NaCl Adaptation Differentially Remodels Membranes and Elevates Barotolerance of Salmonella enterica Serovar Typhimurium Relative to Escherichia coli O157:H7 Under High-Pressure Processing
摘要
The efficacy of high-pressure processing (HPP) on Escherichia coli O157:H7 and Salmonella enterica serovar Typhimurium was compared after adaptation to 0.5–5% (w/v) NaCl. Across NaCl levels, 500 MPa achieved undetectable counts faster than 400 MPa when evaluated by direct enumeration. However, recovery assays revealed substantially injured subpopulations, particularly for S. Typhimurium. At 500 MPa, E. coli O157:H7 was inactivated below the detection limit within 30 s, whereas S. Typhimurium required 120 s for similar effect, indicating a higher barotolerance of S. Typhimurium after NaCl adaptation, which was underestimated by direct plating alone. Fatty acid methyl ester analysis showed species-distinct remodeling: in S. Typhimurium, unsaturated fatty acids decreased and ≤ C16 chains increased, elevating the weighted-average melting temperature (WAMT). In E. coli O157:H7, chain-length redistribution with increased unsaturation decreased WAMT. Laurdan generalized polarization (GP) was unchanged in E. coli O157:H7 but decreased in S. Typhimurium (higher fluidity). DiBAC4(3) showed increased polarization in S. Typhimurium and greater depolarization in E. coli O157:H7 after adaptation. qRT-PCR (16 genes shared by both species) showed broad upregulation in S. Typhimurium (15/16 with log2FC ≥ 2; rpoS = 4.42), but minimal responses in E. coli O157:H7 (e.g., rpoS = 1.29). Collectively, NaCl adaptation conditions membranes and transcriptional programs in a species-specific manner that elevates the HPP barotolerance of S. Typhimurium. The inclusion of resuscitation-based recovery and consideration of salt history are therefore critical for HPP validation in liquid foods.