TABLE 4.
Disk diffusion performance characteristics compared to broth microdilutiona
| Organism(s) | No. of isolates | % (no.) with agreement or error |
|||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 30-μg HardyDisks (FDA cleared) |
30-μg MASTDISCS (RUO) |
||||||||||||||||||||||
| CLSI |
FDAb
(n = 73) |
EUCAST |
CLSI |
FDAb
|
EUCAST |
||||||||||||||||||
| CA | mE | ME | VME | CA | mE | ME | VME | CA | ME | VME | CA | mE | ME | VME | CA | mE | ME | VME | CA | ME | VME | ||
| Carbapenem-resistant Enterobacterales | 58 | 91 (53) | 9 (5) | 0 | 0 | 84 (49) | 16 (9) | 0 | 0 | 88 (51) | 17 (7) | 0 | 88 (51) | 12 (7) | 0 | 86 (50) | 14 (8) | 0 | 0 | 90 (52) | 14 (6) | 0 | |
| Carbapenemase-producing CRE | 26 | 88 (23) | 12 (3) | 0 | 0 | 81 (21) | 19 (5) | 0 | 0 | 88 (23) | 12 (3) | 0 | 88 (23) | 12 (3) | 0 | 0 | 81 (21) | 19 (5) | 0 | 0 | 92 (24) | 8 (2) | 0 |
| Non-carbapenemase-producing CRE | 32 | 94 (30) | 6 (2) | 0 | 0 | 88 (28) | 12 (4) | 0 | 0 | 88 (28) | 12 (4) | 0 | 88 (28) | 12 (4) | 0 | 0 | 91 (29) | 9 (3) | 0 | 0 | 88 (28) | 12 (4) | 0 |
| Citrobacter freundii complex | 2 | 50 (1) | 50 (1) | 0 | 0 | 50 (1) | 50 (1) | 0 | 0 | 50 (1) | 100 (1) | 0 | 50 (1) | 50 (1) | 0 | 0 | 50 (1) | 50 (1) | 0 | 0 | 50 (1) | 100 (1) | 0 |
| Enterobacter cloacae complex | 15 | 93 (14) | 7 (1) | 0 | 0 | 80 (12) | 20 (3) | 0 | 0 | 87 (13) | 25 (2) | 0 | 87 (12) | 13 (2) | 0 | 0 | 87 (13) | 13 (2) | 0 | 93 (14) | 7 (1) | 0 | |
| Escherichia coli | 15 | 100 (15) | 0 | 0 | 0 | 100 (15) | 0 | 0 | 0 | 80 (12) | 20 (3) | 0 | 100 (15) | 0 | 0 | 0 | 100 (15) | 0 | 0 | 0 | 87 (13) | 13 (2) | 0 |
| Klebsiella aerogenes | 2 | 100 (2) | 0 | 0 | 0 | 100 (2) | 0 | 0 | 0 | 100 (2) | 0 | 0 | 100 (2) | 0 | 0 | 0 | 100 (2) | 0 | 0 | 0 | 100 (2) | 0 | 0 |
| Klebsiella oxytoca | 6 | 83 (5) | 17 (1) | 0 | 0 | 83 (5) | 17 (1) | 0 | 0 | 83 (5) | 17 (1) | 0 | 100 (6) | 0 | 0 | 0 | 83 (5) | 17 (1) | 0 | 0 | 83 (5) | 17 (1) | 0 |
| Klebsiella pneumoniae | 15 | 87 (13) | 13 (2) | 0 | 0 | 73 (11) | 27 (4) | 0 | 0 | 100 (15) | 0 | 0 | 73 (11) | 27 (4) | 0 | 0 | 73 (11) | 27 (4) | 0 | 0 | 83 (14) | 7 (1) | 0 |
| Serratia marcescens | 3 | 100 (3) | 0 | 0 | 0 | 100 (3) | 0 | 0 | 0 | 100 (3) | 0 | 0 | 100 (3) | 0 | 0 | 0 | 100 (3) | 0 | 0 | 0 | 100 (3) | 0 | 0 |
| Non-glucose-fermenting Gram-negative bacilli | 39 | 85 (33) | 8 (3) | 12 (3) | 0 | 36 (5) | 64 (9) | 0 | 0 | 79 (31) | 15 (4) | 31 (4) | 85 (33) | 15 (6) | 0 | 0 | 50 (7) | 43 (6) | 0 | 25 (1) | 90 (35) | 8 (2) | 15 (2) |
| Pseudomonas aeruginosa | 14 | 93 (13) | 7 (1) | 0 | 0 | 36 (5) | 64 (9) | 0 | 0 | 79 (11) | 14 (2) | 25 (1) | 86 (12) | 14 (2) | 0 | 0 | 50 (7) | 43 (6) | 0 | 25 (1) | 86 (12) | 10 (1) | 25 (1) |
| Acinetobacter baumannii complex | 14 | 64 (9) | 14 (2) | 25 (3) | 0 | 64 (9) | 20 (2) | 33 (3) | 71 (10) | 29 (4) | 0 | 0 | 86 (12)c | 20 (1)c | 11 (1)c | ||||||||
| Stenotrophomonas maltophilia | 11 | 100 (11) | 0 | 0 | 0 | 100 (11) | 0 | 0 | 100 (11) | 0 | 0 | 0 | 100 (11)c | 0 | 0 | ||||||||
| All isolates | 97 | 89 (86) | 8 (8) | 3 (3) | 0 | 75 (54) | 25 (18) | 0 | 85 (82) | 17 (11) | 12 (4) | 87 (84) | 13 (13) | 0 | 0 | 79 (57) | 19 (14) | 0 | 20 (1) | 90 (87) | 13 (8) | 12 (4) | |
CRE, carbapenem-resistant Enterobacterales; FDA, U.S. Food and Drug Administration; CLSI, Clinical and Laboratory Standards Institute; EUCAST, European Committee on Antimicrobial Susceptibility Testing; S, susceptible; I, intermediate; R, resistant; RUO, research use only.
Breakpoints used for this analysis were prior to the 28 September 2020 update. The FDA breakpoints for the Enterobacterales (listed as Enterobacteriaceae on the FDA website) are specific for E. coli, K. pneumoniae, P. mirabilis, and E. cloacae complex. However, we used the breakpoints to interpret all Enterobacterales results in this study.
EUCAST provided disk correlates associated with the susceptible PK-PD breakpoint for A. baumannii and S. maltophilia. Although the PK-PD breakpoint for S is set at ≤2 μg/ml, there were no S. maltophilia isolates tested by EUCAST with MICs of >0.5 μg/ml. Thus, the disk correlate for S. maltophilia is for isolates with MICs of ≤0.5 μg/ml.