Vancomycin-resistance transferability from VanA enterococci to Staphylococcus aureus.

Area of Science:

• Microbiology
• Molecular Biology
• Antimicrobial Resistance

Background:

• Methicillin-resistant Staphylococcus aureus (MRSA) infections with high-level vancomycin-resistance (VRSA) have emerged.
• Patients with VRSA infections often have concurrent vancomycin-resistant Enterococcus (VRE) infections.
• The vanA gene, responsible for high-level vancomycin resistance, is likely transferred horizontally from VRE to S. aureus.

Purpose of the Study:

• To investigate the in vitro conjugative transfer of the vanA gene from vancomycin-resistant Enterococcus (VRE) to Staphylococcus aureus.
• To confirm the transfer and expression of vancomycin resistance in S. aureus transconjugants.

Main Methods:

• Conjugative transfer experiments were performed using five VRE strains (three Enterococcus faecalis, two Enterococcus faecium) as donors and five clinical S. aureus isolates as recipients.
• Vancomycin resistance transfer was confirmed by vanA gene amplification.
• Transconjugant resistance levels were determined by Minimum Inhibitory Concentration (MIC) assays.
• Resistance stability was assessed through serial passages on vancomycin-containing media.

Main Results:

• Two successful vanA gene transfers from E. faecalis to S. aureus were achieved out of 25 mating experiments.
• Transconjugants exhibited vancomycin resistance (MIC 32 μg/ml), lower than the VRE donors (MIC > 128 μg/ml).
• The vancomycin resistance phenotype in transconjugants was stable over multiple passages.
• In vitro transfer was achieved without animal models and used direct vancomycin agar selection.

Conclusions:

• The vanA gene can be conjugatively transferred in vitro from VRE to S. aureus.
• This study provides experimental evidence for a mechanism contributing to VRSA emergence.
• The findings underscore the importance of monitoring VRE and S. aureus coinfections and understanding resistance gene transfer pathways.