Antimicrobial Effectiveness

[dana10ramsey]

Hello, I'm planning on doing my science for project on Measuring Antimicrobial Effectiveness with Zones of Inhibition: https://www.sciencebuddies.org/science- ... #procedure. I have all of my materials but I am a bit confused on how to handle my e coli which I ordered from: http://www.hometrainingtools.com/live-c ... D-ESCHCOL/.

I know this question may seem a bit dumb but does the e coli need to be in liquid form in order for it to work properly? Or can I just transfer it straight from the tube?

And also, I was looking into another project about bacteria resistance to antibiotics. Would amoxycillin be an antibiotic that I could use on e coli?

[SciB]

Hi Dana,

Thanks for choosing us as your virtual mentor! I am happy to answer your questions.

Yes, you are correct. You need to use a liquid culture of E coli to coat your plates. Bacteria are grown in two basic ways—on agar in a Petri dish or slant tube and in ‘broth’ in a flask or culture tube. What you will receive is E coli that have been inoculated onto what is called an agar ‘slant’ inside a sterile tube.

In order to do the antibiotic test on E coli you have to have an evenly spread culture of the bacteria on the test plate and the only way you can do that is by having the E coli bacteria suspended uniformly in a sterile liquid such as broth or buffered saline. OK. I know you are wondering where you can get this. Did you already get the agar test plates? I went to the Carolina Biologicals website http://www.carolina.com/bacteria/escher ... ?question= and found the Endzone kit. The E coli that they offer comes as a liquid broth culture which is ready to spread on the agar plates to make the ‘lawn’ of bacteria for the antibiotic tests.

You have two choices. You can order the liquid culture of E coli from Carolina or you can convert your E coli slant culture into a liquid culture. To do the latter, however, you will need some sterile buffered saline and a sterile pipet to transfer some of it into your E coli tube. Does your school biology lab have sterile solutions and sterile pipets? You can’t use the kind of sterile saline solutions they sell in drugstores for contact lens users because these contain an antibiotic and that would interfere with your experiment.

If you have access to a lab and sterile solutions, your problem is solved. If not, then you will probably have to order the liquid culture of E coli. It is possible to sterilize solutions and pipets using a microwave, but this would require that you get distilled water, make a saline solution in a glass bottle with a top, find a glass dropper that you can use as a pipet, then do a google search for how to sterilize in a microwave.

As for your second question—that’s an easy one! Yes, amoxicillin makes a dandy control as it will kill E coli K12 very effectively. The K12 strain of E coli is not the same as the one that causes human disease, O157:H7. If it were a human pathogen, you would have to get special permission to use it and you would have to work in a lab under Biosafety Level 2 (BSL2) conditions. The drug-resistant strains of bacteria that you are interested in are all dangerous human pathogens and definitely not recommended for science fair projects!

Let us know what you decide to do and we can help you with the details. Unless you can get someone to help you making the liquid culture from the E coli slant, the simplest way to proceed is just to order the liquid E coli K12 culture from Carolina.

Good luck!

Sybee

[dana10ramsey]

Thank you so much. I just decided to order the K12 strain since it seemed like the easier solution