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# preparing appropriate dilution of bacteria suspension

Bacterial suspension dilution MIC

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### #1 Dima

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Posted 09 June 2013 - 01:00 PM

A strain suspension in a turbidity test (spectrophotometer) gave 0.2 . I diluted the fresh culture suspension so the spectrop. read which I understand it s equivalent to 10*7 cfu/ml.

From this diluted inoculum suspension I need to inoculate the two fold dilution wells of testing solvent.

However if I add 200 microliters of the 10*7 cfu/ml inoculum to a 200 micro liter of the antibacterial stock in tube (48 well plates) then i may change the strains density, right? if so, shall I take a percentage from the inoculum suspension and how much?? how do i calculate this?

this is new to me and am trying to make the right volume of inoculum suspension to add to wells.

I want to ensure that I have 10^6 cfu/ml in the wells that contain 200 microliters antibacterial testing solution.

I may need to post another question being new in this interesting field.

### #2 bob1

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Posted 09 June 2013 - 04:46 PM

Yes, taking mixing a suspension with an aliquot of medium will change the density and hence the cfu/ml.

To get 10^6 cfu/well is relatively easy: use V=N/C, just like you would for any other solution N=10^6, C=10^7...

However as you have to make doubling dilutions - presumably you don't actually want 10^6 in each well, you probably want 10^6 in the first column, 5x10^5 in the next etc.

### #3 Dima

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Posted 09 June 2013 - 11:33 PM

Thank you ! therefore i hope I calculated it right:

I have a well of 1000 microliter testing solutions, I inoculate with 100 microliter culture suspension (10^7 cfu/ml). I end up in the first well with 10^6 in that case.

### #4 bob1

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Posted 10 June 2013 - 01:05 AM

Yes, 100ul of a 10^7 cfu/ml solution would give you 10^6 cfu.

### #5 Dima

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Posted 10 June 2013 - 05:00 AM

Thanks!