Inhibition zone diameter values from disc diffusion tests were
recorded manually by the laboratory technicians in 1977 in Lund, in order to
analyze zone size distributions species-wise.
The different locations of the wild-type populations for the two species, E.coli
and P.mirabilis for ampicillin (blue bars) and nalidixic acid (red bars),
respectively, illustrate the need for species-related interpretive breakpoints.
This is even more evident when also other bacterial species are taken into account.