[Cefiderocol: a first and novel class of siderophore cephalosporin for Carbapenem-resistant Gram-negative infection].

Antimicrobial resistance is currently recognized as an urgent concern against public health in worldwide. Carbapenem-resistant (CR) Gram-negative bacteria, such as Enterobacterales, Pseudomonas aeruginosa and Acinetobacter baumannii are listed as critical pathogens which are widely spread and can cause severe and often deadly infections in WHO guidance. Cefiderocol (Fetroja®), a novel and first siderophore cephalosporin, was approved for the infections caused by these problematic CR Gram-negative bacteria in Japan on November 30, 2023. Cefiderocol has unique mechanisms to be incorporated into bacterial cells using bacterial iron transportation system and to be highly stable against most ß-lactamases, which lead to promising antibacterial activity against these Gram-negative bacteria including CR strains in vitro. In CREDIBLE-CR Ph3 trial, cefiderocol showed the good efficacy and safety for patients with CR Gram-negative bacteria. In APEKS-cUTI and APEKS-NP trials, cefiderocol showed non-inferiority and suggested superiority to imipenem/cilastatin in complicated urinary tract infection (cUTI) patients, and non-inferiority to high dose of meropemen in pneumonia patients, respectively. Cefiderocol is expected to be an optimal treatment for CR Gram-negative infections with limited treatment options and would be an important drug to combat the threat of CR bacteria.

Commercially available tests for determining cefiderocol susceptibility display variable performance in the Achromobacter genus.

BACKGROUND: Cefiderocol is a siderophore-conjugated cephalosporin increasingly used in the management of Achromobacter infections. Testing for cefiderocol susceptibility is challenging with distinct recommendations depending on the pathogens. OBJECTIVES: We evaluated the performance of commercial tests for testing cefiderocol susceptibility in the Achromobacter genus and reviewed the literature. METHODS: Diffusion (disks, MIC gradient test strips [MTS], Liofilchem) and broth microdilution (BMD) methods (ComASP™, Liofilchem; UMIC®, Bruker) were compared with the BMD reference method according to the EUCAST guidelines on 143 Achromobacter strains from 14 species with MIC50/90 of ≤ 0.015/0.5 mg/L. A literature search was conducted regardless of method or species. RESULTS: None of the methods tested fulfilled an acceptable essential agreement (EA). MTS displayed the lowest EA (30.8%) after UMIC® (49%) and ComASP™ (76.9%). All methods achieved an acceptable bias, with MICs either underestimated using MTS (-1.3%) and ComASP™ (-14.2%) or overestimated with UMIC® (+ 9.1%). Inhibition zone diameters ranged from 6 to 38 mm (IZD50/90=33/30 mm). UMIC® and ComASP™ failed to categorize one or the two cefiderocol-resistant strains of this study as resistant unlike the diffusion-based methods. The literature review highlighted distinct performance of the available methods according to pathogens and testing conditions. CONCLUSIONS: The use of MTS is discouraged for Achromobacter spp. Disk diffusion can be used to screen for susceptible strains by setting a threshold diameter of 30 mm. UMIC® and ComASP™ should not be used as the sole method but have to be systematically associated with disk diffusion to detect the yet rarely described cefiderocol-resistant Achromobacter sp. strains.

Evaluation and optimization of sample size of neonates and infants for pediatric clinical studies on cefiderocol using a model-based approach.

When planning pediatric clinical trials, optimizing the sample size of neonates/infants is essential because it is difficult to enroll these subjects. In this simulation study, we evaluated the sample size of neonates/infants using a model-based optimal approach for identifying their pharmacokinetics for cefiderocol. We assessed the usefulness of data for estimation performance (accuracy and variance of parameter estimation) from adults and the impact of data from very young subjects, including preterm neonates. Stochastic simulation and estimation were utilized to assess the impact of sample size allocation for age categories in estimation performance for population pharmacokinetic parameters in pediatrics. The inclusion of adult pharmacokinetic information improved the estimation performance of population pharmacokinetic parameters as the coefficient of variation (CV) range of parameter estimation decreased from 4.9%-593.7% to 2.3%-17.3%. When sample size allocation was based on the age groups of gestational age and postnatal age, the data showed 15 neonates/infants would be necessary to appropriately estimate pediatric pharmacokinetic parameters (<20%CV). By using the postmenstrual age (PMA), which is theoretically considered to be associated with the maturation of organs, the number of neonates/infants required for appropriate parameter estimation could be reduced to seven (one and six with <32 and >32 weeks PMA, respectively) to nine (three and six with <37 and >37 weeks PMA, respectively) subjects. The model-based optimal design approach allowed efficient evaluation of the sample size of neonates/infants for estimation of pediatric pharmacokinetic parameters. This approach to assessment should be useful when designing pediatric clinical trials, especially those including young children.

Location, Location, Location: Establishing Design Principles for New Antibacterials from Ferric Siderophore Transport Systems.

This review strives to assemble a set of molecular design principles that enables the delivery of antibiotic warheads to Gram-negative bacterial targets (ESKAPE pathogens) using iron-chelating siderophores, known as the Trojan Horse strategy for antibiotic development. Principles are derived along two main lines. First, archetypical siderophores and their conjugates are used as case studies for native iron transport. They enable the consideration of the correspondence of iron transport and antibacterial target location. The second line of study charts the rationale behind the clinical antibiotic cefiderocol. It illustrates the potential versatility for the design of new Trojan Horse-based antibiotics. Themes such as matching the warhead to a location where the siderophore delivers its cargo (i.e., periplasm vs. cytoplasm), whether or not a cleavable linker is required, and the relevance of cheaters to the effectiveness and selectivity of new conjugates will be explored. The effort to articulate rules has identified gaps in the current understanding of iron transport pathways and suggests directions for new investigations.

Synergistic Activity of Cefiderocol in Combination with Avibactam, Sulbactam or Tazobactam against Carbapenem-Resistant Gram-Negative Bacteria.

We investigated the activity of cefiderocol/ß-lactamase inhibitor combinations against clinical strains with different susceptibility profiles to cefiderocol to explore the potentiality of antibiotic combinations as a strategy to contain the major public health problem of multidrug-resistant (MDR) pathogens. Specifically, we evaluated the synergistic activity of cefiderocol with avibactam, sulbactam, or tazobactam on three of the most "Critical Priority" group of MDR bacteria (carbapenem-resistant Enterobacterales, Pseudomonas aeruginosa, and Acinetobacter baumannii). Clinical isolates were genomically characterized by Illumina iSeq 100. The synergy test was conducted with time-kill curve assays. Specifically, cefiderocol/avibactam, /sulbactam, or /tazobactam combinations were analyzed. Synergism was assigned if bacterial grow reduction reached 2 log10 CFU/mL. We reported the high antimicrobial activity of the cefiderocol/sulbactam combination against carbapenem-resistant Enterobacterales, P. aeruginosa, and A. baumannii; of the cefiderocol/avibactam combination against carbapenem-resistant Enterobacterales; and of the cefiderocol/tazobactam combination against carbapenem-resistant Enterobacterales and P. aeruginosa. Our results demonstrate that all ß-lactamase inhibitors (BLIs) tested are able to enhance cefiderocol antimicrobial activity, also against cefiderocol-resistant isolates. The cefiderocol/sulbactam combination emerges as the most promising combination, proving to highly enhance cefiderocol activity in all the analyzed carbapenem-resistant Gram-negative isolates, whereas the Cefiderocol/tazobactam combination resulted in being active only against carbapenem-resistant Enterobacterales and P. aeruginosa, and cefiderocol/avibactam was only active against carbapenem-resistant Enterobacterales.

Predicting early appropriate therapy for patients infected by carbapenem-resistant Gram-negative pathogens in intensive care units in Italy.

BACKGROUND: Antibiotic resistance among Gram-negative bacteria in intensive care units (ICUs) is linked with high morbidity and mortality in patients. In this study, we estimated the therapeutic coverage of various antibiotics, focusing on cefiderocol and comparators, administered empirically against an infection of unknown origin in the ICU. METHODS: In the ARTEMIS surveillance study, susceptibilities of 624 Italian Gram-negative isolates to amikacin, aztreonam-avibactam, cefiderocol, ceftazidime-avibactam, ceftolozane-tazobactam, colistin, imipenem-relebactam, meropenem, and meropenem-vaborbactam were tested by broth microdilution, and results were interpreted by European Committee on Antimicrobial Susceptibility Testing breakpoints. The susceptibility rates from the ARTEMIS study were extrapolated to Gram-negative isolates obtained from 5,774 patients in Italian ICUs in 2021. The sum of the predicted susceptibilities of individual pathogens represented the overall likelihood of in vitro activity of each antibiotic as early targeted therapy for ICU patients. RESULTS: A total of 624 Italian Gram-negative isolates included 206 Pseudomonas aeruginosa, 138 Acinetobacter baumannii, 187 Klebsiella pneumoniae, and 93 Escherichia coli. Against A. baumannii, K. pneumoniae, P. aeruginosa, and E. coli, the overall susceptibility rates for cefiderocol were 87.7%, 96.8%, 99%, and 100%, respectively; and for comparator agents, 8.7-96.4%, 25.7-100%, 73.3-100%, and 89.2-100%, respectively. Among the subset of meropenem-resistant isolates, susceptibility rates of A. baumannii, K. pneumoniae, and P. aeruginosa to cefiderocol were 86.4%, 96.2% and 100%, respectively. Corresponding susceptibility rates to comparator agents were 0-96.8%, 0-100%, and 6.4-100%, respectively. There were no meropenem-resistant isolates of E. coli. The extrapolation of data to isolates from Italian ICUs showed that the highest likelihood of therapeutic coverage, both overall and among meropenem-resistant isolates, was reported for colistin (96.8% and 72.2%, respectively) and cefiderocol (95.7% and 71.4%, respectively). All other antibiotics were associated with a likelihood below 73% overall and between 0% and 41.4% for meropenem-resistant isolates. CONCLUSIONS: Based on confirmed susceptibility rates and reported ICU prevalence of multiple Gram-negative species, cefiderocol showed a higher predicted therapeutic coverage and utility in ICUs compared with comparator beta-lactam-beta-lactamase inhibitor antibiotics. Cefiderocol may be a promising early treatment option for patients at high risk of carbapenem-resistant Gram-negative bacterial infections in the ICU.

Cefiderocol heteroresistance associated with mutations in TonB-dependent receptor genes in Pseudomonas aeruginosa of clinical origin.

The siderophore-cephalosporin cefiderocol (FDC) presents a promising treatment option for carbapenem-resistant (CR) P. aeruginosa (PA). FDC circumvents traditional porin and efflux-mediated resistance by utilizing TonB-dependent receptors (TBDRs) to access the periplasmic space. Emerging FDC resistance has been associated with loss of function mutations within TBDR genes or the regulatory genes controlling TBDR expression. Further, difficulties with antimicrobial susceptibility testing (AST) and unexpected negative clinical treatment outcomes have prompted concerns for heteroresistance, where a single lineage isolate contains resistant subpopulations not detectable by standard AST. This study aimed to evaluate the prevalence of TBDR mutations among clinical isolates of P. aeruginosa and the phenotypic effect on FDC susceptibility and heteroresistance. We evaluated the sequence of pirR, pirS, pirA, piuA, or piuD from 498 unique isolates collected before the introduction of FDC from four clinical sites in Portland, OR (1), Houston, TX (2), and Santiago, Chile (1). At some clinical sites, TBDR mutations were seen in up to 25% of isolates, and insertion, deletion, or frameshift mutations were predicted to impair protein function were seen in 3% of all isolates (n = 15). Using population analysis profile testing, we found that P. aeruginosa with major TBDR mutations were enriched for a heteroresistant phenotype and undergo a shift in the susceptibility distribution of the population as compared to susceptible strains with wild-type TBDR genes. Our results indicate that mutations in TBDR genes predate the clinical introduction of FDC, and these mutations may predispose to the emergence of FDC resistance.

Antimicrobial susceptibility profile of ceftolozane/tazobactam, ceftazidime/avibactam and cefiderocol against carbapenem-resistant Pseudomonas aeruginosa clinical isolates from Türkiye.

PURPOSE: Carbapenem resistant Pseudomonas aeruginosa (CR-PA) is escalating worldwide and leaves clinicians few therapeutic options in recent years, ß-lactam/ß-lactamase inhibitor combinations (ceftolozane-tazobactam, ceftazidime-avibactam) and a new siderophore cephalosporin (cefiderocol) have been approved for the treatment of P. aeruginosa infection and have shown potent activity against isolates defined as carbapenem resistant. The aim of this study was to determine the phenotypic profile of these agents against CR-PA in the emerging setting of carbapenemases. METHODS: CR-PA clinical isolates were collected from three teaching hospitals in different geographical regions between January 2017-December 2021. All isolates were subjected to phenotypic carbapenemase testing using modified carbapenem inactivation method. MICs were determined by reference broth microdilution and evaluated according to EUCAST standards, while genotypic profiling was determined using PCR methods. RESULTS: 244 CR-PA sourced most frequently from the respiratory tract (32.2%), blood (20.4%) and urine (17.5%) were evaluated. Of all isolates, 32 (13.1%) were phenotypically and 38 (15.6%) were genotypically defined as carbapenemase-positive. The most common carbapenemase was GES (63.1%), followed by VIM (15.8%). The MIC50/90(S%) of ceftazidime/avibactam, ceftolozane/tazobactam and cefiderocol in all CR-PA isolates were 4 and 32 (80%), 1 and > 64 (69%) and 0.25 and 1 mg/L (96%), respectively. Cefiderocol was also the most active agent in carbapenemase-positive isolates (90%). CONSLUSION: While ceftolozane/tazobactam and ceftazidime/avibactam remained highly active against CR-PA devoid of carbapenemases, cefiderocol provided potent in vitro activity irrespective of carbapenemase production. When considering the potential clinical utility of newer agents against CR-PA, regional variations in carbapenemase prevalence must be considered.

A Systematic Review of the Pharmacokinetics and Pharmacodynamics of Novel Beta-Lactams and Beta-Lactam with Beta-Lactamase Inhibitor Combinations for the Treatment of Pneumonia Caused by Carbapenem-Resistant Gram-Negative Bacteria.

BACKGROUND: Novel beta-lactams show activity against many multidrug-resistant Gram-negative bacteria that cause severe lung infections. Understanding pharmacokinetic/pharmacodynamic characteristics of these agents may help optimise outcomes in the treatment of pneumonia. OBJECTIVES: To describe and appraise studies that report pulmonary pharmacokinetic and pharmacodynamic data of cefiderocol, ceftazidime/avibactam, ceftolozane/tazobactam, imipenem/cilastatin/relebactam and meropenem/vaborbactam. METHODS: MEDLINE (PubMed), Embase, Web of Science and Scopus libraries were used for the literature search. Pulmonary population pharmacokinetic and pharmacokinetic/pharmacodynamic studies on adult patients receiving cefiderocol, ceftazidime/avibactam, ceftolozane/tazobactam, imipenem/cilastatin/relebactam, and meropenem/vaborbactam published in peer-reviewed journals were included. Two independent authors screened, reviewed and extracted data from included articles. A reporting guideline for clinical pharmacokinetic studies (ClinPK statement) was used for bias assessment. Relevant outcomes were included, such as population pharmacokinetic parameters and probability of target attainment of dosing regimens. RESULTS: Twenty-four articles were included. There was heterogeneity in study methods and reporting of results, with diversity across studies in adhering to the ClinPK statement checklist. Ceftolozane/tazobactam was the most studied agent. Only two studies collected epithelial lining fluid samples from patients with pneumonia. All the other phase I studies enrolled healthy subjects. Significant population heterogeneity was evident among available population pharmacokinetic models. Probabilities of target attainment rates above 90% using current licensed dosing regiments were reported in most studies. CONCLUSIONS: Although lung pharmacokinetics was rarely described, this review observed high target attainment using plasma pharmacokinetic data for all novel beta-lactams. Future studies should describe lung pharmacokinetics in patient populations at risk of carbapenem-resistant pathogen infections.

Cefiderocol susceptibility of Achromobacter spp.: study of an accurately identified collection of 230 strains.

BACKGROUND: Achromobacter spp. are opportunistic pathogens, mostly infecting immunocompromised patients and patients with cystic fibrosis (CF) and considered as difficult-to-treat pathogens due to both intrinsic resistance and the possibility of acquired antimicrobial resistance. Species identification remains challenging leading to imprecise descriptions of resistance in each taxon. Cefiderocol is a broad-spectrum siderophore cephalosporin increasingly used in the management of Achromobacter infections for which susceptibility data remain scarce. We aimed to describe the susceptibility to cefiderocol of a collection of Achromobacter strains encompassing different species and isolation sources from CF or non-CF (NCF) patients. METHODS: We studied 230 Achromobacter strains (67 from CF, 163 from NCF patients) identified by nrdA gene-based analysis, with available susceptibility data for piperacillin-tazobactam, meropenem and trimethoprim-sulfamethoxazole. Minimal inhibitory concentrations (MICs) of cefiderocol were determined using the broth microdilution reference method according to EUCAST guidelines. RESULTS: Strains belonged to 15 species. A. xylosoxidans represented the main species (71.3%). MICs ranged from ≤ 0.015 to 16 mg/L with MIC50/90 of ≤ 0.015/0.5 mg/L overall and 0.125/2 mg/L against 27 (11.7%) meropenem-non-susceptible strains. Cefiderocol MICs were not related to CF/NCF origin or species although A. xylosoxidans MICs were statistically lower than those of other species considered as a whole. Considering the EUCAST non-species related breakpoint (2 mg/L), 228 strains (99.1%) were susceptible to cefiderocol. The two cefiderocol-resistant strains (A. xylosoxidans from CF patients) represented 3.7% of meropenem-non-susceptible strains and 12.5% of MDR strains. CONCLUSIONS: Cefiderocol exhibited excellent in vitro activity against a large collection of accurately identified Achromobacter strains, irrespective of species and origin.

Impact of extended-spectrum chromosomal AmpC (ESAC) of Escherichia coli on susceptibility to cefiderocol.

The impact of chromosomally encoded wild-type or extended-spectrum (ESAC) AmpC ß-lactamases of Escherichia coli on susceptibility to ceftazidime, cefepime, and cefiderocol was evaluated in different genetic backgrounds, including wild-type, PBP3-modified, and porin-deficient E. coli strains. Recombinant E. coli strains possessing the different backgrounds and producing variable ESACs were evaluated. Although ESAC enzymes conferred resistance to ceftazidime and decreased susceptibility to cefepime as expected, we showed here that cefiderocol was also a substrate of ESAC enzymes. IMPORTANCE: We showed here that chromosomally encoded intrinsic extended-spectrum cephalosporinases of Escherichia coli may impact susceptibility not only to ceftazidime and cefepime but also to cefiderocol.

Cefiderocol for treating severe aerobic Gram-negative bacterial infections: technology evaluation to inform a novel subscription-style payment model.

Background: To limit the use of antimicrobials without disincentivising the development of novel antimicrobials, there is interest in establishing innovative models that fund antimicrobials based on an evaluation of their value as opposed to the volumes used. The aim of this project was to evaluate the population-level health benefit of cefiderocol in the NHS in England, for the treatment of severe aerobic Gram-negative bacterial infections when used within its licensed indications. The results were used to inform the National Institute for Health and Care Excellence guidance in support of commercial discussions regarding contract value between the manufacturer and NHS England. Methods: The health benefit of cefiderocol was first derived for a series of high-value clinical scenarios. These represented uses that were expected to have a significant impact on patients' mortality risks and health-related quality of life. The clinical effectiveness of cefiderocol relative to its comparators was estimated by synthesising evidence on susceptibility of the pathogens of interest to the antimicrobials in a network meta-analysis. Patient-level costs and health outcomes of cefiderocol under various usage scenarios compared with alternative management strategies were quantified using decision modelling. Results were reported as incremental net health effects expressed in quality-adjusted life-years, which were scaled to 20-year population values using infection number forecasts based on data from Public Health England. The outcomes estimated for the high-value clinical scenarios were extrapolated to other expected uses for cefiderocol. Results: Among Enterobacterales isolates with the metallo-beta-lactamase resistance mechanism, the base-case network meta-analysis found that cefiderocol was associated with a lower susceptibility relative to colistin (odds ratio 0.32, 95% credible intervals 0.04 to 2.47), but the result was not statistically significant. The other treatments were also associated with lower susceptibility than colistin, but the results were not statistically significant. In the metallo-beta-lactamase Pseudomonas aeruginosa base-case network meta-analysis, cefiderocol was associated with a lower susceptibility relative to colistin (odds ratio 0.44, 95% credible intervals 0.03 to 3.94), but the result was not statistically significant. The other treatments were associated with no susceptibility. In the base case, patient-level benefit of cefiderocol was between 0.02 and 0.15 quality-adjusted life-years, depending on the site of infection, the pathogen and the usage scenario. There was a high degree of uncertainty surrounding the benefits of cefiderocol across all subgroups. There was substantial uncertainty in the number of infections that are suitable for treatment with cefiderocol, so population-level results are presented for a range of scenarios for the current infection numbers, the expected increases in infections over time and rates of emergence of resistance. The population-level benefits varied substantially across the base-case scenarios, from 896 to 3559 quality-adjusted life-years over 20 years. Conclusion: This work has provided quantitative estimates of the value of cefiderocol within its areas of expected usage within the NHS. Limitations: Given existing evidence, the estimates of the value of cefiderocol are highly uncertain. Future work: Future evaluations of antimicrobials would benefit from improvements to NHS data linkages; research to support appropriate synthesis of susceptibility studies; and application of routine data and decision modelling to assess enablement value. Study registration: No registration of this study was undertaken. Funding: This award was funded by the National Institute for Health and Care Research (NIHR) Health Technology Assessment Policy Research Programme (NIHR award ref: NIHR135591), conducted through the Policy Research Unit in Economic Methods of Evaluation in Health and Social Care Interventions, PR-PRU-1217-20401, and is published in full in Health Technology Assessment; Vol. 28, No. 28. See the NIHR Funding and Awards website for further award information.

This project tested new methods for estimating the value to the NHS of an antimicrobial, cefiderocol, so its manufacturer could be paid fairly even if very little drug is used in order to reduce the risk of bacteria becoming resistant to the product. Clinicians said that the greatest benefit of cefiderocol is when used for complicated urinary tract infections and pneumonia acquired within hospitals caused by two types of bacteria (called Enterobacterales and Pseudomonas aeruginosa), with a resistance mechanism called metallo-beta-lactamase. Because there were no relevant clinical trial data, we estimated how effective cefiderocol and alternative treatments were by doing a systematic literature review of studies that grew bacteria from infections in the laboratory and tested the drugs on them. We linked this to data estimating the long-term health and survival of patients. Some evidence was obtained by asking clinicians detailed questions about what they thought the effects would be based on their experience and the available evidence. We included the side effects of the alternative treatments, some of which can cause kidney damage. We estimated how many infections there would be in the UK, whether they would increase over time and how resistance to treatments may change over time. Clinicians told us that they would also use cefiderocol to treat intra-abdominal and bloodstream infections, and some infections caused by another bacteria called Stenotrophomonas. We estimated how many of these infections there would be, and assumed the same health benefits as for other types of infections. The total value to the NHS was calculated using these estimates. We also considered whether we had missed any additional elements of value. We estimated that the value to the NHS was £18­71 million over 20 years. This reflects the maximum the NHS could pay for use of cefiderocol if the health lost as a result of making these payments rather than funding other NHS services is not to exceed the health benefits of using this antimicrobial. However, these estimates are uncertain due to limitations with the evidence used to produce them and assumptions that had to be made.

[Discovery of a New Siderophore Cephalosporin, Cefiderocol].

Cefiderocol is a novel siderophore-conjugated cephalosporin with a catechol residue acting as an iron chelator. Cefiderocol forms a chelating complex with ferric iron and is transported rapidly into bacterial cells through iron-uptake systems. As a result, cefiderocol shows good activity against Gram-negative bacteria, including carbapenem-resistant isolates that are causing significant global health issues. Cefiderocol has been approved for clinical use in the United States and Europe, where it is being used to treat infection caused by carbapenem-resistant Gram-negative pathogens.

Comparison of available methods to evaluate cefiderocol susceptibility in Acinetobacter spp.

Recently, considerable uncertainty has arisen concerning the appropriate susceptibility testing for cefiderocol in gram-negative bacilli, particularly in the context of its application to Acinetobacter spp. The optimal method for assessing the susceptibility levels of Acinetobacter spp. to cefiderocol remains a subject of debate due to substantial disparities observed in the values obtained through various testing procedures. This study employed four minimum inhibitory concentration (MIC) methodologies and the disk diffusion to assess the susceptibility of twenty-seven carbapenem resistant (CR)-Acinetobacter strains to cefiderocol. The results from our study reveal significant variations in the minimum inhibitory concentration (MIC) values obtained with the different methods and in the level of agreement in interpretation categories between the different MIC methods and the disk diffusion test. Among the MIC methods, there was relatively more consistency in reporting the interpretation categories. For European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints, the categorical agreement (CA) for MIC methods ranged between 66.7 and 81.5%. On the other hand, the essential agreement (EA) values were as low as 18.5-29.6%. The CA between MIC methods and disk diffusion was 81.5%. These results emphasize the need for a reliable, accurate, and clinically validated methodology to effectively assess the susceptibility of Acinetobacter spp. to cefiderocol. The wide variability observed in our study highlights the importance of standardizing the susceptibility testing process for cefiderocol to ensure consistent and reliable results for clinical decision-making.

In vivo emergence of cefiderocol and ceftazidime/avibactam cross-resistance in KPC-producing Klebsiella pneumoniae following ceftazidime/avibactam -based therapies.

We described the emergence of ceftazidime/avibactam and cefiderocol cross-resistance in patients with KPC-producing Klebsiella pneumoniae infections. All strains with ceftazidime/avibactam and cefiderocol cross-resistance showed point mutations on KPC Ω-loop. Taken together, our results indicate that prolonged exposure to ceftazidime/avibactam can confer cross-resistance to ceftazidime/avibactam and cefiderocol.

Cefiderocol utilization in lung transplant recipients at a single center.

BACKGROUND: Multidrug-resistant organisms are increasing and are a significant cause of mortality among lung transplant recipients (LTRs). To assist with this issue, novel pharmacotherapies are being developed. This study describes the utilization of a novel antibiotic, cefiderocol (FDC), in LTRs where limited data exists in the current literature. We primarily assessed the clinical indications, duration of therapy, resistance, and adverse effects. METHODS: Conducted as a single-center retrospective review, this study included adult LTRs who received FDC for at least 24 h. Data, extracted from electronic medical records, encompassed patient demographics, transplant history, antimicrobial dosing, adverse effects, bacterial cultures, and outcomes. The research protocol received institutional review board approval. RESULTS: FDC exhibited effectiveness against multidrug-resistant Pseudomonas aeruginosa, with 26% 30-day mortality and microbiological clearance observed in nine out of 13 cases. Notably, FDC was used in diverse clinical settings, including for prophylaxis, empiric, and targeted treatment. CONCLUSION: Further studies are needed to evaluate optimal clinical indications for FDC use in LTRs.

Glycine restores the sensitivity to antibiotics in multidrug-resistant bacteria.

The management of infections caused by multiresistant bacteria has become of fundamental importance for any medical practice. Glycine is the most common and the simplest non-essential amino acid in humans. Glycine is very effective in improving health and supporting growth and wellbeing of humans and animals. Instead, for many bacteria, high concentrations of glycine induce lysis or deep morphological alterations. The effect of glycine on multidrug resistant (MDR) microorganisms has not yet been extensively researched. The present study was conducted 1) to establish the effect of glycine on different nosocomial pathogens isolated during routine diagnostic investigations; 2) to determine the minimum inhibitory concentration of glycine and the type of activity performed (bacteriostatic or bactericidal) on representative isolates; 3) to test the interaction between glycine and meropenem, cefiderocol, or colistin. The data reported here show a dose-dependent activity of glycine on bacteria and its bactericidal activity on MDR bacteria. Furthermore, we found that the action of glycine restores in vitro the susceptibility of multiresistant nosocomial pathogens to the tested antibiotics.IMPORTANCEAntimicrobial resistance is a constantly growing concern throughout the world, and Italy is among the Western countries where antimicrobial resistance is most widespread. In Tuscany, carbapenemase-producing Enterobacterales are now even endemic. In this study, we challenged some resistant bacteria with a well-known molecule, glycine, the antibacterial properties of which have been known since the past century. This study could bring new insights into combining antibiotics with the simplest of all amino acids. The restoration of sensitivity to the aforementioned antibiotics by a natural compound, already used for clinical purposes, is of extreme importance in an era of proliferation of multiresistant bacteria. The in vivo use of this amino acid in evaluating its effectiveness against infections should be investigated. The low cost of this molecule can also make it easy to use even in low-income countries.

In vitro activity of cefiderocol in Pseudomonas aeruginosa isolates from people with cystic fibrosis recovered during three multicentre studies in Spain.

OBJECTIVES: Despite the introduction of cystic fibrosis transmembrane conductance regulator (CFTR) modulators, Pseudomonas aeruginosa is still a major pathogen in people with cystic fibrosis (pwCF). We determine the activity of cefiderocol and comparators in a collection of 154 P. aeruginosa isolates recovered from pwCF during three multicentre studies performed in 17 Spanish hospitals in 2013, 2017 and 2021. METHODS: ISO broth microdilution was performed and MICs were interpreted with CLSI and EUCAST criteria. Mutation frequency and WGS were also performed. RESULTS: Overall, 21.4% were MDR, 20.8% XDR and 1.3% pandrug-resistant (PDR). Up to 17% of the isolates showed a hypermutator phenotype. Cefiderocol demonstrated excellent activity; only 13 isolates (8.4%) were cefiderocol resistant by EUCAST (none using CLSI). A high proportion of the isolates resistant to ceftolozane/tazobactam (71.4%), meropenem/vaborbactam (70.0%), imipenem/relebactam (68.0%) and ceftazidime/avibactam (55.6%) were susceptible to cefiderocol. Nine out of 13 cefiderocol-resistant isolates were hypermutators (P < 0.001). Eighty-three STs were detected, with ST98 being the most frequent. Only one isolate belonging to the ST175 high-risk clone carried blaVIM-2. Exclusive mutations affecting genes involved in membrane permeability, AmpC overexpression (L320P-AmpC) and efflux pump up-regulation were found in cefiderocol-resistant isolates (MIC = 4-8 mg/L). Cefiderocol resistance could also be associated with mutations in genes related to iron uptake (tonB-dependent receptors and pyochelin/pyoverdine biosynthesis). CONCLUSIONS: Our results position cefiderocol as a therapeutic option in pwCF infected with P. aeruginosa resistant to most recent ß-lactam/ß-lactamase inhibitor combinations.