Antibacterial and Antifungal Activities of Poloxamer Micelles Containing Ceragenin CSA-131 on Ciliated Tissues

Ceragenins exhibit antiviral activity against SARS-CoV-2 by increasing the expression and release of type I interferons upon activation of the host's immune response

The COVID-19 pandemic caused by Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) heavily burdened the entire world socially and economically. Despite a generation of vaccines and therapeutics to confront infection, it remains a threat. Most available antivirals target viral proteins and block their activity or function. While such an approach is considered effective and safe, finding treatments for specific viruses of concern leaves us unprepared for developed resistance and future viral pandemics of unknown origin. Here, we propose ceragenins (CSAs), synthetic amphipathic molecules designed to mimic the properties of cationic antimicrobial peptides (cAMPs), as potential broad-spectrum antivirals. We show that selected CSAs exhibit antiviral activity against SARS-CoV-2 and low-pathogenic human coronaviruses 229E, OC43, and NL63. The mechanism of action of CSAs against coronaviruses is mainly attributed to the stimulation of antiviral cytokines, such as type I interferons or IL-6. Our study provides insight into a novel immunomodulatory strategy that might play an essential role during the current pandemic and future outbreaks.

Nanomaterials and Coatings for Managing Antibiotic-Resistant Biofilms

Biofilms are a global health concern responsible for 65 to 80% of the total number of acute and persistent nosocomial infections, which lead to prolonged hospitalization and a huge economic burden to the healthcare systems. Biofilms are organized assemblages of surface-bound cells, which are enclosed in a self-produced extracellular polymer matrix (EPM) of polysaccharides, nucleic acids, lipids, and proteins. The EPM holds the pathogens together and provides a functional environment, enabling adhesion to living and non-living surfaces, mechanical stability, next to enhanced tolerance to host immune responses and conventional antibiotics compared to free-floating cells. Furthermore, the close proximity of cells in biofilms facilitates the horizontal transfer of genes, which is responsible for the development of antibiotic resistance. Given the growing number and impact of resistant bacteria, there is an urgent need to design novel strategies in order to outsmart bacterial evolutionary mechanisms. Antibiotic-free approaches that attenuate virulence through interruption of quorum sensing, prevent adhesion via EPM degradation, or kill pathogens by novel mechanisms that are less likely to cause resistance have gained considerable attention in the war against biofilm infections. Thereby, nanoformulation offers significant advantages due to the enhanced antibacterial efficacy and better penetration into the biofilm compared to bulk therapeutics of the same composition. This review highlights the latest developments in the field of nanoformulated quorum-quenching actives, antiadhesives, and bactericides, and their use as colloid suspensions and coatings on medical devices to reduce the incidence of biofilm-related infections.

Influence of the Hydrophobicity of Pluronic Micelles Encapsulating Curcumin on the Membrane Permeability and Enhancement of Photoinduced Antibacterial Activity

Apart from its well-known activity as an antimicrobial agent, Curcumin (CURC) has recently started to arouse interest as a photosensitizer in the photodynamic therapy of bacterial infections. The aim of the present study was to evidence the influence of the encapsulation of Curcumin into polymeric micelles on the efficiency of photoinduced microbial inhibition. The influence of the hydrophobicity of the selected Pluronics (P84, P123, and F127) on the encapsulation, stability, and antimicrobial efficiency of CURC-loaded micelles was investigated. In addition, the size, morphology, and drug-loading capacity of the micellar drug delivery systems have been characterized. The influence of the presence of micellar aggregates and unassociated molecules of various Pluronics on the membrane permeability was investigated on both normal and resistant microbial strains of E. coli, S. aureus, and C. albicans. The antimicrobial efficiency on the common pathogens was assessed for CURC-loaded polymeric micelles in dark conditions and activated by blue laser light (470 nm). Significant results in the reduction of the microorganism’s growth were found in cultures of C. albicans, even at very low concentrations of surfactants and Curcumin. Unlike the membrane permeabilization effect of the monomeric solution of Pluronics, reported in the case of tumoral cells, a limited permeabilization effect was found on the studied microorganisms. Encapsulation of the Curcumin in Pluronic P84 and P123 at very low, nontoxic concentrations for photosensitizer and drug-carrier, produced CURC-loaded micelles that prove to be effective in the light-activated inhibition of resistant species of Gram-positive bacteria and fungi.

Effects of Ceragenins and Antimicrobial Peptides on the A549 Cell Line and an In Vitro Co-Culture Model of A549 Cells and Pseudomonas aeruginosa

Pseudomonas aeruginosa is an important pathogen that can adhere to host tissues and epithelial surfaces, especially during chronic infections such as cystic fibrosis (CF) lung infections. The effect of ceragenins and antimicrobial peptides (AMP) on this colonization was investigated in a co-culture infection model. After determining the antimicrobial effects of the substances on P. aeruginosa planktonic cells, their cytotoxicity on the A549 cell line was also determined. After the A549 cell line was infected with P. aeruginosa, the effect of antimicrobials on intracellular bacteria as well as the effects in inhibiting the adhesion of P. aeruginosa were investigated. In addition, LDH release from cells was determined by performing an LDH experiment to understand the cytotoxicity of bacterial infection and antimicrobial treatment on cells. CSA-131 was determined as the antimicrobial agent with the highest antimicrobial activity, while the antimicrobial effects of AMPs were found to be much lower than those of ceragenins. The antimicrobial with the lowest IC₅₀ value was determined as the combination of CSA-131 with Pluronic F127. CSA-13 has been determined to be the most effective antimicrobial with its effectiveness to both intracellular bacteria and bacterial adhesion. Nevertheless, further safety, efficacy, toxicity, and pharmacological studies of ceragenins are needed to evaluate clinical utility.

Drug Delivery Systems Based on Pluronic Micelles with Antimicrobial Activity

Bacterial oral diseases are chronic, and, therefore, require appropriate treatment, which involves various forms of administration and dosing of the drug. However, multimicrobial resistance is an increasing issue, which affects the global health system. In the present study, a commercial amphiphilic copolymer, Pluronic F127, was used for the encapsulation of 1-(5′-nitrobenzimidazole-2′-yl-sulphonyl-acetyl)-4-aryl-thiosemicarbazide, which is an original active pharmaceutical ingredient (API) previously synthesized and characterized by our group, at different copolymer/API weight ratios. The obtained micellar systems, with sizes around 20 nm, were stable during 30 days of storage at 4 °C, without a major increase of the Z-average sizes. As expected, the drug encapsulation and loading efficiencies varied with the copolymer/API ratio, the highest values of 84.8 and 11.1%, respectively being determined for the F127/API = 10/1 ratio. Moreover, in vitro biological tests have demonstrated that the obtained polymeric micelles (PMs) are both hemocompatible and cytocompatible. Furthermore, enhanced inhibition zones of 36 and 20 mm were observed for the sample F127/API = 2/1 against S. aureus and E. coli, respectively. Based on these encouraging results, it can be admitted that these micellar systems can be an efficient alternative for the treatment of bacterial oral diseases, being suitable either by injection or by a topical administration.

In vitro activity of ceragenins against Burkholderia cepacia complex

Burkholderia cepacia complex (Bcc) species are aerobic, Gram-negative and non-fermantative bacilli. Bcc can cause clinical symptoms in patients with cystic fibrosis, ranging from asymptomatic carriage to fatal pneumonia. A pressing need exists for new antimicrobial agents that target Bcc. Ceragenins, CSA-13, CSA-131 and CSA-131 with 5% Pluronic® F127 (CSA-131P), were evaluated against Bcc clinical isolates (n = 42). MICs of ceragenins and conventional antibiotics were determined. Time-kill curve experiments were performed with 1x, 4x MICs of ceragenins and sulfamethoxazole-trimethoprim (SXT), levofloxacin. MIC₅₀/ MIC₉₀ results (mg l^-1) of CSA-13, CSA-131 and CSA-131P were determined as 16/64, 16/128 and 16/128, respectively. CSA-13 and CSA-131 showed bactericidal activity. CSA-13 - levofloxacin combination displayed synergistic activity against Bcc. First-generation (CSA-13) and second-generation (CSA-131 and CSA-131P) ceragenins have significant antimicrobial effects on Bcc. The findings of this study demonstrate that combinations of ceragenins with currently marketed antibiotics could be synergistic in vitro against Bcc isolates. These results suggest that combination therapy with conventional antibiotics could be an alternative approach for treating Bcc infections in the future.

From Marine Metabolites to the Drugs of the Future: Squalamine, Trodusquemine, Their Steroid and Triterpene Analogues

This review comprehensively describes the recent advances in the synthesis and pharmacological evaluation of steroid polyamines squalamine, trodusquemine, ceragenins, claramine, and their diverse analogs and derivatives, with a special focus on their complete synthesis from cholic acids, as well as an antibacterial and antiviral, neuroprotective, antiangiogenic, antitumor, antiobesity and weight-loss activity, antiatherogenic, regenerative, and anxiolytic properties. Trodusquemine is the most-studied small-molecule allosteric PTP1B inhibitor. The discovery of squalamine as the first representative of a previously unknown class of natural antibiotics of animal origin stimulated extensive research of terpenoids (especially triterpenoids) comprising polyamine fragments. During the last decade, this new class of biologically active semisynthetic natural product derivatives demonstrated the possibility to form supramolecular networks, which opens up many possibilities for the use of such structures for drug delivery systems in serum or other body fluids.

New β-Lactam Antibiotics and Ceragenins - A Study to Assess Their Potential in Treatment of Infections Caused by Multidrug-Resistant Strains of Pseudomonas aeruginosa

Background

The increasing number of infections caused by antibiotic resistant strains of Pseudomonas aeruginosa posed a very serious challenge for clinical practice. This standing is driving scientists to develop new antibiotics against these microorganisms.

Methods

In this study, we measured the MIC/MBC values and estimated the ability of tested molecules to prevent bacterial biofilm formation to explore the effectiveness of β-lactam antibiotics ceftolozane/tazobactam, ceftazidime/avibactam, meropenem/vaborbactam, and ceragenins CSA-13, CSA-44, and CSA-131 against 150 clinical isolates of Pseudomonas aeruginosa that were divided into five groups, based on their antibiotic resistance profiles to beta-lactams. Selected strains of microorganisms from each group were also subjected to prolonged incubations (20 passages) with ceragenins to probe the development of resistance towards those molecules. Cytotoxicity of tested ceragenins was evaluated using human red blood cell (RBCs) hemolysis and microscopy observations of human lung epithelial A549 cells after ceragenin treatment. Poloxamer 407 (pluronic F-127) at concentrations ranging from 0.5% to 5% was tested as a potential drug delivery substrate to reduce ceragenin toxicity.

Results

Collected data proved that ceragenins at low concentrations are highly active against clinical strains of Pseudomonas aeruginosa regardless of their resistance mechanisms to conventional antibiotics. Ceragenins also show low potential for resistance development, high antibiofilm activity, and controlled toxicity when used together with poloxamer 407.

Conclusion

This data strongly supports the need for further study directed to develop this group of molecules as new antibiotics to fighting infections caused by antibiotic resistant strains of Pseudomonas aeruginosa.

Antimicrobial Activities of Propolis in Poloxamer Based Topical Gels

Propolis contains a group of compounds with various activities. However, their low solubility is a drawback for the development of pharmaceutical formulations. In this study, poloxamers as a solubilizer and gelling agent were evaluated to develop a topical antimicrobial formulation of propolis. The effects of poloxamer type and concentration on the propolis solubility, release rate, and antimicrobial activities were investigated. Staphylococcus aureus (S. aureus) and Candida albicans (C. albicans) were the representative bacteria and fungi, respectively. At 5%, poloxamer 407 (P407) and poloxamer 188 (P188) enhanced the propolis solubility by 2.86 and 2.06 folds, respectively; at 10%, they were 2.81 and 2.59 folds, respectively. The micelle size in the P188 formulation increased in the presence of propolis, whereas there was no change in the P407 formulation. Release rates of propolis decreased with the P188 concentration increase, which was attributed to viscosity increase. Both P188 and P407 formulations showed antimicrobial activity against S. aureus in a time-kill kinetics assay. However, only the P188 formulation reduced the cell's numbers significantly against C. albicans, compared to the control. We speculate that P188 mixed micelles were more effective in releasing free active compounds to exhibit anti-microbial activity compared to the P407 micelles encapsulating the hydrophobic compounds in their cores. Propolis in P188 formulation is proposed as a potential topical antimicrobial agent based on its activity against both S. aureus and C. albicans.

Multifunctional ultrasmall AgNP hydrogel accelerates healing of S. aureus infected wounds

The increasing emergence of antibiotic resistance coupled with the limited effectiveness of current treatments highlights the need for the development of new treatment modalities. Silver nanoparticles (AgNPs) are a promising alternative with broad-spectrum antibacterial activity. However, the clinical translation of AgNPs have been hampered primarily due to the delivery of unsafe levels of silver ions (Ag⁺) resulting in cellular toxicity and their susceptibility to aggregation resulting in loss of efficacy. Here, we describe a safe and effective, thermo-responsive AgNP hydrogel that provides antibacterial effects in conjunction with wound promoting properties. Using a murine model of wound infection, we demonstrate that the applied AgNP hydrogel to the wound (12 µg silver) not only provides superior bactericidal activity but also reduces inflammation leading to accelerated wound closure when compared to industry-standard silver sulfadiazine (302 µg silver). The AgNP hydrogel-treatment significantly accelerated wound closure at day 4 post-infection (56 closure) compared to both blank hydrogel or Ag SD (74% and 91% closure respectively) with a concurrent increase in PCNA-positive proliferating cells corresponding with a significant 32% improvement in wound re-epithelization compared to the blank hydrogel. Treatment of infected wounds with AgNP hydrogel also decreased neutrophil infiltration, increased anti-inflammatory Ym-1 positive M2 macrophages, and reduced the number of caspase-1 positive apoptotic cells. Therefore, this novel multifunctional AgNP thermo-responsive hydrogel is potentially a safe and effective treatment at much lower concentration for the treatment of wound infections. STATEMENT OF SIGNIFICANCE: In this study, we describe the development of a multifunctional thermo-responsive hydrogel of ultrasmall silver nanoparticles (AgNPs) for controlled and optimized delivery of silver to infected wounds. The in vivo biological effects of the developed hydrogel showed significant S. aureus elimination from infected mouse wounds compared to a commercial antibacterial formulation. The developed AgNP hydrogel optimally regulates inflammatory responses to promote wound healing as indicated by increased cell proliferation and wound re-epithelization. Additionally, AgNP hydrogel shows significant potential in regulating neutrophil infiltration while increasing levels of anti-inflammatory M2 macrophages and reduces the number of apoptotic cells. Therefore, the multifunctional properties of the developed AgNP thermo-responsive hydrogel offers great clinical potential to control bacterial infections and promote wound healing.

In vitro assessment of CSA-131 and CSA-131 poloxamer form for the treatment of Stenotrophomonas maltophilia infections in cystic fibrosis

BACKGROUND

Stenotrophomonas maltophilia is a Gram-negative bacterium resistant to several antibiotics and its prevalence in cystic fibrosis (CF) patients is increasing.

OBJECTIVES

To evaluate the effects of ceragenins, non-peptide mimics of antimicrobial peptides, against both planktonic and biofilm forms of S. maltophilia and the cytotoxicity of ceragenins to the IB3-1 CF cell line.

METHODS

Ceragenin CSA-131, with and without 5% Pluronic® F127 (a non-ionic amphiphilic poloxamer), and ceragenin CSA-13 were evaluated against S. maltophilia clinical isolates (n = 40). MICs and MBCs of ceragenins and conventional antibiotics were determined. Time-kill curve experiments were performed with 1×, 2× and 4× MICs of ceragenins. The highest non-cytotoxic concentrations of ceragenins against IB3-1, a CF cell line, were determined by MTT assay. The effects of ceragenins against biofilm adhesion, formation and mature biofilms were investigated.

RESULTS

CSA-131 with Pluronic® F127 displayed the lowest MICs (MIC50/MIC90: 1/2 mg/L) followed by CSA-131 (MIC50/MIC90: 2/4 mg/L), while those of CSA-13 were much higher (MIC50/MIC90: 16/32 mg/L). According to time-kill curve results, all concentrations at 4× MICs of ceragenins showed bactericidal activity (3 log reduction) after 4 h. While CSA-131 and CSA-131-poloxamer inhibited biofilm adhesion and formation by 87.74% and 83.42%, respectively, after 24 h, CSA-131 was more effective on mature biofilms. Formulating CSA-131 in poloxamer micelles did not affect the cytotoxicity of CSA-131 to IB3-1 cells.

CONCLUSIONS

CSA-131 could be a potential antimicrobial agent for the treatment of S. maltophilia infections in CF, due to its low cytotoxicity on the CF cell line and good antimicrobial and antibiofilm effects.

Bactericidal Properties of Rod-, Peanut-, and Star-Shaped Gold Nanoparticles Coated with Ceragenin CSA-131 against Multidrug-Resistant Bacterial Strains

Background: The ever-growing number of infections caused by multidrug-resistant (MDR) bacterial strains requires an increased effort to develop new antibiotics. Herein, we demonstrate that a new class of gold nanoparticles (Au NPs), defined by shape and conjugated with ceragenin CSA-131 (cationic steroid antimicrobial), display strong bactericidal activity against intractable superbugs. Methods: For the purpose of research, we developed nanosystems with rod- (AuR NPs@CSA-131), peanut-(AuP NPs@CSA-131) and star-shaped (AuS NPs@CSA-131) metal cores. Those nanosystems were evaluated against bacterial strains representing various groups of MDR (multidrug-resistant) Gram-positive (MRSA, MRSE, and MLS_b) and Gram-negative (ESBL, AmpC, and CR) pathogens. Assessment of MICs (minimum inhibitory concentrations)/MBCs (minimum bactericidal concentrations) and killing assays were performed as a measure of their antibacterial activity. In addition to a comprehensive analysis of bacterial responses involving the generation of ROS (reactive oxygen species), plasma membrane permeabilization and depolarization, as well as the release of protein content, were performed to investigate the molecular mechanisms of action of the nanosystems. Finally, their hemocompatibility was assessed by a hemolysis assay. Results: All of the tested nanosystems exerted potent bactericidal activity in a manner resulting in the generation of ROS, followed by damage of the bacterial membranes and the leakage of intracellular content. Notably, the killing action occurred with all of the bacterial strains evaluated, including those known to be drug resistant, and at concentrations that did not impact the growth of host cells. Conclusions: Conjugation of CSA-131 with Au NPs by covalent bond between the COOH group from MHDA and NH₃ from CSA-131 potentiates the antimicrobial activity of this ceragenin if compared to its action alone. Results validate the development of AuR NPs@CSA-131, AuP NPs@CSA-131, and AuS NPs@CSA-131 as potential novel nanoantibiotics that might effectively eradicate MDR bacteria.

Autologous fibrin sealant co-delivered with antibiotics is a robust method for topical antibiotic treatment after sinus surgery

BACKGROUND

Most patients with cystic fibrosis have the risk of pathogenic bacteria being exchanged between their sinuses and lungs.

AIMS

A method for topical application of antibiotics where the antibiotics persist for a long period of time is needed.

MATERIAL AND METHODS

Ten patients with cystic fibrosis and bacterial sinusitis were included. Autologous platelet rich fibrin was mixed with an antibiotic solution and sprayed onto the mucosa at the end of an endoscopic sinus surgery; Colistin, a Ciprofloxacin-Colistin combination or Tobramycin was used. The antibiotic concentration was measured in the sinonasal mucus four, seven and 13 days after surgery.

RESULTS

Nine patients had Pseudomonas aeruginosa in their nose/sinuses at the time of surgery; in eight of these P. aeruginosa was not detected by culture at the final visit. In the majority of the ten included patients the antibiotics were continuously released for more than 7 days. No severe side effects were seen.

CONCLUSIONS

Autologous platelet rich fibrin co-delivered with antibiotics is a feasible method for topical antibiotic treatment in supplementary to sinus surgery.

SIGNIFICANCE

We expect that this treatment is successful for eradication of sinonasal bacterial infections in immunosuppressed patients suffering from recalcitrant sinus infections. The efficacy should be evaluated in randomized controlled trials.

The application of ceragenins to orthopedic surgery and medicine

Osteomyelitis and infections associated with orthopedic implants represent a significant burden of disease worldwide. Ceragenins (CSAs) are a relatively new class of small-molecule antimicrobials that target a broad range of Gram-positive and Gram-negative bacteria as well as fungi, viruses, and parasites. This review sets the context of the need for new antimicrobial strategies by cataloging the common pathogens associated with orthopedic infection and highlighting the increasing challenges of managing antibiotic-resistant bacterial strains. It then comparatively describes the antimicrobial properties of CSAs with a focus on the CSA-13 family. More recently developed members of this family such as CSA-90 and CSA-131 may have a particular advantage in an orthopedic setting as they possess secondary pro-osteogenic properties. In this context, we consider several new preclinical studies that demonstrate the utility of CSAs in orthopedic models. Emerging evidence suggests that CSAs are effective against antibiotic-resistant Staphylococcus aureus strains and can prevent the formation of biofilms. There remains considerable scope for developing CSA-based treatments, either as coatings for orthopedic implants or as local or systemic antibiotics to prevent bone infection.

Surfactant-based prophylaxis and therapy against COVID-19: A possibility

Hand hygiene by washing with soap and water is recommended for the prevention of COVID-19 spread. Soaps and detergents are explained to act by damaging viral spike glycoproteins (peplomers) or by washing out the virus through entrapment in the micelles. Technically, soaps come under a functional category of molecules known as surfactants. Surfactants are widely used in pharmaceutical formulations as excipients. We wonder why surfactants are still not tried for prophylaxis or therapy against COVID-19? That too when many of them have proven antiviral properties. Moreover, lung surfactants have already shown benefits in respiratory viral infections. Therefore, we postulate that surfactant-based prophylaxis and therapy would be promising. We believe that our hypothesis would stimulate debate or new research exploring the possibility of surfactant-based prophylaxis and therapy against COVID-19. The success of a surfactant-based technique would save the world from any such pandemic in the future too.

Nanomedicine for Gene Delivery for the Treatment of Cardiovascular Diseases

Background:

Myocardial infarction (MI) is the most severe ischemic heart disease and di-rectly leads to heart failure till death. Target molecules have been identified in the event of MI including increasing angiogenesis, promoting cardiomyocyte survival, improving heart function and restraining inflammation and myocyte activation and subsequent fibrosis. All of which are substantial in cardiomy-ocyte protection and preservation of cardiac function.

Methodology:

To modulate target molecule expression, virus and non-virus-mediated gene transfer have been investigated. Despite successful in animal models of MI, virus-mediated gene transfer is hampered by poor targeting efficiency, low packaging capacity for large DNA sequences, immunogenicity induced by virus and random integration into the human genome.

Discussion:

Nanoparticles could be synthesized and equipped on purpose for large-scale production. They are relatively small in size and do not incorporate into the genome. They could carry DNA and drug within the same transfer. All of these properties make them an alternative strategy for gene transfer. In the review, we first introduce the pathological progression of MI. After concise discussion on the current status of virus-mediated gene therapy in treating MI, we overview the history and development of nanoparticle-based gene delivery system. We point out the limitations and future perspective in the field of nanoparticle vehicle.

Conclusion:

Ultimately, we hope that this review could help to better understand how far we are with nanoparticle-facilitated gene transfer strategy and what obstacles we need to solve for utilization of na-nomedicine in the treatment of MI.

Alginate-poloxamer beads for clotrimazole delivery: Molecular interactions, mechanical properties, and anticandidal activity

Calcium alginate (CA) beads loaded with clotrimazole (CZ) were modified by adding poloxamer (PLX) in this study. Blends of PLX188 or PLX407 into sodium alginate (SA) dispersions caused a decrease in the SA zeta potential and led to viscosity synergism. SA with carboxyl and hydroxyl groups can interact with the hydroxyl groups of PLX via hydrogen bonding. A stronger interaction of SA with PLX407 was found when compared to the interaction between SA and PLX188. The PLX-CA beads gave a higher CZ entrapment efficiency than the CA beads. The highest PLX content used created an amorphous form of CZ in the beads because of the CZ solubilization by the PLX micelles. The addition of 0.5 or 1% w/v PLX can strengthen the CZ-loaded CA beads. Furthermore, the PLX-CA beads display a lower water uptake than the CA beads. PLX micellization can enhance CZ release and enhance the efficacy of CZ against Candida albicans. This study indicates that the molecular interaction of SA with PLX and the PLX micellization of CZ can improve the characteristics of CZ-loaded CA beads, which offer good potential for use as drug delivery systems or drug reservoirs in tablets for oral candidiasis.

Proteomic Analysis of Resistance of Gram-Negative Bacteria to Chlorhexidine and Impacts on Susceptibility to Colistin, Antimicrobial Peptides, and Ceragenins

Use of chlorhexidine in clinical settings has led to concerns that repeated exposure of bacteria to sub-lethal doses of chlorhexidine might result in chlorhexidine resistance and cross resistance with other cationic antimicrobials including colistin, endogenous antimicrobial peptides (AMPs) and their mimics, ceragenins. We have previously shown that colistin-resistant Gram-negative bacteria remain susceptible to AMPs and ceragenins. Here, we investigated the potential for cross resistance between chlorhexidine, colistin, AMPs and ceragenins by serial exposure of standard strains of Gram-negative bacteria to chlorhexidine to generate resistant populations of organisms. Furthermore, we performed a proteomics study on the chlorhexidine-resistant strains and compared them to the wild-type strains to find the pathways by which bacteria develop resistance to chlorhexidine. Serial exposure of Gram-negative bacteria to chlorhexidine resulted in four- to eight-fold increases in minimum inhibitory concentrations (MICs). Chlorhexidine-resistant organisms showed decreased susceptibility to colistin (8- to 32-fold increases in MICs) despite not being exposed to colistin. In contrast, chlorhexidine-resistant organisms had the same MICs as the original strains when tested with representative AMPs (LL-37 and magainin I) and ceragenins (CSA-44 and CSA-131). These results imply that there may be a connection between the emergence of highly colistin-resistant Gram-negative pathogens and the prevalence of chlorhexidine usage. Yet, use of chlorhexidine may not impact innate immune defenses (e.g., AMPs) and their mimics (e.g., ceragenins). Here, we also show that chlorhexidine resistance is associated with upregulation of proteins involved in the assembly of LPS for outer membrane biogenesis and virulence factors in Pseudomonas aeruginosa. Additionally, resistance to chlorhexidine resulted in elevated expression levels of proteins associated with chaperones, efflux pumps, flagella and cell metabolism. This study provides a comprehensive overview of the evolutionary proteomic changes in P. aeruginosa following exposure to chlorhexidine and colistin. These results have important clinical implications considering the continuous application of chlorhexidine in hospitals that could influence the emergence of colistin-resistant strains.

Susceptibility of Multidrug-Resistant Bacteria, Isolated from Water and Plants in Nigeria, to Ceragenins

The continuous emergence of multidrug resistant pathogens is a major global health concern. Although antimicrobial peptides (AMPs) have shown promise as a possible means of combatting multidrug resistant strains without readily engendering resistance, costs of production and targeting by proteases limit their utility. Ceragenins are non-peptide AMP mimics that overcome these shortcomings while retaining broad-spectrum antimicrobial activity. To further characterize the antibacterial activities of ceragenins, their activities against a collection of environmental isolates of bacteria were determined. These isolates were isolated in Nigeria from plants and water. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) of selected ceragenins and currently available antimicrobials against these isolates were measured to determine resistance patterns. Using scanning electron microscopy (SEM), we examined the morphological changes in bacterial membranes following treatment with ceragenins. Finally, we investigated the effectiveness of ceragenins in inhibiting biofilm formation and destroying established biofilms. We found that, despite high resistance to many currently available antimicrobials, including colistin, environmental isolates in planktonic and biofilm forms remain susceptible to ceragenins. Additionally, SEM and confocal images of ceragenin-treated cells confirmed the effective antibacterial and antibiofilm activity of ceragenins.