Table 1.

MICs of selected β-lactams and β-lactamase contents for representative enterobacters and E. coli transconjugants

Strainβ-Lactamase pI(s)aEtest MIC (μg/ml)b
AmxAmcTicTLcPipPTzFoxCazCtxCroAtmFepCpo
Caz-resistant group
E. cloacaeTSV-9(8.0) + 6.9 >25696>25612812816256>25681280.758
 trccTSV-9(8.5) + 6.9 >2568>25632321.53>2562440.384
 E. cloacaeTSV-213d (8.0) + 6.9 >256128>256256481.52561924630.386
ESC-resistant group
 E. cloacaeTSV-43(8.0) + 6.9 + 5.4>256192>25619212816192>2561232161.516
 trc TSV-43(8.5) + 6.9 >25612>25664641.52>2562340.253
 E. cloacaeTSV-287(8.0) + 8.2 >256192>256128>25664192>256128192>256616
 trc TSV-287(8.5) + 8.2 >2566>25641281224841.5240.250.75
 E. aerogenesTSV-89(8.3) + 8.2 >25612>256>256>25632>256>2562464>25628
 trc TSV-89(8.5) + 8.2 >2568>25661281636462320.51.5
 E. cloacaeTSV-144e (8.0) + 5.4>256192>25612819264>256323232160.382
 trc TSV-144(8.5) + 5.4>2568>2566128820.190.0470.0640.0940.0470.5
 E. cloacaeTSV-68(9.0)>256192>256>256>256>256>256128>256>25696824
 E. aerogenesTSV-272(8.3)1281625619212864>2566424>3280.754
ESC-susceptible group
 E. cloacaeTSV-323f (8.0)256326422960.50.1250.1250.0640.0320.094
 E. cloacaeTSV-123e (9.2)96124343>2560.380.1250.1250.0940.0320.094
 E. aerogenesTSV-92(8.3)128122343>2560.50.190.190.1250.0640.064
E. coli 1R716 (recipient)(8.5)3311.51140.250.0640.0640.1250.0320.047
  • a pIs in parentheses refer to those of β-lactamases considered chromosomal. Boldface numbers indicate pIs of ESBLs.

  • b Abbreviations: Amx, amoxicillin; Amc, amoxicillin-clavulanate; Tic, ticarcillin; TLc, ticarcillin-clavulanate; Pip, piperacillin; PTz, piperacillin-tazobactam; Fox, cefoxitin; Caz, ceftazidime; Ctx, cefotaxime; Cro, ceftriaxone; Atm, aztreonam; Fep, cefepime; Cpo, cefpirome.

  • c trc, transconjugated.

  • d Strains with true-positive Vitek ESBL detection test results.

  • e Two of three strains had false-positive DDST results.

  • f Strains with false-positive Vitek ESBL detection test results.