How can I determine the 0.5 MacFarland of bacterial suspension exactly? Thank you.
Hi
The turbidity of activity of growing bacterial suspension was adjusted to match the turbidity standard of 0.5 McFarland units prepared by mixing 0.5 ml of 1.75 % (w/v) barium chloride dehydrate with 99.5 ml of 1% (v/v) sulphuric acid. This turbidity was equivalent to approximately 1×107 (cfu/ml). The grown suspension was used for further testing.
Usually the turbidity measure in a spectrophotometer is accurate enough. Obviously the most accurate system, but much more time consuming, is seeding the suspension and counting the colonies number.
we measure the standard OD in 625 nm by 0.08-013 turbidity that include
1.5 .108 bacteria
Usually from the bacteria suspension, measure the OD at 600 nm within the range (0.08-0.1). Additinally, for the usage in the log phase and make a dilution of 1:150. and use as is.
you should compare your bacteria's sample with a 0.5 MacFarland tube which you made by previous points.
you should take colony from culture with cotton swab mixing with serum physiology then measuring in McFarland device or you can use O.D. after take 300 ul from o.n culture inoculate in 30 ml MHB
there is also an option of putting your sample in a densitometer . place your bacterial suspension in a densitometer and read it at 0.5
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