Transferable genes putatively conferring elevated minimum inhibitory concentrations of narasin in Enterococcus...

Area of Science:

• Microbiology
• Genetics
• Antimicrobial Resistance

Background:

• Elevated minimum inhibitory concentration (MIC) of the polyether ionophore antibiotic narasin is prevalent in Enterococcus faecium from Swedish broilers.
• Understanding the genetic basis of this resistance is crucial for managing poultry health and antibiotic use.

Purpose of the Study:

• To identify the specific gene(s) responsible for the elevated MIC of narasin in Enterococcus faecium.
• To investigate the genetic mechanism underlying narasin resistance in this bacterial population.

Main Methods:

• Sequencing of six plasmids from resistant Enterococcus faecium isolates.
• Design and application of a PCR assay to screen 100 isolates for specific genetic elements.
• Correlation analysis between gene presence and narasin MIC values.

Main Results:

• A 5.9 kb DNA region, absent in sensitive strains, was identified in plasmids conferring narasin resistance.
• This region contains two genes encoding an ABC-type transporter (permease and ATPase components).
• PCR confirmed a strong correlation between the presence of these ABC transporter genes and a high MIC of narasin (≥ 2 mg/L).

Conclusions:

• The ABC permease and ABC ATPase are identified as the likely genetic mechanism responsible for elevated narasin MIC in Enterococcus faecium from Swedish broilers.
• This represents the first reported instance of a putative transferable mechanism conferring elevated narasin resistance.
• Findings have implications for understanding and combating antimicrobial resistance in veterinary settings.