (controls), and what factors will I be changing (variables)?

Try to elaborate more on what it is exactly you want to investigate first.

Lily

[donnahardy2]

Hi,

To grow fungi, you can use potato dextrose agar. For bacteria you can use nutrient agar. Here is a homemade recipe for both media:

http://en.wikipedia.org/wiki/Potato_dextrose_agar

This recipe does not include a source of nitrogen, so I would recommend adding 2 grams of yeast extract, available from a health food store, to ensure growth of a wide variety of fungi.

For bacteria, you can use the following recipe for nutrient agar:

http://www.science-projects.com/PlatesSelfMade.htm


Since it sounds like sterile swabs would be more convenient for you to use, you can use a sterile swab to collect the microorganisms from a specific surface area for each sample and then transfer the swab to a tube containing 1 ml of sterile water. The microorganisms could then be resuspended into the water by mixing well. You would then transfer 0.1 ml of the water to the surface of each plate and use another sterile swab to spread over the surface of the plate evenly. I recommend that you do a trial run and test this procedure before you do a major experiment. You want to practice your sterile technique and adapt the method to the materials you have available to use. If you will be comparing your results over time, you want to make sure that your technique and growth media will give consistent results.

What will you use for a control in this experiment?

Donna Hardy

[mbadtke]

Vice,
In addition to the great ideas others have posted, something else to think about is how you will count the fungi or bacteria you find on your plates. Will you try to count individual colonies or try to estimate the numbers? If you have too many to count you could also think about diluting your samples before plating. This sounds like a great project!

Matt Badtke

[lilyc]

To elaborate more on what Matt was saying in the previous post, a common way of counting bacteria colonies is using a microscope and a grid. If the bacterial colonies (or fungal colonies) appear fairly evenly distributed on a plate, you may divide up your plate into, for instance ten sections, and only count one or two of the sections, and multiply appropriately to get a good estimate of the number of colonies you have on your plate.

[donnahardy2]

Hi,

I just realized I didn’t completely answer your question. An agar plate is used just one time for one sample. Once the surface has been swabbed and the sample transferred to the surface of the agar plate, the plate is turned upside down and incubated for a few days to allow the bacteria and fungi to grow. A new agar plates will be needed for each sample.

How are your going to tell the difference between bacteria and fungi?


Donna Hardy

[vice]

How do you tell the difference between bacteria and fungus? If you grow on different media can you tell the difference? Vice

[donnahardy2]

Hi,

Fungi grow as furry, fuzzy colonies on an agar plate; they start out as white fuzz and usually turn dark green, brown, or black as spores develop after a few days. Fungal spores are ubiquitous, which means that they are floating around in the air always ready to germinate and grow as soon as they land on a suitable growth medium like an agar plate or a damaged piece of fruit. Bacteria appear as a wide variety of colony types and are usually white or translucent, but can have a wide variety of colors. Yeasts are fungi, but the appearance of the colonies is similar to bacteria. The Science Buddies website guide has a useful guide to introduce this topic.

https://www.sciencebuddies.org/science- ... ates.shtml

Identifying the specific fungi and bacteria in your samples will be outside of the scope of your project, but you should plan to use the official terminology to describe the form, elevation, and margin of the colonies that grow from your samples.

So what is the purpose of your project?


Donna Hardy

[vice]

I am doing 3 solutions 4 ways each. I plan to test for bacteria or fungal growth every 5 days. I am assuming I won't get any growth for 15 days but more like 20+ days. That is at least 36 agar plates for each test. One test is going to be at least 36 if not 48 plates. Or start day 10? The solutions should not get contaminated right away but what if I wait too long? Because of cost, can I do just one set of the 12? Should I do a second set? Vice

[donnahardy2]

Hi,

Your project sounds very ambitious. Are you planning to have separate fungal and bacterial media plates? Do you have time to do a pilot experiment before you invest in so many plates? It sounds like you are planning to do a growth curve, which requires lots of dilution and lots of plates. Can you describe your experimental protocol in a little more detail? I’m not sure why you think that you won’t get growth for 15-20 days. Please include the temperature you will use to incubate the plates. Perhaps I can suggest a protocol that will require fewer plates.


Donna Hardy

[vice]

I am using a syringe to measure .1ml of each solution. How can I sterilize it between solutions. I am doing this at home. If using cotton swabs to streak, do I make four sections like it shows to streak? Or can I just make big streaks across agar? Do the streaks need to follow the same pattern on each plate? Also, I don't have an incubator so once I plate what do I do with plates? One source said to put in plastic bags and turn upside down for three days. Should I section off plates before I streak to help count in case I get growth? I am seeing which solution shows contamination first Vice

[donnahardy2]

Hi Vice,

To sterilize the syringe in between samples, you could use 70% isopropanol, and then rinse it with sterile water 3-4 times. If there is any residual alcohol, it will inhibit the microorganisms, so you want to make sure it is rinsed thoroughly.

Since you are doing this at home, you should put each Petri dish in a zip-lock plastic bag, and invert it and incubate it at ambient temperature, although try to choose the warmest place available. Use a thermometer to measure the temperature of incubation. You should observe the growth of the bacteria/fungi through the plastic bag. Avoid opening the plates since you will be growing unknown microorganisms.

I think you will be using the 0.1 ml/ sample from the syringe to apply your sample to the surface of the Petri dish. After you do this, use a sterile cotton swab to spread the 0.1 ml/ evenly over the portion of the plate you are using. Label the back of the plate with a Sharpie so you will remember what is in the plate.

What kind of agar are you using? Do you have some sort of positive control to use?

Donna Hardy

[vice]

I have two samples of each type of solution I am using. Can I take half from each for one agar plate or should I really use one for each. I may be testing several days and I have 12 types but two of each type. It will be expensive to test both from each type. Vice