OBJECTIVES: During the course of routine screening for vancomycin-resistant enterococci (VRE), we found six Enterococcus faecium isolates positive for vanA by PCR, but susceptible to vancomycin and teicoplanin by phenotypic testing. The aim of this study was to characterize the genetic composition of the Tn1546 vanA gene cluster of these isolates. METHODS: The E. faecium isolates were characterized by antibiotic susceptibility, PFGE and structural analysis of the Tn1546 elements. Plasmids extracted from these isolates were used to determine the presence of the Tn1546 vanA gene cluster by PCR and the genomic organization of the deleted Tn1546 element by primer walking DNA sequencing. RESULTS: The vancomycin-susceptible vanA-positive E. faecium isolates showed three PFGE patterns, and were missing the vanR and vanS genes that are responsible for the activation of transcription of resistance genes. Primer walking sequencing revealed that these genes were completely deleted and that interruptions in the vanA cluster were in the vicinity of insertion sequence elements. CONCLUSIONS: The presence of vancomycin-susceptible vanA-positive E. faecium in clinical samples results from major deletions in the Tn1546 vanA operon. Our findings support the essential role of vanR and vanS for the expression of resistance to vancomycin in enterococci.
OBJECTIVES: During the course of routine screening for vancomycin-resistant enterococci (VRE), we found six Enterococcus faecium isolates positive for vanA by PCR, but susceptible to vancomycin and teicoplanin by phenotypic testing. The aim of this study was to characterize the genetic composition of the Tn1546 vanA gene cluster of these isolates. METHODS: The E. faecium isolates were characterized by antibiotic susceptibility, PFGE and structural analysis of the Tn1546 elements. Plasmids extracted from these isolates were used to determine the presence of the Tn1546 vanA gene cluster by PCR and the genomic organization of the deleted Tn1546 element by primer walking DNA sequencing. RESULTS: The vancomycin-susceptible vanA-positive E. faecium isolates showed three PFGE patterns, and were missing the vanR and vanS genes that are responsible for the activation of transcription of resistance genes. Primer walking sequencing revealed that these genes were completely deleted and that interruptions in the vanA cluster were in the vicinity of insertion sequence elements. CONCLUSIONS: The presence of vancomycin-susceptible vanA-positive E. faecium in clinical samples results from major deletions in the Tn1546 vanA operon. Our findings support the essential role of vanR and vanS for the expression of resistance to vancomycin in enterococci.
Authors: Maulik N Thaker; Lindsay Kalan; Nicholas Waglechner; Alireza Eshaghi; Samir N Patel; Susan Poutanen; Barbara Willey; Bryan Coburn; Allison McGeer; Donald E Low; Gerard D Wright Journal: Antimicrob Agents Chemother Date: 2014-12-15 Impact factor: 5.191
Authors: Ana Paula Marchi; Lauro Vieira Perdigão Neto; Marina Farrel Côrtes; Victor Augusto Camarinha de Castro Lima; Roberta Cristina Ruedas Martins; Lucas Augusto Moyses Franco; Flavia Rossi; Vanderson Rocha; Anna S Levin; Silvia Figueiredo Costa Journal: Braz J Microbiol Date: 2021-10-31 Impact factor: 2.476
Authors: Bryan Coburn; Donald E Low; Samir N Patel; Susan M Poutanen; Dea Shahinas; Alireza Eshaghi; Barbara M Willey; Allison McGeer Journal: J Clin Microbiol Date: 2014-02-12 Impact factor: 5.948
Authors: Virginia M Pierce; Douglas S Kwon; Melis N Anahtar; Juliet T Bramante; Jiawu Xu; Lisa A Desrosiers; Jeffrey M Paer; Eric S Rosenberg Journal: Antimicrob Agents Chemother Date: 2021-10-25 Impact factor: 5.938