I am running a bacterial culture and reading the bacterial density on a spectrophotometer at 600 nm. I blanked with the culture medium and also ran a tube without inoculation as a control.
After some time, the inoculated samples gives me 0.341 but the control (medium alone, as the blank, but kept in the thermostat for the same period as the bacterial culture) gives me 0.022.
What is the threshold in OD600 units to say that the control is not contaminated?
Thank you
Hello, it can happen, the absorption at 600nm of your media can drop during the time if you have some non visible particles,which can precipitate during storage in thermostats it can cause drop of absorption. You can perform filtration of media before sterilisation or after with the use sterile sterile conditions to avid it. Or it can be caused by color change of media during the storage.
There is no exact trash hold for absorption at 600 nm it variate depends from type of nutrient media. But if you have microbial grow it tube 10*5 or above this drop can be negligible.
Good luck!
I didn't really understand why you used a blank and another that you called control.
Normally, for the blank (the 0) you should use the one that you incubated in the same conditions as the bacterial culture, so that the only difference between the blank and bacterial culture is the bacteria that grew and no other difference.
2nd explanation, are you sure that the control is not contaminated, because 0.022 is starting to be non-negligible.
That's the point: The control should have the same OD as there blank (0). How much is 0 in spectrophotometry? Does 0.001 count as contaminated? 0.010? 0.100? The purpose of putting a non-inoculated control was to check if the medium was contaminated.
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