TABLE 1.
Antimicrobial susceptibilities, cefoxitin-cefotaxime antagonism test, and confirmatory test for ESBL production for blood 71 E. cloacae isolates and 1 Enterobacter sp. isolate
| Group (no. of strains) | Cefoxitin-cefotaxime antagonisma | ESBL testa,b | MIC50, MIC range (μg/ml)c
|
MIC50, MIC range (μg/ml)c
|
||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| FOX | CTT | CPD | CAZ | CTX | ATM | FEP | PIP | TZP | TIM | IPM | GEN | AMK | OFX | |||
| Derepressed or partially derepressed mutants (15) | −, 11; +, 4 | −, 15 | >256, 32->256 | 96, 32->256 | >256, 64->256 | 64, 4->256 | 128, 32->256 | 32, 0.25-128 | 3, 0.064-12 | >256, 128->256 | 16, 1->256 | 256, 2->256 | 1, 0.25-2 | 128, 1->128 | 12, 1-32 | 0.25, <0.06-1 |
| Derepressed mutants with ESBL production (21) | −, 21 | +, 18; −, 3 | >256, 48->256 | 128, 4->256 | >256, 48->256 | 128, 16-256 | 256, 16->256 | 64, 0.5-256 | 6, 0.38->32 | >256, 128->256 | 32, 1->256 | 128, 4->256 | 0.5, 0.12-16 | 128, 1->256 | 16, 0.5->256 | 0.09, 0.03-2 |
| Strains with ESBL production (3) | +, 3 | +, 3 | 8, 4-12 | 2, 0.25-2 | 32, 12->256 | 32, 32->256 | 16, 4-32 | >256, 64->256 | 1.5, 0.4-12 | >256, 256->256 | 1, 1-1 | 4, 2-16 | 0.25, 0.25 | 0.25, 0.25-64 | 1, 1-8 | 0.25, <0.06-0.25 |
| Inducible strains without ESBL production (26) | +, 26 | NDd | >256, 0.75->256 | 0.5, 0.19-16 | 2, 0.19-64 | 0.12, 0.02-4 | 0.12, <0.016-4 | 0.06, <0.016-4 | 0.023, 0.006-0.25 | 1, 0.25-32 | 1, <0.016-4 | 1, <0.06-32 | 0.5, 0.12-2 | 0.5, 0.25-128 | 1, 0.5-8 | 0.06, <0.06-8 |
| Undetermined strains (7) | +, 6; −, 1 | +, 7 | >256, 32->256 | 4, 2-64 | 32, 16->256 | 16, 4-32 | 4, 2-128 | 4, 2-64 | 1, 0.016->32 | 128, 32->256 | 1.5, 0.5-4 | 16, 0.5-64 | 0.75, 0.12-1 | 9, 0.9-16 | 3, 1->256 | 0.12, <0.06-0.25 |
The numbers of isolates with negative (−) and positive (+) results are shown.
The confirmatory test for ESBL production was performed by enhancement of the inhibitory zone of cefepime (30 μg) with addition of 10 μg of clavulanic acid and by the double-disk synergy test with cefotaxime, ceftazidme, cefepime, and amoxicillin-clavulanic acid disks.
Abbreviations: FOX, cefoxitin; CTT, cefotetan; CPD, cefpodoxime; CAZ, ceftazidime; CTX, cefotaxime; ATM, aztreonam; FEP, cefepime; PIP, piperacillin; TZP, piperacillin-tazobactam; TIM, ticarcillin-clavulanic acid; IPM, imipenem; GEN, gentamicin; AMK, amikacin; OFX, ofloxacin.
ND, not determined.