Abstract
The high-glucose-induced cytotoxicity in diabetes has been widely recognized. Staphylococcus aureus is the most frequent pathogen isolated from diabetic foot ulcers, but the properties of this bacterium under high glucose conditions remain unclear. S. aureus grew in medium usually forms weak biofilm, and which was significantly increased by addition of glucose. However, extracellular DNA (eDNA), an important component of biofilms, was markedly decreased in presence of 15 mM glucose. The reduced eDNA content was not caused by degradation, because the nuclease activity of biofilm supernatants with glucose was significantly decreased due to the acidic pH of the medium. Under planktonic state, the growth of S. aureus was significantly decreased in the Luria-Bertani (LB) medium supplemented with 25 mM glucose, and the reduced growth of S. aureus by glucose was dose-dependent. Except for glucose, the growth of planktonic S. aureus was also markedly decreased by fructose or sucrose. Amounts of acid metabolites were produced under high glucose conditions, but the survival of planktonic S. aureus was unaffected by these acidic conditions. Cells of S. aureus from the culture medium with glucose had a thinner cell wall and highly resistant to lysostaphin compared with the bacteria cultured in LB medium. mRNA expression of genes encoding pentaglycine bridges, the substrate of lysostaphin, was significantly decreased in S. aureus by glucose. In addition to S. aureus, the growth of Staphylococcus haemolyticus and Staphylococcus epidermidis was also significantly decreased by an excess of glucose, but strains of Enterococcus faecalis, Escherichia coli, and Pseudomonas aeruginosa were unaffected by glucose. In conclusion, the reduced growth of S. aureus under high glucose conditions is due to impairment of the unique cell-wall structure, pentaglycine bridges.
Highlights
Glucose serves as an important carbohydrate for the growth of Staphylococcus aureus
In this study, the colony-forming units (CFUs) of biofilms of S. aureus Newman were unaffected by addition of 15 mM glucose (Figure 1A). Extracellular DNA (eDNA) is an important component of biofilms, and which was markedly decreased by glucose (Figures 1B,C), concordant with results from a previous study (Sugimoto et al, 2018)
Amount of acidic metabolites produced during the biofilm formation under high glucose condition may affect the nuclease activity of biofilm supernatants
Summary
Carbohydrates support the growth of S. aureus under anaerobic conditions and high nitric oxide stress (Richardson et al, 2008; Vitko et al, 2015). In the skin and softtissue infections model, glucose transporters contribute to the growth of S. aureus, which favors the fermentation of glucose over other carbohydrates (Vitko et al, 2016). Our previous study has revealed that fermentation of glucose contributes to aggregation of S. aureus (Luo et al, 2019). These data indicate that glucose is essential for the growth of S. aureus. S. aureus is the most frequent pathogen isolated from diabetic foot ulcers, but the properties of this bacterium under high glucose conditions remain unclear
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