Novel D-form of hybrid peptide (D-AP19) rapidly kills Acinetobacter baumannii while tolerating proteolytic enzymes

Natural peptides and their synthetic congeners acting against Acinetobacter baumannii through the membrane and cell wall: latest progress

Acinetobacter baumannii is one of the deadliest Gram-negative bacteria (GNB), responsible for 2-10% of hospital-acquired infections. Several antibiotics are used to control the growth of A. baumannii. However, in recent decades, the abuse and misuse of antibiotics to treat non-microbial diseases have led to the emergence of multidrug-resistant A. baumannii strains. A. baumannii possesses a complex cell wall structure. Cell wall-targeting agents remain the center of antibiotic drug discovery. Notably, the antibacterial drug discovery intends to target the membrane of the bacteria, offering several advantages over antibiotics targeting intracellular systems, as membrane-targeting agents do not have to travel through the plasma membrane to reach the cytoplasmic targets. Microorganisms, insects, and mammals produce antimicrobial peptides as their first line of defense to protect themselves from pathogens and predators. Importantly, antimicrobial peptides are considered potential alternatives to antibiotics. This communication summarises the recently identified peptides of natural origin and their synthetic congeners acting against the A. baumannii membrane by cell wall disruption.

Antibacterial, Antibiofilm, and Anti-inflammatory Effects of a Novel Thrombin-Derived Peptide in Sepsis Models: Insights into Underlying Mechanisms

We developed two short helical antimicrobial peptides, HVF18-a3 and its d-enantiomer, HVF18-a3-d, derived from the thrombin C-terminal peptide HVF18. These peptides exhibit potent antimicrobial activity against various bacteria by compromising both the outer and inner membranes, with low hemolytic activity. They are stable in the presence of physiological salts and human serum, exhibiting a low potential for developing drug resistance and excellent antibiofilm activity against Gram-negative bacteria. HVF18-a3-d also neutralized lipopolysaccharide (LPS) through direct binding interactions and suppressed the production of inflammatory cytokines through the inflammatory signaling pathway mediated by Toll-like receptor 4 in RAW264.7 cells stimulated with LPS. Both pre- and post-treatment with HVF18-a3-d significantly protected mice against fatal septic shock induced by carbapenem resistant Acinetobacter baumannii. These findings suggest HVF18-a3 and HVF18-a3-d are promising candidates for developing antibiotics against Gram-negative sepsis.

Hybrids of Membrane-Translocating Antimicrobial Peptides Show Enhanced Activity through Membrane Permeabilization

Antimicrobial peptides (AMPs) hold promise as useful tools to combat bacterial infection. Hybrid peptides, made by linking two independent AMPs together through peptide bonds, have the potential for enhancing antimicrobial activity. Here we explore hybrids created by combining two histone-derived antimicrobial peptides (HDAPs), BF2 and DesHDAP1, that each translocate across bacterial membranes. Our work represents the first systematic approach considering the activity and mechanism of hybrids made from two translocating AMPs. BF2/DesHDAP1 hybrids showed increased antimicrobial activity against both Gram-positive and Gram-negative bacteria compared with the parent peptides and no cytotoxicity against eukaryotic cells. Introducing amino acid linkers between the parent peptides did not further enhance the antibacterial activity. The increased antimicrobial activity comes from a mechanistic shift, as hybrid peptides show decreased translocation across bacterial cell membranes but increased membrane permeabilization compared to BF2 and DesHDAP1. These observations lay the groundwork for the further design of hybrid AMPs made from translocating peptides.

Deciphering the Intracellular Action of the Antimicrobial Peptide A11 via an In-Depth Analysis of Its Effect on the Global Proteome of Acinetobacter baumannii

The potential antimicrobial activity and low propensity to induce the development of bacterial resistance have rendered antimicrobial peptides (AMPs) as novel and ideal candidate therapeutic agents for the treatment of infections caused by drug-resistant pathogenic bacteria. The targeting of bacterial membranes by AMPs has been typically considered their sole mode of action; however, increasing evidence supports the existence of multiple and complementary functions of AMPs that result in bacterial death. An in-depth characterization of their mechanism of action could facilitate further research and development of AMPs with higher potency. The current study employs biophysics and proteomics approaches to unveil the mechanisms underlying the antibacterial activity of A11, a potential candidate AMP, against Acinetobacter baumannii, a leading cause of hospital-acquired infections (HAIs) and consequently, a serious global threat. A11 peptide was found to induce membrane depolarization to a high extent, as revealed by flow cytometry and electron microscopy analyses. The prompt intracellular penetration of A11 peptide, observed using confocal microscopy, was found to occur concomitantly with a very low degree of membrane lysis, suggesting that its mode of action predominantly involves a nonlytic killing mechanism. Quantitative proteomics analysis employed for obtaining insights into the mechanisms underlying the antimicrobial activity of A11 peptide revealed that it disrupted energy metabolism, interfered with protein homeostasis, and inhibited fatty acid synthesis that is essential for cell membrane integrity; all these impacted the cellular functions of A. baumannii. A11 treatment also impacted signal transduction associated with the regulation of biofilm formation, hindered the stress response, and influenced DNA repair processes; these are all crucial survival mechanisms of A. baumannii. Additionally, robust antibacterial activity was exhibited by A11 peptide against multidrug-resistant (MDR) and extensively drug-resistant (XDR) clinical isolates of A. baumannii; moreover, A11 peptide exhibited synergy with levofloxacin and minocycline as well as low propensity for inducing resistance. Taken together, the findings emphasize the therapeutic potential of A11 peptide as an antibacterial agent against drug-resistant A. baumannii and underscore the need for further investigation.

The Effects of Different Antimicrobial Peptides (A-11 and AP19) on Isolated Bacteria from Fresh Boar Semen and Semen Quality during Storage at 18 °C

Antibiotic resistance (AMR) is a major public health concern. Antimicrobial peptides (AMPs) could be an alternative to conventional antibiotics. The purpose of this research was to investigate the antimicrobial ability of the synthetic AMPs (i.e., A-11 and AP19) on the most frequently isolated bacteria in boar semen and their effect on extended boar semen quality during storage. We tested the antimicrobial effect of A-11 and AP19 at different concentrations and compared them with gentamicin for inhibiting the growth of E. coli, Pseudomonas aeruginosa and Proteus mirabilis that were isolated from fresh boar semen. In order to evaluate the effect of AMP on semen qualities on days 0, 1, 3, and 5 after storage at 18 °C, seven fresh boar semen samples were collected, diluted with semen extender with antibiotic (i.e., gentamicin at 200 µg/mL, positive control) or without (negative control), and semen extender contained only A-11 or AP19 at different concentrations (i.e., 62.50, 31.25, and 15.625 µg/mL). The total bacterial count was also measured at 0, 24, 36, 48, and 72 h after storage. Comparable to gentamicin, both A-11 and AP19 inhibited the growth of E. coli, Pseudomonas aeruginosa, and Proteus mirabilis at 62.50, 31.25, and 15.625 µg/mL, respectively. Comparing the total bacterial count at 0, 24, 36, 48 and 72 h after storage, the lowest total bacterial concentration was found in the positive control group (p < 0.05), and an inferior total bacterial concentration was found in the treatment groups than in the negative control. On day 1, there is a lower percentage of all sperm parameters in the AP19 group at a concentration of 62.50 µg/mL compared with the other groups. On day 3, the highest percentage of all sperm parameters was found in the positive control and A-11 at a concentration of 31.25 µg/mL compared with the other groups. The AP19 group at 62.5 µg/mL constantly yielded inferior sperm parameters. On day 5, only A-11 at a concentration of 15.625 µg/mL showed a total motility higher than 70%, which is comparable to the positive control. A-11 and AP19 showed antimicrobial activity against E. coli, Pseudomonas aeruginosa and Proteus mirabilis isolated from boar semen. Considering their effect on semen quality during storage, these antimicrobial peptides are an alternative to conventional antibiotics used in boar semen extenders. Nevertheless, the utilization of these particular antimicrobial peptides relied on the concentration and duration of storage.

Design of a novel analogue peptide with potent antibiofilm activities against Staphylococcus aureus based upon a sapecin B-derived peptide

Nowadays, antimicrobial peptides are promising to confront the existing global crisis of antibiotic resistance. Here, a novel analogue peptide (mKLK) was designed based upon a D-form amidated sapecin B-derived peptide (KLK) by replacing two lysine residues with two tryptophan and one leucine by lysine, and inserting one alanine. The mKLK displayed superior amphipathic helixes in which the most of hydrophobic residues are confined to one face of the helix and had a higher hydrophobic moment compared with KLK. The mKLK retained its antibacterial activity and structure in human serum, suggesting its stability to proteolytic degradation. The values of MIC and MBC for mKLK were equal to those of KLK against clinical strains of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible Staphylococcus aureus (MSSA). However, mKLK showed more capability of in vitro inhibiting, eradicating, and dispersing MRSA and MSSA biofilms compared with KLK. Furthermore, a remarkable inhibitory activity of mKLK against MRSA and MSSA biofilms was seen in the murine model of catheter-associated biofilm infection. Results of this study show that mKLK not only exhibits antibacterial activity and serum stability but also a potent biofilm inhibitory activity at sub-MIC concentrations, confirming its potential therapeutic advantage for preventing biofilm-associated MRSA and MSSA infections.

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.

Promising applications of D-amino acids in periprosthetic joint infection

Due to the rise in our aging population, a disproportionate demand for total joint arthroplasty (TJA) in the elderly is forecast. Periprosthetic joint infection (PJI) represents one of the most challenging complications that can occur following TJA, and as the number of primary and revision TJAs continues to rise, an increasing PJI burden is projected. Despite advances in operating room sterility, antiseptic protocols, and surgical techniques, approaches to prevent and treat PJI remain difficult, primarily due to the formation of microbial biofilms. This difficulty motivates researchers to continue searching for an effective antimicrobial strategy. The dextrorotatory-isoforms of amino acids (D-AAs) are essential components of peptidoglycan within the bacterial cell wall, providing strength and structural integrity in a diverse range of species. Among many tasks, D-AAs regulate cell morphology, spore germination, and bacterial survival, evasion, subversion, and adhesion in the host immune system. When administered exogenously, accumulating data have demonstrated that D-AAs play a pivotal role against bacterial adhesion to abiotic surfaces and subsequent biofilm formation; furthermore, D-AAs have substantial efficacy in promoting biofilm disassembly. This presents D-AAs as promising and novel targets for future therapeutic approaches. Despite their emerging antibacterial efficacy, their role in disrupting PJI biofilm formation, the disassembly of established TJA biofilm, and the host bone tissue response remains largely unexplored. This review aims to examine the role of D-AAs in the context of TJAs. Data to date suggest that D-AA bioengineering may serve as a promising future strategy in the prevention and treatment of PJI.

Antimicrobial Peptide Cec4 Eradicates Multidrug-Resistant Acinetobacter baumannii in vitro and in vivo

Introduction

Acinetobacter baumannii has become a major difficulty in the treatment of bacteria-associated infection. The previously reported antimicrobial peptide Cec4 exhibited good and stable activity against A. baumannii in vitro, but the mechanisms and effects in vivo are elusive.

Methods

The effects of Cec4 on bacterial membrane permeability, membrane potential and bacterial reactive oxygen species were measured. The cell membrane localization of antimicrobial peptides was studied by fluorescence labelling. The ability of bacteria to develop resistance to antimicrobial peptides was studied by continuous induction, and transcriptome difference was analysed. The in vivo toxicity of Cec4 against nematodes and mice was studied, and the in vivo therapeutic potential of Cec4 against A. baumannii was assessed.

Results

Cec4 effectively cleared multidrug-resistant A. baumannii by altering bacterial cell membrane permeability, changing bacterial cell membrane polarity, and increasing bacterial intracellular reactive oxygen species. Cec4 affected the expression of the secretion system, outer membrane, and efflux pump genes of A. baumannii. In addition, the bacteria did not acquire stable drug-resistant ability. Cec4 at 1.024 mg/mL did not affect the proliferation of HeLa and HepG2 cells, and Cec4 at 45 mg/kg had little effect on the mortality of Caenorhabditis elegans, even the liver and kidney tissues of mouse. Most importantly, Cec4 could effectively improve the survival rates and reduce the bacterial load of various tissues in the mouse model of infection.

Conclusion

In conclusion, Cec4 can damage the cell membrane of bacteria, and the bacteria is not easy to produce resistance to Cec4. Besides, Cec4 has good potential for the treatment of multidrug-resistant A. baumannii infections.