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Name: Lori
Status: Educator
Grade:  9-12
Location: LA
Country: United States
Date: December 2005

I am helping some students with science fair project. We need to grow a culture of e coli in luria and transfer to nutrient agar plates. Question? What process do I use to propagate the e coli in luria? Do I just transfer a measured amount of bacteria and then let grow? For how long will I have to let them grow before we can plate on agar?
Thanks so much

Assuming you have a 37 degree C incubator, inoculate the Luria broth with an E. coli culture using a sterile pipet or inoculation loop. Place the broth culture in the incubator for 24 hours. The culture should be turbid (cloudy) and contain 10^8 and 10^9 cells/mL. At this point, spread some of the culture on a nutrient agar plate and inculate the plate for 24-48 hours at which time individual colonies should be visible.

Ron Baker, Ph.D.

E coli has a generation time of about 20 minutes, so you will have a good culture to work with by the next day. The broth should be cloudy when you look at it. Then you can take a sterile loop, or sterile cotton swab and transfer it to the nutrient agar. You can purchase sterile swabs from a biological supply company such as Carolina, Ward' or Fisher. Then you will need to grow the E coli on the nutrient agar for another day. If you have an incubator, the bacteria will grow in one day but if you need to grow them at room temp give them another day.

Make sure that you have a way to dispose of the cultures properly-a tub of 10% bleach works nicely. You should also decontaminate any work surfaces with 10% bleach as well.


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