Dear Researcher
I inoculated E.coli O104 in Lettuce and I did cfu counting after spreading on LB with antibiotic ( resistant of E.coli O104 and used to prevent normal flora growth) and on LB without adding any antibiotic. I found more cfu count on LB with antibiotic than on LB without adding any antibiotic. In this experiment, I used LB with antibiotic to prevent normal flora growth? Normally it was supposed to come equal count of cfu on both type of plate or less count on LB with antibiotic since there is more stress because of antibiotic. Mentioningly I found normal flora growth along with E.coli O104 on LB without antibiotic. So now I am not sure whether becasue of normal flora growth less count comes on LB without adding any antibiotic or any other reason? If anybody has any idea about that, please provide me.
Dear Azimun,
How significant is the difference in the numbers?
Did you use the same bacterial solution for both kind of media and did you mix the solution each time you removed a sample? For example, if you have a bacterial solution and plate it onto the first medium in a number of replica and then onto the second, the cells may have had time to settle down.
It may also be worth checking if your antibiotic is still effective.
@ Kulman. Thank you very much for your kind answer. Yes I used same bacterial solution and everytime I mixed and 100ul was transferred and spreaded on both type of plates.
OK. It would be interesting to know if the results are still the same if you switch the sequence of the media plating. For example, if you plated a series of aliquots first onto medium #1 and then onto #2, the cells may have time to divide in the meantime. E. coli can complete it's cell division cycle within 20 minutes. If you see more colonies on medium #1, does this stay the same if you plate on medium #1 last? I assume you took the culture from standard 37°C incubation.
@Kulman. Thank you very much. Yes I took culture from standard 37 degree celcius. For your better understanding, I attached here my experiment protocol. Could you please go through it?
Hi Azimun,
Just came across your question and the subsequent answers by Christoph Kulman. Have you done what he has suggested? If so what were the answers. Also, have you confirmed that your orgamnism is sensitive to the antibiotic that you are using and are you using it in the appropriate concentration?
Awaiting your answers. Good luck. God bless.
Did you have also some other species or genera on antibiotic-free LB medium? If yes, maybe there is some competition for nutrients or production of bacteriocins, which leads to lover counts. Was the difference significant? How many parallels have you provided?
@ Lucia. Thank you very for questions. Yes, I found normal flora growth along with E.coli O104 on antibiotic free LB ( Triplicate) and count of normal flora was more than O104 count in all triplicate plate ) since I inoculated E.coli O104 in Lettuce and I could not completely remove background flora from lettuce before inoculation of E.coli O104.
Then it is possible that there is some competition for nutrients or production of antimicrobial compounds. It would be better, if you apply some diagnostic selective media such EMB Levine blue agar or chromocult coliform agar. or some other media, which suppres growth of for example G+ bacteria (MacConkey, VRBL). Maybe then you find higher counts.
@ Lucia, Thankyou very much for your kind information. Could you please suggest me any reference paper regarding this type of problem if you know?
- Badges
- Science topic
- Similar topics
- Agricultural Science
- Agronomy
- Crop Science
- Crop