Molecular diversity and evolutionary relationships of Tn1546-like elements in enterococci from humans and animals - PubMed (original) (raw)

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

R J Willems et al. Antimicrob Agents Chemother. 1999 Mar.

Abstract

We report on a detailed study on the molecular diversity and evolutionary relationships of Tn1546-like elements in vancomycin-resistant enterococci (VRE) 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 isolates representing the seven RFLP types followed by sequencing of the identified polymorphic regions in 84 other VanA transposons resulted in the identification of 22 different Tn1546 derivatives. Differences between the Tn1546 types included point mutations in orf1, vanS, vanA, vanX, and vanY. Moreover, insertions of an IS1216V-IS3-like element in orf1, of IS1251 in the vanS-vanH intergenic region, and of IS1216V in the vanX-vanY intergenic region were found. The presence of insertion sequence elements was often associated with deletions in Tn1546. Identical Tn1546 types were found among isolates from humans and farm animals in The Netherlands, suggesting the sharing of a common vancomycin resistance gene pool. Application of the genetic analysis of Tn1546 to VRE isolates causing infections in Hospitals in Oxford, United Kingdom, and Chicago, Ill., suggested the possibility of the horizontal transmission of the vancomycin resistance transposon. The genetic diversity in Tn1546 combined with epidemiological data suggest that the DNA polymorphism among Tn1546 variants can successfully be exploited for the tracing of the routes of transmission of vancomycin resistance genes.

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Figures

FIG. 1

FIG. 1

RFLP analysis and physical and genetic maps of Tn_1546_. The position and direction of transcription of genes and open reading frames (orf’s) are indicated with open arrows. Black horizontal bars indicate the position of internal Tn_1546_ fragments used as probes (probes 1 to 4). The numbers 1 to 9 represent the restriction fragments visualized after hybridization with the Tn_1546_-specific probes 1 to 4 and are indicated on the right side of the blot. The positions of the molecular size markers are indicated on the left side of the blot. Letters above the lanes represent the Tn_1546_ RFLP types. Only the restriction enzyme recognition sites relevant for this study are shown. H, _Hae_III; X, _Xba_I. The positions of some restriction sites are indicated in parentheses.

FIG. 2

FIG. 2

Genetic maps of 22 Tn_1546_ types. The thick horizontal lines represent the Tn_1546_ types A1 to A4, B1 to B3, C, D1 to D4, E1 to E7, F1, F2, and G. The positions of genes and open reading frames (orf’s) and the direction of transcription are depicted with open arrows. Dotted boxes represent IS elements. The positions of the first nucleotide upstream and the first nucleotide downstream from the IS insertion sites are depicted. Filled arrows indicate the transcriptional orientations of the inserted IS elements. Deletions (del) are indicated by dotted lines. The positions of base pair mutations are indicated above the different Tn_1546_ types: 1226, T→A (K→stop); 4847, T→C; 7658, T→C (V→A); 8234, G→T (K→N); 9692, C→T (P→L).

FIG. 3

FIG. 3

Hypothetical evolutionary scheme for the various Tn_1546_ derivatives characterized in this study from the archetypal transposon Tn_1546_ (type A1) as described by Arthur et al. in 1993 (5). Boxes represent the different Tn_1546_ types. Filled arrows indicate the transition of Tn_1546_ type A1 to the other Tn_1546_ types. The different DNA rearrangements, insertions, deletions, and point mutations are indicated. Strain GUC has been described by Handwerger et al. (27). 2e, secondary.

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