Evolution and Spread of a Multidrug-Resistant Proteus mirabilis Clone with Chromosomal AmpC-Type Cephalosporinases in Europe

Proteus mirabilis isolates of 1999-2008 from three European countries were analyzed; all carried chromosomal AmpC-type cephalosporinase genes bla CMY of Citrobacter freundii origin ( bla CMY-2 -like genes). Isolates from Poland harbored several bla CMY s ( bla CMY-4, -12, -14, -15, -38 and a new bla CMY-45 ), while isolates from Italy and Greece harbored bla CMY-16 only. Earlier isolates with bla CMY-4 or -12 , recovered in France from Greek and Algerian patients, were also studied. All isolates showed striking similarities. Their bla CMY genes resided within IS Ecp1 transposition modules, named Tn 6093 , characterized by a 110-bp distance between IS Ecp1 and bla CMY , and identical fragments of both C. freundii DNA and a ColE1-type plasmid backbone. Moreover, these modules were inserted into the same chromosomal site, within the pepQ gene. Since ColE1 plasmids carrying IS Ecp1 with similar C. freundii DNA fragments (Tn 6114 ) had been identified earlier, it is likely that a similar molecule had mediated at some stage this DNA transfer between C. freundii and P. mirabilis . Additionally, isolates with bla CMY-12 , -15 and -38 genes harbored a second bla CMY copy within a shorter IS Ecp1 module (Tn 6113 ), always inserted downstream of the ppiD gene. Sequence analysis of all mobile bla CMY-2 -like genes indicated that those integrated in the P. mirabilis chromosome form a distinct cluster that may have evolved by the stepwise accumulation of mutations. All these observations, coupled to strain typing data, suggest that the bla CMY genes studied here may have originated from a single IS Ecp1 -mediated mobilization-transfer-integration process, followed by spread and evolution of a P. mirabilis clone over time and a large geographic area.