from Marc Galimand and Patrice Courvalin writing in Yersinia: Systems Biology and Control:
For many years, Yersinia pestis was considered as uniformly susceptible to antimicrobial agents that are active against Gram-negative bacteria. In 1995, the first two multidrug-resistant strains of Y. pestis were identified in Madagascar and shown to contain self-transmissible plasmids, pIP1202 conferring resistance to all antimicrobial agents recommended for plague treatment and prophylaxis and pIP1203 to a smaller array of drugs. Both plasmids could be transferred by conjugation from the source Y. pestis strains to other Y. pestis and Escherichia coli. Plasmid pIP1203 could be transferred from E. coli to Y. pestis in the midgut of co-infected rat fleas, common vectors of plague. Comparative analysis of the DNA sequence of pIP1202 revealed a shared IncA/C plasmid backbone with multidrug resistant plasmids from Salmonella enterica and Yersinia ruckeri suggesting recent acquisition from a common ancestor. In addition, similar IncA/C backbones were detected in numerous multidrug resistant enterobacterial pathogens isolated from retail meat products in the United States as well as in multidrug resistant plasmids from aquatic environments. This bacterial reservoir of mobile resistance determinants, probably widespread globally, has the potential to disseminate to bacterial pathogens, including Y. pestis, and therefore represents a significant public health concern.
Further reading: Yersinia: Systems Biology and Control