Table 2.

MICs of ampicillin, β-lactam inhibitors, and their combinations conferred by the TEM-1 β-lactamase and various types of mutant derivatives for E. coli JM83

β-Lactamase or mutant derivativeMIC (μg/ml)a
ApClAp + Cl 1bAp + Cl 2Ap + Cl 5Ap + Cl 10SbAp + Sb 5Ap + Sb 10Ap + Sb 20TbAp + Tb 5Ap + Tb 10Ap + Tb 50
c 43244423221NG256444
TEM-116,0003225012564166416,0008,0004,00025632164
18,000321,000500250125324,0002,000NG25664324
31,000321,0001,0005002503225064NG2561256416
4500325005002501253212532NG2561256416
52,000322,0001,00050012532500125NG25664328
62,000322,0001,00050012532500125NG256125648
750032500250125643212532NG25632164
82,000322,0001,00050012532500125NG256125648
98,000324,0002,0001,000250322,000500NG256500648
102,000322,0001,00050012532500125NG25664328
1116,000324,0002,0001,0002506416,00016,0008,0002562,000648
  • a Abbreviations: Ap, ampicillin; Cl, clavulanate; Sb, sulbactam; Tb, tazobactam.

  • b The numbers indicate the fixed concentration (in micrograms per milliliter) of the indicated inhibitor in combination with ampicillin for determination of ampicillin MICs.

  • c −, E. coli JM83 without a plasmid.

  • d NG, no growth in the presence of the lowest concentration of ampicillin tested (0.06 μg/ml for E. coliJM83 and 8 μg/ml for the transformants bearing a β-lactamase).