Therapeutic efficacy of buforin II and rifampin in a rat model of Acinetobacter baumannii sepsis

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 Patented Antimicrobial Peptides from Amphibian Anurans

Since the 1980s, studies of antimicrobial peptides (AMPs) derived from anuran skin secretions have unveiled remarkable structural diversity and a wide range of activities. This study explores the potential of these peptides for drug development by examining granted patents, amino acid modifications related to patented peptides, and recent amphibians' taxonomic updates influencing AMP names. A total of 188 granted patents related to different anuran peptides were found, with Asia and North America being the predominant regions, contributing 65.4% and 15.4%, respectively. Conversely, although the Neotropical region is the world's most diversified region for amphibians, it holds only 3.7% of the identified patents. The antimicrobial activities of the peptides are claimed in 118 of these 188 patents. Additionally, for 160 of these peptides, 66 patents were registered for the natural sequence, 69 for both natural and derivative sequences, and 20 exclusively for sequence derivatives. Notably, common modifications include alterations in the side chains of amino acids and modifications to the peptides' N- and C-termini. This review underscores the biomedical potential of anuran-derived AMPs, emphasizing the need to bridge the gap between AMP description and practical drug development while highlighting the urgency of biodiversity conservation to facilitate biomedical discoveries.

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.

Synergy by Perturbing the Gram-Negative Outer Membrane: Opening the Door for Gram-Positive Specific Antibiotics

New approaches to target antibacterial agents toward Gram-negative bacteria are key, given the rise of antibiotic resistance. Since the discovery of polymyxin B nonapeptide as a potent Gram-negative outer membrane (OM)-permeabilizing synergist in the early 1980s, a vast amount of literature on such synergists has been published. This Review addresses a range of peptide-based and small organic compounds that disrupt the OM to elicit a synergistic effect with antibiotics that are otherwise inactive toward Gram-negative bacteria, with synergy defined as a fractional inhibitory concentration index (FICI) of <0.5. Another requirement for the inclusion of the synergists here covered is their potentiation of a specific set of clinically used antibiotics: erythromycin, rifampicin, novobiocin, or vancomycin. In addition, we have focused on those synergists with reported activity against Gram-negative members of the ESKAPE family of pathogens namely, Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, and/or Acinetobacter baumannii. In cases where the FICI values were not directly reported in the primary literature but could be calculated from the published data, we have done so, allowing for more direct comparison of potency with other synergists. We also address the hemolytic activity of the various OM-disrupting synergists reported in the literature, an effect that is often downplayed but is of key importance in assessing the selectivity of such compounds for Gram-negative bacteria.

Interaction of RecA mediated SOS response with bacterial persistence, biofilm formation, and host response

Antibiotics have a primary mode of actions, and most of them have a common secondary mode of action via reactive species (ROS and RNS) mediated DNA damage. Bacteria have been able to tolerate this DNA damage by SOS (Save-Our-Soul) response. RecA is the universal essential key protein of the DNA damage mediated SOS repair in various bacteria including ESKAPE pathogens. In addition, antibiotics also triggers activation of various other bacterial mechanisms such as biofilm formation, host dependent responses, persister subpopulation formation. These supporting the survival of bacteria in unfriendly natural conditions i.e. antibiotic presence. This review highlights the detailed mechanism of RecA mediated SOS response as well as role of RecA-LexA interaction in SOS response. The review also focuses on inter-connection between DNA damage repair pathway (like SOS response) with other survival mechanisms of bacteria such as host mediated RecA induction, persister-SOS interplay, and biofilm-SOS interplay. This understanding of inter-connection of SOS response with different other survival mechanisms will prove beneficial in targeting the SOS response for prevention and development of therapeutics against recalcitrant bacterial infections. The review also covers the significance of RecA as a promising potent therapeutic target for hindering bacterial SOS response in prevailing successful treatments of bacterial infections and enhancing the conventional antibiotic efficiency.

Evaluation of the antileishmanial effect of polyclonal antibodies and cationic antimicrobial peptides

Leishmaniasis is one of the tropical and subtropical diseases which, according to WHO, has the priority of control. The list of anti-leishmanial drugs is limited and requires side effects, high costs, and long-term treatments. Various species, parasite resistance, and simultaneous diseases are among the factors that affect the effectiveness of treatment. Due to these problems and based on satisfactory records of previous studies using antimicrobial peptides (AMPs) against infectious diseases, this study aimed to evaluate the antileishmanial effect of Leishmania-infected macrophage polyclonal antibody (LIMPA) with or without different concentrations (2, 4, 6, 8, 10, 20, 40, 60, and 100 µg/ml) of CM11 and (40, 80, and 100 µg/ml) BufIIIb, two AMPs, in vitro and their therapeutic effects against CL of Balb/c mice. Results showed that LIMPA induced an anti-proliferative effect on Leishmania major growth in macrophages in vitro and intramacrophage-amastigotes in vivo. CM11 with IC50 of 8.73 and 10.10 μg/ml at 48 hours, and BufIIIb with IC50 of 66.83 and 80.26 μg/ml, at 24 hours showed the most significant inhibition of L. major promastigotes and amastigotes. In addition, the CM11 and BufIIIb, with a CC50 of 9.7 μg/ml and 40.34 μg/ml, showed the most significant inhibition effect on the J774.A1 cell line at 48 hours, respectively. In addition, in vivo experiments using LIMPA with a 0.01 mg/kg dosage showed a significant difference (p < 0.001) in the last week of the measurement compared to the control. The results of this study may be a promising prospect for further investigations.

Biological Membrane-Penetrating Peptides: Computational Prediction and Applications

Peptides comprise a versatile class of biomolecules that present a unique chemical space with diverse physicochemical and structural properties. Some classes of peptides are able to naturally cross the biological membranes, such as cell membrane and blood-brain barrier (BBB). Cell-penetrating peptides (CPPs) and blood-brain barrier-penetrating peptides (B3PPs) have been explored by the biotechnological and pharmaceutical industries to develop new therapeutic molecules and carrier systems. The computational prediction of peptides’ penetration into biological membranes has been emerged as an interesting strategy due to their high throughput and low-cost screening of large chemical libraries. Structure- and sequence-based information of peptides, as well as atomistic biophysical models, have been explored in computer-assisted discovery strategies to classify and identify new structures with pharmacokinetic properties related to the translocation through biomembranes. Computational strategies to predict the permeability into biomembranes include cheminformatic filters, molecular dynamics simulations, artificial intelligence algorithms, and statistical models, and the choice of the most adequate method depends on the purposes of the computational investigation. Here, we exhibit and discuss some principles and applications of these computational methods widely used to predict the permeability of peptides into biomembranes, exhibiting some of their pharmaceutical and biotechnological applications.

Antimicrobial peptides, conventional antibiotics, and their synergistic utility for the treatment of drug-resistant infections

Antimicrobial peptides (AMPs), also known as host defense peptides (HDPs), are important effector immune defense molecules in multicellular organisms. AMPs exert their antimicrobial activities through several mechanisms; thus far, induction of drug resistance through AMPs has been regarded as unlikely. Therefore, they have great potential as new generation antimicrobial agents. To date, more than 30 AMP-related drugs are in the clinical trial phase. In recent years, studies show that some AMPs and conventional antibiotics have synergistic effects. The combined use of AMPs and antibiotics can kill drug-resistant pathogens, prevent drug resistance, and significantly improve the therapeutic effects of antibiotics. In this review, we discuss the progress in synergistic studies on AMPs and conventional antibiotics. An overview of the current understanding of the functional scope of AMPs, ongoing clinical trials, and challenges in the development processes are also presented.

A New Era of Antibiotics: The Clinical Potential of Antimicrobial Peptides

Antimicrobial resistance is a multifaceted crisis, imposing a serious threat to global health. The traditional antibiotic pipeline has been exhausted, prompting research into alternate antimicrobial strategies. Inspired by nature, antimicrobial peptides are rapidly gaining attention for their clinical potential as they present distinct advantages over traditional antibiotics. Antimicrobial peptides are found in all forms of life and demonstrate a pivotal role in the innate immune system. Many antimicrobial peptides are evolutionarily conserved, with limited propensity for resistance. Additionally, chemical modifications to the peptide backbone can be used to improve biological activity and stability and reduce toxicity. This review details the therapeutic potential of peptide-based antimicrobials, as well as the challenges needed to overcome in order for clinical translation. We explore the proposed mechanisms of activity, design of synthetic biomimics, and how this novel class of antimicrobial compound may address the need for effective antibiotics. Finally, we discuss commercially available peptide-based antimicrobials and antimicrobial peptides in clinical trials.

Synergism between Host Defence Peptides and Antibiotics Against Bacterial Infections

Background:

Antimicrobial resistance (AMR) to conventional antibiotics is becoming one of the main global health threats and novel alternative strategies are urging. Antimicrobial peptides (AMPs), once forgotten, are coming back into the scene as promising tools to overcome bacterial resistance. Recent findings have attracted attention to the potentiality of AMPs to work as antibiotic adjuvants.

Methods:

In this review, we have tried to collect the currently available information on the mechanism of action of AMPs in synergy with other antimicrobial agents. In particular, we have focused on the mechanisms of action that mediate the inhibition of the emergence of bacterial resistance by AMPs.

Results and Conclusion:

We find in the literature many examples where AMPs can significantly reduce the antibiotic effective concentration. Mainly, the peptides work at the bacterial cell wall and thereby facilitate the drug access to its intracellular target. Complementarily, AMPs can also contribute to permeate the exopolysaccharide layer of biofilm communities, or even prevent bacterial adhesion and biofilm growth. Secondly, we find other peptides that can directly block the emergence of bacterial resistance mechanisms or interfere with the community quorum-sensing systems. Interestingly, the effective peptide concentrations for adjuvant activity and inhibition of bacterial resistance are much lower than the required for direct antimicrobial action. Finally, many AMPs expressed by innate immune cells are endowed with immunomodulatory properties and can participate in the host response against infection. Recent studies in animal models confirm that AMPs work as adjuvants at non-toxic concentrations and can be safely administrated for novel combined chemotherapies.

A novel, rationally designed, hybrid antimicrobial peptide, inspired by cathelicidin and aurein, exhibits membrane-active mechanisms against Pseudomonas aeruginosa

Antimicrobial peptides (AMPs) are promising alternatives to classical antibiotics for the treatment of drug-resistant infections. Due to their versatility and unlimited sequence space, AMPs can be rationally designed by modulating physicochemical determinants to favor desired biological parameters and turned into novel therapeutics. In this study, we utilized key structural and physicochemical parameters, in combination with rational engineering, to design novel short α-helical hybrid peptides inspired by the well-known natural peptides, cathelicidin and aurein. By comparing homologous sequences and abstracting the conserved residue type, sequence templates of cathelicidin (P0) and aurein (A0) were obtained. Two peptide derivatives, P7 and A3, were generated by amino acid substitution based on their residue composition and distribution. In order to enhance antimicrobial activity, a hybrid analog of P7A3 was designed. The results demonstrated that P7A3 had higher antibacterial activity than the parental peptides with unexpectedly high hemolytic activity. Strikingly, C-terminal truncation of hybrid peptides containing only the α-helical segment (PA-18) and shorter derivatives confer potent antimicrobial activity with reduced hemolytic activity in a length‐dependent manner. Among all, PA-13, showed remarkable broad-spectrum antibacterial activity, especially against Pseudomonas aeruginosa with no toxicity. PA-13 maintained antimicrobial activity in the presence of physiological salts and displayed rapid binding and penetration activity which resulted in membrane depolarization and permeabilization. Moreover, PA-13 showed an anti-inflammatory response via lipopolysaccharide (LPS) neutralization with dose-dependent, inhibiting, LPS-mediated Toll-like receptor activation. This study revealed the therapeutic potency of a novel hybrid peptide, and supports the use of rational design in development of new antibacterial agents.

Antimicrobial peptides as a promising treatment option against Acinetobacter baumannii infections

BACKGROUND

With the increasing rate of antibiotic resistance in Acinetobacter, the World Health Organization introduced the carbapenem-resistant isolates in the priority pathogens list for which innovative new treatments are urgently needed. Antimicrobial peptides (AMPs) are one of the antimicrobial agents with high potential to produce new anti-Acinetobacter drugs. This review aims to summarize recent advances and compare AMPs with anti-Acinetobacter baumannii activity.

METHODS

Active AMPs against Acinetobacter were considered, and essential features, including structure, mechanism of action, anti-A. baumannii potent, and other prominent characteristics, were investigated and compared to each other. In this regard, the Google Scholar search engine and databases of PubMed, Scopus, and Web of Science were used.

RESULTS

Forty-six anti-Acinetobacter peptides were identified and classified into ten groups: Cathelicidins, Defensins, Frog AMPs, Melittin, Cecropins, Mastoparan, Histatins, Dermcidins, Tachyplesins, and computationally designed AMPs. According to the Minimum Inhibitory Concentration (MIC) reports, six peptides of Melittin, Histatin-8, Omega76, AM-CATH36, Hymenochirin, and Mastoparan have the highest anti-A. baumannii power against sensitive and antibiotic-resistant isolates. All anti-Acinetobacter peptides except Dermcidin have a net positive charge. Most of these peptides have alpha-helical structure; however, β-sheet and other structures have been observed among them. The mechanism of action of these antimicrobial agents is divided into two categories of membrane-based and intracellular target-based attack.

CONCLUSION

Evidence from this review indicates that AMPs would be likely among the main anti-A. baumannii drugs in the post-antibiotic era. Also, the application of computer science to increase anti-A. baumannii activity and reduce toxicity could be helpful.

Non-Lytic Antibacterial Peptides That Translocate Through Bacterial Membranes to Act on Intracellular Targets

The advent of multidrug resistance among pathogenic bacteria has attracted great attention worldwide. As a response to this growing challenge, diverse studies have focused on the development of novel anti-infective therapies, including antimicrobial peptides (AMPs). The biological properties of this class of antimicrobials have been thoroughly investigated, and membranolytic activities are the most reported mechanisms by which AMPs kill bacteria. Nevertheless, an increasing number of works have pointed to a different direction, in which AMPs are seen to be capable of displaying non-lytic modes of action by internalizing bacterial cells. In this context, this review focused on the description of the in vitro and in vivo antibacterial and antibiofilm activities of non-lytic AMPs, including indolicidin, buforin II PR-39, bactenecins, apidaecin, and drosocin, also shedding light on how AMPs interact with and further translocate through bacterial membranes to act on intracellular targets, including DNA, RNA, cell wall and protein synthesis.

A Porcine Wound Model of Acinetobacter baumannii Infection

Objective: To better understand Acinetobacter baumannii pathogenesis and to advance drug discovery against this pathogen, we developed a porcine, full-thickness, excisional, monospecies infection wound model.

Approach: The research was facilitated with AB5075, a previously characterized, extensively drug-resistant A. baumannii isolate. The model requires cyclophosphamide-induced neutropenia to establish a skin and soft tissue infection (SSTI) that persists beyond 7 days. Multiple, 12-mm-diameter full-thickness wounds were created in the skin overlying the cervical and thoracic dorsum. Wound beds were inoculated with 5.0 × 10⁴ colony-forming units (CFU) and covered with dressing.

Results:A. baumannii was observed in the wound bed and on the dressing in what appeared to be biofilm. When bacterial burdens were measured, proliferation to at least 10⁶ CFU/g (log₁₀6) wound tissue was observed. Infection was further characterized by scanning electron microscopy (SEM) and peptide nucleic acid fluorescence in situ hybridization (PNA-FISH) staining. To validate as a treatment model, polymyxin B was applied topically to a subset of infected wounds every 2 days. Then, the treated and untreated wounds were compared using multiple quantitative and qualitative techniques to include gross pathology, CFU burden, histopathology, PNA-FISH, and SEM.

Innovation: This is the first study to use A. baumannii in a porcine model as the sole infectious agent.

Conclusion: The porcine model allows for an additional preclinical assessment of antibacterial candidates that show promise against A. baumannii in rodent models, further evaluating safety and efficacy, and serve as a large animal in preclinical assessment for the treatment of SSTI.

Enhanced Efficacy of Combinations of Pexiganan with Colistin Versus Acinetobacter Baumannii in Experimental Sepsis

We investigated the efficacy of colistin combined with pexiganan in experimental mouse models of Acinetobacter baumannii infection.Adult male BALB/c mice received intraperitoneally 1 mL saline containing 2 × 10 CFU of susceptible and multiresistant A. baumannii. Two hours after bacterial challenge, animals received 1 mg/kg of colistin, 1 mg/kg of pexiganan, or 1 mg/kg of colistin plus 1 mg/kg of pexiganan.Blood culture positivity, the quantities of bacteria in the intra-abdominal fluid, the rate of lethality and immunological studies, such as immunophenotyping and NK cytotoxicity, were evaluated.In the in vitro study, A. baumannii showed susceptibility to colistin and pexiganan and a strong synergy was observed by testing colistin combined with pexiganan with fractionary inhibitory concentration index of 0.312 for both strains.In the in vivo study colistin or pexiganan alone showed a good antimicrobial efficacy. When colistin was combined with pexiganan, the positive interaction produced low bacterial counts that were statistically significant versus singly treated groups. For both strains the highest rate of survival was observed in combined-treated groups (90%).Pexiganan increased NK cytotoxic activity over the levels of infected and colistin-treated animals.In conclusion, pexiganan combined with colistin was found to be efficacious against A. baumannii infection.

Characterization and quantitative amino acids analysis of analgesic peptides in cinobufacini injection by size exclusion chromatography, matrix-assisted laser desorption/ionization time of flight mass spectrometry and gas chromatography mass spectrometry

Cinobufacini injection that comes from the water extract of Bufo bufo gargarizans Cantor skin is widely used for cancer treatment in China. Peptide is one of its major types of constituents, however the biological effects and content of this injection are little reported. In present study, the analgesic effect of peptides was determined and evaluated by in-vivo models. To characterize and quantitatively analyze these peptides, a reliable and efficient method combining size exclusion chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry with amino acid analysis was developed. The peptides presented as a series of analogs with similar molecular weights mostly ranging from 2 to 8 kDa. The amino acid analysis by gas chromatography mass spectrometry (GC-MS) was developed to determine both free and combined amino acids (FAA and CAA) in cinobufacini injection. This method achieved good linearity (R(2) , 0.9909-0.9999) and low limit of detection and quantification. FAA and CAA samples were efficiently analyzed by modified Phenomenex EZ: faast procedure. For the sample analysis, the method showed good repeatability (relative standard deviation, RSD ≤ 10%). For most FAA and CAA the mean recoveries were >80% with RSD <10%. The GC-MS based method is useful for quality assurance of both FAA and CAA in cinobufacini injection.

Epinecidin-1 has immunomodulatory effects, facilitating its therapeutic use in a mouse model of Pseudomonas aeruginosa sepsis

Antimicrobial peptides (AMPs) are garnering attention as possible alternatives to antibiotics. Here, we describe the antimicrobial properties of epinecidin-1 against a multidrug-resistant clinical isolate of P. aeruginosa (P. aeruginosa R) and a P. aeruginosa strain from ATCC (P. aeruginosa ATCC 19660) in vivo. The MICs of epinecidin-1 against P. aeruginosa R and P. aeruginosa ATCC 19660 were determined and compared with those of imipenem. Epinecidin-1 was found to be highly effective at combating peritonitis infection caused by P. aeruginosa R or P. aeruginosa ATCC 19660 in mouse models, without inducing adverse behavioral effects or liver or kidney toxicity. Taken together, our results indicate that epinecidin-1 enhances the rate of survival of mice infected with the bacterial pathogen P. aeruginosa through both antimicrobial and immunomodulatory effects.

Validation of a novel murine wound model of Acinetobacter baumannii infection

Patients recovering from traumatic injuries or surgery often require weeks to months of hospitalization, increasing the risk for wound and surgical site infections caused by ESKAPE pathogens, which include A. baumannii (the ESKAPE pathogens are Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). As new therapies are being developed to counter A. baumannii infections, animal models are also needed to evaluate potential treatments. Here, we present an excisional, murine wound model in which a diminutive inoculum of a clinically relevant, multidrug-resistant A. baumannii isolate can proliferate, form biofilms, and be effectively treated with antibiotics. The model requires a temporary, cyclophosphamide-induced neutropenia to establish an infection that can persist. A 6-mm-diameter, full-thickness wound was created in the skin overlying the thoracic spine, and after the wound bed was inoculated, it was covered with a dressing for 7 days. Uninoculated control wounds healed within 13 days, whereas infected, placebo-treated wounds remained unclosed beyond 21 days. Treated and untreated wounds were assessed with multiple quantitative and qualitative techniques that included gross pathology, weight loss and recovery, wound closure, bacterial burden, 16S rRNA community profiling, histopathology, peptide nucleic acid-fluorescence in situ hybridization, and scanning electron microscopy assessment of biofilms. The range of differences that we are able to identify with these measures in antibiotic- versus placebo-treated animals provides a clear window within which novel antimicrobial therapies can be assessed. The model can be used to evaluate antimicrobials for their ability to reduce specific pathogen loads in wounded tissues and clear biofilms. Ultimately, the mouse model approach allows for highly powered studies and serves as an initial multifaceted in vivo assessment prior to testing in larger animals.

Xuebijing Protects Rats from Sepsis Challenged with Acinetobacter baumannii by Promoting Annexin A1 Expression and Inhibiting Proinflammatory Cytokines Secretion

Xuebijing (XBJ) injection is a herbal medicine that has been widely used in the treatment of sepsis in China; however, its role in the development and progression of Acinetobacter baumannii sepsis and the underlying mechanisms remain uninvestigated. In the present study, fifty-four male Wistar rats were randomly assigned to normal-control group, sepsis-control group, and sepsis + XBJ group, each containing three subgroups of different treatment time periods (6, 12, and 24 hrs following injection, resp.). The sepsis model was established by intraperitoneal injection of A. baumannii ATCC 19606. For XBJ treatment, 4 mL/kg XBJ was administrated simultaneously by intravenous injection through caudal vein every 12 hrs. All animals demonstrated ill state, obvious intestinal dysfunction, histopathological lung damages, and overactive inflammatory responses after A. baumannii infection, and these events could be partially reversed by XBJ treatment from the beginning of infection. XBJ induced an increase in the expression of anti-inflammatory mediator annexin A1; however, two proinflammatory cytokines, interleukin-8 (IL-8) and tumor necrosis factor- α (TNF- α ), were decreased at the each monitored time point. These findings suggested that XBJ via its cytokine-mediated anti-inflammatory effects might have a potential role in preventing the progression of A. baumannii infection to sepsis by early administration.

Lipopolysaccharide-deficient Acinetobacter baumannii shows altered signaling through host Toll-like receptors and increased susceptibility to the host antimicrobial peptide LL-37

Infections caused by multidrug-resistant Acinetobacter baumannii have emerged as a serious global health problem. We have shown previously that A. baumannii can become resistant to the last-line antibiotic colistin via the loss of lipopolysaccharide (LPS), including the lipid A anchor, from the outer membrane (J. H. Moffatt, M. Harper, P. Harrison, J. D. Hale, E. Vinogradov, T. Seemann, R. Henry, B. Crane, F. St. Michael, A. D. Cox, B. Adler, R. L. Nation, J. Li, and J. D. Boyce, Antimicrob. Agents Chemother. 54:4971-4977, 2010). Here, we show how these LPS-deficient bacteria interact with components of the host innate immune system. LPS-deficient A. baumannii stimulated 2- to 4-fold lower levels of NF-κB activation and tumor necrosis factor alpha (TNF-α) secretion from immortalized murine macrophages, but it still elicited low levels of TNF-α secretion via a Toll-like receptor 2-dependent mechanism. Furthermore, we show that while LPS-deficient A. baumannii was not altered in its resistance to human serum, it showed increased susceptibility to the human antimicrobial peptide LL-37. Thus, LPS-deficient, colistin-resistant A. baumannii shows significantly altered activation of the host innate immune inflammatory response.

Acinetobacter baumannii: human infections, factors contributing to pathogenesis and animal models

Acinetobacter baumannii has emerged as a medically important pathogen because of the increasing number of infections produced by this organism over the preceding three decades and the global spread of strains with resistance to multiple antibiotic classes. In spite of its clinical relevance, until recently, there have been few studies addressing the factors that contribute to the pathogenesis of this organism. The availability of complete genome sequences, molecular tools for manipulating the bacterial genome, and animal models of infection have begun to facilitate the identification of factors that play a role in A. baumannii persistence and infection. This review summarizes the characteristics of A. baumannii that contribute to its pathogenesis, with a focus on motility, adherence, biofilm formation, and iron acquisition. In addition, the virulence factors that have been identified to date, which include the outer membrane protein OmpA, phospholipases, membrane polysaccharide components, penicillin-binding proteins, and outer membrane vesicles, are discussed. Animal models systems that have been developed during the last 15 years for the study of A. baumannii infection are overviewed, and the recent use of these models to identify factors involved in virulence and pathogenesis is highlighted.

Daptomycin and rifampin alone and in combination prevent vascular graft biofilm formation and emergence of antibiotic resistance in a subcutaneous rat pouch model of staphylococcal infection

OBJECTIVE

To investigate the efficacy of daptomycin and rifampin either alone or in combination in preventing prosthesis biofilm in a rat model of staphylococcal vascular graft infection.

DESIGN

Prospective, randomised, controlled animal study.

MATERIALS

Graft infections were established in the back subcutaneous tissue of adult male Wistar rats by implantation of Dacron prostheses followed by topical inoculation with 2×10(7) colony forming units of Staphylococcus aureus, strain Smith diffuse.

METHODS

The study included a control group, a contaminated group that did not receive any antibiotic prophylaxis and three contaminated groups that received intra-peritoneal daptomycin, rifampin-soaked graft and daptomycin plus rifampin-soaked graft, respectively. Each group included 15 animals. The infection burden was evaluated by using sonication and quantitative agar culture. Moreover, an in vitro antibiotic susceptibility assay for S. aureus biofilms was performed to elucidate the same activity.

RESULTS

When tested alone, daptomycin and rifampin showed good efficacies. Their combination showed efficacies significantly higher than that of each single compound. The in vitro studies showed that minimum inhibitory concentration and minimum bactericidal concentration values for daptomycin were lower in presence of rifampin. Daptomycin prevented the emergence of rifampin resistance.

CONCLUSION

Daptomycin is an important candidate for prevention of staphylococcal biofilm-related infection and rifampin could serve as an interesting anti-staphylococcal antibiotic enhancer.

Confronting multidrug-resistant Acinetobacter baumannii: a review

Multidrug-resistant Acinetobacter baumannii (MDR-AB) infections are difficult to treat owing to the extremely limited armamentarium. The present review reports all available treatment options against MDR-AB, including single molecules, combination schemes, and alternative modes of antimicrobial administration. Additionally, a group of recently reported peptides with anti-MDR-AB activity is described.

Structural contributions to the intracellular targeting strategies of antimicrobial peptides

The interactions of cationic amphipathic antimicrobial peptides (AMPs) with anionic biological membranes have been the focus of much research aimed at improving the activity of such compounds in the search for therapeutic leads. However, many of these peptides are thought to have other polyanions, such as DNA or RNA, as their ultimate target. Here a combination of fluorescence and circular dichroism (CD) spectroscopies has been used to assess the structural properties of amidated versions of buforin II, pleurocidin and magainin 2 that support their varying abilities to translocate through bacterial membranes and bind to double stranded DNA. Unlike magainin 2 amide, a prototypical membrane disruptive AMP, buforin II amide adopts a poorly helical structure in membranes closely mimicking the composition of Gram negative bacteria, such as Escherichia coli, and binds to a short duplex DNA sequence with high affinity, ultimately forming peptide-DNA condensates. The binding affinities of the peptides to duplex DNA are shown to be related to the structural changes that they induce. Furthermore, CD also reveals the conformation of the bound peptide buforin II amide. In contrast with a synthetic peptide, designed to adopt a perfect amphipathic alpha-helix, buforin II amide adopts an extended or polyproline II conformation when bound to DNA. These results show that an alpha-helix structure is not required for the DNA binding and condensation activity of buforin II amide.