Plasmid profiles of drug resistant Shigella boydii types 1–5, 8, 10, 12–14 from Ethiopia (1974–85)

Plasmid profile analysis by agarose gel electrophoresis was performed on 42 drug resistant strains of Shigella boydii serotypes 1–5, 8, 10, 12–14, collected between 1974 and 1985 from endemic cases of shigellosis in Ethiopia, and their Escherichia coli K12 transconjugants. Resistance factors (R factors) were further characterized by incompatibility testing. Patterns of small plasmids, less than 15 kb, were similar within each of the individual S. boydii serotypes. Plasmids of about 3·3–3·7 kb were found in all strains of serotypes 2 and 4. Plasmids of about 4·3–4·6 kb were found in about 86% of strains. Serotypes 1, 2 and 3 were characterized by plasmids of about 5·6–5·7 kb. The 6·4·6–7 kb plasmid was found consistently in serotypes 1, 2, 3, 5, 8, 12 and 13 which were resistant to SSu or had an SSu resistance component in their phenotypes. Large plasmids (155–186 kb) were found in most S. boydii strains. Conjugative drug resistance plasmids, most often coding for three or less drugs, were found in about 26% of drug resistant strains. R-factors, coding for AT resistance (in types 2 and 8), and ASSuT resistance (in type 4), were compatible with all reference plasmids tested. Plasmids belonging to incompatibility groups X and N were found in serotypes 5 and 10, respectively.