The in-vitro rifampicin curing of R-plasmids JR225, BN102, BN106 and F'-plasmid F'lac+/R386 in Escherichia coli K12 rifampicin-resistant host J62-2 is described. The minimum rifampicin curing concentration and the frequency of curing of plasmids from the rifampicin-resistant host cell J62-2 and the isogenic rifampicin-sensitive J62-1 host cell were similar. However, rifampicin did not cure some test R-plasmids such as R222 and RP4 from rifampicin-resistant and rifampicin-sensitive host cells, indicating that it is the R-plasmid itself and not the host strain that determines rifampicin curing.
