[Yersinia pestis. Bacteriology]

The author discusses the evolution in the classification of the bacterium, responsible for plague: first a classification based on phenotypic characteristics, later based on genotypic characteristics, to finally arrive at an evolutionist classification. He treats the seven species of the genus Yersinia that can be distinguished by DNA hybridization. He examines the issue of sequencing and decoding the chromosome and mentions research regarding the phenomenon that the metabolism of the organisms modifies as a reaction to signals of their changing environment. Furthermore the author discusses the efforts to characterize the strains of Y. pestis (antiqua, medievalis and orientalis). Finally he comments on the discovery of a multiresistant strain, isolated in 1995 in Madagascar.