CHLORAMPHENICOL RESISTANCE IN CLOSTRIDIUM-DIFFICILE IS ENCODED ON TN4453 TRANSPOSONS THAT ARE CLOSELY-RELATED TO TN4451 FROM CLOSTRIDIUM-PERFRINGENS

The chloramphenicol resistance gene catD from Clostridium difficile wa s shown to be encoded on the transposons Tn4453a and Tn4453b, which we re structurally and functionally related to Tn4451 from Clostridium pe rfringens. Tn4453a and Tn4453b excised precisely from recombinant plas mids, generating a circular form, as is the case for Tn4451. Evidence that this process is mediated by Tn4453-encoded tnpX genes was obtaine d from experiments which showed that in trans these genes complemented a Tn4451tnpX Delta 1 mutation for excision, Nucleotide sequencing sho wed that the joint of the circular form generated by the excision of T n4453a and Tn4453b was similar to that from Tn4451, These results sugg est that the Tn4453-encoded TnpX proteins bind to similar DNA target s equences and function in a manner comparable to that of TnpX from Tn44 51, Furthermore, it has been shown that Tn4453a and Tn4453b can be tra nsferred to suitable recipient cells by RP4 and therefore are mobiliza ble transposons. It is concluded that, like Tn4451, they must encode a functional tnpZ gene and a target oriT or RSA site. The finding that related transposable elements are present in C. difficile and C. perfr ingens has implications for the evolution and dissemination of antibio tic resistance genes and the mobile elements on which they are found w ithin the clostridia.