# TCID50 - What does it actually tell me?! (Apr/22/2011 )

Hi,

This is a pretty basic question (sorry, i'm new to science and just started PhD)...

I've done a number of TCID50 so understand how to do the experiment and how to calculate the TCID50 using the Reed Muench method. But what I don't quite grasp it what the number you get out at the end actually means?! As in, what are the units? And is it a value per ml if my TCID50 plate consisted of a series of ten fold dilutions? Does a bigger number equate to more virus (or more 'killing power', for want of a better phrase) than a lower value?

Any help much appreciated! Thanks.

I never used it , I just saw it at school, but cant remember much of it.

But the attached documents might help you.

The file TCID.pdf is a paper written about the TCID calculations.. so it should help.

Also:

http://www.sciencegateway.org/protocols/cellbio/cell/moipfu.htm

http://iamanovice.wordpress.com/2011/03/31/tcid50/

http://www.urmc.rochester.edu/mbi/resources/xenopus/protocols/tcid50-protocol.pdf

Thanks for your reply (sorry my thanks are delayed, I ended up in hospital couple of weeks ago and am just getting back on my feet!).

katcvet on Fri Apr 22 12:09:26 2011 said:

Hi,

This is a pretty basic question (sorry, i'm new to science and just started PhD)...

I've done a number of TCID50 so understand how to do the experiment and how to calculate the TCID50 using the Reed Muench method. But what I don't quite grasp it what the number you get out at the end actually means?! As in, what are the units? And is it a value per ml if my TCID50 plate consisted of a series of ten fold dilutions? Does a bigger number equate to more virus (or more 'killing power', for want of a better phrase) than a lower value?

Any help much appreciated! Thanks.

the value obtained is : 10^ ( a number calculated ) TCID50/ml.

we use it when doing titration to the virus inoculated ... so, yes it means per ml.

and yes too, a bigger number correlates with a higher quantity of the virus ...

pito on Tue Apr 26 18:50:47 2011 said:

I never used it , I just saw it at school, but cant remember much of it.

But the attached documents might help you.

The file TCID.pdf is a paper written about the TCID calculations.. so it should help.

Also:

http://www.sciencegateway.org/protocols/cellbio/cell/moipfu.htm

http://iamanovice.wordpress.com/2011/03/31/tcid50/

http://www.urmc.rochester.edu/mbi/resources/xenopus/protocols/tcid50-protocol.pdf

thanks for the attached

Thanks for your reply Nightingale. Am I correct in thinking that if I had added 0.1ml of my dilution series to each well, I would express my result as e.g. 10 ^{6.57} TCID_{50}/0.1ml, and that would mean than if I added 0.1ml of inoculum at a dilution of 10 ^{6.57} to a certain number of wells, I would expect 50% of those to become infected? Or is it preferable to state the TCID50 value per one ml, and to do that I'd multiply my value by 10?

What I also don't understand is why the values seem to go from negative to postive and log to not log at random. If I wanted to calculate the TCID50 so it's in the form of number x (10 to power of number), would I use the positive or the negative 10to the power of value - obv they give different values!

Sorry for all the questions. I can't find a book or paper that just explains this simply, and the more I read the more confused I get - so now I think I'm making a mountain out of a molehill, and I feel like tearing my hair out!

Thanks

katcvet on Wed May 18 07:57:14 2011 said:

Thanks for your reply Nightingale. Am I correct in thinking that if I had added 0.1ml of my dilution series to each well, I would express my result as e.g. 10

^{6.57}TCID

_{50}/0.1ml, and that would mean than if I added 0.1ml of inoculum at a dilution of 10

^{6.57}to a certain number of wells, I would expect 50% of those to become infected? Or is it preferable to state the TCID50 value per one ml, and to do that I'd multiply my value by 10?

What I also don't understand is why the values seem to go from negative to postive and log to not log at random. If I wanted to calculate the TCID50 so it's in the form of number x (10 to power of number), would I use the positive or the negative 10to the power of value - obv they give different values!

Sorry for all the questions. I can't find a book or paper that just explains this simply, and the more I read the more confused I get - so now I think I'm making a mountain out of a molehill, and I feel like tearing my hair out!

Thanks

most welcome

well, we inoculate 0.1 ml but express the TCID50/ml NOT / 0.1 ml ...

i think the latter option is more used than the former, But will ask the virolgy department more on this, since am still new there,

in order to give u the best answer ...

i didn't get your point, on the "negative/positive" point ...

will u kindly restate it once again ??

nevermind !

while exploring the net to find you an answer, found this : virology blog

see, that u r not the only one who is struggling there !

make notice of the Prof's e-mail on the right side of the page ...

Best Wishes.