Potential Use of Fourier-Transform Infrared Spectroscopy as a Rapid Screening Tool for Investigating Nosocomial Outbreaks of ST-80 Vancomycin-Resistant Enterococcus faecium.

Core genome single-nucleotide polymorphism phylogeny was used to characterise a nosocomial outbreak caused by ST-80 Vancomycin-resistant Enterococcus faecium (VREf). It identified 22 of 25 epidemiologically related isolates as belonging to an outbreak cluster. The use of Fourier-transform infrared (FT-IR) spectroscopy with a cluster-defining cut-off of 0.071 resulted in the correct classification of 21 of 22 phylogenetically related isolates in a single cluster. It successfully distinguished three phylogenetically unrelated isolates from the outbreak cluster, along with five ST-80 unrelated control isolates, and five isolates from a previous outbreak in May 2023, yielding only one mischaracterised environmental isolate. These findings support the potential use of FT-IR spectroscopy as a rapid screening tool to assist outbreak investigations. Notably, this study is the first to focus on the performance of FT-IR spectroscopy in the epidemiological analysis of VREf isolates with the same sequence type.