|
Techniques
in Microbiology: Antimicrobial Susceptibility Testing
Table
2*: Zone sizes with different antimicrobial agents
|
Antimicrobial
agent
|
When
testing
against
|
Disc
content
|
Zone
diameter nearest whole mm
|
|
Resistant
|
Intermediate
|
Susceptible
|
| ¤-LACTAMS
|
| Ampicillin |
Enterobacteriaceae |
10
µg
|
<13
|
14-16
|
>17
|
|
Staphylococci |
10
µg
|
<28
|
|
>29
|
|
Enterococci |
10
µg
|
<16
|
|
>17
|
| Carbenicillin |
Pseudomonas
|
100
µg
|
<13
|
14-16
|
>16
|
|
Gram
negatives |
100
µg
|
<19
|
20-22
|
>23
|
| Methicillin |
Staphylococci |
5
µg
|
<9
|
10-13
|
>14
|
| Mezlocillin |
Pseudomonas |
75
µg
|
<15
|
|
>16
|
|
Other
Gram negatives |
75
µg
|
<17
|
18-20
|
>21
|
| Nafcillin |
Staphylococci |
1
µg
|
<10
|
11-12
|
>13
|
| Oxacillin |
Staphylococci |
1
µg
|
<10
|
11-12
|
>13
|
| Penicillin |
Staphylococci |
10
units
|
<28
|
|
>29
|
|
Enterococci |
10
units
|
<14
|
|
>15
|
| Piperacillin |
Pseudomonas |
100
µg
|
<17
|
|
>18
|
|
Other
Gram negatives |
100
µg
|
<17
|
18-20
|
>21
|
| Ticarcillin |
Pseudomonas |
75
µg
|
<14
|
|
>15
|
|
Other
Gram negatives |
75
µg
|
<14
|
15-19
|
>20
|
| ¤-LACTAM/¤-LACTAMASE
INHIBITOR COMBINATIONS |
| Amoxycillin/clavulanic
acid |
Staphylococci |
20/10
µg
|
<19
|
|
>20
|
|
Other
organisms |
20/10
µg
|
<13
|
14-17
|
>18
|
| Ampicillin/sulbactam |
Staph
& Gram -ve |
10/10
µg
|
<11
|
12-14
|
>15
|
| Piperacillin/tazobactam |
Pseudomonas |
100/10
µg
|
<17
|
|
>18
|
|
Other
Gram negatives |
100/10
µg
|
<17
|
18-20
|
>21
|
|
Staphylococci |
100/10
µg
|
<17
|
|
>18
|
| Ticarcillin/clavulanic
acid |
Pseudomonas |
75/10
µg
|
<14
|
|
>15
|
|
Other
Gram negatives |
75/10
µg
|
<14
|
15-19
|
>20
|
|
Staphylococci |
75/10
µg
|
<22
|
|
>23
|
| CEPHEMS |
| Cefamandole |
|
30
µg
|
<14
|
15-17
|
>18
|
| Cefazolin |
|
30
µg
|
<14
|
15-17
|
>18
|
| Cefotaxime |
|
30
µg
|
<14
|
15-22
|
>23
|
| Cefoxitin |
|
30
µg
|
<14
|
15-17
|
>18
|
| Ceftazidime |
|
30
µg
|
<14
|
15-17
|
>18
|
| Ceftizoxime |
|
30
µg
|
<14
|
15-19
|
>20
|
| Ceftriaxone |
|
30
µg
|
<13
|
14-20
|
>21
|
| Cefuroxime
oral |
|
30
µg
|
<14
|
15-22
|
>23
|
| Cefuroxime
parentral |
|
30
µg
|
<14
|
15-17
|
>18
|
| Cephalothin |
|
30
µg
|
<14
|
15-17
|
>18
|
| CARBAPENEMS |
| Imipenem |
|
10
µg
|
<13
|
14-15
|
>16
|
| MONOBACTAMS |
| Aztreonam |
|
30
µg
|
<15
|
16-21
|
>22
|
| GLYCOPEPTIDES |
| Telcoplanin |
|
30
µg
|
<10
|
11-13
|
>14
|
| Vancomycin |
Enterococci |
30
µg
|
<14
|
15-16
|
>17
|
|
Other
Gram positives |
30
µg
|
<9
|
10-11
|
>12
|
| AMINOGLYCOSIDES |
| Amikacin |
|
30
µg
|
<14
|
15-16
|
>17
|
| Gentamicin |
except
high resistant enterococci |
10
µg
|
<12
|
13-14
|
>15
|
| Kanamycin |
|
30
µg
|
<13
|
14-17
|
>18
|
| Netilmycin |
|
30
µg
|
<12
|
13-14
|
>15
|
| Streptomycin |
|
10
µg
|
<11
|
12-14
|
>15
|
| Tobramycin |
|
10
µg
|
<12
|
13-14
|
>15
|
| MACROLIDES |
| Azithromycin |
|
15
µg
|
<13
|
14-17
|
>18
|
| Clarithromycin |
|
15
µg
|
<13
|
14-17
|
>18
|
| Erythromycin |
|
15
µg
|
<13
|
14-22
|
>23
|
| TETRACYCLINES |
| Doxycycline |
|
30
µg
|
<12
|
13-15
|
>16
|
| Minocycline |
|
30
µg
|
<14
|
15-18
|
>19
|
| Tetracycline |
|
30
µg
|
<14
|
15-18
|
>19
|
| QUINOLONES |
| Ciprofloxacin |
|
5
µg
|
<15
|
16-20
|
>21
|
| Enoxacin |
|
10
µg
|
<14
|
15-17
|
>18
|
| Lomefloxacin |
|
10
µg
|
<18
|
19-21
|
>22
|
| Nalidixic
acid |
|
30
µg
|
<13
|
14-18
|
>19
|
| Norfloxacin |
|
10
µg
|
<12
|
13-15
|
>16
|
| Ofloxacin |
|
5
µg
|
<12
|
13-15
|
>16
|
| OTHERS |
| Chloramphenicol |
|
30
µg
|
<12
|
13-17
|
>18
|
| Clindamycin |
|
2
µg
|
<14
|
15-20
|
>21
|
| Nitrofurantoin |
|
300
µg
|
<14
|
15-16
|
>17
|
| Rifampin |
|
5
µg
|
<16
|
17-19
|
>20
|
| Sulfonamides |
|
250/300
µg
|
<12
|
13-16
|
>17
|
| Trimethoprim |
|
5
µg
|
<10
|
11-15
|
>16
|
Trimethoprim/
sulfamethoxazole |
|
1.25/
23.75 µg
|
<10
|
11-15
|
>16
|
*
For Vibrio cholerae, the results of disc diffusion tests for ampicillin,
tetracycline and trimethoprim/sulfamethoxazole correlate with results
obtained by broth microdilution methods.
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