A new high-level gentamicin resistance gene, aph(2'')-Id, in Enterococcus spp

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Enterococcus species are significant nosocomial pathogens.
• High-level aminoglycoside resistance (HLAR) in enterococci complicates treatment, often necessitating combination therapy.
• Existing molecular probes may not detect all aminoglycoside resistance mechanisms.

Purpose of the Study:

• To characterize the gentamicin resistance mechanism in Enterococcus casseliflavus UC73.
• To identify and describe the novel aminoglycoside resistance gene.
• To assess the prevalence of this resistance mechanism in clinical enterococcal isolates.

Main Methods:

• Cloning and nucleotide sequencing of a gentamicin resistance gene from E. casseliflavus UC73.
• Expression of the cloned gene in Escherichia coli to confirm resistance.
• PCR-based screening of clinical enterococcal isolates using a specific probe.
• Pulsed-field gel electrophoresis for clonal analysis.

Main Results:

• A novel gene, aph(2")-Id, encoding a phosphotransferase was identified and characterized.
• The aph(2")-Id gene conferred high-level gentamicin resistance in E. coli transformants.
• The aph(2")-Id gene was detected in 17 of 118 HLAR enterococcal isolates, primarily vancomycin-resistant Enterococcus faecium, belonging to three distinct clones.
• Synergistic killing of E. casseliflavus UC73 was observed with ampicillin combined with amikacin or neomycin.

Conclusions:

• The aph(2")-Id gene represents a newly identified mechanism of high-level aminoglycoside resistance in enterococci.
• The prevalence of aph(2")-Id in clinical isolates suggests its clinical relevance.
• Current screening methods for HLAR in enterococci may require updates to include the detection of aph(2")-Id.