TABLE 2.

Antimicrobial susceptibility test results for 186 bloodstream isolates of ESBL-producing E. coli, K. pneumoniae, and P. mirabilis

Antimicrobial agentE. coli (n = 104)K. pneumoniae (n = 58)P. mirabilis (n = 24)
MIC (μg/ml)aNo. (%) susceptiblebMIC (μg/ml)No. (%) susceptibleMIC (μg/ml)No. (%) susceptible
MIC50MIC90MIC50MIC90MIC50MIC90
Amikacin28102 (98.1)21653 (91.4)2424 (100)
Amoxicillin-clavulanic acid16/8128/6448 (46.1)8/4128/6432 (55.1)2/14/224 (100)
Aztreonam2562560 (0)2562560 (0)0.2510 (0)
Cefoxitin2≥6474 (71.1)2≥6443 (74.1)28100 (0)
Cefepime162560 (0)12560 (0)2320 (0)
Cefotaxime2562560 (0)82560 (0)162560 (0)
Ceftazidime2562560 (0)2562560 (0)4160 (0)
Ciprofloxacin≥16≥169 (8.6)2≥1627 (46.5)≥16≥163 (12.5)
Gentamicin0.5≥3259 (56.7)0.25≥3240 (68.9)≥32≥320 (0)
Imipenem0.250.25104 (100)0.250.2558 (100)1424 (100)
Levofloxacin≥32≥329 (8.6)2≥3228 (48.2)≥32≥323 (12.5)
Meropenem0.030.25104 (100)0.030.2558 (100)0.030.2524 (100)
Piperacillin-tazobactam2/4256/486 (82.7)2/4256/437 (63.8)0.5/41/424 (100)
Trimethoprim-sulfamethoxazole≥4/76≥4/7635 (33.6)0.12/2.38≥4/762 (55.2)0.12/2.38≥4/7614 (58.3)
  • a MIC50 and MIC90 are the MICs at which 50 and 90% of isolates, respectively, are inhibited.

  • b In accordance with CLSI guidelines, all ESBL-producing isolates were considered resistant to all penicillins, cephalosporins, and aztreonam regardless of the MICs that emerged for these drugs during in vitro susceptibility testing (see reference 9).