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From 2012.igem.org

"A dual lethal system to enhance containment of recombinant micro-organisms"
(Torres, B., Jaenecke, S., Timmis, K. N., Garcia, J. L., & Diaz, E., et al. Microbiology. 2003; 149(12):3595-3601
This paper suggest that multi-containment systems are less susceptible to inactivation by mutation events, making them more effective at preventing horizontal gene transfer by bacterial conjugation.
<a href="http://mic.sgmjournals.org/content/149/12/3595" title="Reference Link" target="_blank">Paper on Microbiology</a>