Tn, a Carrier of Tn Family Transposons, Occurs in the Chromosome and in a Genomic Island of Clinical Strains.

Transposons of the accessory gene pool contribute to phenotype and to genome plasticity. We studied local strains to ascertain the encroachment of -type site hunter transposons into clinical settings and their associations with other functional modules. Five different Tn family transposons were detected, all chromosomal. Some were solitary elements; one was in of Tn, a relative of a reported carrier of -type site hunters (class 1 integrons), but most were in of Tn, a new Tn-related transposon of unknown phenotype. Most of the Tn::Tn elements, and some Tn and Tn::Tn elements found in GenBank sequences, were at identical sites in an hypothetical gene of genomic island PAGI-5v. The island in clonally differing strains was at either of two tRNA loci, suggesting lateral transfer to these sites. This observation is consistent with the membership of the prototype PAGI-5 island to the ICE family of mobile genetic elements. Additionally, the site hunters in the nested transposons occupied different positions in the Tn carrier. This suggested independent insertion events on five occasions at least. Tn family members that were -/-defective were found in Tn- and Tn-like carriers in GenBank sequences of non-clinical spp. The transposition events in these cases presumably utilized functions in trans, as can occur with class 1 integrons. We suggest that in the clinical context, strains that carry Tn alone or in PAGI-5v can serve to disseminate functional site hunters; these in turn can provide the requisite -acting functions to assist in the dissemination of class 1 integrons, and hence of their associated antibiotic resistance determinants.