Abstract
The antimicrobial activity of the marine bisindole alkaloid 2,2-bis(6-bromo-3-indolyl) ethylamine (1) and related synthetic analogues (compounds 2–8) against target microorganisms was investigated by Minimum Inhibitory Concentration (MIC) determination. Compound 1 showed the greatest antimicrobial activity with the lowest MIC (8 mg/L) against Escherichia coli, Staphylococcus aureus, and Klebsiella pneumoniae, while the derivatives exhibited higher MICs values (from 16 to 128 mg/L). Compounds 1, 3, 4, and 8, the most active ones, were then tested against E. coli, S. aureus, K. pneumoniae, and Candida albicans during biofilms formation as well as on 24 h developed biofilms. The natural alkaloid 1 inhibited the biofilm formation of all the tested microorganisms up to 82.2% and disaggregated biofilms of E. coli, S. aureus, K. pneumoniae, and C. albicans after 30 min of contact, as assessed by viable plate count and crystal violet (CV) staining (optical density at 570 nm). Synthetic derivatives 3, 4, and 8 displayed anti-biofilm activity toward individual bacterial populations. This study highlights the potential of marine bisindole alkaloid 1 as anti-biofilm agent and shows, through a preliminary structure activity relationship (SAR), the importance of halogens and ethylamine side chain for the antimicrobial and antibiofilm activities of this bisindole series.
Highlights
IntroductionBiofilms represent the predominant phenotype of most bacteria in their natural habitat
Biofilms represent the predominant phenotype of most bacteria in their natural habitat.The biofilm formation requires a first phase of adhesion to the surface, after the cells start to replicate into micro-colonies and to produce an extracellular polymeric substance (EPS), composed of polysaccharides and other macromolecules [1,2]
ATCC 43387, and K. pneumoniae 6/4, while higher values were determined for E. faecalis ATCC 29212 (32 μg/mL), P. aeruginosa ATCC 9027, and C. albicans ATCC 10231 (64 μg/mL) (Table 1)
Summary
Biofilms represent the predominant phenotype of most bacteria in their natural habitat. The biofilm formation requires a first phase of adhesion to the surface, after the cells start to replicate into micro-colonies and to produce an extracellular polymeric substance (EPS), composed of polysaccharides and other macromolecules [1,2]. The EPS plays an important role in biofilm because it helps the bond between the bacteria and the substratum and it protects the colonies from any environmental stress, including antimicrobial treatment [3]. Food surfaces as well as medical environments are suitable surfaces for microbial colonization and subsequently biofilm formation [4], representing a potential risk to transmit pathogens to humans by cross-contaminations. Biofilms that were developed on medical devices are difficult to eradicate due to the significant decrease in the susceptibility to antimicrobials of bacteria organized in biofilm, as compared to their planktonic form [5].
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