Science Buddies: "Ask an Expert"

I am doing a science project where I am testing to see if dental treatments help reduce bacteria in a dogs mouth. So I am going to take a swab of the dogs mouth before and after given a dental chew, I will then transfer this to agar plates to grow? What is the best method to do this? Would I need a control? How do I count bacteria after it is grown?

Hi PearlDaisy,

I hope you are having a great day! Below I have answered your questions and provided some references to aid in the development of your project.

1. I am not too familiar with the bacteria found in a dog's mouth, but I think it would be best to obtain saliva samples to spread on agar plates. I have attached two papers that have used various methods to swab or obtain saliva from dogs (https://jcm.asm.org/content/43/11/5470 and https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4489859/). Your samples would be transferred onto agar plates. However, I think you should dilute your samples (as mentioned in the papers) to make the plate counting method more reliable. If you do not dilute your samples, you will likely have many colonies growing together on your plates, which will be impossible to count. I also think you should focus on identifying 1-2 of the colony types that you get from the initial samples and further isolating them (streak for isolation) to get pure colonies. It is likely that you will get many colony types, which may get overwhelming. You can use morphology, Gram staining, selective media, and other quick methods to identify bacteria types (see more about identification here: https://asm.org/Articles/2020/February/ ... wth,-Stain).

2. I think starting with LB agar and nutrient agar would be good for the samples. If you wanted to be more selective, you could use blood agar or anaerobe agar.

3. Your control would be the saliva samples obtained prior to giving the dogs dental chews, since you will be comparing the samples obtained after giving the dental chew with the bacteria from before dental treatment.

4. Bacteria growth can be quantified using the plate counting method, which involves counting the number of viable colonies on the plate and multiplying it by the dilution factor and taking into account the volume of sample in which you plated.

I know this is a lot of information, but I hope I have been of help to you as you begin planning your project! If you need clarification of anything I have written or any more questions arise, please feel free to respond on this forum!

--Brandi