Chemical class

Antibiotic

Disk symbol

Disk content

Resistant

Intermediate

Susceptible

Aminoglycosides

Gentamicin

GM

10 µg

<18 mm S. aureus

<22 mm

CoNS

-

≥18 mm

S. aureus

≥22 mm

CoNS

β-lactams

Ampicillin

AP

25 μg

<18 mm

-

≥18 mm

Cephalosporins (also a β-lactam)

Cefoxitin

FOX

30 µg

<22 mm

-

≥22 mm

Fluoroquinolones

Ciprofloxacin

CIP

5 µg

<20 mm

-

≥20 mm

Macrolides

Erythromycin

E

15 µg

<18 mm

18 - 20 mm

≥21 mm

Tetracyclines

Tetracycline

T

30 µg

<19 mm

19 - 21 mm

≥22 mm

Other

Rifampicin

RP

5 µg

<23 mm

23 - 25 mm

≥26 mm