Science Buddies: "Ask an Expert"

Hi,
For my project I'm testing antibiotic effectivity in vitro on bacteria S. Marcescens and B. Cereus. I wanted to culture a little amount of each bacteria in luria broth so I can make a McFarland suspension and spread it into petri dishes to conduct my experiment. I was wondering a few things. 1. Can S. marcescens and B. Cereus be cultured in luria broth (not in a luria broth agar plates)? 2. How do I go about this? I'll most likely be purchasing the bacteria in vials so do I just pour the contents of the vial into how many mL's of lb broth and incubate it? (I'll be needing 30 plates per bacteria to swab bacteria into) 3. What are the concentration standards for a .5 McFarland suspension and what should I suspend it in, water?
Thanks in advance!

Hi
due to this website
http://www.microbelibrary.org/index.php ... marcescens
luria agar is a good choice for S. marcescens.
and you should know that broths are used to increase the number of bacteria and after that mostly transferred into agar plates.
wish it helped.
i will let you know if i got more information.
best regards
kamran banan

Hi,
Thank you very much for that info. I'm just not sure how broth culturing works. When you place a little bacteria in a lot of broth in an incubator, will the bacteria multiply and consume the broth so eventually all that's left is bacteria suspended in a little broth? More importantly, do you use this for a .5 McFarland suspension or how do you dilute it? This is the main thing, I don't understand the standards of the .5 McFarland suspension and how to dilute it?

Thanks for your help so far,
apunjabi

Hi
i don' understand what are you trying to do but we usually dissolve the bacteria in Distilled water than take it to the broth. actually for picking up those bacteria you should Centrifuge that broth. do you have access to any?

Hi,
I do have a centrifuge but it is very small and I'd prefer not to use it. How much bacteria do I need per how much distilled water to swab 60 100mm diameter agar plates? Considering this I could figure out how feasible centrifuging would be.

In addition, I can purchase the bacteria in a nutrient plate, a nutrient broth, or a freeze dry MicroKwik(R) culture. Which one do you think is best for what I'm doing? I have the links to where I'm purchasing them from here: http://www.carolina.com/product/serrati ... estMatches and http://www.carolina.com/product/living+ ... hes&page=1

I hope this helps.

Hi
if you are going to purchase the bacteria then you don't need any broth or distilled water. let me give you an example of when would you need broth : think you want to find lactobacillus in clay ,which is very hard, and if you culture from that clay the other bacteria wont let your lactobacillus live there so you use an MRS broth which is not suitable for other bacteria but your lactobacillus can live there. it is the reason of using broth.
if you had any other questions don't hesitate.
best regards
Kamran Banan

Hi,
The thing is, if I purchase the bacteria it only comes in 5mL suspension of bacteria but I want to dilute and culture that to 50mL so I have enough to spread in 60 plates. That is what I don't understand how to do.

hi
even in that case you don't need broths. you only need to pure culture (if i am not mistaken the name) (i mean the method in which you pour your whole liquid on the agar plate) after that you will have a petri dish full of bacteria and then you could pick up the colonies with loop or swap and culture it on other petri dishes. if you think the amount of your suspension is low and couldn't support the whole petri dish (that i don't think so) you can add some distilled water or physiological serum (preferred) then shake it well and then pour it on your petri dish. i will not promise but i try to put a video of how you should do so. if you dont understand what i mean. (speed of internet in our country is so low it is the reason i can not promise that)
wish it helped.
Kamran Banan
P.S. it says for 30 students: it means at least 30 petri dishes. if i were you i would culture it normally because in the method above you are making 30 petri dishes one and this means wasting 29 plate bacteria !