Hi,
I'm currently trying to figure out a viable method to approximate the number of CFUs that can be formed from a cell suspension. Right now, I have been measuring the suspension's absorbance at 600nm using a spectrophotometer then perform a series of dilutions followed by inoculation onto an agar plate in duplicates but after my latest (less satisfactory) trial, I have decided to explore further methods while I continue working on this. If you have any input on my current method, I'd love to discuss it as well.
Kind regards,
Kenny.
The only reliable way to measure the CFUs in a suspension of bacterial cells is plating dilutions of the cells and counting colonies. It's tedious and time-consuming, but there is no other satisfactory method, as far as I can tell.
It's worth noting that the colony-forming unit (CFU) is defined by the plating method.
The OD600 method, as you found, is not reliable. That is because dead and live cells both scatter light at 600 nm, clumps of cells scatter more than individual cells, and the optical density is not directly proportional to the cell number except over a narrow range. Also, it has to be calibrated for every strain and growth condition.
The only reliable way to measure the CFUs in a suspension of bacterial cells is plating dilutions of the cells and counting colonies. It's tedious and time-consuming, but there is no other satisfactory method, as far as I can tell.
It's worth noting that the colony-forming unit (CFU) is defined by the plating method.
The OD600 method, as you found, is not reliable. That is because dead and live cells both scatter light at 600 nm, clumps of cells scatter more than individual cells, and the optical density is not directly proportional to the cell number except over a narrow range. Also, it has to be calibrated for every strain and growth condition.
I too agree with Dr. Adam B Shapiro where we have to do serial counting which is the most accurate method. However, as far as you use the same strains and same growth conditions, you can develop a growth curve and do plating and measure OD600 values. Then you can develop a graph for Absorbance and CFU count. Thereby you can have an estimation.
Thank You,
Amal.
The most common way is to dilute your cell suspension, incubate on petri dishes, and count the colonies. Your CFUs can be calculated by this equation:
CFU/mL = number of colonies * dilution factor
You can see the link below for more detail:
https://sciencing.com/calculate-cfu-dilution-7806269.html
Regards,
K
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