LAUSR

Abstract The ybgC gene (encoding for acyl-CoA thioesterase) was shown to play a crucial role in the survival of Salmonella Enteritidis (S. Enteritidis) in egg white in our previous study. In this study, the resistance mechanisms of S. Enteritidis wild-type, △ybgC mutant, and △ybgC-C complemented strains to lysozyme (a major antibacterial component of egg white) were explored by survival ability test, cell membrane characterization, and gene expression analysis. Our results showed that a 6-log reduction was observed with the △ybgC mutant after incubation in egg white filtrate-lysozyme (FEW-LY) for 24 h, compared to the wild-type and △ybgC-C complemented strains. Meanwhile, the △ybgC mutant exhibited a significant increase in outer membrane permeability, along with the alteration from a rod to a spherical shape and the occurrence of cell lysis. Additionally, the amount of C14:0 and C17:0 cyclo fatty acids was decreased, while that of C18:1ω7c and C19:0 cyclo ω8c fatty acids was increased, respectively, in response to lysozyme by the deletion of ybgC. Genes responsible for the synthesis of fatty acids (fadR, fabBDG, acpP, cfa, and tesAB), phospholipid (aas, plsB, and plsC), and lipid A (lpxA) were up-regulated in the △ybgC mutant after exposure to lysozyme. Taken together, these results indicate that deletion of ybgC induced the expression of membrane lipid composition-related genes probably contributing to alterations in fatty acid and phospholipid composition in S. Enteritidis, which resulted in an increase in outer membrane permeability conducing to a reduced resistance to lysozyme. Moreover, the ybgC gene has potential as a novel molecular target for controlling S. Enteritidis in eggs.