Plasmid profiles of antibiotic-resistantShigella dysenteriaetypes 2, 3, 4, 6 and 7 isolated in Ethiopia during 1976–85

Abstract

SUMMARY: Plasmid profile analysis by agarose gel electrophoresis was carried out on 37 drug-resistant strains ofShigella dysenteriaetypes 2, 3, 4, 6 and 7. These strains were collected between 1976 and 1985 in Addis Ababa, Ethiopia.The plasmid profile ofS. dysenteriaetype 2 strains with R-type CSSuT did not show middle-sized plasmids likely to code for CSSuT resistance. All strains contained a large plasmid of about 120 megadaltons (MDa), and a cryptic plasmid of about 2·2 MDa. The plasmid profiles ofS. dysenteriaetype 3 with R-types ACSSuT, SSuT and SSu showed a 4·2 MDa SSu-determinant, which was demonstrated inEscherichia coliK12 recipients resulting from triparental crosses. The ACT determinant inS. dysenteriaetype 3 with R-type ACSSuT is probably chromosomally mediated. Cryptic plasmids of about 3·0 and 2·2 MDa were found in allS. dysenteriaetype 3 isolates. The 4·2 MDa plasmid featured prominently in the plasmid profiles ofS. dysenteriaetypes 4, 6 and 7 with R-types SSuT and SSu. However, this plasmid was not mobilizable by triparental crosses. There was a relative paucity of transferable plasmids in non-Shiga bacillus isolates. However, incompatibility group N plasmids, coding for tetracycline resistance, were detected.