Antimicrobial Activity of Murepavadin Tested against Clinical Isolates of Pseudomonas aeruginosa from the United States, Europe, and China

Antimicrobial peptides and their application to combat implant-associated infections - opportunities and challenges

Despite minimally invasive surgeries and advancements in aseptic techniques, implant-associated infections are a significant complication in post-surgical implantation of medical devices. The standard practice of systemic antibiotic administration is often ineffective due to the development of bacterial antibiotic resistance, poor antibiotic penetration into biofilms, and low antibiotic bioavailability at the infected site. Infected implants are typically salvaged by tissue resection and antibacterial reinforcements during revision surgery. Towards this end, antimicrobial peptides (AMPs) have emerged as a promising alternative to traditional antibiotics to combat infections. Herein, a comprehensive overview of antimicrobial peptides, their structure and function, comparison with conventional antibiotics, antimicrobial properties, mechanisms of action of AMPs, and bacterial resistance to AMPs in relation to antibiotics are discussed. Furthermore, stimuli-responsive AMP delivery and contact killing via AMP coatings on implant surfaces are deliberated. We discuss various methods of AMP immobilization and coatings on implant materials through physico-chemical coating strategies. The review also addresses the clinical status and current limitations of AMP coatings such as proteolytic instability and potential cytotoxicity. Finally, we conclude with future directions to develop small, effective AMP mimetics and encapsulation of AMPs within nanocarriers to improve antimicrobial properties and design-controlled release systems for sustained antimicrobial activity.

Understanding the pathophysiology of Pseudomonas aeruginosa colonization as a guide for future treatment for chronic leg ulcers

Chronic leg wounds represent a major burden of disease worldwide, costing health care systems billions of dollars each year. Aside from the financial implications, they also impose a significant physical and psychosocial burden on the patient, their relatives and/or carers, and the community. Whilst measures such as maintenance of wound hygiene, debridement, dressings and compression are the current standard of care, complete healing is not always achievable and ulcer recurrence is common. Thus, there is still a gap to breach in terms of understanding the intricate pathophysiology of chronic wounds and the role this plays on treatment and management. Pseudomonas aeruginosa has been linked to poor wound healing, with the pathogen being frequently isolated from chronic leg ulcers. Characterized by its multi-drug resistance, targeting P. aeruginosa requires the development of novel therapeutic options. Thus, the aim of this literature review is to describe the pathophysiology of P. aeruginosa in chronic leg ulcers and discuss novel treatment strategies. Here, we describe the key molecular mechanisms driving the observed clinical effect of P. aeruginosa on wounds and discuss novel strategies of molecular targeting of this common bacteria, establishing new approaches that could benefit patients with chronic hard to heal wounds.

The role of artificial intelligence and machine learning in predicting and combating antimicrobial resistance

Antimicrobial resistance (AMR) is a major threat to global public health. The current review synthesizes to address the possible role of Artificial Intelligence and Machine Learning (AI/ML) in mitigating AMR. Supervised learning, unsupervised learning, deep learning, reinforcement learning, and natural language processing are some of the main tools used in this domain. AI/ML models can use various data sources, such as clinical information, genomic sequences, microbiome insights, and epidemiological data for predicting AMR outbreaks. Although AI/ML are relatively new fields, numerous case studies offer substantial evidence of their successful application in predicting AMR outbreaks with greater accuracy. These models can provide insights into the discovery of novel antimicrobials, the repurposing of existing drugs, and combination therapy through the analysis of their molecular structures. In addition, AI-based clinical decision support systems in real-time guide healthcare professionals to improve prescribing of antibiotics. The review also outlines how can AI improve AMR surveillance, analyze resistance trends, and enable early outbreak identification. Challenges, such as ethical considerations, data privacy, and model biases exist, however, the continuous development of novel methodologies enables AI/ML to play a significant role in combating AMR.

[Clinical characteristics and risk factors of carbapenem-resistant Pseudomonas aeruginosa infection in children]

OBJECTIVES

To investigate the clinical characteristics of carbapenem-resistant Pseudomonas aeruginosa (CRPA) infection in children and the risk factors for such infection.

METHODS

A retrospective analysis was conducted among 60 children with CRPA infection (CRPA group) who were hospitalized in Shenzhen Children's Hospital, China Medical University, from January 2018 to September 2023, and 82 children with carbapenem-sensitive Pseudomonas aeruginosa infection during the same period were randomly selected as the control group. A multivariate logistic regression analysis was used to investigate the risk factors for CRPA infection.

RESULTS

Among the 60 children with CRPA infection, 31 (52%) were admitted to the intensive care unit (ICU), and the lower respiratory tract was the main detection site in 32 children (53%). The univariate analysis showed that sex, history of invasive treatment within 1 year, antibiotic use before admission, presence of underlying condition, ICU admission, invasive procedure after admission, antibiotic use for >14 days, and the type of antibiotics used of ≥3 were associated with CRPA infection (P<0.05). The multivariate logistic regression analysis showed that the history of invasive treatment within 1 year (OR=3.228, P<0.05), antibiotic use before admission (OR=4.052, P<0.05), antibiotic use for >14 days (OR=4.961, P<0.05), and the type of antibiotics used of ≥3 (OR=3.687, P<0.05) were independent risk factors for CRPA infection in children.

CONCLUSIONS

CRPA infection in children may be associated with a history of invasive treatment within the past year, antibiotic use before admission, duration of antibiotic use after admission, and the diversity of antibiotic types used.

Murepavadin Enhances the Killing Efficacy of Ciprofloxacin against Pseudomonas aeruginosa by Inhibiting Drug Efflux

Pseudomonas aeruginosa is a multidrug-resistant Gram-negative pathogen and one of the leading causes of ventilator-associated pneumonia and infections in patients with chronic obstructive pulmonary disease and cystic fibrosis. Murepavadin is a peptidomimetic that specifically targets outer-membrane lipopolysaccharide transport protein LptD of P. aeruginosa. In this study, we find that murepavadin enhances the bactericidal efficacy of ciprofloxacin. We further demonstrate that murepavadin increases intracellular accumulation of ciprofloxacin by suppressing drug efflux. In addition, the murepavadin-ciprofloxacin combination exhibits a synergistic bactericidal effect in an acute murine pneumonia model. In conclusion, our results identify an effective drug combination for the treatment of P. aeruginosa infections.

Synthesis of the Antimicrobial Peptide Murepavadin Using Novel Coupling Agents

The problem of antimicrobial resistance is becoming a daunting challenge for human society and healthcare systems around the world. Hence, there is a constant need to develop new antibiotics to fight resistant bacteria, among other important social and economic measures. In this regard, murepavadin is a cyclic antibacterial peptide in development. The synthesis of murepavadin was undertaken in order to optimize the preparative protocol and scale-up, in particular, the use of new activation reagents. In our hands, classical approaches using carbodiimide/hydroxybenzotriazole rendered low yields. The use of novel carbodiimide and reagents based on OxymaPure® and Oxy-B is discussed together with the proper use of chromatographic conditions for the adequate characterization of peptide crudes. Higher yields and purities were obtained. Finally, the antimicrobial activity of different synthetic batches was tested in three Pseudomonas aeruginosa strains, including highly resistant ones. All murepavadin batches yielded the same highly active MIC values and proved that the chiral integrity of the molecule was preserved throughout the whole synthetic procedure.

Murepavadin promotes the killing efficacies of aminoglycoside antibiotics against Pseudomonas aeruginosa by enhancing membrane potential

Murepavadin is a peptidomimetic that specifically targets the lipopolysaccharide transport protein LptD of Pseudomonas aeruginosa. Here, we found that murepavadin enhances the bactericidal efficacies of tobramycin and amikacin. We further demonstrated that murepavadin enhances bacterial respiration activity and subsequent membrane potential, which promotes intracellular uptake of aminoglycoside antibiotics. In addition, the murepavadin-amikacin combination displayed a synergistic bactericidal effect in a murine pneumonia model.

Structural Insights into the Lipopolysaccharide Transport (Lpt) System as a Novel Antibiotic Target

Lipopolysaccharide (LPS) is a critical component of the extracellular leaflet within the bacterial outer membrane, forming an effective physical barrier against environmental threats in Gram-negative bacteria. After LPS is synthesized and matured in the bacterial cytoplasm and the inner membrane (IM), LPS is inserted into the outer membrane (OM) through the ATP-driven LPS transport (Lpt) pathway, which is an energy-intensive process. A trans-envelope complex that contains seven Lpt proteins (LptA-LptG) is crucial for extracting LPS from the IM and transporting it across the periplasm to the OM. The last step in LPS transport involves the mediation of the LptDE complex, facilitating the insertion of LPS into the outer leaflet of the OM. As the Lpt system plays an essential role in maintaining the impermeability of the OM via LPS decoration, the interactions between these interconnected subunits, which are meticulously regulated, may be potential targets for the development of new antibiotics to combat multidrug-resistant Gram-negative bacteria. In this review, we aimed to provide an overview of current research concerning the structural interactions within the Lpt system and their implications to clarify the function and regulation of LPS transport in the overall process of OM biogenesis. Additionally, we explored studies on the development of therapeutic inhibitors of LPS transport, the factors that limit success, and future prospects.

Mutations in genes lpxL1, bamA, and pmrB impair the susceptibility of cystic fibrosis strains of Pseudomonas aeruginosa to murepavadin

Murepavadin is a peptidomimetic exhibiting specific inhibitory activity against Pseudomonas species. In the present study, its in vitro activity was assessed on 230 cystic fibrosis (CF) strains of Pseudomonas aeruginosa isolated from 12 French hospitals, in comparison with 12 other antipseudomonal antibiotics. Although murepavadin is still in preclinical stage of development, 9.1% (n = 21) of strains had a minimum inhibitory concentration (MIC) >4 mg/L, a level at least 128-fold higher than the modal MIC value of the whole collection (≤0.06 mg/L). Whole-genome sequencing of these 21 strains along with more susceptible isogenic counterparts coexisting in the same patients revealed diverse mutations in genes involved in the synthesis (lpxL1 and lpxL2) or transport of lipopolysaccharides (bamA, lptD, and msbA), or encoding histidine kinases of two-component systems (pmrB and cbrA). Allelic replacement experiments with wild-type reference strain PAO1 confirmed that alteration of genes lpxL1, bamA, and/or pmrB can decrease the murepavadin susceptibility from 8- to 32-fold. Furthermore, we found that specific amino acid substitutions in histidine kinase PmrB (G188D, Q105P, and D45E) reduce the susceptibility of P. aeruginosa to murepavadin, colistin, and tobramycin, three antibiotics used or intended to be used (murepavadin) in aerosols to treat colonized CF patients. Whether colistin or tobramycin may select mutants resistant to murepavadin or the opposite needs to be addressed by clinical studies.

Resistance is futile: targeting multidrug-resistant bacteria with de novo Cys-rich cyclic polypeptides

The search for novel antimicrobial agents to combat microbial pathogens is intensifying in response to rapid drug resistance development to current antibiotic therapeutics. The use of disulfide-rich head-to-tail cyclized polypeptides as molecular frameworks for designing a new type of peptide antibiotics is gaining increasing attention among the scientific community and the pharmaceutical industry. The use of macrocyclic peptides, further constrained by the presence of several disulfide bonds, makes these peptide frameworks remarkably more stable to thermal, biological, and chemical degradation showing better activities when compared to their linear analogs. Many of these novel peptide scaffolds have been shown to have a high tolerance to sequence variability in those residues not involved in disulfide bonds, able to cross biological membranes, and efficiently target complex biomolecular interactions. Hence, these unique properties make the use of these scaffolds ideal for many biotechnological applications, including the design of novel peptide antibiotics. This article provides an overview of the new developments in the use of several disulfide-rich cyclic polypeptides, including cyclotides, θ-defensins, and sunflower trypsin inhibitor peptides, among others, in the development of novel antimicrobial peptides against multidrug-resistant bacteria.

Lipopolysaccharide as an antibiotic target

Gram-negative bacteria, including Escherichia coli, Pseudomonas aeruginosa and Acinetobacter baumannii are amongst the highest priority drug-resistant pathogens, for which new antibiotics are urgently needed. Whilst antibiotic drug development is inherently challenging, this is particularly true for Gram-negative bacteria due to the presence of the outer membrane, a highly selective permeability barrier that prevents the ingress of several classes of antibiotic. This selectivity is largely due to an outer leaflet composed of the glycolipid lipopolysaccharide (LPS), which is essential for the viability of almost all Gram-negative bacteria. This essentiality, coupled with the conservation of the synthetic pathway across species and recent breakthroughs in our understanding of transport and membrane homeostasis has made LPS an attractive target for novel antibiotic drug development. Several different targets have been explored and small molecules developed that show promising activity in vitro. However, these endeavours have met limited success in clinical testing and the polymyxins, discovered more than 70 years ago, remain the only LPS-targeting drugs to enter the clinic thus far. In this review, we will discuss efforts to develop therapeutic inhibitors of LPS synthesis and transport and the reasons for limited success, and explore new developments in understanding polymyxin mode of action and the identification of new analogues with reduced toxicity and enhanced activity.

Murepavadin induces envelope stress response and enhances the killing efficacies of β-lactam antibiotics by impairing the outer membrane integrity of Pseudomonas aeruginosa

Pseudomonas aeruginosa is a ubiquitous opportunistic pathogen that can cause a variety of acute and chronic infections. The bacterium is highly resistant to numerous antibiotics. Murepavadin is a peptidomimetic antibiotic that blocks the function of P. aeruginosa lipopolysaccharide (LPS) transport protein D (LptD), thus inhibiting the insertion of LPS into the outer membrane. In this study, we demonstrated that sublethal concentrations of murepavadin enhance the bacterial outer membrane permeability. Proteomic analyses revealed the alteration of protein composition in bacterial inner and outer membranes following murepavadin treatment. The antisigma factor MucA was upregulated by murepavadin. In addition, the expression of the sigma E factor gene algU and the alginate synthesis gene algD was induced by murepavadin. Deletion of the algU gene reduces bacterial survival following murepavadin treatment, indicating a role of the envelope stress response in bacterial tolerance. We further demonstrated that murepavadin enhances the bactericidal activities of β-lactam antibiotics by promoting drug influx across the outer membrane. In a mouse model of acute pneumonia, the murepavadin-ceftazidime/avibactam combination showed synergistic therapeutic effect against P. aeruginosa infection. In addition, the combination of murepavadin with ceftazidime/avibactam slowed down the resistance development. In conclusion, our results reveal the response mechanism of P. aeruginosa to murepavadin and provide a promising antibiotic combination for the treatment of P. aeruginosa infections.IMPORTANCEThe ever increasing resistance of bacteria to antibiotics poses a serious threat to global public health. Novel antibiotics and treatment strategies are urgently needed. Murepavadin is a novel antibiotic that blocks the assembly of lipopolysaccharide (LPS) into the Pseudomonas aeruginosa outer membrane by inhibiting LPS transport protein D (LptD). Here, we demonstrated that murepavadin impairs bacterial outer membrane integrity, which induces the envelope stress response. We further found that the impaired outer membrane integrity increases the influx of β-lactam antibiotics, resulting in enhanced bactericidal effects. In addition, the combination of murepavadin and a β-lactam/β-lactamase inhibitor mixture (ceftazidime/avibactam) slowed down the resistance development of P. aeruginosa. Overall, this study demonstrates the bacterial response to murepavadin and provides a new combination strategy for effective treatment.

Ceftazidime-avibactam and comparators against Pseudomonas aeruginosa isolates collected globally and in each geographical region between 2017-2020

OBJECTIVES

The objective of this study was to assess the distribution and antimicrobial susceptibility of Pseudomonas aeruginosa isolates against ceftazidime-avibactam (CAZ-AVI) and a panel of comparator agents collected globally and in each region from 2017-2020 from the Antimicrobial Testing Leadership and Surveillance program.

METHODS

Susceptibility and minimum inhibitory concentration of all P. aeruginosa isolates were determined using broth microdilution methodology according to the Clinical and Laboratory Standards Institute guidelines.

RESULTS

Of the total 29746 isolates of P. aeruginosa collected, 20.9% were multidrug resistant (MDR), 20.7% were extremely drug resistant (XDR), 8.4% were CAZ-AVI-resistant (CAZ-AVI-R), and 3.0% were MBL-positive. Amongst the MBL-positive isolates, the proportion of VIM-positive isolates was highest (77.8%). The highest proportion of MDR (25.5%), XDR (25.0%), MBL-positive (5.7%), and CAZ-AVI-R (12.3%) isolates were in Latin America. Amongst the sources, the highest proportion of isolates were from respiratory sources (43.0%), and the majority of isolates were from non-intensive care unit wards (71.2%). Overall, all P. aeruginosa isolates (90.9%) showed high susceptibility to CAZ-AVI. However, MDR and XDR isolates were less susceptible to CAZ-AVI (≤60.7). The only comparators to which all isolates of P. aeruginosa showed good overall susceptibility were colistin (99.1%) and amikacin (90.5%). However, only colistin was active (≥98.3%) against all the resistant isolates.

CONCLUSION

CAZ-AVI presents a potential treatment option against P. aeruginosa infections. However, active monitoring and surveillance, especially of the resistant phenotypes, is warranted for effective treatment of infections caused by P. aeruginosa.

Age of Antibiotic Resistance in MDR/XDR Clinical Pathogen of Pseudomonas aeruginosa

Antibiotic resistance in Pseudomonas aeruginosa remains one of the most challenging phenomena of everyday medical science. The universal spread of high-risk clones of multidrug-resistant/extensively drug-resistant (MDR/XDR) clinical P. aeruginosa has become a public health threat. The P. aeruginosa bacteria exhibits remarkable genome plasticity that utilizes highly acquired and intrinsic resistance mechanisms to counter most antibiotic challenges. In addition, the adaptive antibiotic resistance of P. aeruginosa, including biofilm-mediated resistance and the formation of multidrug-tolerant persisted cells, are accountable for recalcitrance and relapse of infections. We highlighted the AMR mechanism considering the most common pathogen P. aeruginosa, its clinical impact, epidemiology, and save our souls (SOS)-mediated resistance. We further discussed the current therapeutic options against MDR/XDR P. aeruginosa infections, and described those treatment options in clinical practice. Finally, other therapeutic strategies, such as bacteriophage-based therapy and antimicrobial peptides, were described with clinical relevance.

Lipopolysaccharide structure modulates cationic biocide susceptibility and crystalline biofilm formation in Proteus mirabilis

Chlorhexidine (CHD) is a cationic biocide used ubiquitously in healthcare settings. Proteus mirabilis, an important pathogen of the catheterized urinary tract, and isolates of this species are often described as "resistant" to CHD-containing products used for catheter infection control. To identify the mechanisms underlying reduced CHD susceptibility in P. mirabilis, we subjected the CHD tolerant clinical isolate RS47 to random transposon mutagenesis and screened for mutants with reduced CHD minimum inhibitory concentrations (MICs). One mutant recovered from these screens (designated RS47-2) exhibited ~ 8-fold reduction in CHD MIC. Complete genome sequencing of RS47-2 showed a single mini-Tn5 insert in the waaC gene involved in lipopolysaccharide (LPS) inner core biosynthesis. Phenotypic screening of RS47-2 revealed a significant increase in cell surface hydrophobicity and serum susceptibility compared to the wildtype, and confirmed defects in LPS production congruent with waaC inactivation. Disruption of waaC was also associated with increased susceptibility to a range of other cationic biocides but did not affect susceptibility to antibiotics tested. Complementation studies showed that repression of smvA efflux activity in RS47-2 further increased susceptibility to CHD and other cationic biocides, reducing CHD MICs to values comparable with the most CHD susceptible isolates characterized. The formation of crystalline biofilms and blockage of urethral catheters was also significantly attenuated in RS47-2. Taken together, these data show that aspects of LPS structure and upregulation of the smvA efflux system function in synergy to modulate susceptibility to CHD and other cationic biocides, and that LPS structure is also an important factor in P. mirabilis crystalline biofilm formation.

Anti-Pseudomonas aeruginosa Vaccines and Therapies: An Assessment of Clinical Trials

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that causes high morbidity and mortality in cystic fibrosis (CF) and immunocompromised patients, including patients with ventilator-associated pneumonia (VAP), severely burned patients, and patients with surgical wounds. Due to the intrinsic and extrinsic antibiotic resistance mechanisms, the ability to produce several cell-associated and extracellular virulence factors, and the capacity to adapt to several environmental conditions, eradicating P. aeruginosa within infected patients is difficult. Pseudomonas aeruginosa is one of the six multi-drug-resistant pathogens (ESKAPE) considered by the World Health Organization (WHO) as an entire group for which the development of novel antibiotics is urgently needed. In the United States (US) and within the last several years, P. aeruginosa caused 27% of deaths and approximately USD 767 million annually in health-care costs. Several P. aeruginosa therapies, including new antimicrobial agents, derivatives of existing antibiotics, novel antimicrobial agents such as bacteriophages and their chelators, potential vaccines targeting specific virulence factors, and immunotherapies have been developed. Within the last 2-3 decades, the efficacy of these different treatments was tested in clinical and preclinical trials. Despite these trials, no P. aeruginosa treatment is currently approved or available. In this review, we examined several of these clinicals, specifically those designed to combat P. aeruginosa infections in CF patients, patients with P. aeruginosa VAP, and P. aeruginosa-infected burn patients.

Chimeric Peptidomimetic Antibiotic Efficiently Neutralizes Lipopolysaccharides (LPS) and Bacteria-Induced Activation of RAW Macrophages

Peptide antibiotics have gathered attention given the urgent need to discover antimicrobials with new mechanisms of action. Their extended role as immunomodulators makes them interesting candidates for the development of compounds with dual mode of action. The objective of this study was to test the anti-inflammatory capacity of a recently reported chimeric peptidomimetic antibiotic (CPA) composed of polymyxin B nonapeptide (PMBN) and a macrocyclic β-hairpin motif (MHM). We investigated the potential of CPA to inhibit lipopolysaccharide (LPS)-induced activation of RAW264.7 macrophages. In addition, we elucidated which structural motif was responsible for this activity by testing CPA, its building blocks, and their parent compounds separately. CPA showed excellent LPS neutralizing activity for both smooth and rough LPSs. At nanomolar concentrations, CPA completely inhibited LPS-induced nitric oxide, TNF-α, and IL-10 secretion. Murepavadin, MHM, and PMBN were incapable of neutralizing LPS in this assay, while PMB was less active compared to CPA. Isothermal titration calorimetry showed strong binding between the CPA and LPS with similar binding characteristics also found for the other compounds, indicating that binding does not necessarily correlate with neutralization of LPS. Finally, we showed that CPA-killed bacteria caused significantly less macrophage activation than bacteria killed with gentamicin, heat, or any of the other compounds. This indicates that the combined killing activity and LPS neutralization of CPA can prevent unwanted inflammation, which could be a major advantage over conventional antibiotics. Our data suggests that immunomodulatory activity can further strengthen the therapeutic potential of peptide antibiotics and should be included in the characterization of novel compounds.

Clinical Distribution and Drug Resistance of Pseudomonas aeruginosa in Guangzhou, China from 2017 to 2021

The aim of the current study was to analyse the distribution of antimicrobial drug resistance (AMR) among Pseudomonas aeruginosa (P. aeruginosa, PA) isolates from Guangdong Provincial People's Hospital (GDPH) from 2017 to 2021, and the impact of the COVID-19 outbreak on changes in the clinical distribution and drug resistance rate of P. aeruginosa to establish guidelines for empiric therapy. Electronic clinical data registry records from 2017 to 2021 were retrospectively analysed to study the AMR among P. aeruginosa strains from GDPH. The strains were identified by VITEK 2 Compact and MALDI-TOF MS, MIC method or Kirby-Bauer method for antibiotic susceptibility testing. The results were interpreted according to the CLSI 2020 standard, and the data were analysed using WHONET 5.6 and SPSS 23.0 software. A total of 3036 P. aeruginosa strains were detected in the hospital from 2017 to 2021, and they were primarily distributed in the ICU (n = 1207, 39.8%). The most frequent specimens were respiratory tract samples (59.6%). The detection rate for P. aeruginosa in 5 years was highest in September, and the population distribution was primarily male(68.2%). For the trend in the drug resistance rate, the 5-year drug resistance rate of imipenem (22.4%), aztreonam (21.5%) and meropenem (19.3%) remained at high levels. The resistance rate of cefepime decreased from 9.4% to 4.8%, showing a decreasing trend year by year (p < 0.001). The antibiotics with low resistance rates were aminoglycoside antibiotics, which were gentamicin (4.4%), tobramycin (4.3%), and amikacin (1.4%), but amikacin showed an increasing trend year by year (p = 0.008). Our analysis indicated that the detection rate of clinically resistant P. aeruginosa strains showed an upwards trend, and the number of multidrug-resistant (MDR) strains increased year by year, which will lead to stronger pathogenicity and mortality. However, after the outbreak of COVID-19 in 2020, the growth trend in the number of MDR bacteria slowed, presumably due to the strict epidemic prevention and control measures in China. This observation suggests that we should reasonably use antibiotics and treatment programs in the prevention and control of P. aeruginosa infection. Additionally, health prevention and control after the outbreak of the COVID-19 epidemic (such as wearing masks, washing hands with disinfectant, etc., which reduced the prevalence of drug resistance) led to a slowdown in the growth of the drug resistance rate of P. aeruginosa in hospitals, effectively reducing the occurrence and development of drug resistance, and saving patient's treatment costs and time.

Treatment of MDR Gram-Negative Bacteria Infections: Ongoing and Prospective

Antimicrobial resistance is a serious public health concern across the world. Gram-negative resistance has propagated over the globe via various methods, the most challenging of which include extended-spectrum β-lactamases, carbapenemases, and AmpC enzymes. Gram-negative bacterial infections are difficult to treat in critically extremely sick persons. Resistance to different antibiotic treatments nearly always lowers the probability of proper empirical coverage, sometimes resulting in severe outcomes. Multidrug resistance can be combated with varying degrees of success using a combination of older drugs with high toxicity levels and novel therapeutics. The current therapies for multidrug-resistant Gram-negative bacteria are discussed in this review, which includes innovative medications, older pharmaceuticals, creative combinations of the two, and therapeutic targets.

Efficacy and In Vitro Activity of Novel Antibiotics for Infections With Carbapenem-Resistant Gram-Negative Pathogens

Infections by Gram-negative multi-drug resistant (MDR) bacterial species are difficult to treat using available antibiotics. Overuse of carbapenems has contributed to widespread resistance to these antibiotics; as a result, carbapenem-resistant Enterobacterales (CRE), A. baumannii (CRAB), and P. aeruginosa (CRPA) have become common causes of healthcare-associated infections. Carbapenems, tigecycline, and colistin are the last resource antibiotics currently used; however, multiple reports of resistance to these antimicrobial agents have been documented worldwide. Recently, new antibiotics have been evaluated against Gram-negatives, including plazomicin (a new aminoglycoside) to treat CRE infection, eravacycline (a novel tetracycline) with in vitro activity against CRAB, and cefiderocol (a synthetic conjugate) for the treatment of nosocomial pneumonia by carbapenem-non-susceptible Gram-negative isolates. Furthermore, combinations of known β-lactams with recently developed β-lactam inhibitors, such as ceftazidime-avibactam, ceftolozane-tazobactam, ceftazidime-tazobactam, and meropenem-vaborbactam, has been suggested for the treatment of infections by extended-spectrum β-lactamases, carbapenemases, and AmpC producer bacteria. Nonetheless, they are not active against all carbapenemases, and there are reports of resistance to these combinations in clinical isolates.This review summarizes and discusses the in vitro and clinical evidence of the recently approved antibiotics, β-lactam inhibitors, and those in advanced phases of development for treating MDR infections caused by Gram-negative multi-drug resistant (MDR) bacterial species.

Leaks in the Pipeline: a Failure Analysis of Gram-Negative Antibiotic Development from 2010 to 2020

The World Health Organization (WHO) has warned that our current arsenal of antibiotics is not innovative enough to face impending infectious diseases, especially those caused by multidrug-resistant Gram-negative pathogens. Although the current preclinical pipeline is well stocked with novel candidates, the last U.S. Food and Drug Administration (FDA)-approved antibiotic with a novel mechanism of action against Gram-negative bacteria was discovered nearly 60 years ago. Of all the antibiotic candidates that initiated investigational new drug (IND) applications in the 2000s, 17% earned FDA approval within 12 years, while an overwhelming 62% were discontinued in that time frame. These "leaks" in the clinical pipeline, where compounds with clinical potential are abandoned during clinical development, indicate that scientific innovations are not reaching the clinic and providing benefits to patients. This is true for not only novel candidates but also candidates from existing antibiotic classes with clinically validated targets. By identifying the sources of the leaks in the clinical pipeline, future developmental efforts can be directed toward strategies that are more likely to flow into clinical use. In this review, we conduct a detailed failure analysis of clinical candidates with Gram-negative activity that have fallen out of the clinical pipeline over the past decade. Although limited by incomplete data disclosure from companies engaging in antibiotic development, we attempt to distill the developmental challenges faced by each discontinued candidate. It is our hope that this insight can help de-risk antibiotic development and bring new, effective antibiotics to the clinic.

Mammals' humoral immune proteins and peptides targeting the bacterial envelope: from natural protection to therapeutic applications against multidrug‐resistant Gram ‐negatives

Mammalian innate immunity employs several humoral ‘weapons’ that target the bacterial envelope. The threats posed by the multidrug‐resistant ‘ESKAPE’ Gram‐negative pathogens (Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) are forcing researchers to explore new therapeutic options, including the use of these immune elements. Here we review bacterial envelope‐targeting (peptidoglycan and/or membrane‐targeting) proteins/peptides of the mammalian immune system that are most likely to have therapeutic applications. Firstly we discuss their general features and protective activity against ESKAPE Gram‐negatives in the host. We then gather, integrate, and discuss recent research on experimental therapeutics harnessing their bactericidal power, based on their exogenous administration and also on the discovery of bacterial and/or host targets that improve the performance of this endogenous immunity, as a novel therapeutic concept. We identify weak points and knowledge gaps in current research in this field and suggest areas for future work to obtain successful envelope‐targeting therapeutic options to tackle the challenge of antimicrobial resistance.

Emerging Strategies to Combat β-Lactamase Producing ESKAPE Pathogens

Since the discovery of penicillin by Alexander Fleming in 1929 as a therapeutic agent against staphylococci, β-lactam antibiotics (BLAs) remained the most successful antibiotic classes against the majority of bacterial strains, reaching a percentage of 65% of all medical prescriptions. Unfortunately, the emergence and diversification of β-lactamases pose indefinite health issues, limiting the clinical effectiveness of all current BLAs. One solution is to develop β-lactamase inhibitors (BLIs) capable of restoring the activity of β-lactam drugs. In this review, we will briefly present the older and new BLAs classes, their mechanisms of action, and an update of the BLIs capable of restoring the activity of β-lactam drugs against ESKAPE (Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) pathogens. Subsequently, we will discuss several promising alternative approaches such as bacteriophages, antimicrobial peptides, nanoparticles, CRISPR (clustered regularly interspaced short palindromic repeats) cas technology, or vaccination developed to limit antimicrobial resistance in this endless fight against Gram-negative pathogens.

Polymyxin B resistance rates in carbapenem-resistant Pseudomonas aeruginosa isolates and a comparison between Etest® and broth microdilution methods of antimicrobial susceptibility testing

Polymyxin B has been considered to be the last line of defense for life-threatening infections caused by multiple drug resistant gram-negative pathogens, including carbapenem-resistant Pseudomonas aeruginosa (CRPA). The present study analyzed CRPA resistance to polymyxin B in the Suzhou district of China. Additionally, polymyxin B resistance rates were compared in different parts of the world to determine global trends. The present study also assessed the reliability and effectiveness of the Etest^® in a clinical setting, as laboratories lack a reliable and efficient susceptibility test for polymyxin B. The susceptibility rate of polymyxin B reached 96.0%, which is in accordance with results obtained from the United States of America, Europe, Africa and the majority of Asian countries. However, the rate of polymyxin B non-susceptibility (resistant or intermediate) in Singapore is 0.53 (95% confidence interval, 0.12-0.93). In addition, the susceptibility rate of polymyxin B determined via Etest^® was not significantly increased compared with that determined via broth microdilution (98.0 vs. 96.0%; P=0.558). Essential and categorical agreement rates reached 98.0%. In conclusion, the polymyxin B resistance rate of CRPA isolates is relatively low in the majority of countries, with the exception of Singapore. Furthermore, Etest^® may be a reliable clinical method for the measurement of polymyxin B resistance in CRPA isolates.

Susceptibility of Pseudomonas aeruginosa Recovered from Cystic Fibrosis Patients to Murepavadin and 13 Comparator Antibiotics

The objective was to determine the in vitro antimicrobial susceptibility of Pseudomonas aeruginosa isolates cultured from cystic fibrosis (CF) patients and explore associations between strain sequence type and susceptibility. Fourteen antibiotics and antibiotic combinations, including the novel antibacterial peptide murepavadin, were tested for activity against 414 Pseudomonas aeruginosa isolates cultured from respiratory samples of CF patients. The complete genomes of the isolates were sequenced, and minimum spanning trees were constructed based on the sequence types (STs). Percentages of resistance according to CLSI 2019 breakpoints were as follows: cefepime, 14%; ceftazidime, 11%; ceftazidime-avibactam, 7%; ceftolozane-tazobactam, 3%; piperacillin-tazobactam, 12%; meropenem, 18%; imipenem, 32%; aztreonam, 23%; ciprofloxacin, 30%; gentamicin, 30%; tobramycin, 12%; amikacin, 18%; and colistin, 4%. Murepavadin MIC₅₀ and MIC₉₀ were 0.12 mg/liter and 2 mg/liter, respectively. There were no apparent clonal clusters associated with resistance, but higher MICs did appear to occur more often in STs with multiple isolates than in single ST isolates. In general, the CF isolates showed a wide genetic distribution. P. aeruginosa CF isolates exhibited the lowest resistance rates against ceftolozane-tazobactam, ceftazidime-avibactam, and colistin. Murepavadin demonstrated the highest activity on a per-weight basis and may therefore become a valuable addition to the currently available antibiotics for treatment of respiratory infection in people with CF.

Mutations in pmrB Confer Cross-Resistance between the LptD Inhibitor POL7080 and Colistin in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a major bacterial pathogen associated with a rising prevalence of antibiotic resistance. We evaluated the resistance mechanisms of P. aeruginosa against POL7080, a species-specific, first-in-class antibiotic in clinical trials that targets the lipopolysaccharide transport protein LptD. We isolated a series of POL7080-resistant strains with mutations in the two-component sensor gene pmrB.

Pseudomonas aeruginosa is a major bacterial pathogen associated with a rising prevalence of antibiotic resistance. We evaluated the resistance mechanisms of P. aeruginosa against POL7080, a species-specific, first-in-class antibiotic in clinical trials that targets the lipopolysaccharide transport protein LptD. We isolated a series of POL7080-resistant strains with mutations in the two-component sensor gene pmrB. Transcriptomic and confocal microscopy studies support a resistance mechanism shared with colistin, involving lipopolysaccharide modifications that mitigate antibiotic cell surface binding.

Emergent Polymyxin Resistance: End of an Era?

Until recently, the polymyxin antibiotics were used sparingly due to dose limiting toxicities. However, the lack of therapeutic alternatives for infections caused by highly resistant Gram-negative bacteria has led to the increased use of the polymyxins. Unfortunately, the world has witnessed increased rates of polymyxin resistance in the last decade, which is likely in part due to its irrational use in human and veterinary medicine. The spread of polymyxin resistance has been aided by the dissemination of the transferable polymyxin-resistance gene, mcr, in humans and the environment. The mortality of colistin-resistant bacteria (CoRB) infections varies in different reports. However, poor clinical outcome was associated with prior colistin treatment, illness severity, complications, and multidrug resistance. Detection of polymyxin resistance in the clinic is possible through multiple robust and practical tests, including broth microdilution susceptibility testing, chromogenic agar testing, and molecular biology assays. There are multiple risk factors that increase a person’s risk for infection with a polymyxin-resistant bacteria, including age, prior colistin treatment, hospitalization, and ventilator support. For patients that are determined to be infected by polymyxin-resistant bacteria, various antibiotic treatment options currently exist. The rising trend of polymyxin resistance threatens patient care and warrants effective control.

DRAMP 2.0, an updated data repository of antimicrobial peptides

Data Repository of Antimicrobial Peptides (DRAMP, http://dramp.cpu-bioinfor.org/ ) is an open-access comprehensive database containing general, patent and clinical antimicrobial peptides (AMPs). Currently DRAMP has been updated to version 2.0, it contains a total of 19,899 entries (newly added 2,550 entries), including 5,084 general entries, 14,739 patent entries, and 76 clinical entries. The update covers new entries, structures, annotations, classifications and downloads. Compared with APD and CAMP, DRAMP contains 14,040 (70.56% in DRAMP) non-overlapping sequences. In order to facilitate users to trace original references, PubMed_ID of references have been contained in activity information. The data of DRAMP can be downloaded by dataset and activity, and the website source code is also available on dedicatedly designed download webpage. Although thousands of AMPs have been reported, only a few parts have entered clinical stage. In the paper, we described several AMPs in clinical trials, including their properties, indications and clinicaltrials.gov identifiers. Finally, we provide the applications of DRAMP in the development of AMPs.

Emerging therapies against infections with Pseudomonas aeruginosa

Infections with Pseudomonas aeruginosa have been marked with the highest priority for surveillance and epidemiological research on the basis of parameters such as incidence, case fatality rates, chronicity of illness, available options for prevention and treatment, health-care utilization, and societal impact. P. aeruginosa is one of the six ESKAPE pathogens that are the major cause of nosocomial infections and are a global threat because of their capacity to become increasingly resistant to all available antibiotics. This review reports on current pre-clinical and clinical advances of anti-pseudomonal therapies in the fields of drug development, antimicrobial chemotherapy, vaccines, phage therapy, non-bactericidal pathoblockers, outer membrane sensitizers, and host defense reinforcement.

Treatment of Infections Due to MDR Gram-Negative Bacteria

The treatment of multidrug-resistant Gram-negative bacteria (MDR-GNB) infections in critically ill patients presents many challenges. Since an effective treatment should be administered as soon as possible, resistance to many antimicrobial classes almost invariably reduces the probability of adequate empirical coverage, with possible unfavorable consequences. In this light, readily available patient's medical history and updated information about the local microbiological epidemiology remain critical for defining the baseline risk of MDR-GNB infections and firmly guiding empirical treatment choices, with the aim of avoiding both undertreatment and overtreatment. Rapid diagnostics and efficient laboratory workflows are also of paramount importance both for anticipating diagnosis and for rapidly narrowing the antimicrobial spectrum, with de-escalation purposes and in line with antimicrobial stewardship principles. Carbapenem-resistant Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii are being reported with increasing frequencies worldwide, although with important variability across regions, hospitals and even single wards. In the past few years, new treatment options, such as ceftazidime/avibactam, meropenem/vaborbactam, ceftolozane/tazobactam, plazomicin, and eravacycline have become available, and others will become soon, which have provided some much-awaited resources for effectively counteracting severe infections due to these organisms. However, their optimal use should be guaranteed in the long term, for delaying as much as possible the emergence and diffusion of resistance to novel agents. Despite important progresses, pharmacokinetic/pharmacodynamic optimization of dosages and treatment duration in critically ill patients has still some areas of uncertainty requiring further study, that should take into account also resistance selection as a major endpoint. Treatment of severe MDR-GNB infections in critically ill patients in the near future will require an expert and complex clinical reasoning, of course taking into account the peculiar characteristics of the target population, but also the need for adequate empirical coverage and the more and more specific enzyme-level activity of novel antimicrobials with respect to the different resistance mechanisms of MDR-GNB.

Pharmacokinetics and Pharmacodynamics of Murepavadin in Neutropenic Mouse Models

Murepavadin (POL7080) represents the first member of a novel class of outer membrane protein-targeting antibiotics. It specifically interacts with LptD and inhibits lipopolysaccharide (LPS) transport. Murepavadin is being developed for the treatment of serious infections by Pseudomonas aeruginosa We determined the plasma protein binding and the pharmacokinetics of murepavadin in plasma and epithelial lining fluid (ELF; pulmonary) in infected animals, and we determined the exposure-response relationship. Treatment of CD-1 neutropenic mice was started 2 h after infection using murepavadin at different dosing frequencies for 24 h, and the number of CFU per lung was determined. The sigmoid maximum-effect model was used to fit the dose-response, and the pharmacodynamic index (PDI) response was used to determine the PDI values, resulting in a static effect and 1-log kill reduction. Using R ² as an indicator of the best fit, the area under the concentration-time curve for the unbound fraction of the drug (fAUC)/MIC ratio correlated best with efficacy. The mean AUC required to provide a static effect was 36.83 mg h/liter (fAUC = 8.25 mg h/liter), and that to provide a 1-log reduction was 44.0 mg h/liter (fAUC = 9.86 mg h/liter). The mean static fAUC/MIC was determined to be 27.78, and that for a 1-log reduction was 39.85. These data may serve to determine doses in humans that are likely to be efficacious.

In Vitro Activity of Ceftazidime-Avibactam and Aztreonam-Avibactam against OXA-48-Carrying Enterobacteriaceae Isolated as Part of the International Network for Optimal Resistance Monitoring (INFORM) Global Surveillance Program from 2012 to 2015

Enterobacteriaceae producing the Ambler class D OXA-48 carbapenemase, combined with additional resistance mechanisms, such as permeability defects or cocarriage of class A, B, or C β-lactamases, can become highly resistant to most β-lactams currently in use, including carbapenems. A total of 45,872 Enterobacteriaceae clinical isolates collected in 39 countries as part of the International Network for Optimal Resistance Monitoring (INFORM) global surveillance study in 2012 to 2015 were tested for susceptibility to β-lactams and comparator agents using the Clinical and Laboratory Standards Institute broth microdilution methodology and screened for the presence of β-lactamases. The bla _OXA-48 and bla _OXA-48-like genes were detected in 333 isolates across 14 species of Enterobacteriaceae collected in 20 countries across the globe. Few agents tested were effective in vitro against the overall collection of OXA-48-producers (n = 265), with tigecycline (MIC₉₀, 2 µg/ml; 92.5% susceptible), ceftazidime-avibactam (MIC₉₀, 4 µg/ml; 92.5% susceptible), and aztreonam-avibactam (MIC₉₀, 0.5 µg/ml; 99.6% of isolates with MIC ≤8 µg/ml) demonstrating the greatest activity. Similarly, colistin (MIC₉₀, 1 µg/ml; 94.2% susceptible), tigecycline (MIC₉₀, 2 µg/ml; 92.6% susceptible), ceftazidime-avibactam (MIC₉₀, >128 µg/ml; 89.7% susceptible), and aztreonam-avibactam (MIC₉₀, 4 µg/ml; 100% of isolates with MIC ≤8 µg/ml) were most active against OXA-48-like-positive isolates (n = 68). The in vitro activity of ceftazidime-avibactam was improved against the subset of metallo-β-lactamase (MBL)-negative, OXA-48- and OXA-48-like-positive isolates (99.2% and 100% susceptible, respectively). The data reported here support the continued investigation of ceftazidime-avibactam and aztreonam-avibactam for the treatment of infections caused by carbapenem-resistant Enterobacteriaceae carrying OXA-48 and OXA-48-like β-lactamases in combination with serine- or metallo-β-lactamases.

Past and Present Perspectives on β-Lactamases

β-Lactamases, the major resistance determinant for β-lactam antibiotics in Gram-negative bacteria, are ancient enzymes whose origins can be traced back millions of years ago. These well-studied enzymes, currently numbering almost 2,800 unique proteins, initially emerged from environmental sources, most likely to protect a producing bacterium from attack by naturally occurring β-lactams. Their ancestors were presumably penicillin-binding proteins that share sequence homology with β-lactamases possessing an active-site serine. Metallo-β-lactamases also exist, with one or two catalytically functional zinc ions. Although penicillinases in Gram-positive bacteria were reported shortly after penicillin was introduced clinically, transmissible β-lactamases that could hydrolyze recently approved cephalosporins, monobactams, and carbapenems later became important in Gram-negative pathogens. Nomenclature is based on one of two major systems. Originally, functional classifications were used, based on substrate and inhibitor profiles. A later scheme classifies β-lactamases according to amino acid sequences, resulting in class A, B, C, and D enzymes. A more recent nomenclature combines the molecular and biochemical classifications into 17 functional groups that describe most β-lactamases. Some of the most problematic enzymes in the clinical community include extended-spectrum β-lactamases (ESBLs) and the serine and metallo-carbapenemases, all of which are at least partially addressed with new β-lactamase inhibitor combinations. New enzyme variants continue to be described, partly because of the ease of obtaining sequence data from whole-genome sequencing studies. Often, these new enzymes are devoid of any phenotypic descriptions, making it more difficult for clinicians and antibiotic researchers to address new challenges that may be posed by unusual β-lactamases.

Pharmacokinetics, Tolerability, and Safety of Murepavadin, a Novel Antipseudomonal Antibiotic, in Subjects with Mild, Moderate, or Severe Renal Function Impairment

This open-label, nonrandomized, single-dose, phase 1 study evaluated the pharmacokinetics and safety of murepavadin, a novel peptide antibiotic for the treatment of serious Pseudomonas aeruginosa infections. The study was conducted in 32 subjects of either sex in 4 groups (up to 8 per group) with mild (group 1), moderate (group 2), and severe (group 3) renal function impairment or with normal renal function (group 4). The degree of renal impairment of the subjects was classified at screening according to the estimated creatinine clearance (CL_Cr) according to the Cockcroft-Gault equation. All subjects received a single 2.2-mg/kg of body weight intravenous infusion of murepavadin administered over 3 h. Exposure to murepavadin in plasma increased in subjects with renal function impairment, with the area under the plasma concentration-time curve from zero to infinity (AUC_0-∞) increasing about 2.0- to 2.5-fold for subjects with renal function impairment compared to subjects with normal renal function, whereas the increases in maximum observed plasma concentration (C_max) were about 1.5-fold for subjects with renal function impairment compared to subjects with normal renal function. The total clearance (CL) of murepavadin was lower in all groups of subjects with renal function impairment, with group means ranging from 2.4 liters/h to 3.8 liters/h, compared to 7.0 liters/h in subjects with normal renal function. Accordingly, the terminal elimination half-life (t_1/2) prolonged up to 24 h with decreasing renal function compared to 7.7 h in subjects with normal renal function. Murepavadin was well tolerated in all renal function groups. As the elimination of murepavadin is affected by renal function, a dose adjustment is warranted in subjects with impaired renal function. (This paper has been registered at ClinicalTrials.gov under identifier NCT02110459.).