Science Buddies: "Ask an Expert"

HI, I need help! My project is what Area has the most bacteria? (BAthroom doorknob for an example.) What should I do just watch the bacteria grow and see what area has the most? or find the shapes and elavation? SHould find what type of bacteria i have found or just see what area has the most bacteria?I looked at the photo taking info on science buddies it didn't help me! how can I take good photos of bacteria in petri dishes without it being blurry? Also what stake pictures of?[/hould i u][/u] PLeaseeee help asap!

I have another question. How do I count bacteria colnies? I have tried but I keep losing count there are so many of them! AndDo I detrimine which area has the most bacteria by the number of colonies? ANd my final question is what does it matter if the bacteria elavation, form, and margin, and color are different then others?
-THX!

Hi,

It is better to have more information than less. For example, let's say one area has a lot more colonies than another area. But, the area with fewer colonies has more staphylococcus bacteria. That area may actually be more of a health hazard than the first one! So, it is always good to take notes, even if you don't end up using the information in your experiment.

I cannot help you with taking good pictures, because I do not know what camera you are using or how it works. I suggest reading the camera's manual and see what you need to do to take close-up shots.

I would take pictures of each petri dish, so I could go back and look at them. Also, if anything interesting grows, you can take even closer pictures for your display board. Think about what you want to show on your board, and take pictures of it now while the bacteria are growing!

Hi,

I have also merged your posts; please keep all of your questions in this one thread.

If you can't count all of the colonies on a plate, divide the plate into sections (it helps to use a Sharpie and a ruler), count the colonies in that section, and then multiply by how many sections you have.

Generally, students do assume that more colonies=more bacteria. Remember, each of your colonies came from a single bacterium that you picked up with the swab.

Form, elevation, margin, etc. matter because they indicate that you have different bacterial species, which may be more or less pathogenic (disease causing) on your plate. So, you might also consider counting how many different types of bacteria you find.

You make the sections, like a pie; the size of the sections has to be the same, but you can have as many as you want depending on how many colonies you can count. I would start by dividing the plate into 4 equal sections and then seeing if you can count all the colonies in one (randomly selected) section. If not, divide each section in half so you have 8, and count all the colonies in one of the sections.

As I said before, generally, students do assume that more colonies=more bacteria in a particular area. Remember, each of your colonies came from a single bacterium that you picked up with the swab.

Hi,
is it possible for bacterial colinies to go away or merge with another one? I am asking this because when I count them one time it was 56 now its 50 am i just counting wrong?

Hi there,

It could be a counting error, but it is certainly possible for the bacterial colonies to grow large enough that they appear to merge together. In fact, sometimes the growth comes out as what is called a "lawn," in which you cannot distinguish any individual colonies. It is not likely that your colonies went away; even if they died, you would still see them on the petri dish.

Do the colonies look larger than the first time you counted? If so, it is likely that some of them may have grown together.

I hope that helps!

Heather

I just wanted to add that it may be useful to dilute out the bacteria a bit before plating them on the plates. This way you there would be less to count and you could then adjust for the dilution factor to get the original amount.

Mike