Results are out! Find what you Get quick advice or join the chat
Hey! Sign in to get help with your study questionsNew here? Join for free to post

Calculating colony forming units?

Announcements Posted on
Let our uni choice search tool match you with your perfect university 19-11-2015
  1. Offline

    Hope this is in the right place, if not sorry!
    I'm a bit stuck on what i'm supposed to be doing in this calculation.. If anyone could give me some pointers i'd really appreciate it

    "Soil suspension has been prepared as follows: 10g soil was made up to 15ml with peptone solution. You are provided with a 10^-4 dilution of the original suspension. This was prepared in two steps; 0.1ml of suspension was added to 9.9ml peptone to give 10^-2 dilution. This was repeated to give the 10^-4 dilution.
    Calculate the number of colony forming units (CFUs) per gram of soil in your sample, take careful account of the dilution used for counting in your calculation"

    I prepared 10^-5 10^-6 and 10^-7 dilutions by removing 0.5ml each time to the new dilution.
    I plated 1ml samples of the four dilutions. Then after incubating I counted 300 colonies in the 10^-5 dilution..

    Now i'm stuck on what to do to calculate per ml or g .. I know to multiple the number of colonies by the dilution factor so 300 * 10^5 .. but do I need to do something else to get the answer?


Submit reply


Thanks for posting! You just need to create an account in order to submit the post
  1. this can't be left blank
    that username has been taken, please choose another Forgotten your password?
  2. this can't be left blank
    this email is already registered. Forgotten your password?
  3. this can't be left blank

    6 characters or longer with both numbers and letters is safer

  4. this can't be left empty
    your full birthday is required
  1. By joining you agree to our Ts and Cs, privacy policy and site rules

  2. Slide to join now Processing…

Updated: October 26, 2011
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Today on TSR

Applying to uni

The latest advice and trending discussions are all here

What's your favourite kitchen utensil?
Quick reply
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.