Table 1.
Antimicrobial Susceptibility Test Results of Uropathogenic Escherichia coli Isolates to Ceftazidime and Cefoxitin Cephalosporins to Confirm Extended-Spectrum β-Lactamase and AmpC Production
| |
ESBL detection |
ESBL confirmation |
AmpC confirmation |
|||||
|---|---|---|---|---|---|---|---|---|
| Isolate ID | A: Ceftazidime MIC > 16 μg/mL | Inter. | B: Difference in zone size > 5 mm | Inter. | C: Cefoxitin disk zone < 18 mm) | Inter. | D: Disk approximation | Inter. |
| UPEC 1 | >16 | POS | 21 | POS | 20 | NEG | NEG | NEG |
| UPEC 2 | >16 | POS | 12 | POS | 15 | POS | NEG | NEG |
| UPEC 3 | >16 | POS | 14 | POS | 26 | NEG | NEG | NEG |
| UPEC 4 | >16 | POS | 14 | POS | 20 | NEG | NEG | NEG |
| UPEC 5 | >16 | POS | 14 | POS | 22 | NEG | NEG | NEG |
| UPEC 6 | >16 | POS | 17 | POS | 24 | NEG | NEG | NEG |
| UPEC 7 | >16 | POS | 15 | POS | 23 | NEG | NEG | NEG |
| UPEC 8 | >16 | POS | 17 | POS | 20 | NEG | NEG | NEG |
| UPEC 9 | >16 | POS | 17 | POS | 12 | POS | NEG | NEG |
| UPEC 10 | >16 | POS | 17 | POS | 20 | NEG | NEG | NEG |
| UPEC 11 | >16 | POS | 16 | POS | 22 | NEG | NEG | NEG |
| UPEC 12 | >16 | POS | 8 | POS | 20 | NEG | NEG | NEG |
| UPEC 13 | >16 | POS | 10 | POS | 17 | POS | NEG | NEG |
| UPEC 14 | >16 | POS | 15 | POS | 24 | NEG | NEG | NEG |
| UPEC 15 | >16 | POS | 21 | POS | 25 | NEG | NEG | NEG |
| UPEC 16 | >16 | POS | 16 | POS | 21 | NEG | NEG | NEG |
| UPEC 17 | >16 | POS | 10 | POS | 20 | NEG | NEG | NEG |
| UPEC 18 | >16 | POS | 15 | POS | 13 | POS | NEG | NEG |
| UPEC 19 | >16 | POS | 17 | POS | 23 | NEG | NEG | NEG |
| UPEC 20 | >16 | POS | 13 | POS | 17 | POS | NEG | NEG |
| UPEC 21 | >16 | POS | 13 | POS | 23 | NEG | NEG | NEG |
| UPEC 22 | >16 | POS | 19 | POS | 17 | POS | NEG | NEG |
| UPEC 23 | >16 | POS | 8 | POS | 23 | NEG | NEG | NEG |
| Klebsiella pneumoniae (ATCC 700603) | — | — | 10 | POS | — | — | — | — |
| E. coli CMY-2 (MRSN#570581) | — | — | — | — | 6 | POS | NEG | NEG |
| E. coli (ATCC#25922) | — | — | 0 | NEG | 22 | NEG | NEG | NEG |
ESBL and AmpC production were confirmed using CLSI-approved phenotypic tests. A: Ceftazidime minimum inhibitory concentration (MIC) of >16 μg/mL. B: Difference in zone size >5 mm for the ceftazidime (30 μg) + clavulanic acid (10 μg) disk compared with the ceftazidime (30 μg) disc (ESBL POS). C: AmpC screening test using the cefoxitin disc (30 μg). Inhibition zone size <18 mm, AmpC screen POS. D: Disk approximation confirmatory test for AmpC production using the cefoxitin disk (30 μg) and cefotaxime disk (30 μg).
CLSI, Clinical and Laboratory Standards Institute; ESBL, extended-spectrum β-lactamase; Inter., interpretation of the test result; MIC, minimum inhibition concentration; MRSN, Multidrug-Resistant Organism Repository and Surveillance Network; NEG, no flattening of the zone of inhibition toward cefoxitin (30 μg); POS, flattening of the zone of inhibition toward cefoxitin (30 μg); UPEC, uropathogenic Escherichia coli.