Table 2.

β-Lactam MICs for the CTX-M-8-producing C. amalonaticus and its E. coli derivatives

β-Lactam(s)MIC for strain:
C. amalonaticus Rio-2 (pRio-2)aE. coli HB101 TrRio-2 (pRio-2)bE. coli DH5α C1Rio-2 (pC1Rio-2)cE. coli HB101 TR4 (pTR4)dE. coli DH5α
Amoxicillin>2,048>2,048>2,048>2,0482
Amoxicillin + cae 641632161
Ticarcillin>2,048>2,048>2,048>2,0482
Ticarcillin + ca641632162
Cephalothin>1,0241,024>1,0242564
Cefoxitin42422
Cefotaxime328160.120.06
Cefotaxime + ca0.250.060.060.060.06
Aztreonam64480.250.12
Aztreonam + ca0.500.120.120.120.12
Ceftazidime640.5010.50.25
Ceftazidime + ca10.120.120.50.25
Cefepime8240.120.06
Cefepime + ca0.060.060.060.060.06
Cefpirome16480.120.06
Cefpirome + ca0.120.060.060.060.06
Imipenem0.120.250.250.120.06
  • a C. amalonaticus Rio-2 producing β-lactamase CTX-M-8 along with a TEM-1 penicillinase.

  • b E. coli HB101 harboring natural plasmid pRio-2, which encodes β-lactamase CTX-M-8 along with a TEM-1 penicillinase.

  • c E. coli DH5α harboring recombinant plasmid pC1Rio-2, which encodes β-lactamase CTX-M-8.

  • d E. coli HB101 harboring plasmid pTR4, which encodes β-lactamase TEM-1.

  • e ca, clavulanate at fixed concentration of 2 μg/ml.