Resistance to antibiotics poses a major global threat according to the World Health Organization. Restoring the activity of existing drugs is an attractive alternative to address this challenge. One of the most efficient mechanisms of bacterial resistance involves the expression of efflux pump systems capable of expelling antibiotics from the cell. Although there are efflux pump inhibitors (EPIs) available, these molecules are toxic for humans. We hypothesized that permeability-increasing antimicrobial peptides (AMPs) could lower the amount of EPI necessary to sensitize bacteria to antibiotics that are efflux substrates. To test this hypothesis, we measured the ability of polymyxin B nonapeptide (PMBN), to synergize with antibiotics in the presence of EPIs. Assays were performed using planktonic and biofilm-forming cells of Pseudomonas aeruginosa strains overexpressing the MexAB-OprM efflux system. Synergy between PMBN and EPIs boosted azithromycin activity by a factor of 2,133 and sensitized P. aeruginosa to all tested antibiotics. This reduced several orders of magnitude the amount of inhibitor needed for antibiotic sensitization. The selected antibiotic-EPI-PMBN combination caused a 10 million-fold reduction in the viability of biofilm forming cells. We proved that AMPs can synergize with EPIs and that this phenomenon can be exploited to sensitize bacteria to antibiotics.

Anti-microbial peptides (AMPs), small biologically active molecules, produced by different organisms through their innate immune system, have become a considerable subject of interest in the request of novel therapeutics. Most of these peptides are cationic-amphipathic, exhibiting two main mechanisms of action, direct lysis and by modulating the immunity. The most commonly reported activity of AMPs is their anti-bacterial effects, although other effects, such as anti-fungal, anti-viral, and anti-parasitic, as well as anti-tumor mechanisms of action have also been described. Their anti-parasitic effect against leishmaniasis has been studied. Leishmaniasis is a neglected tropical disease. Currently among parasitic diseases, it is the second most threating illness after malaria. Clinical treatments, mainly antimonial derivatives, are related to drug resistance and some undesirable effects. Therefore, the development of new therapeutic agents has become a priority, and AMPs constitute a promising alternative. In this work, we describe the principal families of AMPs (melittin, cecropin, cathelicidin, defensin, magainin, temporin, dermaseptin, eumenitin, and histatin) exhibiting a potential anti-leishmanial activity, as well as their effectiveness against other microorganisms.

Background: Pseudomonas aeruginosa is a Gram-negative pathogen that frequently causes life-threatening infections in immunocompromised patients. We previously showed that subinhibitory concentrations of short synthetic peptides permeabilize P. aeruginosa and enhance the lethal action of co-administered antibiotics. Methods: Long-term permeabilization caused by exposure of multidrug-resistant P. aeruginosa strains to peptide P4–9 was investigated by measuring the uptake of several antibiotics and fluorescent probes and by using confocal imaging and atomic force microscopy. Results: We demonstrated that P4–9, a 13-amino acid peptide, induces a growth delay (i.e. post-antibiotic effect) of 1.3 h on a multidrug-resistant P. aeruginosa clinical isolate. Remarkably, when an independently P4–9-treated culture was allowed to grow in the absence of the peptide, cells remained sensitive to subinhibitory concentrations of antibiotics such as ceftazidime, fosfomycin and erythromycin for at least 2 h. We designated this persistent sensitization to antibiotics occurring in the absence of the sensitizing agent as Post-Antibiotic Effect associated Permeabilization (PAEP). Using atomic force microscopy, we showed that exposure to P4–9 induces profound alterations on the bacterial surface and that treated cells need at least 2 h of growth to repair those lesions. During PAEP, P. aeruginosa mutants overexpressing either the efflux pump MexAB-OprM system or the AmpC β-lactamase were rendered sensitive to antibiotics that are known substrates of those mechanisms of resistance. Finally, we showed for the first time that the descendants of bacteria surviving exposure to a membrane disturbing peptide retain a significant level of permeability to hydrophobic compounds, including propidium iodide, even after 20 h of growth in the absence of the peptide. Conclusions: The phenomenon of long-term sensitization to antibiotics shown here may have important therapeutic implications for a combined peptide-antibiotic treatment because the peptide would not need to be present to exert its antibiotic enhancing activity as long as the target organism retains sensitization to the antibiotic.

Infection is one of the major issues associated with the failure of orthopedic devices, mainly due to implant bacterial colonization, biofilm formation, and associated antibiotic resistance. Antimicrobial peptides (AMP) are a promising alternative to conventional antibiotics given their broad-spectrum of activity, low propensity to induce bacterial resistance, and ability to modulate host immune responses. Dhvar5 (LLLFLLKKRKKRKY) and MSI78 (GIGKFLKKAKKFGKAFVKILKK) are two AMP with broad-spectrum activity against bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), one of the most problematic etiologic agents in Orthopedic Devices-Related Infections (ODRI). This work aims to evaluate the bactericidal, immunomodulatory and osteogenic potential of Dhvar5- and MSI78-coated titanium surfaces (AMP-Ti). Two AMP-Ti surfaces were successfully obtained by grafting Dhvar5 (0.8 ± 0.1 µM/mm²) or MSI78 (0.5 ± 0.3 µM/mm²) onto titanium substrates through a polydopamine layer. Both AMP-Ti were bactericidal against MRSA, eradicating bacteria upon contact for 6 h in a culture medium supplemented with human plasma proteins. The AMP-Ti immunomodulatory potential was evaluated using human primary macrophages, by assessing surfaces capacity to induce pro-/anti-inflammatory (M1/M2) markers and cytokines. While in naïve conditions both AMP-Ti surfaces slightly promoted the M2 marker CD163, in response to LPS and IFN-γ (simulating a bacterial infection), both AMP increased the M1 marker CCR7 and enhanced macrophage secretion of pro-inflammatory IL-6 and TNF-α cytokines, particularly for Ti-MSI78 surfaces. Additionally, both AMP-Ti surfaces were cytocompatible and promoted osteoblastic cell differentiation. This proof-of-concept study demonstrated the high potential of Dhvar5- and MSI78-Ti as antimicrobial coatings for ODRI prevention. STATEMENT OF SIGNIFICANCE: This study investigates the bactericidal effects of the antimicrobial peptides Dhvar5 and MSI78, immobilized on titanium (Ti) surfaces through a polydopamine coating, aiming at the prevention of Orthopedic-Device Related Infections (ODRIs). The developed coatings displayed MRSA-sterilizing activity, while revealing an immunomodulatory potential towards macrophages and promoting osteoblastic cell differentiation. This strategy allows a quick and easy immobilization of high quantities of AMP, unlike most other approaches, thus favoring its clinical translation.

Objective: To extract and identify the chemical composition of the polysaccharide isolated from the Eucalyptus cultivated in Lebanon and to evaluate its antioxidant activity. Materials: The water-soluble polysaccharide was isolated from Eucalyptus leaves, and its structure was identified by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, and carbon-13 nuclear magnetic resonance. The antioxidant activity of the active ingredient was screened for its radical scavenging ability using 2,2-diphenyl-1-picryl-hydrazyl radical (DPPH) test. Results: The results of the DPPH test have shown that fucoidan, the polysaccharide isolated from Eucalyptus, exhibited almost the same antioxidant activity against DPPH· as the ascorbic acid did at 100 μg/mL. Conclusions: This natural molecule extracted from a medicinal plant has a promising antioxidant activity and could be used in pharmaceutical and medical applications

The pathogenesis of Staphylococcus aureus acute and chronic wound infections is associated with biofilm formation. This study investigated the antimicrobial and antibiofilm potential of CHAPK-SH3blys, a bacteriophage-derived endolysin, against S. aureus strains implicated in chronic wound infections. CHAPK-SH3blys exhibited potent antibacterial activity with a minimum inhibitory concentration (MIC) of 3.9 µg/mL. Biofilm assays conducted under static and dynamic wound-like conditions showed a concentration-dependent reduction in biofilm metabolic activity, with up to a 4-log reduction in viable cells at concentrations 50 times the MIC. Further investigations revealed that CHAPK-SH3blys showed biocompatibility with human cell lines and did not induce an inflammatory response. Notably, prolonged exposure to sub-MIC levels did not lead to resistance development in S. aureus . These findings highlight CHAPK-SH3blys as a promising therapeutic agent for the treatment of biofilm-associated S. aureus wound infections. IMPORTANCE: Successful treatment of wound infections, which is most commonly caused by the bacteria Staphylococcus aureus , is compromised by bacterial colonization resulting in slime layer or biofilm formation in the wound bed. Associated antimicrobial resistance (AMR) and limited treatment options can also impair wound healing and further highlight the need for the development and use of novel antimicrobial therapies. This study explores the antibiofilm and antimicrobial effectiveness of a bacteriophage-derived endolysin named CHAPK-SH3blys against S. aureus strains implicated in chronic wound infections. Bacteriophage-derived endolysin represents novel antimicrobial agents, and in this study, we demonstrate the effectiveness of this agent in treating wound and biofilm- related infections under wound-like conditions in the laboratory without affecting the immune response or inducing antimicrobial resistance. Due to the urgent public health need to develop alternative antimicrobial agents to combat biofilm-associated infections, our study highlights CHAPK-SH3blys as a promising and exciting candidate for further therapeutic development.