Cefiderocol: A Novel Siderophore Cephalosporin against Multidrug-Resistant Gram-Negative Pathogens

Photosensitizer-Amplified Antimicrobial Materials for Broad-Spectrum Ablation of Resistant Pathogens in Ocular Infections

The emergence of multidrug resistant (MDR) pathogens and the scarcity of new potent antibiotics and antifungals are one of the biggest threats to human health. Antimicrobial photodynamic therapy (aPDT) combines light and photosensitizers to kill drug-resistant pathogens; however, there are limited materials that can effectively ablate different classes of infective pathogens. In the present work, a new class of benzodiazole-paired materials is designed as highly potent PDT agents with broad-spectrum antimicrobial activity upon illumination with nontoxic light. The results mechanistically demonstrate that the energy transfer and electron transfer between nonphotosensitive and photosensitive benzodiazole moieties embedded within pathogen-binding peptide sequences result in increased singlet oxygen generation and enhanced phototoxicity. Chemical optimization renders PEP3 as a novel PDT agent with remarkable activity against MDR bacteria and fungi as well as pathogens at different stages of development (e.g., biofilms, spores, and fungal hyphae), which also prove effective in an ex vivo porcine model of microbial keratitis. The chemical modularity of this strategy and its general compatibility with peptide-based targeting agents will accelerate the design of highly photosensitive materials for antimicrobial PDT.

Emerging challenges in antimicrobial resistance: implications for pathogenic microorganisms, novel antibiotics, and their impact on sustainability

Overuse of antibiotics is accelerating the antimicrobial resistance among pathogenic microbes which is a growing public health challenge at the global level. Higher resistance causes severe infections, high complications, longer stays at hospitals and even increased mortality rates. Antimicrobial resistance (AMR) has a significant impact on national economies and their health systems, as it affects the productivity of patients or caregivers due to prolonged hospital stays with high economic costs. The main factor of AMR includes improper and excessive use of antimicrobials; lack of access to clean water, sanitation, and hygiene for humans and animals; poor infection prevention and control measures in hospitals; poor access to medicines and vaccines; lack of awareness and knowledge; and irregularities with legislation. AMR represents a global public health problem, for which epidemiological surveillance systems have been established, aiming to promote collaborations directed at the well-being of human and animal health and the balance of the ecosystem. MDR bacteria such as E. coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus spp., Acinetobacter spp., and Klebsiella pneumonia can even cause death. These microorganisms use a variety of antibiotic resistance mechanisms, such as the development of drug-deactivating targets, alterations in antibiotic targets, or a decrease in intracellular antibiotic concentration, to render themselves resistant to numerous antibiotics. In context, the United Nations issued the Sustainable Development Goals (SDGs) in 2015 to serve as a worldwide blueprint for a better, more equal, and more sustainable existence on our planet. The SDGs place antimicrobial resistance (AMR) in the context of global public health and socioeconomic issues; also, the continued growth of AMR may hinder the achievement of numerous SDGs. In this review, we discuss the role of environmental pollution in the rise of AMR, different mechanisms underlying the antibiotic resistance, the threats posed by pathogenic microbes, novel antibiotics, strategies such as One Health to combat AMR, and the impact of resistance on sustainability and sustainable development goals.

Synthesis, characterisation and antibacterial activity of novel Ga(III) polypyridyl catecholate complexes

Ga(III) polypyridyl catecholate complexes of type [Ga(bipy)2(O,O)](NO3) or [Ga(phen)2(O,O)](NO3) respectively were readily synthesised on reaction of Ga(NO3)3 in methanol with 1 equivalent of catecholate ligand (2,3-DHBA, 3,4-DHBA, 2,3,4-THBA or CafA) and then 2 equivalents of either bipy or phen. The complexes were characterised in full including by X-ray crystallography, which established that the catecholate ligands coordinate the Ga(III) centres in a bidentate manner via the two deprotonated hydroxy groups. All Ga(III) complexes exhibited good in vitro antibacterial activity against the Gram-negative pathogenic bacteria Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa. The complexes were inactive against the Gram-positive pathogenic bacteria Staphylococcus aureus including against a methicillin-resistant Staphylococcus aureus strain (MRSA). [Ga(bipy)2(2,3-DHBA-2H)](NO3)·1.5H2O (1) was shown to be non toxic in vivo in larvae of Galleria mellonella at doses up to 2000 μg mL-1 and to offer protection at doses of 100 and 250 μg mL-1 at 48 and 96 h to larvae infected with P. aeruginosa.

Characterization of blaKPC-2 and blaNDM-1 Plasmids of a K. pneumoniae ST11 Outbreak Clone

The most common resistance mechanism to carbapenems is the production of carbapenemases. In 2021, the Pan American Health Organization warned of the emergence and increase in new carbapenemase combinations in Enterobacterales in Latin America. In this study, we characterized four Klebsiella pneumoniae isolates harboring bla_KPC and bla_NDM from an outbreak during the COVID-19 pandemic in a Brazilian hospital. We assessed their plasmids' transference ability, fitness effects, and relative copy number in different hosts. The K. pneumoniae BHKPC93 and BHKPC104 strains were selected for whole genome sequencing (WGS) based on their pulsed-field gel electrophoresis profile. The WGS revealed that both isolates belong to ST11, and 20 resistance genes were identified in each isolate, including bla_KPC-2 and bla_NDM-1. The bla_KPC gene was present on a ~56 Kbp IncN plasmid and the bla_NDM-1 gene on a ~102 Kbp IncC plasmid, along with five other resistance genes. Although the bla_NDM plasmid contained genes for conjugational transfer, only the bla_KPC plasmid conjugated to E. coli J53, without apparent fitness effects. The minimum inhibitory concentrations (MICs) of meropenem/imipenem against BHKPC93 and BHKPC104 were 128/64 and 256/128 mg/L, respectively. Although the meropenem and imipenem MICs against E. coli J53 transconjugants carrying the bla_KPC gene were 2 mg/L, this was a substantial increment in the MIC relative to the original J53 strain. The bla_KPC plasmid copy number was higher in K. pneumoniae BHKPC93 and BHKPC104 than in E. coli and higher than that of the bla_NDM plasmids. In conclusion, two ST11 K. pneumoniae isolates that were part of a hospital outbreak co-harbored bla_KPC-2 and bla_NDM-1. The bla_KPC-harboring IncN plasmid has been circulating in this hospital since at least 2015, and its high copy number might have contributed to the conjugative transfer of this particular plasmid to an E. coli host. The observation that the bla_KPC-containing plasmid had a lower copy number in this E. coli strain may explain why this plasmid did not confer phenotypic resistance against meropenem and imipenem.

Structural Requirements for Ga3+ Coordination in Synthetic Analogues of the Siderophore Piscibactin Deduced by Chemical Synthesis and Density Functional Theory Calculations

Stereoselective total synthesis of several analogues of piscibactin (Pcb), the siderophore produced by different pathogenic Gram-negative bacteria, was performed. The acid-sensitive α-methylthiazoline moiety was replaced by a more stable thiazole ring, differing in the configuration of the OH group at the C-13 position. The ability of these Pcb analogues to form complexes with Ga³⁺ as a mimic of Fe³⁺ showed that the configuration of the hydroxyl group at C-13 as 13S is crucial for the chelation of Ga³⁺ to preserve the metal coordination, while the presence of a thiazole ring instead of the α-methylthiazoline moiety does not affect such coordination. A complete ¹H and ¹³C NMR chemical shift assignment of the diastereoisomer mixtures around C9/C10 was done for diagnostic stereochemical disposition. Additionally, density functional theory calculations were performed not only for confirming the stereochemistry of the Ga³⁺ complex among the six possible diastereoisomers but also for deducing the ability of these to form octahedral coordination spheres with gallium. Finally, the lack of antimicrobial activity of Pcb and Pcb thiazole analogue Ga³⁺ complexes against Vibrio anguillarum agrees with one of the roles of siderophores in protecting pathogens from metal ion toxicity. The efficient metal coordination shown by this scaffold suggests its possible use as a starting point for the design of new chelating agents or vectors for the development of new antibacterials that exploit the "Trojan horse" strategy using the microbial iron uptake mechanisms. The results obtained will be of great help in the development of biotechnological applications for these types of compounds.

Drug‑resistant Acinetobacter baumannii: From molecular mechanisms to potential therapeutics (Review)

Bacterial drug resistance is increasingly becoming an important problem that needs to be solved urgently in modern clinical practices. Infection caused by Acinetobacter baumannii is a serious threat to the life and health of patients. The drug resistance rate of Acinetobacter baumannii strains is increasing, thus research on the drug resistance of Acinetobacter baumannii has also seen an increase. When patients are infected with drug-resistant Acinetobacter baumannii, the availability of suitable antibiotics commonly used in clinical practices is becoming increasingly limited and the prognosis of patients is worsening. Studying the molecular mechanism of the drug resistance of Acinetobacter baumannii is fundamental to solving the problem of drug-resistant Acinetobacter baumannii and potentially other 'super bacteria'. Drug resistance mechanisms primarily include enzymes, membrane proteins, efflux pumps and beneficial mutations. Research on the underlying mechanisms provides a theoretical basis for the use and development of antibiotics and the development of novel treatment methods.

Antimicrobial Activity of Ceftazidime-Avibactam, Ceftolozane-Tazobactam, Cefiderocol, and Novel Darobactin Analogs against Multidrug-Resistant Pseudomonas aeruginosa Isolates from Pediatric and Adolescent Cystic Fibrosis Patients

The emergence and spread of antimicrobial resistance (AMR) in Gram-negative pathogens, such as carbapenem-resistant Pseudomonas aeruginosa, pose an increasing threat to health care. Patients with immunodeficiencies or chronic pulmonary disease, like cystic fibrosis (CF), are particularly vulnerable to Pseudomonas infections and depend heavily on antibiotic therapy. To broaden limited treatment options, this study evaluated the potency of the recently licensed drugs ceftazidime-avibactam (CZA), ceftolozane-tazobactam (C/T), and cefiderocol (FDC) as well as two novel preclinical antibiotics, darobactins B (DAR B) and B9 (DAR B9), against clinical P. aeruginosa isolates derived from respiratory samples of CF patients. We observed high levels of resistance to all three newly licensed drugs, with cefiderocol exhibiting the best activity. From the 66 investigated P. aeruginosa isolates, a total of 53% were resistant to CZA, 49% to C/T, and 30% to FDC. Strikingly, 52 of the evaluated isolates were obtained from CF patients prior to market introduction of the drugs. Thus, our results suggest that resistance to CZA, C/T, and FDC may be due to preexisting resistance mechanisms. On the other hand, our two novel preclinical compounds performed better than (CZA and C/T) or close to (FDC) the licensed drugs-most likely due to the novel mode of action. Thus, our results highlight the necessity of global consistency in the area of antibiotic stewardship to prevent AMR from further impairing the potency of antibiotics in clinical practice. Ultimately, this study demonstrates the urgency to support the development of novel antimicrobials, preferably with a new mode of action such as darobactins B and B9, two very promising antimicrobial compounds for the treatment of critically ill patients suffering from multidrug-resistant Gram-negative (MRGN) infections. IMPORTANCE Antimicrobial resistance (AMR) represents an ever increasing threat to the health care system. Even recently licensed drugs are often not efficient for the treatment of infections caused by Gram-negative bacteria, like Pseudomonas aeruginosa, a causative agent of lung infections. To address this unmet medical need, innovative antibiotics, which possess a new mode of action, need to be developed. Here, the antibiogram of clinical isolates derived from cystic fibrosis patients was generated and new bicyclic heptapeptides, which inhibit the outer membrane protein BamA, exhibited strong activity, also against multidrug-resistant isolates.

Clinical efficacy and safety of cefiderocol for resistant Gram-negative infections: a real-life, single-centre experience

OBJECTIVES

Cefiderocol is a 'siderophore' cephalosporin active against Gram-negative bacteria, including carbapenem-resistant strains. Data on the use of cefiderocol in real life are limited. We evaluated the efficacy and safety of cefiderocol in the context of our hospital clinical practice.

METHODS

This was a single-centre, observational, retrospective clinical study. We collected data for all patients who received cefiderocol therapy in our hospital, with a focus on clinical outcomes and adverse events.

RESULTS

The study cohort included 28 patients, with a median age of 73 years (25-83 years) and a high burden of co-morbidities. Up to 45 Gram-negative isolates were cultured from the study patients, the most common pathogen being Acinetobacter baumannii (31.1%). Cefiderocol was mostly prescribed for pneumonia (37.8% of cases), bloodstream infection (24.4%), urinary tract infection (22.2%) and intra-abdominal infection (20%), and largely as salvage therapy (92.8%). Of the 18 patients for whom follow-up cultures were available, 14 (77.8%) achieved eradication of the causative micro-organism. Therapeutic success (improvement/resolution of infection) occurred in 64.3% of cases at 7 days and 50% at 14 days from treatment start. Treatment failed in 9 cases (32.1%). No effects on kidney, liver or bone marrow function were observed.

CONCLUSIONS

Cefiderocol showed fair efficacy and excellent tolerability in highly co-morbid patients with a range of multiresistant infections. It may be an option for infections due to colistin-resistant pathogens, when other regimens fail or in cases at risk of kidney dysfunction.

Epidemiology, antimicrobial resistance, and mortality risk factors of carbapenem resistant gram-negative bacteria in hematopoietic stem cell transplantation recipients

Introduction

Carbapenem resistant gram-negative bacteria (CRGNB) infection is more and more frequent in patients after hematopoietic stem cell transplantation (HSCT), and the prognosis is very poor. The purpose of this study was to investigate the clinical characteristics and risk factors for mortality with CRGNB infection in HSCT recipients, and to provide useful information for guiding the application of antibiotics and improving the prognosis in the future.

Methods

Electronic medical records of CRGNB infected patients who underwent HSCT in Xiangya Hospital from January 1, 2015 to June 30, 2022 were collected. At the same time, 1:1 case-control matching was performed according to gender, age and disease type. The epidemiological characteristics and drug resistance of patients with CRGNB infection and non-CRGNB infection were compared. Logistic regression and Cox regression analysis were used to determine the risk factors for CRGNB acquisition and death respectively, and a prediction model of overall survival was constructed by R language.

Results and Discussion

The crude infection rate of CRGNB in HSCT recipients was 7.42%, and the mortality rate was 47.1%. CRGNB was resistant to most commonly used antibiotics. Time interval from diagnosis to transplantation >180 days (HR=7.886, 95% CI 2.624-23.703, P=0.000), septic shock (HR=6.182, 95% CI 2.605-14.671, P=0.000), platelet count < 20 × 10⁹/L (HR=2.615, 95% CI 1.152-5.934, P=0.022) and total bilirubin > 34.2 μmol/L (HR=7.348, 95% CI 2.966-18.202, P=0.000) at the initial stage of infection were 4 independent risk factors associated with mortality. CRGNB infection has become a serious threat to HSCT recipients. Clinicians should pay high attention to it and actively seek personalized treatment strategies suitable for local medical conditions.

Intravenous Fosfomycin: A Potential Good Partner for Cefiderocol. Clinical Experience and Considerations

Multidrug resistant Gram-negative bacteremia represents a therapeutic challenge clinicians have to deal with. This concern becomes more difficult when causing germs are represented by carbapenem resistant Acinetobacter baumannii or difficult-to-treat Pseudomonas aeruginosa. Few antibiotics are available against these cumbersome bacteria, although literature data are not conclusive, especially for Acinetobacter. Cefiderocol could represent a valid antibiotic choice, being a molecule with an innovative mechanism of action capable of overcoming common resistance pathways, whereas intravenous fosfomycin may be an appropriate partner either enhancing cefiderocol activity or avoiding resistance development. Here we report two patients with MDR Gram negative bacteremia who were successfully treated with a cefiderocol/fosfomycin combination.

Fighting antibiotic resistance-strategies and (pre)clinical developments to find new antibacterials

Antibacterial resistance is one of the greatest threats to human health. The development of new therapeutics against bacterial pathogens has slowed drastically since the approvals of the first antibiotics in the early and mid-20^th century. Most of the currently investigated drug leads are modifications of approved antibacterials, many of which are derived from natural products. In this review, we highlight the challenges, advancements and current standing of the clinical and preclinical antibacterial research pipeline. Additionally, we present novel strategies for rejuvenating the discovery process and advocate for renewed and enthusiastic investment in the antibacterial discovery pipeline.

Efficacy of Cefiderocol in Experimental Stenotrophomonas maltophilia Pneumonia in Persistently Neutropenic Rabbits

Stenotrophomonas maltophilia is an important cause of pneumonia in immunocompromised patients. Cefiderocol is a parenteral siderophore cephalosporin with potent in vitro activity against S. maltophilia. We evaluated the efficacy of cefiderocol in a neutropenic rabbit model of S. maltophilia pneumonia in comparison to trimethoprim-sulfamethoxazole (TMP-SMX). The cefiderocol area under the plasma drug concentration-time curve extrapolated to 8 h (AUC_0–8) was lower (423.0 ± 40.9 μg·h/mL versus 713.6 ± 40.1 μg·h/mL) and clearance higher (252.77 ± 38.9 mL/h/kg versus 142.6 ± 32.9 mL/h/kg) in infected versus noninfected rabbits. We studied a clinical bloodstream S. maltophilia isolate with an MIC of 0.03 μg/mL of cefiderocol. Time spent above the MIC of cefiderocol for the majority of S. maltophilia isolates in rabbits recapitulated the plasma concentration-time profile observed in adult humans at the licensed dose of 2 g given intravenously (i.v.). Experimental groups consisted of 120 mg/kg cefiderocol i.v. every 8 hours (q8h); TMP-SMX, 5 mg/kg i.v. Q12h, and untreated controls (UCs). Treatment was administered for 10 days. Survival in cefiderocol-treated rabbits (87%) was greater than that in TMP-SMX-treated (25%; P < 0.05) and UC (0%; P < 0.05) groups. There was no residual bacterial burden in lung tissue or bronchoalveolar lavage (BAL) fluid in the cefiderocol group. Residual bacterial burden was present in lung tissue and BAL fluid in the TMP-SMX group but was decreased in comparison to UCs (P < 0.001). Lung weights (markers of pulmonary injury) were decreased in cefiderocol-treated versus TMP-SMX (P < 0.001) and UC (P < 0.001) groups. Cefiderocol is highly active in treatment of experimental S. maltophilia pneumonia, laying the foundation for future clinical investigations against this lethal infection in immunocompromised patients.

Epidemiology, Mechanisms of Resistance and Treatment Algorithm for Infections Due to Carbapenem-Resistant Gram-Negative Bacteria: An Expert Panel Opinion

Antimicrobial resistance represents a serious threat for global health, causing an unacceptable burden in terms of morbidity, mortality and healthcare costs. In particular, in 2017, carbapenem-resistant organisms were listed by the WHO among the group of pathogens for which novel treatment strategies are urgently needed. Fortunately, several drugs and combinations have been introduced in recent years to treat multi-drug-resistant (MDR) bacteria. However, a correct use of these molecules is needed to preserve their efficacy. In the present paper, we will provide an overview on the epidemiology and mechanisms of resistance of the most common MDR Gram-negative bacteria, proposing a treatment algorithm for the management of infections due to carbapenem-resistant bacteria based on the most recent clinical evidence.

Emergence of High-Level Cefiderocol Resistance in Carbapenem-Resistant Klebsiella pneumoniae from Bloodstream Infections in Patients with Hematologic Malignancies in China

Cefiderocol is a novel siderophore cephalosporin exhibiting potent antimicrobial activities. Although cefiderocol has not been approved in China, resistance is emerging. A multicenter study was performed to evaluate the cefiderocol resistance in carbapenem-resistant Klebsiella pneumoniae (CRKP) strains from bloodstream infections in patients with hematologic malignancies in China. Clinical data analysis and whole-genome sequencing were conducted for collected cefiderocol-resistant CRKP strains. CRISPR-Cas9 system was employed to construct site-specific mutagenesis for gene cirA. Plasmid curing and cloning were performed to assess the effect of β-lactamases on cefiderocol resistance. Total 86 CRKP strains were collected. The MICs of cefiderocol ranged from 0.06 to >256 mg/L. Among four cefiderocol-nonsusceptible strains (4/86, 4.7%), two cefiderocol-resistant strains AR8538 (MIC = 32 mg/L) and AR8416 (MIC > 256 mg/L) were isolated from two patients with acute lymphocytic leukemia (frequency of resistance, 2/86, 2.3%). Metallo- and serine-β-lactamase inhibitors addition would decrease the MIC of cefiderocol from 32 to 1 mg/L in AR8538, which harbors blaSHV-12, blaDHA-1, and two copies of blaNDM-1 in different plasmids. Avibactam did not impact cefiderocol susceptibility of AR8416, which produces NDM-5. However, we found a deficient CirA in AR8416. Using the same K serotype strain D3, we proved CirA deficiency or carrying NDM individually reduced cefiderocol susceptibility, but their simultaneously existence rendered a high-level cefiderocol resistance. In summary, the resistance of CRKP against cefiderocol is mediated by multiple factors, including the deficiency of CirA, metallo- or serine-β-lactamases, while a high-level cefiderocol resistance could be rendered by the combined effect of NDM expression and CirA deficiency. IMPORTANCE Cefiderocol-resistant CRKP strains are emerging in bloodstream infections in Chinese patients with hematologic malignancies, although cefiderocol has not been approved for clinical use in China. Our study proved that the resistance of CRKP against cefiderocol is mediated by multiple factors, including the deficiency of CirA, metallo- or serine-β-lactamases, while a high-level cefiderocol resistance could be rendered by the combined effect of NDM expression and CirA deficiency. As NDM production is one of the most critical mechanisms resulting in carbapenem resistance, it would pose great challenges on the clinical efficacy of cefiderocol in future.

Pharmacokinetics, Pharmacodynamics, and Dose Optimization of Cefiderocol during Continuous Renal Replacement Therapy

BACKGROUND

The need for continuous renal replacement therapy (CRRT) in critically ill patients with serious infections is associated with clinical failure, emergence of resistance, and excess mortality. These poor outcomes are attributable in large part to subtherapeutic antimicrobial exposure and failure to achieve target pharmacokinetic/pharmacodynamic (PK/PD) thresholds during CRRT. Cefiderocol is a novel siderophore cephalosporin with broad in vitro activity against resistant pathogens and is often used to treat critically ill patients, including those receiving CRRT, despite the lack of data to guide dosing in this population.

OBJECTIVE

The aim of this study was to evaluate the PK and PD of cefiderocol during in vitro and in vivo CRRT and provide optimal dosing recommendations.

METHODS

The PK and dialytic clearance of cefiderocol was evaluated via an established in vitro CRRT model across various modes, filter types, and effluent flow rates. These data were combined with in vivo PK data from nine patients receiving cefiderocol while receiving CRRT from phase III clinical trials. Optimal dosing regimens and their respective probability of target attainment (PTA) were assessed via an established population PK model with Bayesian estimation and 1000-subject Monte Carlo simulations at each effluent flow rate.

RESULTS

The overall mean sieving/saturation coefficient during in vitro CRRT was 0.90 across all modes, filter types, effluent flow rates, and points of replacement fluid dilution tested. Adsorption was negligible at 10.9%. Three-way analysis of variance (ANOVA) and multiple linear regression analyses demonstrated that effluent flow rate is the primary driver of clearance during CRRT and can be used to calculate optimal cefiderocol doses required to match the systemic exposure observed in patients with normal renal function. Bayesian estimation of these effluent flow rate-based optimal doses in nine patients receiving CRRT from the phase III clinical trials of cefiderocol revealed comparable mean (± standard deviation) area under the concentration-time curve values as patients with normal renal function (1709 ± 539 mg·h/L vs. 1494 ± 58.4 mg·h/L; p = 0.26). Monte Carlo simulations confirmed these doses achieved >90% PTA against minimum inhibitory concentrations ≤4 mg/L at effluent flow rates from 0.5 to 5 L/h.

CONCLUSION

The optimal dosing regimens developed from this work have been incorporated into the prescribing information for cefiderocol, making it the first and only antimicrobial with labeled dosing for CRRT. Future clinical studies are warranted to confirm the efficacy and safety of these regimens.

Infections Due to Acinetobacter baumannii-calcoaceticus Complex: Escalation of Antimicrobial Resistance and Evolving Treatment Options

Bacteria within the genus Acinetobacter (principally A. baumannii-calcoaceticus complex [ABC]) are gram-negative coccobacilli that most often cause infections in nosocomial settings. Community-acquired infections are rare, but may occur in patients with comorbidities, advanced age, diabetes mellitus, chronic lung or renal disease, malignancy, or impaired immunity. Most common sites of infections include blood stream, skin/soft-tissue/surgical wounds, ventilator-associated pneumonia, orthopaedic or neurosurgical procedures, and urinary tract. Acinetobacter species are intrinsically resistant to multiple antimicrobials, and have a remarkable ability to acquire new resistance determinants via plasmids, transposons, integrons, and resistance islands. Since the 1990s, antimicrobial resistance (AMR) has escalated dramatically among ABC. Global spread of multidrug-resistant (MDR)-ABC strains reflects dissemination of a few clones between hospitals, geographic regions, and continents; excessive antibiotic use amplifies this spread. Many isolates are resistant to all antimicrobials except colistimethate sodium and tetracyclines (minocycline or tigecycline); some infections are untreatable with existing antimicrobial agents. AMR poses a serious threat to effectively treat or prevent ABC infections. Strategies to curtail environmental colonization with MDR-ABC require aggressive infection-control efforts and cohorting of infected patients. Thoughtful antibiotic strategies are essential to limit the spread of MDR-ABC. Optimal therapy will likely require combination antimicrobial therapy with existing antibiotics as well as development of novel antibiotic classes.

New Antibiotics for Hospital-Acquired Pneumonia and Ventilator-Associated Pneumonia

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) represent one of the most common hospital-acquired infections, carrying a significant morbidity and risk of mortality. Increasing antibiotic resistance among the common bacterial pathogens associated with HAP and VAP, especially Enterobacterales and nonfermenting gram-negative bacteria, has made the choice of empiric treatment of these infections increasingly challenging. Moreover, failure of initial empiric therapy to cover the causative agents associated with HAP and VAP has been associated with worse clinical outcomes. This review provides an overview of antibiotics newly approved or in development for the treatment of HAP and VAP. The approved antibiotics include ceftobiprole, ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, and cefiderocol. Their major advantages include their high activity against multidrug-resistant gram-negative pathogens.

Analysis of the clinical pipeline of treatments for drug resistant bacterial infections: despite progress, more action is needed

There is an urgent global need for new strategies and drugs to control and treat multidrug-resistant bacterial infections. In 2017, the World Health Organization (WHO) released a list of 12 antibiotic-resistant priority pathogens and began to critically analyze the antibacterial clinical pipeline. This review analyzes “traditional” and “nontraditional” antibacterial agents and modulators in clinical development current on 30 June 2021 with activity against the WHO priority pathogens mycobacteria and Clostridioides difficile. Since 2017, 12 new antibacterial drugs have been approved globally, but only vaborbactam belongs to a new antibacterial class. Also innovative is the cephalosporin derivative cefiderocol, which incorporates an iron-chelating siderophore that facilitates Gram-negative bacteria cell entry. Overall, there were 76 antibacterial agents in clinical development (45 traditional and 31 nontraditional), with 28 in phase 1, 32 in phase 2, 12 in phase 3, and 4 under regulatory evaluation. Forty-one out of 76 (54%) targeted WHO priority pathogens, 16 (21%) were against mycobacteria, 15 (20%) were against C. difficile, and 4 (5%) were nontraditional agents with broad-spectrum effects. Nineteen of the 76 antibacterial agents have new pharmacophores, and 4 of these have new modes of actions not previously exploited by marketed antibacterial drugs. Despite there being 76 antibacterial clinical candidates, this analysis indicated that there were still relatively few clinically differentiated antibacterial agents in late-stage clinical development, especially against critical-priority pathogens. We believe that future antibacterial research and development (R&D) should focus on the development of innovative and clinically differentiated candidates that have clear and feasible progression pathways to the market.

Clinical Pharmacokinetics and Pharmacodynamics of Cefiderocol

Cefiderocol is a new broad-spectrum cephalosporin antibiotic with promising activity against various Gram-negative bacteria including carbapenem-resistant strains. A chlorocatechol group in the C-3 side chain provides cefiderocol with a siderophore activity, improving its stability against β-lactamases and facilitating the transportation of cefiderocol across outer bacterial membranes. Cefiderocol shows linear pharmacokinetics over a broad range of clinically relevant doses, with unchanged renal excretion constituting the main route of elimination. Geometric means (coefficient of variation) of the volume of distribution and clearance in individuals with normal kidney function were 15.8 (15%) L and 4.70 (27%) L/h, respectively. In patients with end-stage renal disease, clearance was 1.10 (24%) L/h. Time above the minimum inhibitory concentration is the main predictor of efficacy. There is no evidence for clinically relevant interactions of cefiderocol with other drugs mediated by metabolizing enzymes or drug transporters. Simulations based on population pharmacokinetic modeling suggest that dosing regimens should be adjusted based on kidney function to optimize therapeutic exposure to cefiderocol. Clinical efficacy trials indicated that cefiderocol is non-inferior to imipenem/cilastatin in the treatment of complicated urinary tract infections and acute uncomplicated pyelonephritis, and to meropenem in the treatment of nosocomial pneumonia. In the one study currently available, cefiderocol performed similarly to the best available therapy in the treatment of severe carbapenem-resistant Gram-negative infections regarding clinical and microbiological efficacy. In summary, cefiderocol shows favorable pharmacokinetic/pharmacodynamic properties and an acceptable safety profile, suggesting that cefiderocol might be a viable option to treat infections with bacteria resistant to other antibiotics.

Contemporary Perspective on the Treatment of Acinetobacter baumannii Infections: Insights from the Society of Infectious Diseases Pharmacists

The purpose of this narrative review is to bring together the most recent epidemiologic, preclinical, and clinical findings to offer our perspective on best practices for managing patients with A. baumannii infections with an emphasis on carbapenem-resistant A. baumannii (CRAB). To date, the preferred treatment for CRAB infections has not been defined. Traditional agents with retained in vitro activity (aminoglycosides, polymyxins, and tetracyclines) are limited by suboptimal pharmacokinetic characteristics, emergence of resistance, and/or toxicity. Recently developed and US Food and Drug Administration (FDA)-approved β-lactam/β-lactamase inhibitor agents do not provide enhanced activity against CRAB. On balance, cefiderocol and eravacycline demonstrate potent in vitro activity and are well tolerated, but clinical data for patients with CRAB infections do not yet support widespread use. Given that CRAB has the capacity to infect vulnerable patients and preferred regimens have not been identified, we advocate for combination therapy. Our preferred regimen for critically ill patients infected, or considered to be at high risk for CRAB, includes meropenem, polymyxin B, and ampicillin/sulbactam. Importantly, site of infection, severity of illness, and local epidemiology are essential factors to be considered in selecting combination therapies. Molecular mechanisms of resistance may unveil preferred combinations at individual centers; however, such data are often unavailable to treating clinicians and have not been linked to improved clinical outcomes. Combination strategies may also pose an increased risk for antibiotic toxicity and Clostridioides difficile infection, and should therefore be balanced by understanding patient goals of care and underlying health conditions. Promising therapies that are in clinical development and/or under investigation include durlobactam-sulbactam, cefiderocol combination regimens, and bacteriophage therapy, which may over time eliminate the need for the continued use of polymyxins. Future goals for CRAB management include pathogen-focused treatment paradigms that are based on molecular mechanisms of resistance, local susceptibility rates, and the availability of well-tolerated, effective treatment options.

FrpA is the outer membrane piscibactin transporter in Vibrio anguillarum: structural elements in synthetic piscibactin analogues required for transport

Piscibactin (Pcb) is a labile siderophore widespread among Vibrionaceae. Its production is a major virulence factor of some fish pathogens such as Photobacterium damselae subsp. piscicida and Vibrio anguillarum. Although FrpA was previously suggested as the putative outer membrane transporter (OMT) for ferri-piscibactin, its role in piscibactin uptake was never demonstrated. In this work, we generated mutants of V. anguillarum defective in FrpA and analyzed their ability to use piscibactin as iron source. The results showed that inactivation of frpA completely disables piscibactin utilization, and the original phenotype could be restored by gene complementation, confirming that FrpA is the OMT that mediates ferri-Pcb uptake. Additionally, the ability of several Pcb thiazole analogues, with different configurations at positions 9, 10, and 13, to be internalized through FrpA, was evaluated measuring their ability to promote growth under iron deficiency of several indicator strains. The results showed that while those analogues with a thiazole ring maintain almost the same activity as Pcb, the maintenance of the hydroxyl group present in natural piscibactin configuration at position C-13 is crucial for Fe³⁺ chelation and, in consequence, for the recognition of the ferri-siderophore by the cognate OMT. All these findings allowed us to propose a Pcb analogue as a good candidate to vectorize antimicrobial compounds, through the Trojan horse strategy, to develop novel compounds against bacterial fish diseases.

Escalating antimicrobial resistance among Enterobacteriaceae: focus on carbapenemases

Introduction: Over the past few decades, antimicrobial resistance (AMR) has skyrocketed globally among bacteria within the Family Enterobacteriaceae (i.e. Enterobacter spp, Klebsiella spp, Escherichia coli, Proteus spp, Serratia marcescens, Citrobacter spp, and others). Enterobacteriaceae are intestinal flora and are important pathogens in nosocomial and community settings. Enterobacteriaceae spread easily between humans and may acquire AMR via plasmids or other mobile resistance elements. The emergence and spread of multidrug resistant (MDR) clones have greatly limited therapeutic options. Some infections are untreatable with existing antimicrobials.Areas covered: The authors discuss the escalation of CRE globally, the epidemiology and outcomes of CRE infections, the optimal therapy, and the potential role of several new antimicrobials to combat MDR organisms. An exhaustive search for literature related to Enterobacteriaceae was performed using PubMed, using the following key words: antimicrobial resistance; carbapenemases; Enterobacterales; Enterobacteriaceae; Klebsiella pneumoniae; Escherichia coli; global epidemiology; metallo-β-lactamases; multidrug resistance; New Delhi Metalloproteinase-1 (NDM-1); plasmidsExpert opinion: Innovation and development of new classes of antibacterial agents are critical to expand effective therapeutic options. The authors encourage the judicious use of antibiotics and aggressive infection-control measures are essential to minimize the spread of AMR.

New drugs for difficult bugs: management of multidrug-resistant gram-negative infections in solid organ transplant recipients

PURPOSE OF REVIEW

Multidrug-resistant Gram-negative bacteria remain a significant threat to patient and allograft survival. Management of these infections in solid organ transplant (SOT) recipients remains challenging due to a limited antimicrobial pipeline and reliance on novel agents, which have not been systematically evaluated in the transplant population.

RECENT FINDINGS

Novel antimicrobials, including the second-generation β-lactam/β-lactamase inhibitors, cefiderocol, plazomicin and eravacycline, have been developed to combat infections due to multidrug-resistant Gram-negative infections, but each has microbiologic and therapeutic niches and warrant further study in SOT recipients.

SUMMARY

This review summarizes therapeutic options for extended-spectrum β-lactamase-producing Enterobacterales, carbapenem-resistant Enterobacterales and Pseudomonas aeruginosa with difficult-to-treat resistance in SOT recipients and emphasizes recently approved antimicrobial agents.

The Whole Is Bigger than the Sum of Its Parts: Drug Transport in the Context of Two Membranes with Active Efflux

Cell envelope plays a dual role in the life of bacteria by simultaneously protecting it from a hostile environment and facilitating access to beneficial molecules. At the heart of this ability lie the restrictive properties of the cellular membrane augmented by efflux transporters, which preclude intracellular penetration of most molecules except with the help of specialized uptake mediators. Recently, kinetic properties of the cell envelope came into focus driven on one hand by the urgent need in new antibiotics and, on the other hand, by experimental and theoretical advances in studies of transmembrane transport. A notable result from these studies is the development of a kinetic formalism that integrates the Michaelis-Menten behavior of individual transporters with transmembrane diffusion and offers a quantitative basis for the analysis of intracellular penetration of bioactive compounds. This review surveys key experimental and computational approaches to the investigation of transport by individual translocators and in whole cells, summarizes key findings from these studies and outlines implications for antibiotic discovery. Special emphasis is placed on Gram-negative bacteria, whose envelope contains two separate membranes. This feature sets these organisms apart from Gram-positive bacteria and eukaryotic cells by providing them with full benefits of the synergy between slow transmembrane diffusion and active efflux.

Mechanisms of Antibiotic Resistance in Important Gram-Positive and Gram-Negative Pathogens and Novel Antibiotic Solutions

Multidrug-resistant bacteria have on overwhelming impact on human health, as they cause over 670,000 infections and 33,000 deaths annually in the European Union alone. Of these, the vast majority of infections and deaths are caused by only a handful of species-multi-drug resistant Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus spp., Acinetobacter spp. and Klebsiella pneumoniae. These pathogens employ a multitude of antibiotic resistance mechanisms, such as the production of antibiotic deactivating enzymes, changes in antibiotic targets, or a reduction of intracellular antibiotic concentration, which render them insusceptible to multiple antibiotics. The purpose of this review is to summarize in a clinical manner the resistance mechanisms of each of these 6 pathogens, as well as the mechanisms of recently developed antibiotics designed to overcome them. Through a basic understanding of the mechanisms of antibiotic resistance, the clinician can better comprehend and predict resistance patterns even to antibiotics not reported on the antibiogram and can subsequently select the most appropriate antibiotic for the pathogen in question.

Clinical efficacy and safety of cefiderocol in the treatment of acute bacterial infections: A systematic review and meta-analysis of randomised controlled trials

OBJECTIVES

The aim of this study was to investigate the clinical efficacy and safety of cefiderocol in the treatment of acute bacterial infections.

METHODS

The PubMed, Embase and Cochrane Library databases as well as the clinical trials registries of ClinicalTrials.gov and the WHO International Clinical Trials Registry Platform were searched up to 8 November 2020. Only randomised controlled trials (RCTs) that compared the treatment efficacy of cefiderocol with that of other antibiotics for adult patients with acute bacterial infections were included in this meta-analysis. The primary outcome was clinical response at test of cure (TOC).

RESULTS

Three RCTs, including one phase 2 and two phase 3 trials, were included. No significant difference in clinical response rate was observed between cefiderocol and comparators [odds ratio (OR)=1.04]. In a subgroup analysis, no significant difference was observed in the clinical response at TOC between cefiderocol and comparators in patients with nosocomial pneumonia (OR=0.92) or complicated urinary tract infection (OR=1.28). In addition, all-cause mortality at Days 14 and 28 did not differ between the cefiderocol and control groups (14-day mortality, OR=1.25; 28-day mortality, OR=1.12). Furthermore, cefiderocol was associated with similar microbiological response to comparators at the TOC assessment (OR=1.44). Finally, cefiderocol was associated with a similar risk of adverse events as comparators.

CONCLUSION

Cefiderocol can achieve similar clinical and microbiological responses as comparators for patients with serious bacterial infections. In addition, cefiderocol shares a safety profile similar to that of comparators.

The Odd Couple(s): An Overview of Beta-Lactam Antibiotics Bearing More Than One Pharmacophoric Group

β-lactam antibiotics are among the most important and widely used antimicrobials worldwide and are comprised of a large family of compounds, obtained by chemical modifications of the common scaffolds. Usually these modifications include the addition of active groups, but less frequently, molecules were synthesized in which either two β-lactam rings were joined to create a single bifunctional compound, or the azetidinone ring was joined to another antibiotic scaffold or another molecule with a different activity, in order to create a molecule bearing two different pharmacophoric functions. In this review, we report some examples of these derivatives, highlighting their biological properties and discussing how this strategy can lead to the development of innovative antibiotics that can represent either novel weapons against the rampant increase of antimicrobial resistance, or molecules with a broader spectrum of action.

In vitro and in vivo activity of GT-1, a novel siderophore cephalosporin, and GT-055, a broad-spectrum β-lactamase inhibitor, against biothreat and ESKAPE pathogens

Antimicrobial-resistance (AMR) has become an increasingly difficult issue to overcome for bacteria associated with both community- and hospital-acquired infections as well as potential biodefense threats. The need to identify new therapeutics of novel classes and/or with unique mechanisms is critical to combatting AMR in the coming years. GT-1 (LCB10-0200), a siderophore-linked cephalosporin, is one such novel option and is formulated to be used either alone or in combination with a novel broad-spectrum β-lactamase inhibitor, GT-055 (LCB18-055). This study assessed the in vitro and in vivo efficacy of GT-1 and GT-055 against a broad array of multi-drug resistant and biothreat pathogens. Here, we demonstrated sub-4 µg ml^-1 efficacy against a number of pathogens in vitro. We further determined that in mice infected via aerosol route with Yersinia pestis, efficacy of GT-1/GT-055 treatment is at least equivalent to the comparator antibiotic, ciprofloxacin.