Multiple copies of functional, Tet(M)-encoding Tn916-like elements in a clinical Enterococcus faecium isolate.

Area of Science:

• Microbiology
• Genetics
• Antimicrobial Resistance

Background:

• Tn916 and related elements are prevalent in clinical enterococci, facilitating the spread of resistance genes.
• The number of Tn916 copies in clinical isolates is often assumed to be one, but this has not been systematically investigated.

Purpose of the Study:

• To investigate the copy number and characteristics of Tn916-like elements in a clinical Enterococcus faecium isolate.
• To determine the functional capabilities (excision and transfer) of these elements.

Main Methods:

• Genomic analysis of a clinical Enterococcus faecium isolate.
• Cloning of Tn916-like elements into plasmid vectors.
• Transformation and conjugation experiments in E. coli and E. faecium.

Main Results:

• Identification of three distinct, excision-proficient Tn916-like elements in the E. faecium genome.
• All elements contain tet(M) genes conferring tetracycline and minocycline resistance.
• Two elements (Tn6085a, Tn6085b) are identical and contain a Group II intron; the third (Tn6084) also contains the intron and an ISEfa11 insertion.
• Demonstration of excision from plasmids and transfer to recipient strains.

Conclusions:

• Clinical E. faecium isolates can harbor multiple, nearly identical Tn916-like elements.
• These elements encode Tet(M)-mediated resistance and retain mobility, contributing to antimicrobial resistance spread.