Evaluating the Antimicrobial and Antibiofilm Activity of a Lipid Extract from the Giant Kelp Macrocystis pyrifera

Abstract

Skin and soft tissue infections (SSTIs) affect millions of individuals worldwide, every year. SSTIs vary in complexity and severity, ranging from superficial skin infections such as impetigo to more severe, polymicrobial, biofilm-forming bacterial infections that establish in chronic wounds or burns. Prevalent bacterial isolates found in simple and complex SSTIs are Staphylococcus aureus and Pseudomonas aeruginosa, respectively. Antibiotics are commonly prescribed to treat simple SSTIs, however the emergence of multi-drug resistant bacterial strains and the intrinsic antibiotic resistance of biofilms make complex SSTIs more difficult to treat. The increased clinical demand has spearheaded the search for novel antimicrobials from natural sources. Seaweeds have adapted to competition and predation by producing secondary metabolites, some of which exhibit antimicrobial activity. The aim of this project was to investigate the antimicrobial and anti-biofilm activity of a lipid- and pigment-rich extract from Macrocystis pyrifera (giant kelp). A chloroform:methanol (CHCl3:MeOH) extraction of M. pyrifera seaweed was performed. The agar diffusion assay was then used to determine the antimicrobial activity of this extract against clinically relevant S. aureus and P. aeruginosa. A zone of inhibition (ZOI) against S. aureus LAC USA300 (14.73 ± 0.33 mm) and S. aureus Newman (13.37 ± 3.36 mm) was observed with the extract when in a MeOH vehicle, but no activity was evident against P. aeruginosa. In a biofilm eradication assay, treatment with the extract led to a decrease in the bacterial number of S. aureus Newman and LAC USA300. To isolate active compounds within the extract, single column fractionation with CHCl3 and MeOH was performed. Fraction 24 (in MeOH) showed antimicrobial activity, with ZOI observed against S. aureus LAC USA300 (16.75 ± 2.47 mm) and S. aureus Newman (16.99 ± 1.39 mm). These findings indicate that M. pyrifera extract and fraction 24 possess antimicrobial activity against strains of S. aureus and may have utility in the treatment of SSTIs. Further analysis is however needed to comprehensively identify which compounds within this seaweed are responsible for its antimicrobial activity.