Evaluation of Pseudomonas aeruginosa pathogenesis and therapeutics in military-relevant animal infection models

A Review of Omadacycline for Potential Utility in the Military Health System for the Treatment of Wound Infections

INTRODUCTION

Combat-related wound infections complicate the recovery of wounded military personnel, contributing to overall morbidity and mortality. Wound infections in combat settings present unique challenges because of the size and depth of the wounds, the need to administer emergency care in the field, and the need for subsequent treatment in military facilities. Given the increase in multidrug-resistant pathogens, a novel, broad-spectrum antibiotic is desired across this continuum of care when the standard of care fails. Omadacycline was FDA-approved in 2018 for treatment of adults with acute bacterial skin and skin structure infections (ABSSSI), as well as community-acquired bacterial pneumonia (CABP). It is a broad-spectrum antibiotic with activity against gram-positive, gram-negative, and atypical bacterial pathogens, including multidrug-resistant species. Omadacycline can overcome commonly reported tetracycline resistance mechanisms, ribosomal protection proteins, and efflux pumps, and is available in once-daily intravenous or oral formulations. In this review, we discuss the potential role of omadacycline, which is included in the Department of Defense Formulary, in the context of combat wound infections.

MATERIALS AND METHODS

A literature review was undertaken for manuscripts published before July 21, 2023. This included a series of publications found via PubMed and a bibliography made publicly available on the Paratek Pharmaceuticals, Inc. website. Publications presenting primary data published in English on omadacycline in relation to ESKAPEE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Escherichia coli, and Enterobacter species) pathogens and Clostridioides difficile, including in vitro, in vivo, and clinical data were included.

RESULTS

Of 260 identified records, 66 were included for evidence review. Omadacycline has in vitro activity against almost all the ESKAPEE pathogens, apart from P. aeruginosa. Importantly, it has activity against the four most prevalent bacterial pathogens that cause wound infections in the military healthcare system: S. aureus, including methicillin-resistant S. aureus, A. baumannii, K. pneumoniae, and E. coli. In vivo studies in rats have shown that omadacycline is rapidly distributed in most tissues, with the highest tissue-to-blood concentration ratios in bone mineral. The clinical efficacy of omadacycline has been assessed in three separate Phase 3 studies in patients with ABSSSI (OASIS-1 and OASIS-2) and with CABP (OPTIC). Overall, omadacycline has an established safety profile in the treatment of both ABSSSI and CABP.

CONCLUSIONS

Omadacycline has broad-spectrum activity, the option to be orally administered and an established safety profile, making it a potentially attractive replacement for moxifloxacin in the military individual first aid kit, especially when accounting for the increasing resistance to fluoroquinolones. Further studies and clinical evaluation are warranted to support broader use of omadacycline to treat combat wound infections in the military healthcare system.

Aerosolized delivery of ESKAPE pathogens for murine pneumonia models

Murine pneumonia models for ESKAPE pathogens serve to evaluate novel antibacterials or to investigate immunological responses. The majority of published models uses intranasal or to a limited extent the intratracheal instillation to challenge animals. In this study, we propose the aerosol delivery of pathogens using a nebulizer. Aerosol delivery typically results in homogeneous distribution of the inoculum in the lungs because of lower particle size. This is of particular importance when compounds are assessed for their pharmacokinetic and pharmacodynamic (PK/PD) relationships as it allows to conduct several analysis with the same sample material. Moreover, aerosol delivery has the advantage that it mimics the 'natural route' of respiratory infection. In this short and concise study, we show that aerosol delivery of pathogens resulted in a sustained bacterial burden in the neutropenic lung infection model for five pathogens tested, whereas it gave a similar result in immunocompetent mice for three out of five pathogens. Moreover, a substantial bacterial burden in the lungs was already achieved 2 h post inhalation. Hence, this study constitutes a viable alternative for intranasal administration and a refinement of murine pneumonia models for PK/PD assessments of novel antibacterial compounds allowing to study multiple readouts with the same sample material.

Emerging In Vitro Models for the Study of Infection and Pathogenesis of Pseudomonas aeruginosa and Testing of Antibacterial Agents

Several animal models have been developed to study infection strategies and pathogenesis of Pseudomonas aeruginosa. Some of these models are also used in preclinical and clinical research. However, these models are increasingly showing their limitations, including in recapitulating human diseases such as cystic fibrosis, which is strongly linked to P. aeruginosa infection. The emerging field of human organoids and organs-on-a-chip is expected to provide answers to the need for in vitro modeling of human diseases. Here, we describe the first recent efforts that will hopefully provide the basis for the development of advanced in vitro models for the study of P. aeruginosa infection and pathogenesis and the testing of antibacterial agents.

Targeted treatment of injured nestmates with antimicrobial compounds in an ant society

Infected wounds pose a major mortality risk in animals. Injuries are common in the ant Megaponera analis, which raids pugnacious prey. Here we show that M. analis can determine when wounds are infected and treat them accordingly. By applying a variety of antimicrobial compounds and proteins secreted from the metapleural gland to infected wounds, workers reduce the mortality of infected individuals by 90%. Chemical analyses showed that wound infection is associated with specific changes in the cuticular hydrocarbon profile, thereby likely allowing nestmates to diagnose the infection state of injured individuals and apply the appropriate antimicrobial treatment. This study demonstrates that M. analis ant societies use antimicrobial compounds produced in the metapleural glands to treat infected wounds and reduce nestmate mortality.

Pseudomonas aphyarum sp. nov., Pseudomonas fontis sp. nov., Pseudomonas idahonensis sp. nov. and Pseudomonas rubra sp. nov., isolated from in, and around, a rainbow trout farm

During a large-scale bacterial culturing effort of biofilms in the vicinity of a rainbow trout aquaculture facility in Idaho, USA, 10 isolates were identified as having pathogen-inhibiting activity and were characterized further. These isolates were shown to be Gram-negative, rod-shaped bacteria belonging to the genus Pseudomonas. Whole-genome comparisons and multi-locus sequence analysis using four housekeeping genes (16S rRNA, gyrA, rpoB and rpoD) showed that these 10 isolates clustered into four distinct species groups. These comparisons also indicated that these isolates were below the established species cutoffs for the genus Pseudomonas. Further phenotypic characterization using API 20NE, API ZYM and Biolog GENIII assays and chemotaxonomic analysis of cellular fatty acids were carried out. Based on the genomic, physiological and chemotaxonomic properties of these isolates, we concluded that these strains composed four novel species of the genus Pseudomonas. The proposed names are as follows: Pseudomonas aphyarum sp. nov. consisting of strains ID233, ID386T and ID387 with ID386T (=DSM 114641T=ATCC TSD-305T) as the type strain; Pseudomonas rubra sp. nov. consisting of strains ID291T, ID609 and ID1025 with ID291T (=DSM 114640T=ATCC TSD-303T) as the type strain; Pseudomonas idahonensis sp. nov. consisting of strains ID357T and ID1048 with ID357T (=DSM 114609T=ATCC TSD-304T) as the type strain; and Pseudomonas fontis sp. nov. consisting of strains ID656T and ID681 with ID656T (=DSM 114610T=ATCC TSD-306T) as the type strain.

Mycelium-based biomaterials as smart devices for skin wound healing

Introduction: Recently, mycelia of Ganoderma lucidum and Pleurotus ostreatus, edible fungi, have been characterized in vitro as self-growing biomaterials for tissue engineering since they are constituted of interconnected fibrous networks resembling the dermal collagen structure. Aim: This work aims to investigate the biopharmaceutical properties of G. lucidum and P. ostreatus mycelia to prove their safety and effectiveness in tissue engineering as dermal substitutes. Methods: The mycelial materials were characterized using a multidisciplinary approach, including physicochemical properties (morphology, thermal behavior, surface charge, and isoelectric point). Moreover, preclinical properties such as gene expression and in vitro wound healing assay have been evaluated using fibroblasts. Finally, these naturally-grown substrates were applied in vivo using a murine burn/excisional wound model. Conclusions: Both G. lucidum and P. ostreatus mycelia are biocompatible and able to safely and effectively enhance tissue repair in vivo in our preclinical model.

Pseudomonas aeruginosa PAO1 outer membrane vesicles-diphtheria toxoid conjugate as a vaccine candidate in a murine burn model

Pseudomonas aeruginosa is an opportunistic pathogen considered a common cause of nosocomial infection with high morbidity and mortality in burn patients. Immunoprophylaxis techniques may lower the mortality rate of patients with burn wounds infected by P. aeruginosa; consequently, this may be an efficient strategy to manage infections caused by this bacterium. Several pathogenic Gram-negative bacteria like P. aeruginosa release outer membrane vesicles (OMVs), and structurally OMV consists of several antigenic components capable of generating a wide range of immune responses. Here, we evaluated the immunogenicity and efficacy of P. aeruginosa PA-OMVs (PA-OMVs) conjugated with the diphtheria toxoid (DT) formulated with alum adjuvant (PA-OMVs-DT + adj) in a mice model of burn wound infection. ELISA results showed that in the group of mice immunized with PA-OMVs-DT + adj conjugated, there was a significant increase in specific antibodies titer compared to non-conjugated PA-OMVs or control groups. In addition, the vaccination of mice with PA-OMVs-DT + adj conjugated generated greater protective effectiveness, as seen by lower bacterial loads, and eightfold decreased inflammatory cell infiltration with less tissue damage in the mice burn model compared to the control group. The opsonophagocytic killing results confirmed that humoral immune response might be critical for PA-OMVs mediated protection. These findings suggest that PA-OMV-DT conjugated might be used as a new vaccine against P. aeruginosa in burn wound infection.

Surviving the host: Microbial metabolic genes required for growth of Pseudomonas aeruginosa in physiologically-relevant conditions

Pseudomonas aeruginosa, like other pathogens, adapts to the limiting nutritional environment of the host by altering patterns of gene expression and utilizing alternative pathways required for survival. Understanding the genes essential for survival in the host gives insight into pathways that this organism requires during infection and has the potential to identify better ways to treat infections. Here, we used a saturated transposon insertion mutant pool of P. aeruginosa strain PAO1 and transposon insertion sequencing (Tn-Seq), to identify genes conditionally important for survival under conditions mimicking the environment of a nosocomial infection. Conditions tested included tissue culture medium with and without human serum, a murine abscess model, and a human skin organoid model. Genes known to be upregulated during infections, as well as those involved in nucleotide metabolism, and cobalamin (vitamin B₁₂) biosynthesis, etc., were required for survival in vivo- and in host mimicking conditions, but not in nutrient rich lab medium, Mueller Hinton broth (MHB). Correspondingly, mutants in genes encoding proteins of nucleotide and cobalamin metabolism pathways were shown to have growth defects under physiologically-relevant media conditions, in vivo, and in vivo-like models, and were downregulated in expression under these conditions, when compared to MHB. This study provides evidence for the relevance of studying P. aeruginosa fitness in physiologically-relevant host mimicking conditions and identified metabolic pathways that represent potential novel targets for alternative therapies.

Anti-CRISPR proteins as a therapeutic agent against drug-resistant bacteria

The continuous deployment of various antibiotics to treat multiple serious bacterial infections leads to multidrug resistance among the bacterial population. It has failed the standard treatment strategies through different antibacterial agents and serves as a significant threat to public health worldwide at devastating levels. The discovery of anti-CRISPR proteins catches the interest of researchers around the world as a promising therapeutic agent against drug-resistant bacteria. Anti-CRISPR proteins are known to inhibit bacterial CRISPR-Cas defense systems in multiple possible ways. The CRISPR-Cas nucleoprotein assembly provides adaptive immunity in bacteria against diverse categories of phage infections. Parallelly, phages also try to break the CRISPR-Cas barrier by producing anti-CRISPR proteins, leading to growth inhibition and bacterial lysis. This review begins with a brief description of the bacterial CRISPR-Cas system, followed by a detailed portrayal of anti-CRISPR proteins, including their discovery and evolution, mechanism of action, regulation of expression, and potential applications in the healthcare sector as an alternative therapeutic strategy to combat severe bacterial infections.

Genomic Analysis of Carbapenem-Resistant Pseudomonas aeruginosa Isolated From Urban Rivers Confirms Spread of Clone Sequence Type 277 Carrying Broad Resistome and Virulome Beyond the Hospital

The dissemination of antibiotic-resistant priority pathogens beyond hospital settings is both a public health and an environmental problem. In this regard, high-risk clones exhibiting a multidrug-resistant (MDR) or extensively drug-resistant (XDR) phenotype have shown rapid adaptation at the human-animal-environment interface. In this study, we report genomic data and the virulence potential of the carbapenemase, São Paulo metallo-β-lactamase (SPM-1)-producing Pseudomonas aeruginosa strains (Pa19 and Pa151) isolated from polluted urban rivers, in Brazil. Bioinformatic analysis revealed a wide resistome to clinically relevant antibiotics (carbapenems, aminoglycosides, fosfomycin, sulfonamides, phenicols, and fluoroquinolones), biocides (quaternary ammonium compounds) and heavy metals (copper), whereas the presence of exotoxin A, alginate, quorum sensing, types II, III, and IV secretion systems, colicin, and pyocin encoding virulence genes was associated with a highly virulent behavior in the Galleria mellonella infection model. These results confirm the spread of healthcare-associated critical-priority P. aeruginosa belonging to the MDR sequence type 277 (ST277) clone beyond the hospital, highlighting that the presence of these pathogens in environmental water samples can have clinical implications for humans and other animals.