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Volume 49, Number 6, December 2016

Comparison of vanA gene mRNA levels between vancomycin-resistant Enterococci presenting the VanA or VanB phenotype with identical Tn1546-like elements 

Hong Shen, Yingmei Liu, Jiuxin Qu, Bin Cao


Corresponding author:

Bin Cao 


Background and purpose: 

During the routine screening of vancomycin-resistant Enterococci faecium (VREfm) we found that VanA phenotype–vanA genotype and VanB phenotype–vanA genotype isolates had an identical Tn1546-like element structure. This study aimed to evaluate the genetic background and vanA gene expression to identify the mechanisms of the development of the VanB phenotype–vanA genotype VREfm.




Twelve VREfm isolates were collected from a 1500-bed tertiary-care teaching hospital in Beijing. Genetic variations of the Tn1546-like element were determined by an overlapping polymerase chain reaction assay and sequencing. The genetic background was determined by pulsed-field gel electrophoresis and mutilocus sequence typing. vanA gene expression was evaluated using a TaqMan quantitative real-time polymerase chain reaction. 



For the 12 isolates, six isolates with the VanA phenotype–vanA genotype and six with the VanB phenotype–vanA genotype were identified. According to the structure analysis of the Tn1546-like elements, our isolates were divided into two types. In the four isolates of type A, IS1542 and IS1216V were inserted into the orf2-vanR and vanX-vanY regions, respectively. In the eight isolates of type D, a similar insertion as type A occurred, except for an ISEfa4 insertion into IS1542. A significant difference in vanA gene expression was observed between the VanA and VanB phenotype isolates in type A, but not in type D. Mutilocus sequence typing and pulsed-field gel electrophoresis analysis showed that these isolates have a different genetic background. 



Our results indicated that the occurrence of the VanB phenotype–vanA genotype might not completely depend on the structure of Tn1546-like elements and vanA gene expression.



Key words:

Enterococci faecium, teicoplanin, Tn1546-like elements, vancomycin resistance