Re: what is the definition of sensitive strain?

When one asks a question, one should always include some context with it. Since there was no such context provided in the question, I will answer the question that I think you are asking.

I'm assuming that by sensitive strain, you are referring to a strain of microbes that is killed by an antibiotic. Strains that are affected (killed or inhibited) by an antibiotic are said to be susceptible or sensitive to that antibiotic. Strains unaffected by the antibiotic are said to be resistant. So, a sensitive strain would be one that is susceptible to or sensitive to an antibiotic and thus dies in response to effective concentrations of the antibiotic in question.