Tn1546 structures and multilocus sequence typing of vanA-containing enterococci of animal, human and food origin

To characterize the Tn1546 structure and to perform the genetic typing of 51 PFGE-unrelated vanA-containing enterococci of different origin (clinical, food and faecal samples of healthy humans and healthy poultry).

Tn1546 structure was characterized by a PCR primer walking strategy and sequencing. Multilocus sequence typing (MLST) was performed for Enterococcus faecium and Enterococcus faecalis strains, and esp and hyl genes were detected by PCR.

Nine different Tn1546 structures were identified in the studied strains. Type I was the most prevalent structure (75%) (identical to GenBank M97297). Two new Tn1546 structures were identified (in three clinical and animal strains), containing two new insertion sequences (ISs; ISEfa11 disrupting vanS and ISEfa10 disrupting orf1). An additional new Tn1546 structure was found in one animal strain, containing ISEf1 interrupting vanY and IS1542 in the orf2-vanR region. A high diversity of sequence types (STs) was detected among clinical (6 ST/18 strains) and non-clinical E. faecium strains (18 ST/24 strains). STs associated with clonal complexes CC17 and CC9 were mainly detected among clinical and non-clinical E. faecium strains, respectively. Seven new STs were identified in non-clinical strains. The esp and hyl genes were only found among clinical E. faecium strains.

A moderate variability in Tn1546 structure has been detected among unrelated vanA-containing enterococci of different origins, showing three new structures including two new ISs. A high diversity of STs was detected among E. faecium strains, especially among non-clinical strains, and new STs have been identified.