FURTHER CHARACTERIZATION OF COMPLEMENT RESISTANCE CONFERRED ON ESCHERICHIA-COLI BY THE PLASMID GENES TRAT OF R100 AND ISS OF COLV,I-K94

The traT gene product was evidently responsible for the complement resistance of the R100 plasmid. This resistance was compared with that specified by the iss gene of the ColV-I-K94 plasmid. The levels of resistance specified by the 2 genes were similar; there was no additive effect on resistance when both genes were present together. Under conditions in which traT and iss conferred at least a 50- and 10-fold increase in survival, respectively, the consumption of C[complement component]6, C7, C8 and C9 was the same for bacteria with and without the plasmid genes. Thus, it apparently was the action of the terminal complex, not its formation, which was blocked by traT and iss.