Minimal inhibitory concentrations of sulbactam/ampicillin against drug sensitive and drug resistant isolates of Mycobacterium tuberculosis.

A total of 92 isolates of Mycobacterium tuberculosis consisting of equal numbers of sensitive and resistant strains was tested for their susceptibility to sulbactam and ampicillin (in the ratio of 1:2) on Lowenstein-Jensen (LJ) and 7H11 agar media. The geometric mean MIC was 63.97 micrograms/ml for the drug sensitive strains and 65.92 micrograms/ml for the resistant strains, and the overall mean was 65.01 micrograms/ml. The high MIC on LJ medium could be attributed to the higher protein content which resulted in greater binding of sulbactam/ampicillin. On the other hand, the geometric mean MIC on 7H11 medium was 26.73 micrograms/ml for sensitive strains and 23.82 micrograms/ml for resistant strains; the overall mean being 25.23 micrograms/ml. Although these MICs of sulbactam-ampicillin are higher than those reported earlier, they can be easily achieved in serum. Further studies on experimental tuberculosis and in humans will be needed to prove the efficacy of sulbactam/ampicillin in the treatment of patients with multidrug resistant tuberculosis.