FIG 5.
Concept of plasmid evolution and transmission across three bacterial species. P. aeruginosa blaIMP-8 was isolated approximately 2.5 years prior to the first isolation of Citrobacter species harboring blaIMP-8, leading to the hypothesis of a transfer of plasmid A from P. aeruginosa to Citrobacter species. Occurrences of the C. freundii and C. cronae blaIMP-8 genes started at the same time; thus, the timeline does not suggest a specific direction of the transfer. However, the existence of the transposon region in the chromosome of C. freundii cluster Cf2 (marked with a black triangle) makes it the most likely host of the merging of plasmid A and B, which are linked by two copies of the transposon region. Solid arrows represent the transmission sequence resulting from this hypothesis.