why is this method of testing antimicrobials inaccurate??

Question

test microorganisms are spread onto the surface of agar plates ,then filter paper disks impregnated with different antimicribial agaents are placed onto the inoculated plates.the plates are then examinated for inhibition zones following incubation

Answer 1

The test depends on the readers judgement, not on clinical data ie the "best" antimicrobial action is deemed by the judgement of the size of the clear area around the paper;

Answer 2

Its inaccurate because you do not have quantitative data. You don't have kill counts (survival rates).

In the lab we inoculate a sterile filter with our bacteria at a known dilution, and put it on an agar plate that contains the antimicrobial. A few days latter (depending on the bacteria) we transfer them onto a fresh plate free from antimicrobial. We also do a control plate at the same dilution, and compare colony forming unit counts.

Answer 3

do you know the quantities?

exactly how many organisms do you have.. you can't say can you!

You can only give a percentage of effected bacteria not the actual amount.

Also is this a one off, contamination, anomolies, who knows what could've happened whilst you weren't looking.

How old was the bacteria, how do you know some of it hadn't died during or before the test?!