Molecular diversity and evolutionary relationships of Tn1546-like elementsin enterococci from humans and animals

We report on a detailed study on the molecular diversity and evolutionary r elationships of Tn1546-like elements in vancomycin-resistant enterococci (V RE) from humans and animals. Restriction fragment length polymorphism (RFLP ) analysis of the VanA transposon of 97 VRE revealed seven different Tn1546 types. Subsequent sequencing of the complete VanA transposons of 13 VRE is olates representing the seven RFLP types followed by sequencing of the iden tified polymorphic regions in 84 other VanA transposons resulted in the ide ntification of 22 different Tn1546 derivatives. Differences between the Tn1 546 types included point mutations in orf1, vanS, vanA, vanX, and vanY. Mor eover, insertions of an ISI216V-IS3-like element in orf1, of IS1251 in the vanS-vanH intergenic region, and of IS1216V in the vanX-vanY intergenic reg ion were found. The presence of insertion sequence elements was often assoc iated with deletions in Tn1546. Identical Tn1546 types were found among iso lates from humans and farm animals in The Netherlands, suggesting the shari ng of a common vancomycin resistance gene pool. Application of the genetic analysis of Tn1546 to VRE isolates causing infections in hospitals in Oxfor d, United Kingdom, and Chicago, III., suggested the possibility of the hori zontal transmission of the vancomycin resistance transposon. The genetic di versity in Tn1546 combined with epidemiological data suggest that the DNA p olymorphism among Tn1546 variants can successfully be exploited for the tra cing of the routes of transmission of vancomycin resistance genes.