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Getting cultures to specific cfu


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#1 Microbiology123

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Posted 19 March 2021 - 02:49 AM

Hello I need to get a culture to specific cfu per ml. Do I make a culture and leave it overnight. Then use haemocytometer to see how many bacteria are in there and then work out how much I need to dilute it by. ?

#2 Phil Geis

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Posted 19 March 2021 - 05:35 AM

Suggest you develop a standard curve - OD v. cfu.  Hematcytomer counts are a pain - esp. for bacteria



#3 Microbiology123

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Posted 19 March 2021 - 05:57 AM

Thankyou for your suggestion. As far as I can see devices to measure OD is very expensive. I have been struggling with the haemocytometer for bacteria

#4 Microbiology123

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Posted 19 March 2021 - 08:27 AM

Would you expect all the bacteria to be the same size in your sample on the cytometer. Seems like some are smaller than others.

#5 Phil Geis

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Posted 20 March 2021 - 04:33 AM

Bacteria are hard to see and reliably count using a hemacytometer.  Look for a used Klett meter.



#6 Microbiology123

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Posted 20 March 2021 - 10:35 AM

Thankyou I will. Is there a calculation you do when you have the turbidity measurement to see how many bacteria you have ?

#7 Phil Geis

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Posted 20 March 2021 - 11:00 AM

No - take an OD AND a cfu count at various dilutions of a culture and plot OD v. log cfu.  Using that plot - you can roughly estimate count colony count based on OD.



#8 Microbiology123

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Posted 20 March 2021 - 11:16 AM

Thankyou !




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