Dear Sagar

Visually the M.tb grows in clumps and settles down at bottom while growing in shaking conditions. When one see this visually culture lies in bottom and media is bit clear above. If you see the turbitidity in initial 2-3 days you must go for sterility testing as described below.

We just take an aliquot from the culture and spot it on TSA and let the plate in incubator for 2 days. If there is something else than M.tb it must grow most  probably. 

Hope this helps!

Best reagrds

Samsher Singh

IIIM Jammu

We are usually plaiting 10 uL of TB culture on blood agar and incubating it for 48hours.

And also contamination in Bubos media can be easily visible by changes in turbidity. TB producing clumps and any bacterial contamination will give uniform turbidity in Dubos media.

This pdf It may help