Table 5. Phenotypic Confirmatory Tests for ESBLs.
| Clinical isolates, Strains | CAZ 30 μg | CAZ-CLA 30/10 μg | CTX 30 μg | CTX-CLA 30/10 μg |
|---|---|---|---|---|
| NUBL793 (K.oxytoca CTX-M1) | 26 | 27 | 18 | 23 |
| NUBL810 (K. oxytoca CTX-M2) | 24 | 30 | 15 | 28 |
| NUBL1520 | 27 | 27 | 22 | 24 |
| NUBL1521 | 20 | 21 | 13 | 12 |
| NUBL1522 | 21 | 20 | 21 | 21 |
| NUBL1523 | 21 | 21 | 23 | 23 |
| NUBL1524 | 21 | 21 | 21 | 22 |
| NUBL1525 | 21 | 21 | 23 | 23 |
| NUBL1526 | 23 | 23 | 23 | 22 |
| NUBL1527 | 23 | 24 | 24 | 25 |
| NUBL1528 | 28 | 30 | 26 | 27 |
| NUBL1529 | 26 | 24 | 24 | 25 |
| NUBL1530 | 22 | 22 | 23 | 23 |
| NUBL1531 | 25 | 26 | 25 | 27 |
Confirmatory testing requires the use of both CAZ and CTX, alone and in combination with CLA. According to the CLSI, “a ≥5 mm increase in the zone diameter for either antimicrobial agent tested in combination with CLA vs. its zone when tested alone = ESBL.”
Abbreviations: ESBL, extended-spectrum β-lactamase; CAZ, ceftazidime; CLA, clavulanic acid; CTX, cefotaxime.