Chemical compositions and in vitro antibacterial/antibiofilm activities of seaweeds Ganonema farinosum and Dictyopteris polypodioides from the Mediterranean Sea

Abstract

In the era of ongoing antimicrobial resistance crisis, there is an unprecedented need for the development of novel antimicrobial options. The purpose of this study was to assess antibacterial and antibiofilm activities of the Mediterranean red seaweed: Ganonema farinosum and brown seaweed: Dictyopteris polypodioides against Escherichia coli ATCC 25922, Klebsiella pneumoniae ATCC 700603, Enterococcus faecalis ATCC 29212, and Staphylococcus aureus ATCC 25923. The methanolic and chloroformic extracts obtained from G. farinosum and D. polypodioides specifically exhibited antibacterial activity against Gram-positive bacteria. When used in combination with the commonly prescribed antibiotic ciprofloxacin, the methanolic and chloroformic G. farinosum and D. polypodioides extracts demonstrated additive and synergistic effects against Gram-positive bacteria. Since biofilm formation is a complicating factor in many infections, we have tested the impact of extracts on inhibiting biofilm formation, which revealed significant inhibitions in the biofilm formation of Gram-positive bacteria at sub-MIC concentrations. Gas chromatography mass spectrometry (GC-MS) analysis of both seaweed species revealed the presence of several bioactive compounds including some with previously demonstrated anti-quorum sensing potency. Collectively, our data reveal selective antibacterial and antibiofilm activity by G. farinosum and D. polypodioides against Gram-positive bacteria, which could be further investigated as potential new avenues against bacterial infections.