Characterization of complement resistance in Escherichia coli conferred by the antibiotic resistance plasmid R100

We have examined the effect of the antibiotic resistance plasmid, R100, on the complement (C) mediated killing of Escherichia coli K-12 strains. The viabilities, in dilute normal rabbit serum (NRS), of 5 such strains were compared with the viabilities of the same strains harboring R100. For 1 strain, J6-2, we also measured the effect of R100 on viability in normal human serum (NHS) and in guinea pig serum (GPS); in NRS, NHS,and GPS devoid of classical C pathway activity; and in NHS devoid of alternative pathway activity. Finally, we compared the depletion of individual complement components in sera exposed to J6-2 and J6-2 harboring R100. Our results demonstrate that 1) R100 renders E. coli K-12 resistant to killing by NRS, NHS, and GPS; 2) the level of resistance, which ranges from 30- to 10,000-fold, is strain dependent and serum dependent; 3) R100 inhibits killing by both the classical and alternative C pathway. Resistance appears to involve a disruption on the C pathway subsequent to the activation of C5.