Abstract
Bacterial biofilms are complex biological systems that are difficult to eradicate at a medical, industrial, or environmental level. Biofilms confer bacteria protection against external factors and antimicrobial treatments. Taking into account that about 80% of human infections are caused by bacterial biofilms, the eradication of these structures is a great priority. Biofilms are resistant to old-generation antibiotics, which has led to the search for new antimicrobials from different sources, including deep oceans/seas. In this study, 675 extracts obtained from 225 cyanobacteria and microalgae species (11 phyla and 6 samples belonging to unknown group) were obtained from different culture collections: The Blue Biotechnology and Ecotoxicology Culture Collection (LEGE-CC), the Coimbra Collection of Algae (ACOI) from Portugal, and the Roscoff Culture Collection (RCC) from France. The largest number of samples was made up of the microalgae phylum Chlorophyta (270) followed by Cyanobacteria (261). To obtain a large range of new bioactive compounds, a method involving three consecutive extractions (hexane, ethyl acetate, and methanol) was used. The antibiofilm activity of extracts was determined against seven different bacterial species and two Candida strains in terms of minimal biofilm inhibitory concentration (MBIC). The highest biofilm inhibition rates (%) were achieved against Candida albicans and Enterobacter cloacae. Charophyta, Chlorophyta, and Cyanobacteria were the most effective against all microorganisms. In particular, extracts of Cercozoa phylum presented the lowest MBIC50 and MBIC90 values for all the strains except C. albicans.
Highlights
Bacterial biofilms are formed by aggregates of microorganisms within a complex biological system composed of assemblages of sessile cells adherent to each other or to a surface
The results showed that 205 hexane extracts exhibited the best antibiofilm activity, followed by
The results showed that 205 hexane extracts exhibited the best antibiofilm activity, followed by extracts obtained with methanol and 189 extracts presenting inhibitory activity obtained with ethyl extracts obtained with methanol and extracts presenting inhibitory activity obtained with acetate
Summary
Bacterial biofilms are formed by aggregates of microorganisms within a complex biological system composed of assemblages of sessile cells adherent to each other or to a surface. Biofilms are Antibiotics 2019, 8, 77; doi:10.3390/antibiotics8020077 www.mdpi.com/journal/antibiotics. Antibiotics 2019, 8, 77 embedded in an extracellular polymeric substance (EPS) matrix composed mainly of polysaccharides, lipids, proteins, and external DNA (eDNA) [1]. Biofilms provide bacteria protection against external factors such as temperature, pH variations, desiccation, oxidization, ultraviolet radiation, and metal ions. Biofilms are able to evade innate and/or adaptive immune defenses and avoid antimicrobial treatments by several mechanisms [2,3,4]. Biofilms have the capacity to attach to both biotic and abiotic surfaces, increasing the colonization of medical devices such as urinary and intravenous catheters, mechanical heart valves, endotracheal tubes, and prosthesis joints [5].
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