Enzymatic Synthesis of KDN-Containing Sialylated Lactuloses and their Bacteriostatic Activities on Staphylococcus aureus

Sialic acids are found in various biological tissues and are known to play important roles in many biological processes. However, many sialylated oligosaccharides are not adequately available to study their biological functions and potential uses. Herein, we reported an efficient synthetic approach to obtain sialylated lactulose containing deaminoneuraminc acid (KDN). Both KDNα2,3lactulose and KDNα2,6lactulose were synthesized via one-pot multienzyme sialylation system. The bacteriostatic activities of these two sialylated lactuloses against Staphylococcus aureus (S. aureus) were analyzed by using approach of optical density OD600 measurements. In addition, integrity of cell membrane of S. aureus was examined by fluorescence analysis, protein leakage quantification and electron scanning microscope (SEM). The results showed that the maximum inhibition ratios of KDNα2,3lactulose and KDNα2,6lactulose within the first 10 h was up to 34.33% and 32.18%, respectively. KDNα2,3lactulose displayed slightly better inhibition against the growth of S. aureus than that of KDNα2,6lactulose. The addition of KDNα2,3lactulose and KDNα2,6lactulose caused a significant decrease (pandlt;0.05) in fluorescence intensity compared with control to 47.05and#177;3.06% and 51.16and#177;2.40, respectively, indicated that those two sialylated lactuloses had some extent interference with nucleic acids synthesis or caused decomposition of nucleic acids in S. aureus cells. Fluorescence microscopy results showed that S. aureus of KDNα2,3lactulose and KDNα2,6lactulose group present obvious loss of viability. The leakage amount of proteins in S. aureus treated with KDNα2,3lactulose and KDNα2,6lactulose increased by 223 μg/mL and 205.4 μg/mL, respectively. The morphological alterations on the cells observed by SEM confirmed that KDN-containing sialylated lactuloses possessed antibacterial activities. In a word, KDN-containing sialylated lactuloses have certain effects on inhibiting the growth of S. aureus.