Restriction endonucleases in clinical isolates of Shigella spp

Thirteen restriction endonuclease-containing strains were isolated from a collection of 186 clinical isolates of Shigella spp. Among these, eight and five isolates carried isoschizomers of EcoRII and NciI, respectively. The former restriction-modification (R-M) system was homologous to that of EcoRII and was located on plasmids with sizes of 46.6 or 55.6 kb. Isolates producing NciI isoschizomers contained a 5.7-kb non-transferable plasmid. Together with antimicrobial susceptibility tests and plasmid profile studies, it is concluded that these two R-M systems are not widely spread but confined to strains with similar antibiotic resistance and plasmid profile.