Combinations of early generation antibiotics and antimicrobial peptides are effective against a broad spectrum of bacterial biothreat agents

Arg-biodynamers as antibiotic potentiators through interacting with Gram-negative outer membrane lipopolysaccharides

Antimicrobial resistance is becoming more prominent day after day due to a number of mechanisms by microbes, especially the sophisticated biological barriers of bacteria, especially in Gram-negatives. There, the lipopolysaccharides (LPS) layer is a unique component of the outer leaflet of the outer membrane which is highly impermeable and prevents antibiotics from passing passively into the intracellular compartments. Biodynamers, a novel class of dynamically bio-responsive polymers, may open new perspectives to overcome this particular barrier by accommodating various secondary structures and form supramolecular structures in such bacterial microenvironments. Generally, bio-responsive polymers are not only candidates as bio-active molecules against bacteria but also carriers via their interactions with the cargo. Based on their dynamicity, design flexibility, biodegradability, biocompatibility, and pH-responsiveness, we investigated the potential of two peptide-based biodynamers for improving antimicrobial drug delivery. By a range of experimental methods, we discovered a greater affinity of Arg-biodynamers for bacterial membranes than for mammalian membranes as well as an enhanced LPS targeting on the bacterial membrane, opening perspectives for enhancing the delivery of antimicrobials across the Gram-negative bacterial cell envelope. This could be explained by the change of the secondary structure of Arg-biodynamers into a predominant β-sheet character in the LPS microenvironment, by contrast to the α-helical structure typically observed for most lipid membrane-permeabilizing peptides. In comparison to poly-L-arginine, the intrinsic antibacterial activity of Arg-biodynamers was nearly unchanged, but its toxicity against mammalian cells was >128-fold reduced. When used in bacterio as an antibiotic potentiator, however, Arg-biodynamers improved the minimum inhibitory concentration (MIC) against Escherichia coli by 32 times compared to colistin alone. Similar effect has also been observed in two stains of Pseudomonas aeruginosa. Arg-biodynamers may therefore represent an interesting option as an adjuvant for antibiotics against Gram-negative bacteria and to overcome antimicrobial resistance.

Acidic pH modulates Burkholderia cenocepacia antimicrobial susceptibility in the cystic fibrosis nutritional environment

IMPORTANCE

Burkholderia cenocepacia causes severe infections in cystic fibrosis (CF) patients. CF patients are prone to reoccurring infections due to the accumulation of mucus in their lungs, where bacteria can adhere and grow. Some of the antibiotics that inhibit B. cenocepacia in the laboratory are not effective for CF patients. A major contributor to poor clinical outcomes is that antibiotic testing in laboratories occurs under conditions that are different from those of sputum. CF sputum may be acidic and have increased concentrations of iron and zinc. Here, we used a medium that mimics CF sputum and found that acidic pH decreased the activity of many of the antibiotics used against B. cenocepacia. In addition, we assessed susceptibility to more than 500 antibiotics and found four active compounds against B. cenocepacia. Our findings give a better understanding of the lack of a relationship between susceptibility testing and the clinical outcome when treating B. cenocepacia infections.

In vitro evaluation of antioxidant, cytotoxic, trypanocidal and antimicrobial activities of lignin obtained from Caesalpinia ferrea leaves and its use as an excipient in the release of oxacillin and fluconazole

In this context, the objective of this work was to isolate an alkaline lignin from the leaves of C. ferrea, in addition to investigating different biological activities and its use in the production of releasing tablets in vitro. Initially, the analysis of the composition of the leaves was performed, the contents were: cellulose (33.09 ± 0.3 %), hemicellulose (25.13 ± 0.1 %), lignin (18.29 ± 0.1 %), extractives (17.28 ± 1.0 %) and ash (6.20 ± 0.1 %). The leaves were fractionated to obtain alkaline lignin. The yield of obtaining lignin was 80.12 ± 0.1 %. The obtained lignin was characterized by the techniques: elemental analysis, FTIR, UV/Vis, 2D-NMR, GPC, TGA/DTG, DSC and PY-GC/MS. The results showed that the lignin obtained is of the GSH type, of low molecular weight and thermally stable. The in vitro antioxidant activity was evaluated by different assays promoting results only for DPPH (559.9 ± 0.8 μg/mL) and ABTS (484.1 ± 0.1 μg/mL) being able to promote low antioxidant activity. In addition, it showed low cytotoxicity in normal mammalian cells and promising antitumor and trypanocidal activity. Regarding antimicrobial activity, it was able to inhibit the growth of a strain of Staphylococcus aureus resistant to methicillin, presenting MIC values equal to the standard antibiotic oxacillin. It was also able to inhibit a strain of Candida albicans HAM13 sensitive to fluconazole. In addition, lignin promoted a synergistic effect by promoting a decrease in MIC against these two strains evaluated. Finally, lignin proved to be an excipient with potential for controlled release of antimicrobials.

Antimicrobial Peptide Synergies for Fighting Infectious Diseases

Antimicrobial peptides (AMPs) are essential elements of thehost defense system. Characterized by heterogenous structures and broad-spectrumaction, they are promising candidates for combating multidrug resistance. Thecombined use of AMPs with other antimicrobial agents provides a new arsenal ofdrugs with synergistic action, thereby overcoming the drawback of monotherapiesduring infections. AMPs kill microbes via pore formation, thus inhibitingintracellular functions. This mechanism of action by AMPs is an advantage overantibiotics as it hinders the development of drug resistance. The synergisticeffect of AMPs will allow the repurposing of conventional antimicrobials andenhance their clinical outcomes, reduce toxicity, and, most significantly,prevent the development of resistance. In this review, various synergies ofAMPs with antimicrobials and miscellaneous agents are discussed. The effect ofstructural diversity and chemical modification on AMP properties is firstaddressed and then different combinations that can lead to synergistic action,whether this combination is between AMPs and antimicrobials, or AMPs andmiscellaneous compounds, are attended. This review can serve as guidance whenredesigning and repurposing the use of AMPs in combination with other antimicrobialagents for enhanced clinical outcomes.

Advancements, challenges and future perspectives on peptide-based drugs: Focus on antimicrobial peptides

Among other health related issues, the rising concerns on drug resistance led to look for alternative pharmaceutical drugs that are effective both against infectious and noninfectious diseases. Antimicrobial peptides (AMPs) emerged as potential therapeutic molecule with wide range of applications. With their limitations, AMPs have gained reputable attentions in research as well as in the pharmaceutical industry. This review highlighted the historical background, research trends, technological advancements, challenges, and future perspectives in the development and applications of peptide drugs. Some vital questions related with the need for pharmaceutical production, factors for the slow and steady journey, the importance of oral bioavailability, and the drug resistance possibilities of AMPs were raised and addressed accordingly. Therefore, the current study is believed to provide a profound understanding in the past and current scenarios and future directions on the therapeutic impacts of peptide drugs.

Efficacy of Treatment with the Antibiotic Novobiocin against Infection with Bacillus anthracis or Burkholderia pseudomallei

The microbial pathogens Burkholderia pseudomallei and Bacillus anthracis are unrelated bacteria, yet both are the etiologic agents of naturally occurring diseases in animals and humans and are classified as Tier 1 potential biothreat agents. B. pseudomallei is the gram-negative bacterial agent of melioidosis, a major cause of sepsis and mortality globally in endemic tropical and subtropical regions. B. anthracis is the gram-positive spore-forming bacterium that causes anthrax. Infections acquired by inhalation of these pathogens are challenging to detect early while the prognosis is best; and they possess innate multiple antibiotic resistance or are amenable to engineered resistance. Previous studies showed that the early generation, rarely used aminocoumarin novobiocin was very effective in vitro against a range of highly disparate biothreat agents. The objective of the current research was to begin to characterize the therapeutic efficacy of novobiocin in mouse models of anthrax and melioidosis. The antibiotic was highly efficacious against infections by both pathogens, especially B. pseudomallei. Our results supported the concept that specific older generation antimicrobials can be effective countermeasures against infection by bacterial biothreat agents. Finally, novobiocin was shown to be a potential candidate for inclusion in a combined pre-exposure vaccination and post-exposure treatment strategy designed to target bacterial pathogens refractory to a single medical countermeasure.

Anthrax Meningoencephalitis and Intracranial Hemorrhage

The neurological sequelae of Bacillus anthracis infection include a rapidly progressive fulminant meningoencephalitis frequently associated with intracranial hemorrhage, including subarachnoid and intracerebral hemorrhage. Higher mortality than other forms of bacterial meningitis suggests that antimicrobials and cardiopulmonary support alone may be insufficient and that strategies targeting the hemorrhage might improve outcomes. In this review, we describe the toxic role of intracranial hemorrhage in anthrax meningoencephalitis. We first examine the high incidence of intracranial hemorrhage in patients with anthrax meningoencephalitis. We then review common diseases that present with intracranial hemorrhage, including aneurysmal subarachnoid hemorrhage and spontaneous intracerebral hemorrhage, postulating applicability of established and potential neurointensive treatments to the multimodal management of hemorrhagic anthrax meningoencephalitis. Finally, we examine the therapeutic potential of minocycline, an antimicrobial that is effective against B. anthracis and that has been shown in preclinical studies to have neuroprotective properties, which thus might be repurposed for this historically fatal disease.

Layered and integrated medical countermeasures against Burkholderia pseudomallei infections in C57BL/6 mice

Burkholderia pseudomallei, the gram-negative bacterium that causes melioidosis, is notoriously difficult to treat with antibiotics. A significant effort has focused on identifying protective vaccine strategies to prevent melioidosis. However, when used as individual medical countermeasures both antibiotic treatments (therapeutics or post-exposure prophylaxes) and experimental vaccine strategies remain partially protective. Here we demonstrate that when used in combination, current vaccine strategies (recombinant protein subunits AhpC and/or Hcp1 plus capsular polysaccharide conjugated to CRM197 or the live attenuated vaccine strain B. pseudomallei 668 ΔilvI) and co-trimoxazole regimens can result in near uniform protection in a mouse model of melioidosis due to apparent synergy associated with distinct medical countermeasures. Our results demonstrated significant improvement when examining several suboptimal antibiotic regimens (e.g., 7-day antibiotic course started early after infection or 21-day antibiotic course with delayed initiation). Importantly, this combinatorial strategy worked similarly when either protein subunit or live attenuated vaccines were evaluated. Layered and integrated medical countermeasures will provide novel treatment options for melioidosis as well as diseases caused by other pathogens that are refractory to individual strategies, particularly in the case of engineered, emerging, or re-emerging bacterial biothreat agents.

Algal Phlorotannins as Novel Antibacterial Agents with Reference to the Antioxidant Modulation: Current Advances and Future Directions

The increasing drug resistance of infectious microorganisms is considered a primary concern of global health care. The screening and identification of natural compounds with antibacterial properties have gained immense popularity in recent times. It has previously been shown that several bioactive compounds derived from marine algae exhibit antibacterial activity. Similarly, polyphenolic compounds are generally known to possess promising antibacterial capacity, among other capacities. Phlorotannins (PTs), an important group of algae-derived polyphenolic compounds, have been considered potent antibacterial agents both as single drug entities and in combination with commercially available antibacterial drugs. In this context, this article reviews the antibacterial properties of polyphenols in brown algae, with particular reference to PTs. Cell death through various molecular modes of action and the specific inhibition of biofilm formation by PTs were the key discussion of this review. The synergy between drugs was also discussed in light of the potential use of PTs as adjuvants in the pharmacological antibacterial treatment.

Multidrug resistance crisis during COVID-19 pandemic: Role of anti-microbial peptides as next-generation therapeutics

The decreasing effectiveness of conventional drugs due to multidrug-resistance is a major challenge for the scientific community, necessitating development of novel antimicrobial agents. In the present era of coronavirus 2 (COVID-19) pandemic, patients are being widely exposed to antimicrobial drugs and hence the problem of multidrug-resistance shall be aggravated in the days to come. Consequently, revisiting the phenomena of multidrug resistance leading to formulation of effective antimicrobial agents is the need of the hour. As a result, this review sheds light on the looming crisis of multidrug resistance in wake of the COVID-19 pandemic. It highlights the problem, significance and approaches for tackling microbial resistance with special emphasis on anti-microbial peptides as next-generation therapeutics against multidrug resistance associated diseases. Antimicrobial peptides exhibit exceptional mechanism of action enabling rapid killing of microbes at low concentration, antibiofilm activity, immunomodulatory properties along with a low tendency for resistance development providing them an edge over conventional antibiotics. The review is unique as it discusses the mode of action, pharmacodynamic properties and application of antimicrobial peptides in areas ranging from therapeutics to agriculture.

Synergistic effect and antibiofilm activity of an antimicrobial peptide with traditional antibiotics against multi-drug resistant bacteria

Combined treatment of AMPs with classical antibiotics has gained interest because it often results in a synergistic antibacterial effect. We demonstrated here that Pt5-1c, an AMP derived from phosvitin, had antibacterial activity against the MDR bacteria (S. aureus USA500, E. coli 577 and K. pneumoniae 2182) in the presence of serum. On this basis, we showed that Pt5-1c was synergistically active with traditional antibiotics (oxacillin, vancomycin, streptomycin and azithromycin) against the three MDR bacteria growing as biofilms in vitro and in vivo. Moreover, Pt5-1c restored sensitivity of S. aureus USA500 to oxacillin and vancomycin, E. coli 577 to streptomycin and K. pneumoniae 2182 to azithromycin. Importantly, long-term exposure to Pt5-1c did not give rise to antimicrobial resistance. Collectively, these data not only suggest a promising combinatorial therapy strategy to combat antibiotics-tolerant infections but also present a possibility of Pt5-1c being used to prolong the application of antibiotics including oxacillin, vancomycin, streptomycin and azithromycin, that are under threat of becoming ineffective due to antibiotic resistance.

Antibiotic Therapy of Plague: A Review

Plague-a deadly disease caused by the bacterium Yersinia pestis-is still an international public health concern. There are three main clinical forms: bubonic plague, septicemic plague, and pulmonary plague. In all three forms, the symptoms appear suddenly and progress very rapidly. Early antibiotic therapy is essential for countering the disease. Several classes of antibiotics (e.g., tetracyclines, fluoroquinolones, aminoglycosides, sulfonamides, chloramphenicol, rifamycin, and β-lactams) are active in vitro against the majority of Y. pestis strains and have demonstrated efficacy in various animal models. However, some discrepancies have been reported. Hence, health authorities have approved and recommended several drugs for prophylactic or curative use. Only monotherapy is currently recommended; combination therapy has not shown any benefits in preclinical studies or case reports. Concerns about the emergence of multidrug-resistant strains of Y. pestis have led to the development of new classes of antibiotics and other therapeutics (e.g., LpxC inhibitors, cationic peptides, antivirulence drugs, predatory bacteria, phages, immunotherapy, host-directed therapy, and nutritional immunity). It is difficult to know which of the currently available treatments or therapeutics in development will be most effective for a given form of plague. This is due to the lack of standardization in preclinical studies, conflicting data from case reports, and the small number of clinical trials performed to date.

Insights into antimicrobial peptides in fighting anthrax: A review

Anthrax is an infectious disease occurring worldwide and is a threat to global society due to its possible misuse as a biological weapon. Bacillus anthracis is the etiologic agent of this disease which can be transmitted via inhalation, ingestion, and skin contact. Globally, it is estimated around 2000 anthrax cases occur per year. Upon infection, the organism can cause cytolysis of macrophage and produce exotoxin capable of inducing edema and lymphatic blockage. Another challenge posed by the organism is the ability to form spores in harsh conditions. Various antibiotics have been used to fight the disease. However, like many other microbes, B. anthracis may develop resistance, thus the discovery of new therapeutics is urgently required. Antimicrobial peptides (AMPs) have been discovered since 1980s and attracted researchers in the antimicrobial field. In this review, the work and studies on the attempts to discover potent AMPs to treat anthrax together with the brief overview of the synthesis and modification pathways of several AMPs have been presented.

Host defense peptide IDR-1002 associated with ciprofloxacin as a new antimicrobial and immunomodulatory strategy for dental pulp revascularization therapy

Regenerative therapies such as dental pulpal revascularization appear as an option for traumatized immature permanent teeth. However, the triple antibiotic paste - TAP (metronidazole, minocycline, and ciprofloxacin), used for these therapies, can generate cytotoxicity and dentin discoloration. In contrast, host defense peptides (HDPs) are promising antimicrobial and immunomodulatory biomolecules for dentistry. This study aimed to evaluate in vitro the antimicrobial activity (against Staphylococcus aureus and Enterococcus faecalis) and the immunomodulatory potential (by the evaluation of IL-1α, IL-6, IL-12, IL-10, TNF-α and NO, in RAW 264.7 macrophages and IL-6, TGF-β and NO, in L929 fibroblast) of synthetic peptides (DJK-6, IDR-1018, and IDR-1002), compared to TAP in an in vitro infection model containing heat-killed antigens from E. faecalis and S. aureus. Furthermore, the synergistic potential of ciprofloxacin and IDR-1002 was evaluated by checkerboard. Ciprofloxacin was the best antimicrobial of TAP, besides acting in synergism with IDR-1002. TAP was pro-inflammatory (p < 0.05), while the association of ciprofloxacin and IDR-1002 presented an anti-inflammatory profile mainly in the presence of both heat-killed antigens (p < 0.05). Based on these results, ciprofloxacin associated with IDR-1002 may demonstrate an efficient antimicrobial and immunomodulatory action in this in vitro model. Further in vivo studies may determine the real potential of this combination.

Genome-Scale Metabolic Modeling for Unraveling Molecular Mechanisms of High Threat Pathogens

Pathogens give rise to a wide range of diseases threatening global health and hence drawing public health agencies' attention to establish preventative and curative solutions. Genome-scale metabolic modeling is ever increasingly used tool for biomedical applications including the elucidation of antibiotic resistance, virulence, single pathogen mechanisms and pathogen-host interaction systems. With this approach, the sophisticated cellular system of metabolic reactions inside the pathogens as well as between pathogen and host cells are represented in conjunction with their corresponding genes and enzymes. Along with essential metabolic reactions, alternate pathways and fluxes are predicted by performing computational flux analyses for the growth of pathogens in a very short time. The genes or enzymes responsible for the essential metabolic reactions in pathogen growth are regarded as potential drug targets, as a priori guide to researchers in the pharmaceutical field. Pathogens alter the key metabolic processes in infected host, ultimately the objective of these integrative constraint-based context-specific metabolic models is to provide novel insights toward understanding the metabolic basis of the acute and chronic processes of infection, revealing cellular mechanisms of pathogenesis, identifying strain-specific biomarkers and developing new therapeutic approaches including the combination drugs. The reaction rates predicted during different time points of pathogen development enable us to predict active pathways and those that only occur during certain stages of infection, and thus point out the putative drug targets. Among others, fatty acid and lipid syntheses reactions are recent targets of new antimicrobial drugs. Genome-scale metabolic models provide an improved understanding of how intracellular pathogens utilize the existing microenvironment of the host. Here, we reviewed the current knowledge of genome-scale metabolic modeling in pathogen cells as well as pathogen host interaction systems and the promising applications in the extension of curative strategies against pathogens for global preventative healthcare.

Antimicrobial Peptides: Classification, Design, Application and Research Progress in Multiple Fields

Antimicrobial peptides (AMPs) are a class of small peptides that widely exist in nature and they are an important part of the innate immune system of different organisms. AMPs have a wide range of inhibitory effects against bacteria, fungi, parasites and viruses. The emergence of antibiotic-resistant microorganisms and the increasing of concerns about the use of antibiotics resulted in the development of AMPs, which have a good application prospect in medicine, food, animal husbandry, agriculture and aquaculture. This review introduces the progress of research on AMPs comprehensively and systematically, including their classification, mechanism of action, design methods, environmental factors affecting their activity, application status, prospects in various fields and problems to be solved. The research progress on antivirus peptides, especially anti-coronavirus (COVID-19) peptides, has been introduced given the COVID-19 pandemic worldwide in 2020.

Synergies with and Resistance to Membrane-Active Peptides

Membrane-active peptides (MAPs) have long been thought of as the key to defeating antimicrobial-resistant microorganisms. Such peptides, however, may not be sufficient alone. In this review, we seek to highlight some of the common pathways for resistance, as well as some avenues for potential synergy. This discussion takes place considering resistance, and/or synergy in the extracellular space, at the membrane, and during interaction, and/or removal. Overall, this review shows that researchers require improved definitions of resistance and a more thorough understanding of MAP-resistance mechanisms. The solution to combating resistance may ultimately come from an understanding of how to harness the power of synergistic drug combinations.

Engineered Cationic Antimicrobial Peptides (eCAPs) to Combat Multidrug-Resistant Bacteria

The increasing rate of antibiotic resistance constitutes a global health crisis. Antimicrobial peptides (AMPs) have the property to selectively kill bacteria regardless of resistance to traditional antibiotics. However, several challenges (e.g., reduced activity in the presence of serum and lack of efficacy in vivo) to clinical development need to be overcome. In the last two decades, we have addressed many of those challenges by engineering cationic AMPs de novo for optimization under test conditions that typically inhibit the activities of natural AMPs, including systemic efficacy. We reviewed some of the most promising data of the last two decades in the context of the advancement of the field of helical AMPs toward clinical development.