Characterization of the role of ybgC in lysozyme resistance of Salmonella Enteritidis

Authors: QIN, XIAOJIE - Shanghai Jiaotong University; DONG, RUI - Shanghai Jiaotong University; HE, SHOUKUI - Shanghai Jiaotong University; ZHOU, XIUJUAN - Shanghai Jiaotong University; ZHANG, ZENGFENG - Shanghai Jiaotong University; CUI, YAN - Shanghai Jiaotong University; SHI, CHUNLEI - Shanghai Jiaotong University; Liu, Yanhong; SHI, XIANMING - Shanghai Jiaotong University

Submitted to: Food Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/25/2019
Publication Date: 6/26/2019
Citation: Qin, X., Dong, R., He, S., Zhou, X., Zhang, Z., Cui, Y., Shi, C., Liu, Y., Shi, X. 2019. Characterization of the role of ybgC in lysozyme resistance of Salmonella Enteritidis. Food Control. 109:106732. https://doi.org/10.1016/j.foodcont.2019.106732.
DOI: https://doi.org/10.1016/j.foodcont.2019.106732

Interpretive Summary: Salmonella is a major bacterial foodborne pathogen with many different types referred to as serotypes or serovars. One serotype within Salmonella known as Salmonella Enteritidis causes human salmonellosis primarily through consumption of eggs or egg products. It is important to understand how this pathogen is able to survive in eggs and cause human illness. One gene found in S. Enteritidis named ybgC, encoding for an enzyme known as acyl-CoA thioesterase, plays a role in the survival of Salmonella Enteritidis in eggs. To gain a better understanding of how this gene contributes to the survival of S. Enteritidis in liquid eggs, the ybgC gene was removed from the S. Enteritidis genome forming what is referred to as a mutant strain, and the characteristics of the mutant strain were investigated. Our results showed that the ybcC gene affects membrane permeability, which weakens the Salmonella bacterium by altering its shape and affecting entry of nutrients. Thus, this gene can be exploited as a novel molecular target for development of strategies to control S. Enteritidis in eggs, and consequently preventing human illness.

Technical Abstract: The ybgC gene (encoding for acyl-CoA thioesterase) was shown to play a crucial 24 role in the survival of Salmonella Enteritidis (S. Enteritidis) in egg white in our 25 previous study. In this study, the resistance mechanisms of S. Enteritidis wild-type, 26 delta ybgC mutant, and delta ybgC-C complemented strains to lysozyme (a major 27 antibacterial component of egg white) were explored by survival ability test, cell 28 membrane characterization, and gene expression analysis. Our results showed that a 29 6-log reduction was observed with the delta ybgC mutant after incubation in egg white 30 filtrate-lysozyme (FEW-LY) for 24 h, compared to the wild-type and deltaybgC-C 31 complemented strains. Meanwhile, the delta ybgC mutant exhibited a significant increase 32 in outer membrane permeability, along with the alteration from a rod to a spherical 33 shape and the occurrence of cell lysis. Additionally, the amount of C14:0 and C17:0 34 cyclo fatty acids was decreased, while that of C18:1'7c and C19:0 cyclo '8c fatty 35 acids was increased, respectively, in response to lysozyme by the deletion of ybgC. 36 Genes responsible for the synthesis of fatty acids (fadR, fabBDG, acpP, cfa, and 37 tesAB), phospholipid (aas, plsB, and plsC), and lipid A (lpxA) were up-regulated in 38 the delta ybgC mutant after exposure to lysozyme. Taken together, these results indicate 39 that deletion of ybgC induced the expression of membrane lipid composition-related 40 genes probably contributing to alterations in fatty acid and phospholipid composition 41 in S. Enteritidis, which resulted in an increase in outer membrane permeability 42 conducing to a reduced resistance to lysozyme. Moreover, the ybgC gene has potential 43 as a novel molecular target for controlling S. Enteritidis in eggs.