Greetings,
Recently, I've come across a paper which experimenting on the antibacterial test using disc diffusion. An interesting thing I stumble upon is the result were categorized according to 3 types of sensitivity i.e. resistant (7 mm zone), moderately sensitive (8-14 mm zone) and sensitive (>15 mm zone) .
My question is pretty simple, where did this sensitivity standards coming from? Is there a standard on it like ASTM?
I just recently jump on the biology field from being a physicist (I'm still one) so there are a lot of things I want to learn. I'm sorry if my question is too simple...
Here I also attached the table related to my question. Thank you.
I have no heard of the grading/staging of the bacterial sensitivity in the anti-microbial test, but some authors might have tried to group the bacterial sensitivity into different stages/grades, eg: resistant, sensitive like the one you have shown. This can ease the discussion writing.
However, one of the cons is that if your results are not good/very close, (touch wood), for examples, all results shown are between 1 to 3mm, then you will find it difficult to group/stage them.
Besides, it is also difficult to justify how resistant is a bacteria. For example, methicillin resistant S. aureus (MRSA) is very resistant to antibiotics like ampicillin and normal S. aureus (SA) can be killed by ampicillin if no resistant is developed. So, it will be unfair to say MRSA is resistant to ampicillin and normal SA is sensitive, due to their genetic nature in resisting different drug/compounds.
Thank you very much Sir Zx Chong for your answer and clarification.
First, there is no simple or bad question, all scientists are learning more and more everyday.
Concerning your question, if you are working on antibiotics you can use one of WHO protocols to know sensitivity or resistance of many strains and zones of inhibition respectively.
If you are working on plant extracts it is different according to authors, just try to compare papers to find zones of inhibition.
But in my work I find that there is no link between zone of inhibition and resistance, with some extract there is no zone of inhibition and when I change the method (dilution technique) I find a result. The problem is the diffusion of the extract.
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