Drug-Resistance of Enteric Bacteria

Superinfection of a host bacterium with two R factor

Abstract

E. coli 0-26 and E. coli K-12 were superinfected with three types of R factor: R (CM), R (TC) and R (SM). When R (CM) or R (TC) factor was superinfected to R⁺ (TC) or R⁺ (CM) cell, interferrence between the two factors was always found, i. e. 1) decrease of transmission frequency of R factor, comparing with the case that R^-cell was used as a recipient, 2) substitution of the two R factors, 3) unstable existence of doubly infected R factors.
Between R (SM) and R (TC) or R (SM) and R (CM) factor, interference between the two R factors was not found. Doubly resistant cells were easily obtained, indicating that the double resistance (SM. TC or SM. CM) was stable after successive subculturieg and the cells carried two types of R factor (R (SM) and R (TC), or R (SM) and R (CM)).
But one of the two R factors was transferred segregately to recipient by conjugation, suggesting that the two R factors existed separately in a host bacterium. When R (TC) and R (CM) factors were doubly infected to a host bacterium, (CM. TC) resistant cells were obtained. As the result of interaction between the two types of R factor present in a host bacterium, recombinant factor was obtained R31 (CM. TC). The recomb inant factor was able to transfer its resistance by conjugation and was also transduced as one unit into E. coli K-12 by PIkc phage.