Table 2.

MICs of β-lactams and β-lactamase inhibitor combinations for E. coli MV1190 producing the TEM-1 and mutant TEM β-lactamases

Strain or amino acid changes from TEM-1aDesignationMIC (μg/ml)b
AMXAMX + CLAcTICTIC + CLAcPIPPIP + TZBdCLDCTXCAZCAZ + CLAcFEPAZMTEM
TEM-1e TEM-1>1,024256>1,02425612832640.060.50.250.120.254
M69LTEM-33>1,024>1,024>1,0241,02412864160.060.50.25≤0.060.254
M69L, N276DTEM-35>1,024>1,0241,02451212832160.060.250.25≤0.060.124
R244CTEM-311,02451264648420.060.250.12≤0.060.124
G238STEM-19>1,024161,0241632≤13210.50.250.120.54
G238S, M69L>1,024325121632≤1320.250.250.250.120.258
G238S, M69L, N276D>1,0241285123232≤1320.120.250.250.250.124
G238S, R244C1,02412864168240.060.250.25≤0.060.124
G238S, E104KTEM-15>1,024161,0243232≤132880.250.2548
G238S, E104K, M69L>1,024321,0246432≤132440.250.2514
G238S, E104K, M69L, N276DTEM-50>1,0241281,02412832≤132440.50.524
G238S, E104K, R244C1,02464256648≤140.060.250.250.2514
R164STEM-12>1,024321,02432642320.1280.25118
R164S, M69L>1,0242565126432≤180.1280.250.514
R164S, M69L, N276D>1,0241,02451212832280.06820.50.54
R164S, R244C1,0242561684220.060.250.25≤0.060.124
R164S, E104KTEM-26>1,02416>1,0243264≤181640.51168
R164S, E104K, M69L>1,024641,0246464280.56421164
R164S, E104K, M69L, N276D>1,02425651212832280.12648144
R164S, E104K, R244C512641283232820.06410.2518
E. coli MV1190 (recipient strain)8422≤1≤120.060.120.12≤0.060.124
  • a M69L refers to an amino acid substitution of leucine for methionine at position 69 in the TEM-1 β-lactamase protein sequence. The single amino acid codes for the other substitutions are as follows: N, asparagine; D, aspartate; G, glycine; R, arginine; C, cysteine; S, serine; E, glutamate; and K, lysine.

  • b AMX, amoxicillin; CLA, clavulanate; TIC, ticarcillin; PIP, piperacillin; TZB, tazobactam; CLD, cephaloridine; CTX, cefotaxime; CAZ, ceftazidime; FEP, cefepime; AZM, aztreonam; TEM, temocillin.

  • c Fixed concentration of clavulanate (2 μg/ml).

  • d Fixed concentration of tazobactam (4 μg/ml).

  • e TEM with amino acid modifications engineered to be identical to natural TEM-1.