Table 2.

MICs of β-lactam antibiotics and specific activities ofE. cloacae AmpC in E. coli STC172 and JRG582 containing the E. coli ampD andP. aeruginosa ampD and ampE genes

StrainRelevant genotypeMIC (μg/ml)β-Lactamase activityaFold increase in activity vs noninduced
AmpicillinCefotaximeNoninducedInducedb
STC172/pEC1C/pBGS19+ ampC+ampR+ ampD11 ampE+ 1,024323,260 ± 19023,490 ± 1,2407.2
STC172/pEC1C/pNH5 ampC+ ampR+ampD+ampE+ 80.559 ± 386 ± 51.5
STC172/pEC1C/pHUL4D ampC+ ampR+ampD+ampE+ 1282116 ± 52,420 ± 13021
STC172/pEC1C/pHUL4DE-2 ampC+ ampR+ampD+ampE+ 1281113 ± 52,930 ± 19926
STC172/pEC1C/pHUL4DE-1 ampC+ ampR+ampD+ ampE+ ORF-1644175 ± 71,260 ± 607.2
JRG582/pEC1C/pBGS19+ ampC+ampR+ Δ(ampDE)21,02464103,280 ± 6,230109,400 ± 7,1101.1
JRG582/pEC1C/pNH5 ampC+ ampR+ampD+ 8<0.5216 ± 14481 ± 292.2
JRG582/pEC1C/pHUL4D ampC+ ampR+ampD+ 1288226 ± 168,670 ± 51038
JRG582/pEC1C/pHUL4DE-2 ampC+ ampR+ampD+ampE+ 1288414 ± 397,050 ± 40017
JRG582/pEC1C/pHUL4DE-1 ampC+ ampR+ampD+ ampE+ ORF-12562241 ± 193,970 ± 30017
  • a All of the induction experiments were performed in duplicate, and the results presented are averages of two determinations. β-Lactamase activity is expressed as nanomoles of nitrocefin hydrolyzed per minute per milligram of protein.

  • b Induction was carried out with 4 μg of cefoxitin per ml.