Variability of IncHI1 plasmids from Salmonella typhi with special reference to Peruvian plasmids encoding resistance to trimethoprim and other antibiotics.

In spite of extensive DNA homology among IncHI1 plasmids, ApaI and XbaI restriction digests of plasmids from Peruvian Salmonella typhi varied considerably from other IncHI1 plasmids isolated previously. IncHI1 plasmids appear to be undergoing a process of modular evolution, probably by sequential acquisition of resistance determinants.