Victoria Drauch Victoria Drauch Nicola Palmieri Nicola Palmieri Joachim Spergser Joachim Spergser Karin Hummel Karin Hummel Marlene Brandstetter Marlene Brandstetter Christian Kornschober Christian Kornschober Michael Hess Michael Hess Elsevier 2025 The zoonotic pathogen S. Infantis is of emerging importance, making detection in poultry critical. Phenotypic changes, which are significant for standardized control programs via EN/ISO 6579-1:2017, could lead to pathogens remaining undetected, increasing the risk of food-borne outbreaks. This study investigates an S. Infantis strain with both normal growth (NCP) and atypical HAS-negative colony variant (ACV) from an Austrian broiler farm. NCP and ACV underwent comprehensive analyses, including stability tests, electron microscopy, whole-genome sequencing, transcriptomics, and proteomics. Our findings demonstrate a stable atypical colony variant exhibiting acquired resistance against cefoxitin in ACV. Genomic analysis identified 9 single nucleotide polymorphisms (SNPs) and two deletions, affecting genes involved in porphyrin and sulfur metabolism. Key factors were a mutation disrupting cysG, which is essential for siroheme biosynthesis and a vital cofactor in sulfur metabolism, and a stop codon in menD (2-oxoglutarate decarboxylase), crucial for small colony variant appearance. Consequently, we hypothesize that these mutations lead to a deficiency in siroheme, as well as anaerobic sulfur respiration altogether resulting in the HAS-negative phenotype. Functional network analysis highlighted compensatory upregulation of alternative metabolic pathways, including nitrate metabolism, propanoate metabolism and mixed-acid fermentation, which may aid ACV's persistence and adaptation under anaerobic conditions. Reduced flagellin expression suggests a mechanism for immune evasion. These genetic and metabolic adaptations likely respond to environmental stressors, such as oxidative stress from disinfectants or antimicrobial pressure, leading to the emergence of the HAS-negative phenotype. Consequently, this study provides insights into the genetic and biochemical adaptations of an atypical S. Infantis variant. PDFDocument eng 2025-04-07T07:45:24.312043Z 2025 Enterica Serovar Typhimurium Small-Colony Variants Hydrogen-Sulfide Electron-Acceptor Ethanolamine Resistance Emergence Men 3507358 b application/pdf http://creativecommons.org/licenses/by/4.0/