I am working on M. smegmatis, and i want to calculate the CFU/ml concentration for the cell growth i obtain using the OD at 600 nm. Kindly tell me what is the corresponding value of CFU/ml for 0.1 OD at 600 nm
Dear Pritish,
Please read the following and examine Figure 2 in page 289 (attached file):
In quantifying cfu/mL by colony counting, colonies were not observed until the 9th day of incubation. During log phase, the generation time was calculated in 24.91 h. Figure 2 shows the correlation of the growth curves generated from the different methods. The correlation between cfu/mL quantification and OD600 measurement was the lowest (R2 = 0.8913, Figure 2A), followed by the correlation between cfu/mL quantification and turbidity measurement (R2 = 0.9252, Figure 2B). OD600 and turbidity measurements were highly correlated (R2 = 0.9823, Figure 2C). We determined in M. tuberculosis H37Rv ATCC 27294 that 1 McFarland unit is equivalent to either 1.97 × 106 cfu/mL or 0.39 OD600, and an OD600 measurement of 1 is equivalent to either 3.13 × 107 cfu/mL or 3.66 McFarland units.
Braz J Microbiol. 2013; 44(1): 287–289.
Published online 2013 May 31. doi: 10.1590/S1517-83822013000100042
PMCID: PMC3804212
Measuring of Mycobacterium tuberculosis growth. A correlation of the optical measurements with colony forming units
Katia Peñuelas-Urquides,1,2 Licet Villarreal-Treviño,2 Beatriz Silva-Ramírez,3 Liliana Rivadeneyra-Espinoza,4 Salvador Said-Fernández,5 and Mario Bermúdez de León1
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Abstract
The quantification of colony forming units (cfu), turbidity, and optical density at 600 nm (OD600) measurements were used to evaluate Mycobacterium tuberculosis growth. Turbidity and OD600measurements displayed similar growth curves, while cfu quantification showed a continuous growth curve. We determined the cfu equivalents to McFarland and OD600 units.
Keywords: bacterial growth, colony forming units, McFarland, Mycobacterium tuberculosis, optical density
Hoping this will be helpful,
Rafik
You could use a McFarland standard, for example 0.5. It would correlate OD600 with CFU/mL.
the mc farland standard is standardized for gram negative bacteria, especially e coli. other bacteria that vary in size and shape as mycobacterium smegmatis ill not be exactly comparable. but approximately. I would suggest to pick an optical density and use it all the time as the absolute cell number is very hard to find out and also does not matter most of the time as long as it is constant and reproducible. read Sutton measurement of microbial cells by optical density greetings martin
I didn't know that. I used that standard in Staphylococcus aureus. But good answer to keep in mind!
I think that standard curve suggested by Asif Sukri is better and reproducible.
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