Suppose you measure the zones of inhibition between rounds 1

Suppose you measure the zones of inhibition between rounds 1 and 2 of your paired Kirby-Bauer testing and find that they stay the SAME. What does this suggest? The bacteria has become more RESISTANT with repeated low-dose exposure to the antimicrobial. The bacteria has become more SENSITIVE with repeated low-dose exposure to the antimicrobial. There has been no significant change in sensitivity/resistance as a result of repeated, low-dose exposures to the antimicrobial. I must have done something wrong.

Solution

The answer is: There has been no significant change in sensitivity/ resistance as a result of repeated, low - dose exposure to the antimicrobial.

If the zones of inhibition between rounds 1 and 2 of paired Kirby Bauer testing are same then there has been no significant change in sensitivity/ resistance as a result of repeated, low - dose exposure to the antimicrobial.