The anti-biofilm potential of commonly discarded agro-industrial residues against opportunistic pathogens

• We evaluated the antibiofilm potential of 14 extracts from agro-industrial residues.
• The extracts of geopropolis and pomegranate showed promising anti-biofilm activity.
• These extracts did not show considerable toxic effects in Galleria mellonella model.
• Extracts from agro-industrial residues can aid in therapy of infectious diseases.

Brazil is one of the largest producers of agro-industrial residues in the world. The aim of the study was to evaluate the anti-biofilm potential of hydroalcoholic extracts from agro-industrial residues. Organic residues from different parts were obtained from companies and subjected to hydroalcoholic extraction. A total of 14 extracts from the species Theobroma cacao (cocoa), Coffea arabica (coffee), Psidium guajava (guava), Citrus sinensis (orange), Malus domestica (apple), geopropolis, Punica granatum (pomegranate) and Solanum lycopersicum (tomato) were obtained and screened for their MIC/MBC against reference microorganisms (eleven bacterial strains and one yeast strain). The most bioactive extracts were chemically characterized by GC/MS and tested for their ability to inhibit adhesion, kill mature biofilm cells, and disrupt biofilm morphology. Eight extracts showed antimicrobial activity with MIC values ranging from 31.25 to 2000 μg/ml and MBC/MFC ranging from 62.50 to 4000 μg/ml. The extracts of geopropolis, pomegranate batchs #1 and #2 and coffee were able to inhibit adhesion at their MICs by 23% to 80% depending on the strain. At 10×MIC, three extracts also inhibited mature biofilm of seven pathogens. Toxicity tests were performed in vivo with the extracts of geopropolis, pomegranate 1 and pomegranate 2 in G. mellonella larvae. At the dose of 50 mg/kg, the extracts did not exert considerable acute toxic effects in the larvae over a period of 72 h. The extracts from agro-industrial residues have promising anti-biofilm activity against opportunistic pathogens of clinical relevance in the medical and dental settings.