Characterization and in vitro antibacterial activity of sulfated polysaccharides from freshwater alga Cladophora crispata

Barada River is characterized by an abundant growth of freshwater algae. Cladophora sp. algae have emerged as a new source of bioactive compounds. In this research Cladophora crispata was cultivated with the outdoor method, and algal sulfated polysaccharides (SPs) were extracted by an ultrasonic-assisted extraction method. After extraction, gel filtration was used to purify the crude SPs, SP compounds were determined and selected, and the effect of purified SPs as antibacterial agents was investigated. The purified extract gave two fractions (F1 and F2). The chemical components of both crude and purified SPs were then determined. The highest carbohydrate content (74.12%) and protein content (4.02%) was found in the crude extract, while the highest sulfate content (12.17%) was found in purified fraction F2, and the highest uronic acid content (18.46%) was found in purified fraction F1. Fourier transform infrared spectroscopy (FT-IR) was used to confirm that the crude extract and fractions consist of sugar, uronic acids, protein and sulfate groups. Both F1 and F2 consisted of rhamnose, galactose, xylose and ribose based on high performance liquid chromatography (HPLC) separation. Each fraction showed an inhibitory effect on Gram-positive and Gram-negative bacteria. F2 has the lowest minimum inhibitory concentration (MIC) value against Staphylococcus aureus , Bacillus anthracis , Enterobacter aerogenes and Pseudomonas aeruginosa , where its MIC values were 6, 13, 25 and 30 mg ml(−1), respectively. Algae polysaccharides are of key interest due to their antibacterial properties, which has led to them being included in pharmaceutics and food applications.