Minimum Inhibitory
Concentrations
(mcg/mL)

Disk Diffusion
(zone diameter in mm)

Pathogen

S

I

R

S

I

R

Enterobacterales

M100 standard is recognized

Salmonella spp.

M100 standard is recognized

Pseudomonas aeruginosa

M100 standard is recognized

Staphylococcus spp.

M100 standard is recognized

Enterococcus spp.

M100 standard is recognized

Haemophilus influenzae and
parainfluenzae

M100 standard is recognized

Neisseria gonorrhoeae

M100 standard is recognized

Streptococcus pneumoniae

≤1

 2

≥4

≥21

 16-20

≤15

Streptococcus spp. β-
Hemolytic Group

≤1

 2

≥4

≥21

 16-20

≤15

Bacillus anthracis

M45 standard is recognized

-

-

-

Yersinia pestis

M45 standard is recognized

-

-

-

S = Susceptible; I = Intermediate; R = Resistant

Exceptions to the recognized standard

For these bacteria listed below, susceptibility test interpretive criteria are not recognized at this time:

Acinetobacter spp.

Other Non-Enterobacterales

Neisseria meningitidis