Molecular typing of multi-drug resistant Shigella dysenteriae type 1 by plasmid analysis and pulsed-field gel electrophoresis

Recently, an outbreak of dysentery due to multi-drug resistant Shigella dysenteriae type 1 strains was reported along the coastal area of Kenya and shortly thereafter another outbreak appeared in the outskirts of Nairobi. We analysed 22 multi-drug resistant S. dysenteriae type 1 strains isolated from cases in the latter oubreak using plasmid deoxyribonucleic acid (DNA) profiles and pulsed-field gel electrophoresis of genomic DNA. All isolates were resistant to commonly available drugs including ampicillin, trimethoprim, sulphamethoxazole, chloramphenicol, tetracycline and streptomycin with minimum inhibitory concentrations >64 mu g/mL, but were fully sensitive to gentamicin. Only 2 strains were resistant to nalidixic acid. Analysis of plasmid DNA and genomic DNA revealed that all 22 strains were clonally related. It is likely that the present outbreak was related to that on the coast, as suggested by the similarity in drug susceptibility data. The drug susceptibility and molecular epidemiological data provide a useful baseline for future monitoring of epidemic and endemic S. dysenteriae activity in East Africa.