サルモネラ・チフィムリウムにおけるマイクロシンY耐性経路FhuA-SbmAによる転写再プログラムと病原性増強

Salmonella Typhimurium poses critical safety risks owing to its multidrug resistance and persistence in food matrices. To address this threat, we focused on microcin Y (MccY) a lasso peptide with potent activity against multidrug-resistant S. typhimurium and elucidated how mutations in the FhuA/SbmA receptors mediate MccY resistance and differentially affect bacterial virulence. Molecular docking revealed that MccY tended to bind to the N-terminal segment of FhuA within its β-barrel cavity, with key interaction sites including FhuA_564Leu-MccY_5His (2.5 Å hydrogen bond, MIC = 200 μg/mL) and sites such as FhuA_129Ser/FhuA_147Asn (MIC = 100-200 μg/mL). For SbmA, MccY forms hydrogen bonds with SbmA_204Asn-MccY_20Tyr (3.1 Å, MIC = 1.0 μg/mL), SbmA_320Asn-MccY_21Gly (2.9 Å, MIC = 200 μg/mL), and SbmA_361Gln-MccY_21Gly (2.9 Å, MIC = 2.0 μg/mL). The susceptibility of MccY's lasso structure domains to resistance was ranked as follows: tail < ring < loop. FhuA/SbmA mutations enhance MccY resistance (MIC>250 μg/mL) via receptor conformational changes, with FhuA_Ala63Gly, and FhuA_401Met402Arg conferring higher resistance than SbmA_Gly254Glu, and SbmA_Gln361Leu. Chrome Azure S assays confirmed that these mutations, particularly FhuA_401Met402Arg insertions and SbmA_Gly254Glu, and SbmA_Gln361Leu substitutions, disrupt iron transport. Notably, FhuA mutants exhibited altered siderophore utilization, extracellular iron accumulation, enhanced biofilm formation (p < 0.05), increased flagellar motility (migration 1.7-2.7 cm), and attenuated virulence. In contrast, SbmA mutants showed broader metabolic remodeling and downregulated invasive virulence genes (prgI, invE), which correlates with enhanced in vivo virulence in mice. FhuA/SbmA mutations in S. typhimurium drive resistance, adaptive fitness, and pathogenicity through defined receptor-ligand interactions. This work provides a molecular framework for developing integrated antimicrobial approaches to mitigate the spread of resistant pathogens.