Table 1.
Test characteristics of screening methods for ESBL production in 271 Enterobacter isolates (37 ESBL positive; 234 ESBL negative), using genotypic detection of ESBL as the reference methoda
| ESBL screening method | MIC (mg/liter) | Sensitivity (%) | Specificity (%) | PPV (%) | NPV (%) | Isolates meeting screening criteria (% of all isolates) (n = 271) |
|---|---|---|---|---|---|---|
| Broth microdilution | ||||||
| Ceftriaxoneb and/or ceftazidimeb | >1 | 100 | 63 | 30 | 100 | 124 (46) |
| Cefotaximeb and/or ceftazidime | >1 | 100 | 68 | 33 | 100 | 113 (42) |
| Cefpodoximeb | >4 | 100 | 37 | 20 | 100 | 185 (68) |
| Cefepime | >1 | 100 | 86d | 53d | 100 | 70 (26)d |
| Vitek 2 | ||||||
| AES “ESBL production” | 92c | 87d | 52d | 99c | 65 (24)d |
PPV, positive predictive value; NPV, negative predictive value; AES, advanced expert system.
Indicator cephalosporins and ESBL screening breakpoints recommended by CLSI for ESBL screening in E. coli, Klebsiella spp., and Proteus mirabilis. These breakpoints are equivalent to the EUCAST clinical susceptible/intermediate breakpoints, except for cefpodoxime (EUCAST susceptible breakpoint, ≤1 mg/liter).
P > 0.05 for comparison of sensitivity and NPV between Vitek 2 AES and the broth microdilution ESBL screening methods. Three ESBL-producing E. cloacae isolates (2 CTX-M-9, 1 SHV-12) were identified as ESBL-positive “high-level cephalosporinase” producers instead of ESBL producers.
P < 0.001 for comparison of specificity, PPV, and number of isolates meeting screening criteria between Vitek 2 AES or the MIC of cefepime (>1 mg/liter) and the other broth microdilution ESBL screening methods.