Differential antibiotic susceptibilities of starved Mycobacterium tuberculosis isolates

Abstract

We compared the efficacies of 17 agents against rapidly growing and starved Mycobacterium tuberculosis H37Rv. Few compounds have significant activity at attainable concentrations. However, two phenothiazine compounds at similar concentrations were bactericidal for starved and growing cells. These drugs appear to target a process important in both replicating and nonreplicating bacteria.

FIG. 1.

Drug susceptibility of log-phase (▪) and 6-week-starved (○) M. tuberculosis H37Rv. Cultures were treated in triplicate with rifampin, isoniazid, chlorpromazine, or trifluoperazine at different concentrations for 7 days. Control samples of both starved and log-phase M. tuberculosis H37Rv were incubated without drugs for 7 days. Then cultures were washed twice with PBS and their viability assessed by plating followed by CFU counting. Values represent the means ± standard errors of the means of triplicate determinations (except with the starved-cell rifampin test, which was performed in duplicate). Units on the y axis are bacterial counts (log₁₀ CFU/ml), and units on x axis are concentrations in mg/ml.