Toxin-antitoxin (TA) loci are typically two-component systems that encode a stable toxin, which binds an essential host target leading to cell growth arrest and/or cell death, and an unstable antitoxin, which prevents the cytotoxic activity of the toxin. The ubiquitous presence of these loci in bacterial genomes, along with their demonstrated toxicity not only in the native but also in heterologous systems, has provided the possibility of their use in wide-spectrum antibacterials. Mycobacterium tuberculosis contains nearly 40 TA loci, most of which are yet to be characterized. Here we report the heterologous toxicity of these TA loci in Escherichia coli and show that only a few of the M. tuberculosis-encoded toxins can inhibit E. coli growth and have a killing effect. This killing effect can be suppressed by coexpression of the cognate antitoxin. This work has identified functional TA pairs for sequences that are presently unannotated in the mycobacterial genome. These toxins need to be further tested for their activity in the native host and other organism backgrounds and growth environments for utilization of their antibacterial potential.