Tetracycline resistance heterogeneity in Enterococcus faecium

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Tetracycline (Tet) resistance is a significant concern in clinical settings.
• Enterococcus faecium is a common cause of hospital-acquired infections.
• Understanding the genetic basis of Tet resistance in E. faecium is crucial for effective treatment strategies.

Purpose of the Study:

• To identify and localize tetracycline (Tet) resistance determinants in wild-type clinical isolates of Enterococcus faecium.
• To characterize the types and locations (plasmid or chromosomal) of Tet resistance genes.
• To investigate the genetic mechanisms underlying Tet resistance in E. faecium.

Main Methods:

• Conjugation experiments were used to transfer Tet determinants into a plasmid-free Enterococcus faecalis recipient.
• DNA-DNA hybridization was employed to identify classes of Tet determinants (L, M, O).
• Plasmid and chromosomal localization of resistance genes were determined.

Main Results:

• Various Tet determinants (Tcr, Tcr-Mnr) were identified in 30 E. faecium isolates.
• Tet L and Tet M were the most prevalent determinants, often found together.
• Tet M was frequently located on Tn916-like elements, indicating mobile genetic element involvement.
• One strain exhibited a novel conjugative Tcr-Mnr marker.

Conclusions:

• Enterococcus faecium exhibits significant genetic complexity regarding tetracycline resistance.
• The presence of multiple resistance determinants and mobile genetic elements contributes to the spread of resistance.
• These findings underscore the need for ongoing surveillance and understanding of antimicrobial resistance mechanisms.