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

The effect of a biological containment system in Escherichia coli based on the stochastic induction ofa lethal gene, hok,8 was investigated in the gastrointestinal system of 33 germ-free rats. E. coli BJ16, identical to E. coli BJ4 originally isolated from a rat, but containing a plasmid pPKLlOO 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 BJI 7, 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.