PLAGUE PANDEMICS INVESTIGATED BY RIBOTYPING OF YERSINIA-PESTIS STRAINS

Yersinia pestis is the causative agent of plague, a disease which has caused the deaths of millions of people and which persists now in ende mic foci. The rRNA gene restriction patterns (i.e., ribotypes) of 70 s trains of Y. pestis, isolated on the five continents over a period of 72 years, were determined by hybridization with a 16S-23S rRNA probe f rom Escherichia coli. The combination of the EcoRI and EcoRV patterns resulted in the elucidation of 16 ribotypes. Two of them (B and O) cha racterized 65.7% of the strains studied, while the 14 other ribotypes were found in no more than three strains each. A relationship was esta blished between biovars and ribotypes: strains of biovar Orientalis we re of ribotypes A to G, those of biovar Antiqua were of ribotypes F to O, and those of biovar Medievalis were of ribotypes O and P. Great he terogeneity in rRNA restriction patterns mas found among strains isola ted in Africa; this heterogeneity was less pronounced among Asian isol ates and was completely absent from the American strains. Pulsed-field gel electrophoresis was performed on the DNAs of some strains, but it appeared that different colonies from the same strain displayed diffe rent pulsed-field gel electrophoresis patterns and therefore that this technique was not suitable for comparison of Y. pestis isolates. In c ontrast, the ribotypes of individual colonies within a given strain we re stable and mere not modified after five passages in vivo. A clear c orrelation between the history of the three plague pandemics and the r ibotypes of the strains could be established.