Functional and physiological characterization of the Tn21 cassette for resistance genes in Tn2426

Abstract

The Tn21 subgroup of class I1 transposons plays an important role in the dissemination of resistance genes and especially in the epidemic spread of multi-resistance. This ability reflects the variety of resistance genes that associate with the streptomycinIspectinomycin-resistance gene (aadA) of Tn21. Deletion experiments with Tn2426, a typical member of the Tn21 subgroup, and sequencing of the region that accommodates additional resistance genes revealed significant structural characteristics. Each resistance gene was flanked by short, directly repeated recombinationally active sequences with unexpected variability in their sequence and length. The consensus for a recombinationally active sequence appeared to be 13 bp in length (TAAAACAANGNNA), compared to previous estimates of 54 bp. This sequence, in combination with the product of the integrase gene, is responsible for the genetic variability of members of the Tn21 family of transposable elements and the dissemination of multi-resistance.

Carbapenem-hydrolyzing beta-lactamases

“…However, the upstream DNA sequence diverged approximately 20 base pairs 5Ј of the initiation codon. A search of the GenBank DNA sequences (11) against the upstream sequence of the K. pneumoniae gene indicated nearly 100% identity between this sequence and the tnpI integrase gene of Tn21-like transposons (49,88). The metallo-␤-lactamase gene is located within a recombination repeat unit which lies at the 3Ј end of tnpI (49,88).…”

“…A search of the GenBank DNA sequences (11) against the upstream sequence of the K. pneumoniae gene indicated nearly 100% identity between this sequence and the tnpI integrase gene of Tn21-like transposons (49,88). The metallo-␤-lactamase gene is located within a recombination repeat unit which lies at the 3Ј end of tnpI (49,88). This observation indicates that the metallo-␤-lactamase gene probably resides on a transposable element, on a plasmid, in a strain known for sharing its plasmids with other bacteria.…”

Transposons Tn 1696 and Tn 21 and Their Integrons In4 and In2 Have Independent Origins

“…In all cases P2 is associated with P c (weak). The additional sequences include In8 in Tn2603 (31), the integron in Tn2426 (54), and In10 in Tn4000 (41), which are known to be closely related to Tn21 on the basis of restriction mapping (39). In two further cases, In14 (plasmid R) (47) and an unnumbered integron found in the chromosome of a multidrug-resistant S. flexneri strain (34), the sequence adjacent to the IRi of the integron has been reported (14,34) and is identical to the Tn21 sequence.…”

Overexpression and characterization of the chromosomal aminoglycoside 6'-N-acetyltransferase from Enterococcus faecium

“…The acc(6Ј)-Ii gene from E. faecium CIP 54-32 has been cloned and sequenced, and it shows significant homology to other AAC(6Ј)-coding genes (4). The enterococcal gene encodes a 182-amino-acid protein which demonstrates roughly 10 to 20% similarity to most other AAC(6Ј) enzymes and over 40% similarity to AAC(6Ј)-Ia from Citrobacter diver-sus (28) and Shigella sonnei (31); as such, AAC(6Ј)-Ia and -Ii form a third structural subfamily of AAC(6Ј) proteins (23).…”