Table 1.

Antimicrobial susceptibilities and pIs of β-lactamases of K. pneumoniae clinical isolates and their transconjugants

pI(s) of β-lactamase(s)bNo. of strainsMIC50 (μg/ml) ofa:MIC90 (μg/ml) of:
AMPCFXCTXCAZATMAMPCFXCTXCAZATM
Clinical isolates
 8.224>512832256512>5123264512>512
 7.610>512832164>512166464128
 8.2, 5.9c 1>512864256512
 8.2, 5.9c 1>5121664512512
 8.2, 8.0c 1>5126464512>512
 7.6, 8.0c 1>512>512256328
 7.6, 5.4c 1>5124256328
Transconjugants
 8.219>51244864>51281632256
 7.6951242<1<1>512321682
 7.6, 5.4c 1>51241682
E. colirecipientc 440.250.50.125
  • a MICs were determined in agar dilution tests (13). AMP, ampicillin; CFX, cefoxitin; CTX, cefotaxime; CAZ, ceftazidime; ATM, aztreonam.

  • b In addition to the chromosomal SHV-type β-lactamase of K. pneumoniae.

  • c MIC, not MIC50.