Contribution of Fourier transform infrared spectroscopy for outbreak investigation of carbapenem-resistant <i>Acinetobacter baumannii</i>

The value of Fourier transform infrared (FTIR) spectroscopy as an investigation tool for outbreaks caused by <i>Acinetobacter baumannii</i> remains inconclusive. Here, we used FTIR as a real-time tool to investigate a carbapenem-resistant <i>A. baumannii</i> (CRAB) outbreak and later compared the FTIR results to results of whole genome sequencing (WGS). We used single-nucleotide polymorphism (SNP) analysis to confirm the correct FTIR cutoff and validate FTIR clustering. The outbreak occurred mainly in a general intensive care unit of an Israeli tertiary care hospital and involved 22 patients detected between December 2022 and August 2023. Isolates from 21 patients and two environmental sources were analyzed by FTIR. Eleven representative isolates underwent WGS. We performed SNP analysis using the earliest isolate as the reference. FTIR revealed that the outbreak was comprised of three clusters and four singletons. FTIR results were concordant with WGS for the 11 sequenced isolates. FTIR had higher discriminatory power than multilocus sequence typing. Within-cluster SNP differences were up to 21 SNPs. This finding confirmed that the cutoff we chose to define FTIR clusters (0.252) was appropriate. FTIR uncovered that what appeared to be one CRAB outbreak was actually three parallel outbreaks. FTIR analysis of CRAB outbreaks yields results similar to WGS, but faster and at a lower cost. A SNP threshold of less than 21 SNPs is appropriate when analyzing an <i>A. baumannii</i> outbreak.IMPORTANCEThis study demonstrated that Fourier transform infrared (FTIR) spectroscopy could effectively identify <i>Acinetobacter baumannii</i> outbreaks. Serving as a practical and rapid alternative to whole genome sequencing, FTIR can significantly accelerate <i>A. baumannii</i> outbreak confirmation, resulting in effective infection control interventions.