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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.
