Louis-David Guay

Campylobacter spp. is one of the most prevalent causes of zoonotic foodborne infections associated with diarrhea in humans. The growing threat of antibiotic resistance calls for innovative approaches. The antimicrobial lipopeptide brevibacillin produced by Brevibacillus laterosporus and its synthetic analog brevibacillin Thr1 showed promising activity against Salmonella and E. coli. The latter is a 1602.13 Da positively charged (+3) synthetic peptide of 13 residues that showed reduced cytotoxicity (IC₅₀ of 32.2 µg/mL against Caco-2 cells) and hemolytic activity (1.2% hemolysis at 128 µg/mL) compared to the native peptide. It contains an N-terminal L-isoleucic fatty acid chain and four non-proteinogenic amino acids and ends with valinol at its C-terminus. One key structural modification is the substitution of α,β-dehydrobutyric acid with threonine. We investigated the antimicrobial potential of the synthetic brevibacillin Thr1 analog against a collection of 44 clinical Campylobacter spp. that were obtained from two reference laboratories. Susceptibility testing revealed marked resistance to ciprofloxacin, tetracycline, and ampicillin among the strains, with more than half expressing a multidrug-resistant phenotype. The genomes of the 44 strains were sequenced to study the genes responsible for their antimicrobial resistance. Tetracycline resistance was associated with tet(O), ciprofloxacin resistance with mutations in gyrA and regulatory sequences modulating the expression of an efflux system, and aminoglycoside resistance with genes of the aph family. The brevibacillin Thr1 analog was produced by chemical synthesis, and evaluation of its activity against a subset of clinical strains by microdilution revealed minimum inhibitory concentration and minimum bactericidal concentration ranging from 8 µg/mL to 64 µg/mL. The peptide was active against multidrug-resistant isolates with a bactericidal effect. Of note, despite numerous attempts, it proved impossible to select Campylobacter spp. for resistance to the brevibacillin Thr1 analog. These results underline the potential of lipopeptides, notably brevibacillin, as antimicrobial alternatives against antibiotic-resistant Campylobacter bacterial infections.

Background: The emergence of multidrug-resistant (MDR) Staphylococcus aureus presents a critical global health challenge due to treatment failures and high mortality rates. Faced with this growing threat, new antimicrobials with original modes of action are urgently needed, and antimicrobial peptides proved to be promising alternatives. Objectives: The aim of this study is to explore the structure–function relationship of the lipopeptide humimycin A, compare the spectrum of activity of the synthetic analogs against a panel of S. aureus isolates, and investigate their binding to the humimycin target, the lipid II flippase MurJ. Methods: Humimycin A and 15 analogs were produced by solid-phase peptide synthesis, and their antimicrobial activity was evaluated by agar diffusion and microtitration assays against 19 S. aureus isolates from bovine mastitis and other pathogens. Results: Among the synthesized peptides, four humimycin analogs exhibited activity against methicillin-sensitive and methicillin-resistant S. aureus, as well as several isolates in the panel, including MDR S. aureus, with minimal inhibitory concentration values ranging from 0.5 to 256 µg/mL. Results from the structure–activity relationship study showed that the β-hydroxymyristoyl lipid chain and C-terminal carboxylic acid are essential for antimicrobial efficacy. In presence of human erythrocytes, the active humimycin analogs exhibited moderate hemolytic activity, suggesting selectivity indexes ranging from 3 to 27 against the more sensitive S. aureus strains. Critical micelle concentration measurements elucidated micelle formation and proved to not be essential for the antibacterial activity. Molecular docking and 100 ns simulations with the lipid II flippase MurJ (PDB: 5T77) provided favorable binding energy. Conclusions: The findings underscore the potential of humimycin analogs as antimicrobials for preventing and treating MDR S. aureus infections in veterinary, animal husbandry, and human medicine.

The antimicrobial lipopeptide brevibacillin is a non-ribosomally synthesized peptide produced by Brevibacillus laterosporus with inhibitory activity against several clinically relevant Gram-positive pathogenic bacteria such as Staphylococcus aureus, Listeria monocytogenes, and Clostridium difficile. In this study, we report the total synthesis of brevibacillin and analogues thereof as well as structure–activity relationship and cytotoxicity studies. Several novel synthetic analogues exhibited high inhibitory activities with minimal inhibitory concentration values in the low micromolar range against several bacteria including Gram-positive L. monocytogenes, S. aureus, Enterococcus faecalis, and Clostridium perfringens as well as Gram-negative Campylobacter coli and Pseudomonas aeruginosa. Of particular interest, four analogues showed a broad spectrum of action and greater antimicrobial activity versus cytotoxicity ratios than native brevibacillin. With a more accessible and efficient production process and improved pharmacological properties, these synthetic analogues are promising candidates to prevent and control the proliferation of various pathogens in the food industry as well as veterinary and human medicine.

Multidrug-resistant Clostridium perfringens infections are a major threat to the poultry industry. Effective alternatives to antibiotics are urgently needed to prevent these infections and limit the spread of multidrug-resistant bacteria. The aim of the study was to produce by chemical synthesis a set of enterocins of different subgroups of class II bacteriocins and to compare their spectrum of inhibitory activity, either alone or in combination, against a panel of twenty C. perfringens isolates. Enterocins A, P, SEK4 (class IIa bacteriocins), B (unsubgrouped class II bacteriocin), and L50 (class IId leaderless bacteriocin) were produced by microwave-assisted solid-phase peptide synthesis. Their antimicrobial activity was determined by agar well diffusion and microtitration methods against twenty C. perfringens isolates and against other pathogens. The FIC_INDEX of different combinations of the selected enterocins was calculated in order to identify combinations with synergistic effects. The results showed that synthetic analogs of L50A and L50B were the most active against C. perfringens. These peptides also showed the broadest spectrum of activity when tested against other non-clostridial indicator strains, including Listeria monocytogenes, methicillin-resistant Staphylococcus aureus, Streptococcus suis, Streptococcus pyogenes, Enterococcus cecorum, Enterococcus faecalis, as well as Gram-negative bacteria (Campylobacter coli and Pseudomonas aeruginosa), among others. The selected synthetic enterocins were combined on the basis of their different mechanisms of action, and all combinations tested showed synergy or partial synergy against C. perfringens. In conclusion, because of their high activity against C. perfringens and other pathogens, the use of synthetic enterocins alone or as a consortium can be a good alternative to the use of antibiotics in the poultry sector.

Metallaphotoredox catalysis was used to prepare N -Fmoc-protected homotyrosine and allowed the total on-resin synthesis of the cyclic peptide anabaenopeptin F.