Study of a Conditional Suicide System for Biological Containment of Bacteria in Germ-free Rats

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Abstract
The effect of a biological containment system in Escherichia coli based on the stochastic induction of a lethal gene, hok,8 was investigated in the gastrointestinal system of 33 germ-free rats. E. coliBJ16, identical to E. coli BJ4 originally isolated from a rat, but containing a plasmid pPKL100 with the hok gene, was given to germ-free rats. In these rats a plasmid-free and a plasmid-containing population was formed and co-existed in the gut. When given to gnotobiotic rats which had been initially monoassociated with E. coli BJ4, the E. coli BJ16 (hok +) was eliminated at a faster rate than E. coli BJ17, identical to E. coli BJ4 but carrying a plasmid pMG33 without the hok gene. Expressed as T90, the time used for a 90 per cent reduction of the bacterial concentration, the mean elimination for E. coli BJ16 (hok +) was 2.8 d and for E. coli BJ17 (hok-) was 5.3 d, indicating an effect of the hok gene in a competition situation.