Potential use of Fourier-transform infrared spectroscopy as a rapid screening tool for investigating nosocomial outbreaks of ST-80 vancomycin-resistant Enterococcus faecium

Fourier-transform infrared (FT-IR) spectroscopy is a non-genomic, spectrum-based typing technology useful for characterizing outbreaks of multidrug-resistant organisms. To assess the performance of FT-IR spectroscopy in characterizing ST-80 vancomycin-resistant Enterococcus faecium (VREf) isolates from a nosocomial outbreak. Core-genome single-nucleotide polymorphism phylogeny was used as a reference method to characterize a nosocomial outbreak caused by ST-80 VREf. It identified 22 of 25 epidemiologically related isolates as belonging to an outbreak cluster. The use of FT-IR spectroscopy with a cluster-defining cut-off of 0.071 resulted in the correct classification of 21 out 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 mischaracterized 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.