Diversity of Tn 1546 and Its Role in the Dissemination of Vancomycin-Resistant Enterococci in Portugal

Abstract

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 Tn 1546 variants were identified, all located on plasmids (30 to 250 kb). Some Tn 1546 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 Tn 1546 were scarcely detected, while alterations upstream of vanR and downstream of vanA were frequently identified involving mutations ( vanS and vanX ), deletions ( vanY ), insertions (IS 1216V , IS Ef1 , and IS 19 ; sequences with or without homology with others available in GenBank databases), and different genetic rearrangements. Most Tn 1546 variants contained IS 1216V (14 types) or IS Ef1 (6 types). IS 1216V was found alone or associated with an IS 3 -like element at different orientations and positions in Tn 1546 from human, animal, and environmental samples. IS Ef1 was located within vanX - vanY region at nucleotide 9044 of Tn 1546 variants mostly associated with clinical isolates, suggesting a common genetic platform. IS 19 was observed within the vanX - vanY region in one Tn 1546 variant from poultry. Recent spread of VRE in Portugal reflects a complex epidemiology involving both clonal spread and plasmid dissemination containing a variety of Tn 1546 types. Apparent Tn 1546 heterogeneity among enterococci from human, animal, and environmental sources might reflect frequent genetic exchange events and evolution of particular widely disseminated genetic elements.