Restriction patterns of MDR plasmids cleaved with HindIII to show differences between RFLP1, the most common pre-1994 pattern, and RFLP7, the predominant post-1994 pattern. Lanes 1, 2, and 4, pattern 1 Salmonella serovar Typhi strains isolated in 1993; lane 3, pattern 2 Salmonella serovar Typhi strain isolated in 1993; lanes 5 and 8, pattern 7 Salmonella serovar Typhi strains isolated in 1996; lane 6, pattern 7′ plasmid isolated in 1996; lane 7, pattern 7′′ plasmid isolated in 1996; lane λ, DNA markers at 23, 9.4, 6.5, 4.3, 2.3, and 2.0 kb.