Phytochemical screening, metabolite profiling and enhanced antimicrobial activities of microalgal crude extracts in co-application with silver nanoparticle

Abstract

Background

Microalgae is one of the major sources of natural compounds with antimicrobial activity. The metabolite profiling of the extracts could identify the bioactive compounds based on methanol (MET), ethanol (ETH), chloroform (CHL), hexane (HEX) and water (W) solvent systems. The microalgal crude extracts in co-application with silver nanoparticles (AgNPs) had enhanced antimicrobial activity with potential to overcome the global problem of microbial antibiotic resistance.

Results

Chlorella sp. exhibited the highest lipid, N. oculata the highest total saturated fatty acids (TSFA), and T. suecica the highest mono-unsaturated (MUFA) and poly-unsaturated fatty acids (PUFA). The highest carbohydrate, protein and total phenolics contents (TPCs) were attained by N. oculata. The highest total flavonoids contents (TFCs), and chlorophyll a and b were in T. suecica, while comparable level of carotenoids were found in all species. For high-performance thin-layer chromatography (HPTLC) analyses, the eicosapentaenoic acid (EPA) with high peaks were detected in T. suecica-HEX and N. oculata-CHL; and β-carotene in Chlorella sp.-ETH. The gas chromatography–mass spectrometry (GC–MS) analyses showed high 13-docosenamide (Z)- in T. suecica-HEX; phytol in N. oculata-HEX; and neophytadiene in Chlorella sp.-ETH. The AgNPs–MCEs–MET and HEX at the 1.5:1 ratios exhibited strong activities against Bacillus subtilis, Streptococcus uberis, and Salmonella sp.; and the AgNPs–T. suecica-HEX and MET and AgNPs–Chlorella sp.-HEX at the 1.5:1 ratios exhibited activities against Klebsiella pneumoniae.

Conclusion

Different bioactive components were detected in the MCEs based on the HPTLC and GC–MS analyses. Significant antimicrobial activities against the pathogenic microbes were demonstrated by the synergistic effects of the MCEs in co-application with the AgNPs. This could be beneficial in the fight against sensitive and multidrug-resistant bacteria.

Keywords

Microalgae / Solvent systems / Metabolite profiling / Antimicrobial / Silver nanoparticle / Co-application

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Funding

Malaysian Ministry of Higher Education(FRGS/1/2015/SG05/UMT/02/4)