Clonal distribution of multiple-drug-resistant Shigella sonnei strains: identification by means of plasmid pattern analysis.

The spread of particular clones of S. sonnei throughout the territory of the German Democratic Republic within one year was evaluated by means of plasmid pattern analysis of the bacterial isolates. Such epidemic clones are described by their "clone formulae" comprising the phage type, biotype, colicinogenotype, antibiogram and the plasmid pattern type. They were not observed before 1982, but potential progenitor strains could be identified as having occurred sporadically in the years before. The additional application of plasmid pattern analysis revealed a better discrimination of the epidemic distribution of distinct bacterial clones than the use of conventional methods such as phage-typing, biotyping and colicinogenotyping only.