Chemical characteristics and anti-Escherichia coli mechanism of water-soluble extracts from yeast cell walls

Abstract

Background: Antimicrobial resistance is a threat to global public health and requires the development of new antibiotic alternatives to treat bacterial infection. Infection with Escherichia coli (E. coli) is the most common cause of diarrhea in pigs, especially in weaning piglets. The objective of this study was to characterize chemical properties of water-soluble extract (WSE) obtained from yeast cell wall, and study its antibacterial activity and antimicrobial mechanisms against E. coli. Results: WSE was extracted from yeast cell wall by hot water, followed by anhydrous ethanol precipitation and deproteinization by Sevag method to obtain water-soluble polysaccharides (WSP, accounting for 76.53 ± 5.91% by weight of WSE). WSP was purified by DEAE-52 cellulose column and Sephadex G-100 column to obtain three fractions of polysaccharides, WSNP, WSAP-1 and WSAP-2. Physicochemical properties of them were then characterized. The average molecular weights of WSNP, WSAP-1 and WSAP-2 were 105,130, 94,581 and 91,247 Da, respectively. WSNP was composed of glucosamine (GlcN), glucose (Glc), mannose (Man) and glucuronic acid (GlcA) in a molar ratio of 8.6:55.2:34.4:1.8, WSAP-1 was consisted of GlcN, Glc and Man in a molar ratio of 10.9:42.2:46.9, and WSAP-2 was consisted of GlcN, galactose (Gal), Glc and Man in a molar ratio of 9.0:1.0:55.1:34.9. Spectral analysis indicated that all three polysaccharides had pyran polysaccharides, triple-helix structure, α- and β-glycosidic bond. The minimum inhibitory concentrations of WSE and WSP on E.coli were 25 mg/mL and 100 mg/mL, respectively. WSE can not only disrupt the integrity of the cell wall and membrane of E.coli, but also increase the permeability of the outer membrane. Conclusions: Our research elucidated chemical composition and structure of WSNP, WSAP-1 and WSAP-2. WSE exerted its bactericidal activity by damaging the bacterial cell wall and membrane and increasing outer membrane permeability. Yeast cell wall products have been recommended as a potential alternative to antibiotics. This work provides more information, regarding chemical properties and anti-E. coli mechanism of WSE, and facilitates the application of yeast cell wall products as a promising antibiotic alternative in animal feed.