Identification of potential therapeutic antimicrobial peptides against Acinetobacter baumannii in a mouse model of pneumonia

Near-infrared in vivo imaging system for dynamic visualization of lung-colonizing bacteria in mouse pneumonia

In vivo imaging of bacterial infection models enables noninvasive and temporal analysis of individuals, enhancing our understanding of infectious disease pathogenesis. Conventional in vivo imaging methods for bacterial infection models involve the insertion of the bacterial luciferase LuxCDABE into the bacterial genome, followed by imaging using an expensive ultrasensitive charge-coupled device (CCD) camera. However, issues such as limited light penetration into the body and lack of versatility have been encountered. We focused on near-infrared (NIR) light, which penetrates the body effectively, and attempted to establish an in vivo imaging method to evaluate the number of lung-colonizing bacteria during the course of bacterial pneumonia. This was achieved by employing a novel versatile system that combines plasmid-expressing firefly luciferase bacteria, NIR substrate, and an inexpensive, scientific complementary metal-oxide semiconductor (sCMOS) camera. The D-luciferin derivative "TokeOni," capable of emitting NIR bioluminescence, was utilized in a mouse lung infection model of Acinetobacter baumannii, an opportunistic pathogen that causes pneumonia and is a concern due to drug resistance. TokeOni exhibited the highest sensitivity in detecting bacteria colonizing the mouse lungs compared with other detection systems such as LuxCDABE, enabling the monitoring of changes in bacterial numbers over time and the assessment of antimicrobial agent efficacy. Additionally, it was effective in detecting A. baumannii clinical isolates and Klebsiella pneumoniae. The results of this study are expected to be used in the analysis of animal models of infectious diseases for assessing the efficacy of therapeutic agents and understanding disease pathogenesis.

IMPORTANCE

Conventional animal models of infectious diseases have traditionally relied upon average assessments involving numerous individuals, meaning they do not directly reflect changes in the pathology of an individual. Moreover, in recent years, ethical concerns have resulted in the demand to reduce the number of animals used in such models. Although in vivo imaging offers an effective approach for longitudinally evaluating the pathogenesis of infectious diseases in individual animals, a standardized method has not yet been established. To our knowledge, this study is the first to develop a highly versatile in vivo pulmonary bacterial quantification system utilizing near-infrared luminescence, plasmid-mediated expression of firefly luciferase in bacteria, and a scientific complementary metal-oxide semiconductor camera. Our research holds promise as a useful tool for assessing the efficacy of therapeutic drugs and pathogenesis of infectious diseases.

Current treatment strategies for targeting virulence factors and biofilm formation in Acinetobacter baumannii

A higher prevalence of Acinetobacter baumannii infections and mortality rate has been reported recently in hospital-acquired infections (HAI). The biofilm-forming capability of A. baumannii makes it an extremely dangerous pathogen, especially in device-associated hospital-acquired infections (DA-HAI), thereby it resists the penetration of antibiotics. Further, the transmission of the SARS-CoV-2 virus was exacerbated in DA-HAI during the epidemic. This review specifically examines the complex interconnections between several components and genes that play a role in the biofilm formation and the development of infections. The current review provides insights into innovative treatments and therapeutic approaches to combat A. baumannii biofilm-related infections, thereby ultimately improving patient outcomes and reducing the burden of HAI.

A Comprehensive Review of Recent Research into the Effects of Antimicrobial Peptides on Biofilms-January 2020 to September 2023

Microbial biofilm formation creates a persistent and resistant environment in which microorganisms can survive, contributing to antibiotic resistance and chronic inflammatory diseases. Increasingly, biofilms are caused by multi-drug resistant microorganisms, which, coupled with a diminishing supply of effective antibiotics, is driving the search for new antibiotic therapies. In this respect, antimicrobial peptides (AMPs) are short, hydrophobic, and amphipathic peptides that show activity against multidrug-resistant bacteria and biofilm formation. They also possess broad-spectrum activity and diverse mechanisms of action. In this comprehensive review, 150 publications (from January 2020 to September 2023) were collected and categorized using the search terms 'polypeptide antibiotic agent', 'antimicrobial peptide', and 'biofilm'. During this period, a wide range of natural and synthetic AMPs were studied, of which LL-37, polymyxin B, GH12, and Nisin were the most frequently cited. Furthermore, although many microbes were studied, Staphylococcus aureus and Pseudomonas aeruginosa were the most popular. Publications also considered AMP combinations and the potential role of AMP delivery systems in increasing the efficacy of AMPs, including nanoparticle delivery. Relatively few publications focused on AMP resistance. This comprehensive review informs and guides researchers about the latest developments in AMP research, presenting promising evidence of the role of AMPs as effective antimicrobial agents.

Recent advances in antimicrobial peptide-based therapy

Antimicrobial peptides (AMPs) are a group of polypeptide chains that have the property to target and kill a myriad of microbial organisms including viruses, bacteria, protists, etc. The first discovered AMP was named gramicidin, an extract of aerobic soil bacteria. Further studies discovered that these peptides are present not only in prokaryotes but in eukaryotes as well. They play a vital role in human innate immunity and wound repair. Consequently, they have maintained a high level of intrigue among scientists in the field of immunology, especially so with the rise of antibiotic-resistant pathogens decreasing the reliability of antibiotics in healthcare. While AMPs have promising potential to substitute for common antibiotics, their use as effective replacements is barred by certain limitations. First, they have the potential to be cytotoxic to human cells. Second, they are unstable in the blood due to action by various proteolytic agents and ions that cause their degradation. This review provides an overview of the mechanism of AMPs, their limitations, and developments in recent years that provide techniques to overcome those limitations. We also discuss the advantages and drawbacks of AMPs as a replacement for antibiotics as compared to other alternatives such as synthetically modified bacteriophages, traditional medicine, and probiotics.

Interaction and simulation studies suggest the possible molecular targets of intrinsically disordered amyloidogenic antimicrobial peptides in Acinetobacter baumannii

Acinetobacter baumannii is one of the causing agents of nosocomial infections. A wide range of antibiotics fails to work against these pathogens. Hence, there is an urgent requirement to develop other therapeutics to solve this problem. Antimicrobial peptides (AMPs) are a diverse group of naturally occurring peptides that have the ability to kill diverse groups of microorganisms. The major challenge of using AMPs as therapeutics is their unstable nature and the fact that most of their molecular targets are still unknown. In this study, we have selected intrinsically disordered and amyloidogenic AMPs, showing activity against A. baumannii, that is, Bactenecin, Cath BF, Citropin 1.1, DP7, NA-CATH, Tachyplesin, and WAM-1. To identify the probable target of these AMPs in A. baumannii, calculation of docking score, binding energy, dissociation constant, and molecular dynamics analysis was performed with selected seventeen possible molecular targets. The result showed that the most probable molecular targets of most of the intrinsically disordered amyloidogenic AMPs were UDP-N-acetylenol-pyruvoyl-glucosamine reductase (MurB), followed by 33-36 kDa outer membrane protein (Omp 33-36), UDP-N-acetylmuramoyl-l-alanyl-d-glutamate-2,6-diaminopimelate ligase (MurE), and porin Subfamily Protein (PorinSubF). Further, molecular dynamics analysis concluded that the target of antimicrobial peptide Bactenecin is MurB of A. baumannii, and identified other molecular targets of selected AMPs. Additionally, the oligomerization capacity of the selected AMPs was also investigated, and it was shown that the selected AMPs form oligomeric states, and interact with their molecular targets in that state. Experimental validation using purified AMPs and molecular targets needs to be done to confirm the interaction.Communicated by Ramaswamy H. Sarma.

Treatment and Management of Acinetobacter Pneumonia: Lessons Learned from Recent World Event

Acinetobacter pneumonia is a significant healthcare-associated infection that poses a considerable challenge to clinicians due to its multidrug-resistant nature. Recent world events, such as the COVID-19 pandemic, have highlighted the need for effective treatment and management strategies for Acinetobacter pneumonia. In this review, we discuss lessons learned from recent world events, particularly the COVID-19 pandemic, in the context of the treatment and management of Acinetobacter pneumonia. We performed an extensive literature review to uncover studies and information pertinent to the topic. The COVID-19 pandemic underscored the importance of infection control measures in healthcare settings, including proper hand hygiene, isolation protocols, and personal protective equipment use, to prevent the spread of multidrug-resistant pathogens like Acinetobacter. Additionally, the pandemic highlighted the crucial role of antimicrobial stewardship programs in optimizing antibiotic use and curbing the emergence of resistance. Advances in diagnostic techniques, such as rapid molecular testing, have also proven valuable in identifying Acinetobacter infections promptly. Furthermore, due to the limited availability of antibiotics for treating infections caused A. baumannii, alternative strategies are needed like the use of antimicrobial peptides, bacteriophages and their enzymes, nanoparticles, photodynamic and chelate therapy. Recent world events, particularly the COVID-19 pandemic, have provided valuable insights into the treatment and management of Acinetobacter pneumonia. These lessons emphasize the significance of infection control, antimicrobial stewardship, and early diagnostics in combating this challenging infection.

In vitro and in vivo antimicrobial potential of lithium complex against multi-drug resistant Acinetobacter baumannii

IMPORTANCE

Multi-drug resistance (MDR) by virtue of evolving resistance and virulence mechanisms among A. baumannii is a global concern which is responsible for lethal hospital-acquired infections. Therefore, it is crucial to develop new therapeutics against it. Metal complexes are compact structures with diverse mechanisms that the pathogens cannot evade easily which make them a strong drug candidate. In this study, we assessed the in vitro and in vivo efficacy of lithium complex {[Li(phen)2 sal]} against biofilm-forming MDR A. baumannii. The lithium complex displayed strong antimicrobial activity and reduced the pre-formed mature biofilm which is key barrier for antimicrobial action. Moreover, it employs oxidative stress as one of its mode of actions and causes cellular rupturing. Lithium complex was non-toxic and was significantly effective to overcome pneumonia in mice model. These results highlight the untapped potential of metal complexes that can be explored and utilized for combating notorious A. baumannii infections.

Perspectives in Searching Antimicrobial Peptides (AMPs) Produced by the Microbiota

Changes in the structure and function of the microbiota are associated with various human diseases. These microbial changes can be mediated by antimicrobial peptides (AMPs), small peptides produced by the host and their microbiota, which play a crucial role in host-bacteria co-evolution. Thus, by studying AMPs produced by the microbiota (microbial AMPs), we can better understand the interactions between host and bacteria in microbiome homeostasis. Additionally, microbial AMPs are a new source of compounds against pathogenic and multi-resistant bacteria. Further, the growing accessibility to metagenomic and metatranscriptomic datasets presents an opportunity to discover new microbial AMPs. This review examines the structural properties of microbiota-derived AMPs, their molecular action mechanisms, genomic organization, and strategies for their identification in any microbiome data as well as experimental testing. Overall, we provided a comprehensive overview of this important topic from the microbial perspective.

In Vivo Acute Toxicity and Therapeutic Potential of a Synthetic Peptide, DP1 in a Staphylococcus aureus Infected Murine Wound Excision Model

Bacterial infections at the surgical sites are one of the most prevalent skin infections that impair the healing mechanism. They account for about 20% of all types of infections and lead to approximately 75% of surgical-site infection-associated mortality. Several antibiotics, such as cephalosporins, fluoroquinolones, quinolones, penicillin, sulfonamides, etc., that are used to treat such wound infections not only counter infections but also disrupt the normal flora. Moreover, antibiotics, when used for a prolonged duration, may impair the formation of new blood vessels, delay collagen production, or inhibit the migration of certain cells involved in wound repair, leading to an impaired healing process. Therefore, there is a dire need for alternate therapeutic approaches against such infections. Antimicrobial peptides have gained considerable attention as a promising strategy to counter these pathogens and prevent the spread of infection. Recently, we have reported a designed peptide, DP1, and its broad-spectrum in vitro antimicrobial activity against Gram-positive and Gram-negative bacteria. In the present study, in vivo acute toxicity of DP1 was evaluated and even at a high dose (20 mg/kg body weight) of DP1, a 100% survival of mice was observed. Subsequently, a Staphylococcus aureus-infected murine wound excision model was established to assess the wound healing efficacy of DP1. The study revealed significant wound healing vis-a-vis attenuated S. aureus bioburden at the wound site and also controlled the oxidative stress depicting anti-oxidant activity as well. Healing of the infected wounds was also verified by histopathological examination. Based on the results of this study, it can be concluded that DP1 improves wound resolution despite infections and promotes the healing mechanism. Hence, DP1 holds compelling potential as a novel antimicrobial drug that requires further explorations in clinical platforms.

An Update on the Therapeutic Potential of Antimicrobial Peptides against Acinetobacter baumannii Infections

The rise in antibiotic-resistant strains of clinically important pathogens is a major threat to global health. The World Health Organization (WHO) has recognized the urgent need to develop alternative treatments to address the growing list of priority pathogens. Antimicrobial peptides (AMPs) rank among the suggested options with proven activity and high potential to be developed into effective drugs. Many AMPs are naturally produced by living organisms protecting the host against pathogens as a part of their innate immunity. Mechanisms associated with AMP actions include cell membrane disruption, cell wall weakening, protein synthesis inhibition, and interference in nucleic acid dynamics, inducing apoptosis and necrosis. Acinetobacter baumannii is a critical pathogen, as severe clinical implications have developed from isolates resistant to current antibiotic treatments and conventional control procedures, such as UV light, disinfectants, and drying. Here, we review the natural AMPs representing primary candidates for new anti-A. baumannii drugs in post-antibiotic-era and present computational tools to develop the next generation of AMPs with greater microbicidal activity and reduced toxicity.

Resistance, Tolerance, Virulence and Bacterial Pathogen Fitness-Current State and Envisioned Solutions for the Near Future

The current antibiotic crisis and the global phenomena of bacterial resistance, inherited and non-inherited, and tolerance-associated with biofilm formation-are prompting dire predictions of a post-antibiotic era in the near future. These predictions refer to increases in morbidity and mortality rates as a consequence of infections with multidrug-resistant or pandrug-resistant microbial strains. In this context, we aimed to highlight the current status of the antibiotic resistance phenomenon and the significance of bacterial virulence properties/fitness for human health and to review the main strategies alternative or complementary to antibiotic therapy, some of them being already clinically applied or in clinical trials, others only foreseen and in the research phase.

Advances of Antimicrobial Peptide-Based Biomaterials for the Treatment of Bacterial Infections

Owing to the increase in multidrug-resistant bacterial isolates in hospitals globally and the lack of truly effective antimicrobial agents, antibiotic resistant bacterial infections have increased substantially. There is thus an urgent need to develop new antimicrobial drugs and their related formulations. In recent years, natural antimicrobial peptides (AMPs), AMP optimization, self-assembled AMPs, AMP hydrogels, and biomaterial-assisted delivery of AMPs have shown great potential in the treatment of bacterial infections. In this review, it is focused on the development prospects and shortcomings of various AMP-based biomaterials for treating animal model infections, such as abdominal, skin, and eye infections. It is hoped that this review will inspire further innovations in the design of AMP-based biomaterials for the treatment of bacterial infections and accelerate their commercialization.

Promising Acinetobacter baumannii Vaccine Candidates and Drug Targets in Recent Years

In parallel to the uncontrolled use of antibiotics, the emergence of multidrug-resistant bacteria, like Acinetobacter baumannii, has posed a severe threat. A. baumannii predominates in the nosocomial setting due to its ability to persist in hospitals and survive antibiotic treatment, thereby eventually leading to an increasing prevalence and mortality due to its infection. With the increasing spectra of drug resistance and the incessant collapse of newly discovered antibiotics, new therapeutic countermeasures have been in high demand. Hence, recent research has shown favouritism towards the long-term solution of designing vaccines. Therefore, being a realistic alternative strategy to combat this pathogen, anti-A. Baumannii vaccines research has continued unearthing various antigens with variable results over the last decade. Again, other approaches, including pan-genomics, subtractive proteomics, and reverse vaccination strategies, have shown promise for identifying promiscuous core vaccine candidates that resulted in chimeric vaccine constructs. In addition, the integration of basic knowledge of the pathobiology of this drug-resistant bacteria has also facilitated the development of effective multiantigen vaccines. As opposed to the conventional trial-and-error approach, incorporating the in silico methods in recent studies, particularly network analysis, has manifested a great promise in unearthing novel vaccine candidates from the A. baumannii proteome. Some studies have used multiple A. baumannii data sources to build the co-functional networks and analyze them by k-shell decomposition. Additionally, Whole Genomic Protein Interactome (GPIN) analysis has utilized a rational approach for identifying essential proteins and presenting them as vaccines effective enough to combat the deadly pathogenic threats posed by A. baumannii. Others have identified multiple immune nodes using network-based centrality measurements for synergistic antigen combinations for different vaccination strategies. Protein-protein interactions have also been inferenced utilizing structural approaches, such as molecular docking and molecular dynamics simulation. Similar workflows and technologies were employed to unveil novel A. baumannii drug targets, with a similar trend in the increasing influx of in silico techniques. This review integrates the latest knowledge on the development of A. baumannii vaccines while highlighting the in silico methods as the future of such exploratory research. In parallel, we also briefly summarize recent advancements in A. baumannii drug target research.

The Role of Antimicrobial Peptides as Antimicrobial and Antibiofilm Agents in Tackling the Silent Pandemic of Antimicrobial Resistance

Just over a million people died globally in 2019 due to antibiotic resistance caused by ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). The World Health Organization (WHO) also lists antibiotic-resistant Campylobacter and Helicobacter as bacteria that pose the greatest threat to human health. As it is becoming increasingly difficult to discover new antibiotics, new alternatives are needed to solve the crisis of antimicrobial resistance (AMR). Bacteria commonly found in complex communities enclosed within self-produced matrices called biofilms are difficult to eradicate and develop increased stress and antimicrobial tolerance. This review summarises the role of antimicrobial peptides (AMPs) in combating the silent pandemic of AMR and their application in clinical medicine, focusing on both the advantages and disadvantages of AMPs as antibiofilm agents. It is known that many AMPs display broad-spectrum antimicrobial activities, but in a variety of organisms AMPs are not stable (short half-life) or have some toxic side effects. Hence, it is also important to develop new AMP analogues for their potential use as drug candidates. The use of one health approach along with developing novel therapies using phages and breakthroughs in novel antimicrobial peptide synthesis can help us in tackling the problem of AMR.

Structure and properties of antimicrobial peptides produced by antagonist microorganisms isolated from Siberian natural objects

Introduction. Public healthcare urgently needs new pharmaceuticals – alternative to traditional antibiotics – that pathogens develop no resistance to. Of special interest in this regard are antimicrobial, ribosomally synthesized bacterial peptides or bacteriocins. In this work, we aimed to study the structure and properties of antimicrobial peptides produced by antagonist microorganisms isolated from the natural objects of the Siberian region. Study objects and methods. The study objects were bacteria isolated from the natural sources of Kuzbass. After culturing bacteria, total protein was precipitated from the culture fluid and separated into fractions by gel permeation HPLC. Their amino acid sequences were determined by MALDI-TOF mass spectrometry. The antibacterial (against Bacillus pumilus and Escherichia coli) and fungicidal (against Aspergillus flavus and Aspergillus niger) properties of the peptides were studied by the disk diffusion method. Results and discussion. Seven peptides with different amino acid sequences were isolated from the culture fluid of bacteria, five of which had no analogues in the PepBank and Uniprot data banks. The peptide with an amino acid sequence of VMCLARKCSQGLIVKAPLM (2061.66 Da) was homologous to the cysteine membrane protein Giardia lamblia P15, and the peptide with an amino acid sequence of AVPSMKLCIQWSPVRASPCVMLGI (2587.21 Da) showed a homology with the Planctomycetes bacterium I41 peptides. We found antibacterial (against gram-positive and gram-negative bacteria) and fungicidal (against Aspergillus) properties in the peptide fractions. Conclusion. Antimicrobial peptides produced by bacteria isolated from the natural objects of the Siberian region can be used to create pharmaceuticals as an alternative to traditional antibiotics to treat infectious diseases.

Multiple roles of ribosomal antimicrobial peptides in tackling global antimicrobial resistance

In the last century, conventional antibiotics have played a significant role in global healthcare. Antibiotics support the body in controlling bacterial infection and simultaneously increase the tendency of drug resistance. Consequently, there is a severe concern regarding the regression of the antibiotic era. Despite the use of antibiotics, host defence systems are vital in fighting infectious diseases. In fact, the expression of ribosomal antimicrobial peptides (AMPs) has been crucial in the evolution of innate host defences and has been irreplaceable to date. Therefore, this valuable source is considered to have great potential in tackling the antimicrobial resistance (AMR) crisis. Furthermore, the possibility of bacterial resistance to AMPs has been intensively investigated. Here, we summarize all aspects related to the multiple applications of ribosomal AMPs and their derivatives in combating AMR.

Assessment of in vitro activities of novel modified antimicrobial peptides against clarithromycin resistant Mycobacterium abscessus

Mycobacterium abscessus (Mab) is one of the most drug resistant bacteria with a high treatment failure rate. Antimicrobial peptides (AMPs) are alternative therapeutic agents against this infection. This study was aimed to assess the in vitro activities of thirteen AMPs (S5, S52, S6, S61, S62, S63, KLK, KLK1, KLK2, Pug-1, Pug-2, Pug-3 and Pug-4) that have never been investigated against drug resistant Mab isolates. Only four novel modified AMPs (S61, S62, S63 and KLK1) provided the lowest minimum inhibitory concentration (MIC) values ranging from 200–400 μg/ml against the Mab ATCC19977 strain. These four potential AMPs were further tested with 16 clinical isolates of clarithromycin resistant Mab. The majority of the tested strains (10/16 isolates, 62.5%) showed ~99% kill by all four AMPs within 24 hours with an MIC <50 μg/ml. Only two isolates (12.5%) with acquired clarithromycin resistance, however, exhibited values <50 μg/ml of four potential AMPs, S61, S62, S63 and KLK1 after 3-days-incubation. At the MICs level, S63 showed the lowest toxicity with 1.50% hemolysis and 100% PBMC viability whereas KLK1 showed the highest hemolysis (10.21%) and lowest PBMC viability (93.52%). S61, S62 and S63 were further tested with clarithromycin-AMP interaction assays and found that 5/10 (50%) of selected isolates exhibited a synergistic interaction with 0.02–0.41 FICI values. This present study demonstrated the potential application of novel AMPs as an adjunctive treatment with clarithromycin against drug resistant Mab infection.

Antimicrobial Peptides: A Potent Alternative to Antibiotics

Antimicrobial peptides constitute one of the most promising alternatives to antibiotics since they could be used to treat bacterial infections, especially those caused by multidrug-resistant pathogens. Many antimicrobial peptides, with various activity spectra and mechanisms of actions, have been described. This review focuses on their use against ESKAPE bacteria, especially in biofilm treatments, their synergistic activity, and their application as prophylactic agents. Limitations and challenges restricting therapeutic applications are highlighted, and solutions for each challenge are evaluated to analyze whether antimicrobial peptides could replace antibiotics in the near future.