Abstract
Staphylococcus aureus (S. aureus) is an extremely halotolerant pathogenic bacterium with high osmotic stress tolerance, and it is frequently encountered in aquatic production and preservation. However, the mechanism underlying the extremely high osmotic stress tolerance of S. aureus remains unclear. In this study, the isobaric tags for relative and absolute quantification (iTRAQ) method was used to identify the differentially expressed proteins (DEPs) under different sodium chloride (NaCl) concentrations. Compared with the control group (0% NaCl), the 10 and 20% NaCl groups had 484 DEPs and 750 DEPs, respectively. Compared with the 10% NaCl group, the 20% NaCl group had 361 DEPs. Among the DEPs, proteins involved in fatty acid synthesis, proline/glycine betaine biosynthesis and transportation, stress tolerance, cell wall biosynthesis and the TCA cycle were upregulated, whereas proteins associated with biofilm formation and pathogenic infections were downregulated. The results obtained in this study indicate that under extremely high osmotic stress, modification of the cell membrane structure, increased biosynthesis and transportation of osmotic protectants, and redistribution of energy metabolism contribute to the osmotic stress tolerance of S. aureus, and the infectious ability of the bacteria may be limited. The aim of this study was to provide new insight into how S. aureus tolerates the high-salt conditions involved in aquatic production and preservation.
Highlights
Staphylococcus aureus is a gram-positive pathogenic bacterium, and it is the most prevalent cause of food-borne infections worldwide
Our results show that the IcaA (0.40-fold, p < 0.001), IcaB (0.54-fold, p > 0.05) and Spa (0.29-fold, p < 0.05) proteins were downregulated in the 20% NaCl group (Supplementary Tables S3, S5) and that the transcriptional levels of the genes encoding these proteins were significantly decreased by 0.50− (p < 0.01), 0.60− (p < 0.01) and 0.30fold (p < 0.01), respectively (Figure 9)
The differentially expressed proteins (DEPs) identified in cells grown in 0, 10, and 20% NaCl via isobaric tags for relative and absolute quantification (iTRAQ) could be categorized into 20 Gene Ontology (GO) functional groups and 24 Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways
Summary
Staphylococcus aureus is a gram-positive pathogenic bacterium, and it is the most prevalent cause of food-borne infections worldwide. 20–30% of the general population carries this symbiotic bacterial pathogen that can result in food poisoning, lead to suppurative infections, acquire drug resistance and cause other medical problems. High-salt conditions can be used as an alternative means to preserve foods, and S. aureus has higher viability than other bacteria in high-salt foods (McCarthy et al, 2012). S. aureus is salt-tolerant and can contaminate almost all cured preparations, such as cold-smoked fish, caviar and salt-smoked fish (Moon et al, 2017). Studies on the mechanism of salt tolerance in S. aureus aim to provide guidance for the prevention and control of contamination by this bacterium during aquatic production and preservation
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