»Year 2025, Volume 16, Pages 1–18
Establishment and Thorough External Validation of an FTIR Spectroscopy Classifier for Salmonella Serogroup Differentiation
Helene Oberreuter1*, Miriam Cordovana2, Martin Dyk1 & Jörg Rau1
1 Chemisches und Veterinäruntersuchungsamt Stuttgart, Fellbach, Germany
2 Bruker Daltonics GmbH & Co. KG, Bremen, Germany
*Corresponding author: Dr. Helene Oberreuter, email: helene.oberreuter@cvuas.bwl.de, tel.: +49 711 3426 1249
Available online: 12 August 2025
DOI: 10.48414/aspects2025/16
Keywords: Salmonella serogroup differentiation, FTIR spectroscopy, classifier validation
Abstract
As one of the most relevant food-borne pathogens, the reliable detection, confirmation and fine-typing of Salmonella strains is very important. Salmonella serotype determination using rabbit antisera is the worldwide-accepted standard, but it is labor intensive, costly, and requires extensive experience. As an alternative, successful discrimination between strains of different serogroups by FTIR spectroscopy has been previously developed for various bacterial groups. For the current study, firstly an FTIR Classifier operating on an IR Biotyper® spectrometer (Bruker, Germany) was designed to distinguish between n = 36 different Salmonella serogroups. An FTIR classifier is an AI-based tool used in FTIR spectroscopy for the analysis and classification of different materials based on their infrared spectra.
Secondly, the differentiation performance of this classifier was determined by a thorough external single-lab validation carried out in accordance with the “Guidelines for Validating Species Identifications Using MALDI-ToF-MS” issued by the German Federal Office of Consumer Protection for a targeted identification. The most common Salmonella serogroups in Europe, serogroups O:4 (B), O:6,7 (C1), O:8 (C2-C3) and O:9 (D1) were chosen as target parameters and validated using a total of n = 1,039 infrared absorbance spectra from a total of n = 167 strains pertaining to n = 39 serogroups. In sum, serogroups O:4, O:6,7 and O:9 perfectly met the adapted guideline requirements and resulted in a > 99 % inclusivity each. Serogroup O:8 arrived at a 96.1 % true-positive rate, due to one deviating strain. This validated classification method can thus be used in routine analysis for quick and easy differentiation of the most common Salmonella serogroups in food surveillance. In addition, when using the cluster analysis tools of the IR BT®, preselecting isolates before subjecting them to thorough serotyping decreases the workload in current routine analyses.
Supplementary material
