Hi both,
According to my understanding, what you said is right yvetteds. In a population of bacteria out in nature, many genes are present and each of these bacteria may express these genes in different ways. When exposed to an antibiotic or antimicrobial substance, this population of bacteria should die off if they are susceptible. However, it is possible that a small percentage of the population may survive due to expressing some gene in a different manner that confers resistance, or there may have been natural mutations that have occurred that (fortunately for those bacteria) confers resistance. Since the "resistant" bacteria are the ones that survive, they are the only ones that will reproduce and eventually all their descendants will have that same resistance.
However, if bacteria are repeatedly exposed to antibiotics, this stress could cause the bacteria to start mutating like crazy in hopes that certain mutations will allow them to cope with and survive this stress. This is potentially how many antibiotic resistant bacteria have arisen in clinical settings because overuse of antibiotics (especially in situations where they are not necessary) can greatly hasten the development of resistance. If you are interested in this topic more, here are some good articles to look at:
1)
http://www.sciencedaily.com/articles/a/ ... stance.htm
2)
http://www.icr.org/article/do-bacteria- ... tibiotics/
Other microbiologists in this forum... I hope I have explained this correctly. If not, feel free to share your opinion or correct anything.
According to my understanding, yvetteds, I think Anthony is saying that he is trying to test whether the bacteria will eventually "develop" resistance against the antimicrobials if you continually expose them to the antimicrobial. So Anthony, that prompts me to ask this question: What is the main question that you are trying to test? From our earlier discussions, it seems like you want to see whether the essential oils you've chosen have antimicrobial activity. In this case, the procedures that you've proposed are sufficient to answer the question of whether your compounds will kill/inhibit growth of your bacteria at whichever concentrations you have chosen to test. However, if your main question is if the bacteria can develop resistance to these antimicrobial compounds after repeated exposure, that will be a more difficult question to answer. First of all, you have to determine their susceptibility to these compounds. If they're already resistant to these compounds, that means that either these compounds don't have antimicrobial activity, or the bacteria are naturally resistant to them. If the bacteria are susceptible to these compounds, you would then have to repeatedly expose these bacteria to the antimicrobial and see if you eventually select for growth of resistant clones. I would suggest to not do this because it can potentially be dangerous if you select for a clone that is highly resistant to your antimicrobial compound because not only can the compound no longer kill your bacteria, but there is no way of knowing how this will affect the bacteria's response to other antimicrobials and antibiotics. However, if other experts have a different opinion, please share. There are also other parameters you have to consider because: 1) You don't know how long you have to expose the bacteria to the antimicrobial to see resistance show up, if it ever even shows up. 2) If all your bacteria died after the first exposure, there will be no other bacteria for you to continually expose the compound to.
And Anthony, one last thing about the culturing without the shaking, you can take the culture out after 24 hours and see if the broth has become more turbid--if it has, that indicates that the bacteria have grown. You should probably just put in a tube with broth but no bacteria inoculated into it as a negative control for growth. Your negative control broth should still remain clear after 24 hours in the incubator, whereas your broth with bacteria inoculated into it should become more turbid if the bacteria did grow!
I think the project you have proposed on looking at the antimicrobial activity of essential oils is already quite interesting and I think it will give some cool results! As for the question about whether you can make antimicrobial resistant clones, I would suggest to not do that due to potential health hazards, BUT... if other experts have any ideas to conduct these experiments safely or think that it's not a huge problem selecting for resistant clones, please share your ideas because I am sure that Anthony would benefit from them! Let me know if I didn't explain some parts clearly, Anthony, or if you have more questions. It is very important for these science fair projects that you clearly understand how these experiments are testing your question/hypothesis!
Best,
Connie
