Unraveling novel Mutation Patterns and Morphological Variations in Two Dalbavancin-resistant MRSA strains in Austria using Whole Genome Sequencing and Transmission Electron Microscopy

Abstract

Purpose: The increasing prevalence of methicillin-resistant Staphylococcus aureus(MRSA) strains resistant to non-beta-lactam antimicrobials poses a significant challenge in treating severe MRSA bloodstream infections. This study explores resistance development and mechanisms in MRSA isolates, especially after the first dalbavancin-resistant MRSA strain in our hospital in 2016. Methods: This study investigated 55 MRSA bloodstream isolates (02/2015–02/2021) from the University Hospital of the Medical University of Vienna, Austria. The MICs of dalbavancin, linezolid, and daptomycin were assessed. Two isolates (16-33 and 19-362) resistant to dalbavancin were analyzed via whole-genome sequencing, with morphology evaluated using transmission electron microscopy (TEM). Results: S.aureusBSI strain 19-362 had two novel missense mutations (p.I515M and p.A606D) in the pbp2 gene. Isolate 16-33 had a 534bp deletion in the DHH domain of GdpP and a SNV in pbp2 (p.G146R). Both strains had mutations in the rpoB gene, but at different positions. TEM revealed significantly thicker cell walls in 16-33 (p < 0.05) compared to 19-362 and dalbavancin-susceptible strains. Over the observed years, a noticeable MIC creep for dalbavancin emerged. None of the MRSA isolates showed resistance to linezolid or daptomycin. Conclusion: Inlight of increasing vancomycin resistance reports, continuous surveillance is essential to comprehend the molecular mechanisms of resistance in alternative MRSA treatment options. Furthermore, based on the observed dalbavancin MIC creep, inclusion of dalbavancin in routine antimicrobial susceptibility testing should be considered.