Characterization and chemical modification of PLN-1, an exopolysaccharide from Phomopsis liquidambari NJUSTb1.

Phomopsis liquidambari is a classical endophytic fungus with great application potential in ecology and agriculture; however, studies on its exopolysaccharides are lacking. Here, we aimed to evaluate the structure and bioactivity of PLN-1, an exopolysaccharide derived from the P. liquidambari NJUSTb1 strain. The structure was elucidated by chromatography/spectral methods and hydrolyzation. Immunomodulation, moisture absorption, and retention properties were investigated after sulfation and carboxymethylation modification. Results showed that PLN-1 contained a linear repeating unit of →[4)-α-d-Glcp-(1→6)-α-d-Glcp-(1→4)-α-d-Glcp-(1→4)-α-d-Glcp-(1→]n, with a molecular weight of 343 kDa. The degrees of substitution of sulfated polysaccharide (S-PLN-1) and carboxymethylated polysaccharide (C-PLN-1) were 1.228 and 0.903, respectively. S-PLN-1 showed stronger moisture absorption and retention properties than PLN (crude EPS), C-PLN1, and PLN-1. Furthermore, PLN, S-PLN-1, and C-PLN-1 stimulated the proliferation of RAW 264.7 cells with no cytotoxicity. The elucidation of PLN-1 in this study paves the way for future applications.

Can the quorum sensing inhibitor resveratrol function as an aminoglycoside antibiotic accelerant against Pseudomonas aeruginosa?

Pseudomonas aeruginosa infection is a serious disease in cystic fibrosis patients and is difficult to treat owing to biofilm persistence and emerging multidrug resistance. Considering the essential role of quorum sensing (QS) in P. aeruginosa infections, the enhanced effects between the quorum sensing inhibitor (QSI) resveratrol and several antibiotics against P. aeruginosa PAO1 were investigated. Crystal violet staining assay revealed that biofilms of P. aeruginosa PAO1 grown in the presence of resveratrol were more susceptible to aminoglycoside antibiotics. Scanning electron and fluorescence microscopy showed architectural disruption of the biofilms when treated with resveratrol and aminoglycoside antibiotics. Furthermore, quantitative reverse transcription PCR (qRT-PCR) analysis demonstrated that expression of lasI and rhlI, two genes encoding enzymes that synthesise signal molecules in QS systems, were inhibited in the P. aeruginosa PAO1 biofilms by resveratrol. These results indicate that the QSI resveratrol can significantly enhance the effects of aminoglycoside antibiotics (e.g. tobramycin, gentamicin, amikacin and netilmicin) on P. aeruginosa PAO1 biofilms. These findings suggest that resveratrol is a potential accelerant in the treatment of P. aeruginosa biofilms and can restore or enhance the efficacy of aminoglycoside antibiotics.