Hi Vishwesh,

I'm not sure what exactly you are thinking about, but when you do a disc diffusion test, you should (unless the strain is completely resistant) see a zone where no bacteria are growing, i..e. the inhibition zone. The edge of the zone may be sharp or have a smaller or larger "haze" with less dense growth. The cause of this haze may be one of the following (not necessarily an exhaustive list):

• Mixed population with different susceptibilities.
• Motile bacteria/swarming
• Bacteria are able to grow for a while before the antibiotic starts inhibiting growth (e.g. trim/sulpha)

Depending on the cause of the haze you need to adapt your interpretation of the zone diameter.

Does this even begin to answer your question?

I must say this is very interesting information.  

The zone of inhibition itself(just think about the zone with no bacterial growth) is sometimes translucent, sometimes completely transparent....I am in a way on about the colour or the transparency of the inhibition zone.

appreciate your help. 

OK, so the colour or transparency of the medium itself changes in the inhibition zone? Interesting... Cloudy, sterile media usually signify a precipitation of something, but that shouldn't happen if you're using a standard medium in your assay.

A couple of thoughts for you to consider: Does the agar change appearance under the growth as well? (This could imply that the bacterium itself causes the change.) Do you see a difference between different antibiotics or different strains? (I.e. is the variable the antibiotic   or the strain?) Have you tried incubating the disc(s) on a plate which has not been inoculated? (If you see a zone with a changed appearance ocn a non-inoculated plate it's definitely an issue of antibiotic causing the change.)

Sorry that I can't give you a better answer than this, but as I recall, I've only seen similar reactions with antibiotics that are coloured in themselves, such as rifampicin.

I think you have pointed me to the right direction. Thanks. I did believe that it has to do something with bacteria. Maybe gases that they produce might interact with the agar giving it the colour or transparency....or something on the similar line.Thank you for your prompt reply.