blaCTX-M-2 gene present in InS21 is associated with Tn1000 and other truncated transposition-related genes.

POWER PABLO; DI CONZA JOSÉ; GUTKIND GABRIEL

EEUU

Congreso; 106th General Meeting. ASM; 2006

ASM

Most CTX-M-encoding genes have been found associated with ISEcp1-like insertion sequences providing not only a vehicle for their mobilization but also strong promoters for their expression. However, blaCTX-M-2, one of the original “outbreak associated” enzymes prevalent in South America, has been found in orf513-based arrangements, contained within unusual class 1 integrons. Recently, experimental work supporting a role of more than one promoter involved in blaCTX-M-2 expression but do not explain how these resistnace mechanisms were so easily disseminated among different species. We analysed the probable association of a complex class 1 integron harbouring blaCTX-M-2 gene (InS21) with transposable elements. A DNA library of Salmonella Infantis pS21 plasmid was constructed. Two sul1-positive clones contained identical fragments of 10,066 bp, was sequenced by a gene walking strategy. The first 7,277 bp sequenced corresponds to the already known 3´ end sequence of InS21 from Salmonella Infantis (accession number AJ311891). The new features found in the remaining of the insert, beyond the orf3::qacED1, include, from 5’ to 3’: (i) a second copy of sul1 gene, and an orf5 with unknown function up to date, constituting the second 3’-CS (3’-CS2) module usually reported in complex class 1 integrons; (ii) 135 bp encoding for the last 44 amino acids of the TniB enzyme, named tniBD2; (iii) the 26-bp IS1326 terminal IR, showing four nucleotide substitutions compared to the equivalent element in In34; (iv) istBD1, encoding for the last 102 amino acids of the IstB protein, and having strict identity with that from In117 (acc. number DQ125241) and In34; (v) a 35-bp Tn1000 terminal IR; and (vi) the last 714 bp of the tnpA gene from Tn1000 (a member of transposon gd). In contrast, In34 and In 117 integrons contain another portion of the tniB gene and the complete sequence of istB gene. At the moment, Tn1000-like elements associated with complex class 1 integrons were not described.