Science Buddies: "Ask an Expert"

I need help to find the precise procedures for my project, What type of bottle plastic or stainless steel has the least amount of bacterial growth. Thank you!

Hi,

Welcome to Science Buddies! This sounds like a great idea for a project. There are a number of ways a project like this could be set up. I recommend that you do some background reading on the topic first so you can decide how to set up the experiment with the resources you have available. Here is an abbreviated project from the Science Buddies website that has a good bibliography on antimicrobial compounds and methods for testing:

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

You should also check out all of the microbiology entries in the project guide section for very basic information on microbiology techniques.

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

One way to do this project would be to put a non-sterile liquid (water, juice, or milk) in the different containers and take samples periodically to count the bacteria. Or, you could monitor one or more parameters such as pH shift, change in impedance, or change in turbidity that would indicate that bacteria have reached threshold levels. Or, a more challenging project would be to study the development of biofilms on the different materials. There are lots of possibilities.

Do you have access to a microbiology laboratory? How do you think you will measure bacterial growth? Please let us know if you need more information.

Donna Hardy

Thank you for the welcome! I do not know how I will measure the bacterial growth. Can you list a few ways? Yes, I will be performing this project in a laboratory under an instructor's supervision. Thank you for the links. I still need help with backround research on my project; especially Bacterial Reactiion with water. I will be using water. First I will need to know how to sterilyze the stainless steel bottles. Where can I find the right agar? Also I need to see if there is any bacteria on the bottles before hand. I am still having trouble with the procedures. Thank you so much This is very helpful.

Hi,

You can sterilize your containers by autoclaving or cooking in a pressure cooker for 15-20 minutes. Or you could soak the bottles in 1 M sodium hydroxide or 70% ethanol for an hour followed by rinsing with sterile distilled water. Actually, running the bottles through a dishwasher cycle would probably do a good job as well. You will need to check the composition of the plastic bottles to make sure these are compatible with whatever method you use.

Bacterial growth rates are traditionally measured by taking samples over time and making dilutions in sterile water and transferring the samples to Petri dishes with agar. The Petri dishes are incubated at a suitable temperature and the individual colonies are counted after incubation. This is called a standard plate count and requires lots of agar, but would give excellent data if you could do it.

You could also do a turbidimetric method and measure the optical density of cultures at 600 nm. Do you have a spectrophotometer or turbidity meter available?

You could also use a method that measures bacterial metabolism to detect growth in a broth culture. For example, pH or electrical impedance. Here is a website that gives a brief review of the possible methods:

http://www.rapidmicrobiology.com/test-m ... -Count.php

Please read through the information that I previously posted from the Science Buddies website and Google for additional information on the various techniques. Try to select a method that you can get the materials to do. Let me know if you need more details on any of the methods.

Good luck!


Donna Hardy

Alright, so I know how to sterylize. How many petri dishes and how much agar will I need? Thankyou so much!