Inhibition of Bacterial and Fungal Biofilm Formation by 675 Extracts from Microalgae and Cyanobacteria

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.

Transposon Insertion in the purL Gene Induces Biofilm Depletion in Escherichia coli ATCC 25922

“…However, fitness was altered in M63 due to the alteration in the purine biosynthetic pathway. Biofilm formation was carried out in M63 medium at 30 °C to favour the expression of genes involved in the biofilm formation [ 20 , 21 , 47 , 48 , 49 , 50 ] as curli fimbriae, aggregated amyloid structures which promote cell aggregation and attachment to abiotic surfaces. They are promoted at a temperature less than 32 °C inducing transcription of the csgDEFG operon [ 51 ].…”

“…Five hundred and thirty-six of a total of 2578 transposon mutants were characterised in terms of biofilm production using a protocol previously standardised in our research group [ 21 ]. Briefly, all isolates were cultured overnight in LB agar at 37 °C in aerobic conditions.…”

“…The cultures were established by the direct colony suspension method at 37 °C with shaking (180 rpm) in LB broth and then grown overnight. After incubation, colonies were diluted 1:100 in 200 µL of M63 medium (13.5 g/L KH 2 PO 4 , 2 g/L (NH 4 ) 2 SO 4 , 5.0 × 10 −4 g/L FeSO 4 , 1 mL 1 M MgSO 4 ·7H 2 O), supplemented with 0.25% glucose and adjusted to pH 7 (with KOH) and tested in 96-well flat-bottomed non-treated polystyrene microtiter plates with lids (Nunc™ Edge 2.0, VWR International, Barcelona, Spain) at 30 °C for 48 h. After incubation, biofilm was quantified using a crystal violet technique previously described by our group [ 21 ]. In brief, liquid culture from M63 medium was carefully removed, and the biofilm mass was washed twice with 210 µL of 1× phosphate-buffered saline (PBS) (pH 7.2) and dried at 65 °C for at least 20 min.…”

The Usefulness of Microalgae Compounds for Preventing Biofilm Infections

“…Recently, in the NoMorFilm project in 2019, Cepas and col. [67], investigated the antibiofilm activity of 675 extracts from 225 microalgae and cyanobacteria species, including the phylum Cercozoa, Charophyta, Chlorophyta, Cryptophyta, Cyanobacteria, Euglenophyta, Glaucophyta, Haptophyta, Miozoa, Ochrophyta, Rhodophyta, and two unknown phyla, against clinically important bacterial and fungal pathogens.…”

“…Circular dot plot representing the biofilm inhibition ratio (%) of each bacterium in relation to the solvent employed (ethyl acetate, hexane, and methanol), according to the microalgae and cyanobacteria phylum. CAL: C. albicans; CPA: C. parapsilopsis; ECO: E. coli; SHO: S. hominis; ECL: E. cloacae; KPE: K. pneumoniae; PAE: P. aeruginosa; SAU: S. aureus; SEP: S. epidermidis [67]…”