Acinetobacter spp., Stenotrophomonas maltophilia, Burkholderia cepacia
- Acinetobater species:
- Gram negative coccobacilli that are non-motile and oxidase negative
- They oxidize sugars, but do not ferment, and do not reduce nitrate
- Identification to species level is unnecessary for clinical isolate
- Nosocomial strains may be multi-drug resistant. Carbapenem resistant strains can occur.
- Stenotrophomonas maltophilia
- Motile, late oxidase positive gram negative rods
- They oxidize, but do not ferment sugars
- They are DNAse positive
- Inherently resistant to carbapenems, which may aid in presumptive identification
- Burkholderia cepacia
- Motile, oxidase variable gram negative rods
- They oxidize, but do not ferment sugars
- Isolates are characteristically resistant to polymyxins
- SENSITIVITY TESTING AND REPORTING
MIC testing is preferable to disk diffusion testing for non-fermenters. However, disk diffusion is more convenient for most clinical laboratories.
QC strains must be tested daily to ensure the validity of test results. The following QC strains must be tested:
- coli ATCC® 29522
- aeruginosa ATCC® 27853
- coli ATCC® 35218 (for β-lactam/β-lactamase inhibitor combinations); with disk diffusion and MIC results within the ranges proposed by the CLSI.
- Acinetobacter spp.
- Ceftazidime and Imipenem should always be tested and reported.
- Other agents may be reported as alternative therapeutic options e.g. Fluoroquinolones, tetracyclines, trimethoprim/sulfamethoxazole, aminoglycosides, etc.
- Polymyxins may be tested by measuring MICs (by broth microdilution or agar dilution) for multi-drug resistant isolates.
- Alternative antimicrobials in each group are not cross-reportable.
- Isolates sensitive to tetracycline are usually sensitive to doxycycline and minocycline; however, some tetracycline resistant isolates may be sensitive to either doxycycline and/or minocycline.
| Preference | Agent
( +disk content where applicable) |
Breakpoints
Disk diffusion Zone diameters |
Interpretive standards
MIC (µg/ml) |
||||
| S | I | R | S | I | R | ||
| 1st line | CEFTAZIDIME (30 µg) | < 14 | 15-17 | > 18 | < 8 | 16 | > 32 |
| 1st line | IMIPENEM (10 µg) | < 13 | 14-15 | > 16 | < 4 | 8 | > 16 |
| 2nd line | PENICILLINS*:
-Piperacillin (100 µg) |
< 17 |
18-20 |
> 21 |
< 16 |
32-64 |
> 128 |
| 2nd line | CEPHALOSPORINS*:
-Cefotaxime (30 µg) -Ceftriaxone (30 µg) -Cefepime (30 µg) |
< 14 < 13 < 14 |
15-22 14-20 15-17 |
> 23 > 21 > 18 |
< 8 < 8 < 8 |
16-32 16-32 16 |
> 64 > 64 > 32 |
| 2nd line | Trimethoprim/ sulfamethoxazole (1.25/23.75) |
< 10 |
11-15 |
> 16 |
< 2/38 |
– |
> 4/76 |
| 2nd line | TETRACYLINES**:
-Tetracycline (30 µg) -Doxycycline (30 µg) -Minocycline (30 µg) |
< 11 < 9 < 12 |
12-14 10-12 13-15 |
> 15 > 13 > 16 |
< 4 < 4 < 4 |
8 8 8 |
> 16 > 16 > 16 |
| 2nd line | AMINOGLYCOSIDES*:
-Gentamicin (10 µg) -Amikacin (30 µg) -Tobramycin (10 µg) |
< 12 < 14 < 12 |
13-14 15-16 13-14 |
> 15 > 17 > 15 |
< 4 < 16 < 4 |
8 32 8 |
> 16 > 64 > 16 |
| 2nd line | FLUOROQUINOLONES:*
-Ciprofloxacin (5 µg) -Levofloxacin (5 µg) |
< 15 < 13 |
16-20 14-16 |
> 21 > 17 |
< 1 < 2 |
2 4 |
> 4 > 8 |
| 2nd line | β-LACTAM/ β-LACTAMASE INHIBITOR COMBINATIONS*:
-Ampicillin/sulbactam (10/10 µg) -Piperacillin/tazobactam (100/10 µg) -Ticarcillin/ clavulanate (75/10 µg) |
< 11 < 17 < 14 |
12-14 18-20 15-19 |
> 15 > 21 > 20 |
< 8/4 < 16/4 < 16/2 |
16/8 32/4-64/4 32/2-64/2 |
> 32/16 > 128/4 > 128/2 |
| 3rd line | Polymyxin-B/ Colistin | <2 | – | >4 | |||
- Stenotrophomonas maltophilia
- Trimethoprim/sulfamethoxazole is the therapeutic agent of choice and must always be reported.
- Carbapenems should not be tested/ reported.
- Other agents may be reported as alternatives e.g., fluoroquinolones, tetracyclines.
- Cephems (cephalosporins including ceftazidime), chloramphenicol, and ticarcillin/clavulanate may be reported based on MIC results.
- Minocycline is the preferable than tetracycline to test against Stenotrophomonas maltophilia strains.
| Preference | Agent
( +disk content where applicable) |
Breakpoints
Disk diffusion Zone diameteres |
Interpretive standards
MIC (µg/ml) |
||||
| S | I | R | S | I | R | ||
| 1st line | Trimethoprim-Sulfamethoxazole
(1.25/23.75 µg) |
< 10 |
11-15 |
> 16 |
< 2/38 |
– |
> 4/76 |
| 2nd line | Levofloxacin | < 13 | 14-16 | > 17 | < 2 | 4 | > 8 |
| 2nd line | Minocycline (30 µg)* | < 14 | 15-18 | > 19 | < 4 | 8 | > 16 |
| 2nd line | Ticarcillin/clavulanate | < 16/2 | 32/2-64/2 | > 128/2 | |||
| 2nd line | CEPHEMS/ Ceftazidime
(30 µg) |
< 8 |
16 |
> 32 |
|||
| 2nd line | Chloramphenicol | < 8 | 16 | > 32 | |||
- Burkholderia cepacia
- Trimethoprim/sulfamethoxazole is the therapeutic agent of choice and must always be reported.
- Polymyxins should not be tested/ reported.
- Other agents may be reported as alternatives e.g. cephems, carbapenems, tetracyclines.
- Fluoroquinolones, chloramphenicol, and ticarcillin/clavulanate may be reported based on MIC results.
| Preference | Agent
( +disk content where applicable) |
Breakpoints
Disk diffusion Zone diameters |
Interpretive standards
MIC (µg/ml) |
||||
| S | I | R | S | I | R | ||
| 1st line | Trimethoprim-Sulfamethoxazole
(1.25/23.75 µg) |
< 10 |
11-15 |
> 16 |
< 2/38 |
– |
> 4/76 |
| 2nd line | CEPHEMS/ Ceftazidime
(30 µg) |
< 17 |
18-20 |
> 21 |
< 8 |
16 |
> 32 |
| 2nd line | Meropenem (10 µg) | < 15 | 16-19 | > 20 | < 4 | 8 | > 16 |
| 2nd line | Minocycline (30 µg)* | < 14 | 15-18 | > 19 | < 4 | 8 | > 16 |
| 2nd line | Ticarcillin/clavulanate | < 16/2 | 32/2-64/2 | > 128/2 | |||
| 2nd line | Levofloxacin | < 2 | 4 | > 8 | |||
| 2nd line | Chloramphenicol | < 8 | 16 | > 32 | |||
Updated July 2018
Dr.Fizza Faroqui
Year V Resident
Department of pathology and laboratory medicince
Aga Khan University Hospital, Karachi