Inhibition of Pseudomonas aeruginosa biofilm formation and expression of virulence genes by selective epimerization in the peptide Esculentin‐1a(1‐21)NH₂

Abstract

Pseudomonas aeruginosa is a pathogenic bacterium known to cause serious human infections, especially in immune‐compromised patients. This is due to its unique ability to transform from a drug‐tolerant planktonic to a more dangerous and treatment‐resistant sessile life form, called biofilm. Recently, two derivatives of the frog skin antimicrobial peptide esculentin‐1a, i.e. Esc(1‐21) and its D‐amino acids containing diastereomer Esc(1‐21)‐1c, were characterized for their powerful anti‐Pseudomonal activity against both forms. Prevention of biofilm formation already in its early stages could be even more advantageous for counteracting infections induced by this bacterium. In this work, we studied how the diastereomer Esc(1‐21)‐1c can inhibit Pseudomonas biofilm formation in comparison to the parent peptide and two clinically‐used conventional antibiotics, i.e. colistin and aztreonam, when applied at dosages below the minimal growth inhibitory concentration. Biofilm prevention was correlated to the peptides’ ability to inhibit Pseudomonas motility and to reduce the production of virulent metabolites, for example, pyoverdine and rhamnolipids. Furthermore, the molecular mechanism underlying these activities was evaluated by studying the peptides’ effect on the expression of key genes involved in the virulence and motility of bacteria, as well as by monitoring the peptides’ binding to the bacterial signaling nucleotide ppGpp. Our results demonstrate that the presence of only two D‐amino acids in Esc(1‐21)‐1c is sufficient to downregulate ppGpp‐mediated expression of biofilm‐associated genes, presumably as a result of higher peptide stability and therefore prolonged interaction with the nucleotide. Overall, these studies should assist efficient design and optimization of new anti‐infective agents with multiple pharmacologically beneficial properties.

Caprine Bactenecins as Promising Tools for Developing New Antimicrobial and Antitumor Drugs

“…It was shown that various AMPs on their own not only eliminate planktonic bacteria, but also weaken the primary adhesion of bacterial cells to the surface, and within the established biofilms can impair the interaction of the elements of extracellular matrix and embedded bacterial cells. In addition, more specific mechanisms were revealed for a number of peptides demonstrating strong antibiofilm capabilities: they can modulate the motility of bacterial cells; affect the quorum sensing signaling; impede the work of the (p)ppGpp alarmone and, by extension, interfere with bacterial stringent response, and reduce the synthesis of various matrix elements or lead to their degradation (Pletzer and Hancock, 2016;Yasir et al, 2018;Casciaro et al, 2019;Shahrour et al, 2019).…”

Inoculum effect of antimicrobial peptides

“…As discussed above, for most AMPs, the bacterial membrane is the main target. Among the peptides investigated in the present study, the natural AMPs indolicidin [Selsted 1992;Falla 1996], LL-37 [Turner 1998, Barns 2013, novocidin [Gottlieb 2008, Nielsen 2010, the bee toxin melittin [Bucki 2004, Yang 2018 [Savini 2020, Casciaro 2019. For instance, indolicidin and LL-37 bind DNA (as many cationic AMPs do), but the role of this phenomenon in the mechanism of bacterial killing is debated [Marchand 2006, Ghosh 2014, Mardirossian 2014, Zhu 2019.…”

Enhanced Antimicrobial and Antibiofilm Effect of New Colistin-Loaded Human Albumin Nanoparticles

“…The biofilm-modulating action of MIC and sub-MICs depends on many factors: type of antimicrobial, mode of action, bacterial strain and susceptibility or resistance of the strain. Moreover, a not-linear dose-dependent effect on biofilm modulation has been reported [ 47 , 48 ].…”