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Antimicrobial Agents and Chemotherapy, March 2008, p. 1001-1008, Vol. 52, No. 3
0066-4804/08/$08.00+0     doi:10.1128/AAC.00999-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Diversity of Tn1546 and Its Role in the Dissemination of Vancomycin-Resistant Enterococci in Portugal

Carla Novais,^1,2 Ana R. Freitas,¹ João C. Sousa,² Fernando Baquero,^3,4 Teresa M. Coque,^3,4, and Luísa V. Peixe^1,*

REQUIMTE, Laboratório de Microbiologia, Faculdade de Farmácia, Universidade do Porto, Porto, Portugal,¹ Laboratório de Microbiologia, Faculdade Ciências da Saúde, Universidade Fernando Pessoa, Porto, Portugal,² Servicio de Microbiologia, Hospital Universitario Ramón y Cajal-CIBER-ESP, Madrid, Spain,³ Unidad de Resistencia a Antibióticos y Virulencia Bacteriana (RYC-CSIC), Madrid, Spain⁴

Received 31 July 2007/ Returned for modification 29 October 2007/ Accepted 26 December 2007

We characterized the molecular diversity of vanA vancomycin-resistant enterococci (VRE; 176 isolates/87 pulsed-field gel electrophoresis types) from different sources and cities in Portugal (1996 to 2004): (i) food animals (FA; n = 38 isolates out of 31 samples), hospitalized humans (HH; n = 101/101), healthy human volunteers (HV; n = 7/4), and environmental sources (n = 30/10). Some strains were isolated from different hosts and persistently recovered for years. Twenty-four Tn1546 variants were identified, all located on plasmids (30 to 250 kb). Some Tn1546 variants were associated with specific sources such as FA (3 types), HH (11 types), or HV (1 type), while others were recovered from isolates of different origins (8 types). Polymorphisms in the central vanRSHA region of Tn1546 were scarcely detected, while alterations upstream of vanR and downstream of vanA were frequently identified involving mutations (vanS and vanX), deletions (vanY), insertions (IS1216V, ISEf1, and IS19; sequences with or without homology with others available in GenBank databases), and different genetic rearrangements. Most Tn1546 variants contained IS1216V (14 types) or ISEf1 (6 types). IS1216V was found alone or associated with an IS3-like element at different orientations and positions in Tn1546 from human, animal, and environmental samples. ISEf1 was located within vanX-vanY region at nucleotide 9044 of Tn1546 variants mostly associated with clinical isolates, suggesting a common genetic platform. IS19 was observed within the vanX-vanY region in one Tn1546 variant from poultry. Recent spread of VRE in Portugal reflects a complex epidemiology involving both clonal spread and plasmid dissemination containing a variety of Tn1546 types. Apparent Tn1546 heterogeneity among enterococci from human, animal, and environmental sources might reflect frequent genetic exchange events and evolution of particular widely disseminated genetic elements.

Published ahead of print on 7 January 2008.

L.P. and T.M.C. contributed equally to the direction, preparation, and writing of the manuscript.