Science Buddies: "Ask an Expert"

I'm planning on doing a microbiology experiment on testing of antimicrobial properties of certain substances. I can only use benign sources of bacteria in my experiments.

I was thinking of using E. Coli K12 since that is non-hazardous bacteria. However, I also thought of using lactobacillus acidophilus since (the bacteria in yogurt) since that might be easier to obtain and work with.

Before I perform the experiment, I'm interested in finding out if
1) what the difference between non-hazardous bacteria (such as E. coli) and more hazardous forms

2) how similiar lactobacillus acidophilus is to E. coli.

My concern is that I might not be able to generalize the results of this experiment to experiments with more harmful bacteria. That is, anti-microbial agents might leave the good bacteria untouched, but might actually prevent microbial growth of the "bad" bacteria. If this were the case, my experiment would not be applicable.

Hi!
This sounds like a really interesting project! Here are some links to check out-
http://www.microbiologyonline.org.uk/ecoli.htm
http://www.hyperactivekids.com/sections ... hilus.html
Although E.Coli K12 is different from the other E.coli strains, it is definitely the safest to use. Ask your science teacher to see if they can assist you should you choose to work w/ other strains. Good luck!

Hi

Using a standard non hazardous bacterium, such as E coli, in these types of experiments is quite common. You are right, some hazardous bacteria might not be killed by the things that kill E coli, and vice versa. However, bacteria that are similar to E coli (ie gram negative rods) probably will.

"Hazardous" just means the bacterium can cause disease in humans/animals. But a hazardous bacterium often has a very closely related nonhazardous bacterium. For example, some strains of E coli cause food poisoning. But not the one that most people use in the lab! They're actually the same species, but one causes disease and another is innocuous. As another example, Bacillus anthracis causes anthrax, but its close relative Bacillus cereus does not. Sometimes it's the plasmids (non-chromosomal DNA) that make a bacterium hazardous. Also, those plasmids can also contain resistance to antibiotics (this is why bacteria in hospitals often resist treatment, they've collected the genes that make them immune).

Lactobacillus is gram-positive (look this term up if you're not sure what I'm talking about--it's a common way of distinguishing bacteria based on their cell walls), so a bit different from E coli. Why not use both bacteria--it would be interesting if a substance kills one but not the other. But using Lactobacillus might be an interesting spin for your project, because it's considered a probiotic--bacteria that are good for you. So maybe you'd like to find substances that don't harm the lactobacillus and thus keep its helpful properties intact? Your science teacher can certainly help you get some E coli, and possibly the Lactobacillus too. Or, it might be fun to isolate it from yogurt...keep in mind there are at least two strains of bacteria that make yogurt, so make sure you've got the one you want.

Good luck!

Your science teacher can probably help you get the E coli, and maybe the other strain too.