Insertion sequences (IS) occur widely within the Tn1546-like elements responsible for VanA glycopeptide resistance in enterococci from several countries. As such insertions can be used as epidemiological markers and for studying horizontal transfer of gene clusters, we investigated the distribution of IS6770, IS1542, IS1216V, IS1476, and IS1251 elements in 26 VanA Enterococcus faecium and 21 VanA Enterococcus faecalis from Brazil. PCR, using genomic DNA as a template, indicated that most of the isolates contained IS6770 (97%), IS1216V (87%) and IS1476 (72%) elements. IS1251 was also detected, but at a higher frequency in E. faecium (80%) than in E. faecalis (14%). None of the isolates harboured IS1542. Only two of 47 isolates had IS elements within their Tn1546-like elements; one possessed IS1251 between vanS and vanH, as reported in the United States; another possessed a novel IS element, designated ISEfa5, located between vanX and vanY. This novel element was found in the genomic DNA of 25 (96%) E. faecium and 11 (52%) E. faecalis. In stability studies, no IS-mediated changes were detected in the Tn1546-like elements of 25 vancomycin-resistant enterococci (VRE) monitored over 11 months. These results suggest that the occurrence of IS in Brazilian isolates is similar to that reported in American isolates, but that these elements occur rarely within the vanA gene clusters. As patterns of IS carriage did not correlate with the PFGE type of the VRE, the prevalence of IS elements in genomic DNA of VRE is not a useful epidemiological marker. However, the presence of IS-modified Tn1546-like elements, which appear to be rare in Brazil, could be a useful molecular marker in local epidemiological studies to monitor the evolution and horizontal transmission of VanA elements.
Bibliographical noteFunding Information:
The authors thank Marcela Savoldi for DNA cloning and sequencing assistance and Joseane Ferreira for technical assistance during the PFGE experiments. We are grateful to Dr. Helio Sader for providing VRE isolates from the city of Sao Paulo; Dr. Pedro Peloso, Dr. Libera M. D. Costa and Dr. Afonso L. Barth for providing isolates from the states of Rio de Janeiro, Parana and Rio Grande do Sul, respectively. We also thank Matthew McKevitt for helpful discussions and critical reading of the manuscript. This work was supported by Fundação de Amparo a Pesquisa do Estado de São Paulo (FAPESP, grants 99/12233-0 and 02/08759-1). I.L.B.C. Camargo was funded by a grant from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq 130486/2001-9).
- Enterococcus faecalis
- Enterococcus faecium
- Glycopeptide resistance
- IS elements