Global prevalence of cefiderocol non-susceptibility in Enterobacterales, Pseudomonas aeruginosa, Acinetobacter baumannii, and Stenotrophomonas maltophilia: a systematic review and meta-analysis

Mortality due to carbapenem-resistant Acinetobacter baumannii bacteraemia: a 5-year cohort study in intensive care patients

OBJECTIVES

Carbapenem-resistant Acinetobacter baumannii (CRAB) has emerged as a major and difficult-to-treat nosocomial pathogen. This study estimated the mortality associated with CRAB bacteraemia in patients receiving treatment in the intensive care unit. A susceptible-infection counterfactual framework was applied to reflect the potential benefit of improved antimicrobial therapy.

METHODS

A 5-year (2019-2023) cohort study was conducted in a tertiary-care referral hospital in Greece. Competing risks survival analysis methods were applied to estimate excess in-hospital mortality because of CRAB bacteraemia by comparing patients infected by CRAB with those infected by other more susceptible Gram-negative bacteria (GNB).

RESULTS

The cohort comprised 400 intensive care patients with GNB bacteraemia (median age 70 years, 65% man). CRAB was the most common pathogen (43%), followed by Klebsiella pneumoniae (12%), Escherichia coli (11%), and Pseudomonas aeruginosa (10%). Patients with CRAB bacteraemia experienced significantly higher in-hospital mortality at 14 days (35% vs. 21%), 28 days (53% vs. 30%), and overall (74% vs. 52%) than patients with other GNB bacteraemia. Multivariable competing risks regression confirmed that CRAB bacteraemia was independently associated with an increased risk of 28-day inpatient death (cause-specific hazard ratio: 1.80, 95% CI: 1.28-2.54; sub-distribution hazard ratio: 1.84, 95% CI: 1.28-2.62), simultaneously lowering the probability of discharge alive (cause-specific hazard ratio: 0.68, 95% CI: 0.38-1.21; sub-distribution hazard ratio: 0.52, 95% CI: 0.30-0.91). Estimation of the attributable fraction suggested that effective antimicrobial management may result in a relative decrease in the risk of in-hospital mortality by 44% (95% CI: 22-61%) in patients with CRAB bacteraemia.

DISCUSSION

CRAB's detrimental role as a leading cause of increased inpatient mortality and prolongation of hospitalization in intensive care patients was demonstrated. These outcomes could improve substantially if more effective antimicrobial treatment becomes available. Nevertheless, considering that CRAB is predominantly a hospital-acquired pathogen, efforts should always be directed towards preventing nosocomial transmission.

Construction of a programmed activation nanosystem based on intracellular hypoxia in cisplatin-resistant tumor cells for reversing cisplatin resistance

Cancer poses a significant threat to human life and health. Cancers treated with cisplatin invariably develop drug resistance. This challenge can be overcome by identifying and exploiting the vulnerabilities acquired by drug-resistant cancer cells, paving the way for finding effective novel treatment options for cisplatin-resistant cancers. Our previous study revealed that cisplatin resistance in cancer cells comes at the cost of increased intracellular hypoxia. In this study, we used 2-nitroimidazole modified hyaluronic acid (HA-NI) as the carrier. The cisplatin-resistant tumor cell specific intracellular hypoxia programmed activation nanomedicine (T/C@HN NPs) was constructed by the hypoxic toxic drug tirapazamine (TPZ) and encapsulating chlorin e6 (Ce6) into HA-NI using polymer assembly technology. The amphiphilic carrier could release free Ce6 molecules under the stimulation of intracellular hypoxic environment, and exhibit specific "activated state" photodynamic properties in cisplatin-resistant tumor cells. Upon irradiation, Ce6-mediated photodynamic therapy further intensifies hypoxia, amplifying its cytotoxicity. This project systematically evaluated the effects of T/C@HN NPs on the identification and recognition of cisplatin-resistant tumors using drug-resistant patient-derived xenograft (PDX) models. This study provides a promising avenue for the development of novel treatment of cisplatin-resistant tumors.

In vitro activity and resistance mechanisms of novel antimicrobial agents against metallo-β-lactamase producers

The carbapenemase-producing Gram-negative organisms represent an urgent clinical and public health concern, as they have been associated with increased mortality and high dissemination in healthcare settings. Although overall incidence rates of infections sustained by metallo-β-lactamase (MβL)-producers have remained lower than those sustained by other carbapenemase-producers, albeit with substantial geographic differences, a significant increase in the prevalence of MβL-producers has been observed over the last decade. The recent development of new antimicrobials expanded the armamentarium to counter the challenge of metallo-β-lactamase (MβL)-producers. Cefiderocol and aztreonam/avibactam are already clinically available and recommended by international guidelines. In addition, two new classes of β-lactam/ β-lactamase combinations are under clinical evaluation: (i) combination of β-lactam with novel boronic-derived inhibitors (e.g. taniborbactam and xeruborbactam), (ii) combination of β-lactam with last generation diazabicyclooctane β-lactamase inhibitors (e.g. zidebactam and nacubactam), active on most of serine-β-lactamases but also showing strong intrinsic activity on PBP-2. This review aims to provide up-to-date data on the characteristics, activity and emerging resistance mechanisms of the armamentarium of clinically available or soon-to-be introduced drugs for the treatment of MβL-producing Gram-negative organisms.

Successful treatment of carbapenem-resistant Acinetobacter baumannii meningitis and purulent ventriculitis using cefiderocol combination therapy: a case report and literature review

The application of cefiderocol in treating carbapenem-resistant Acinetobacter baumannii (CRAB) central nervous system (CNS) infections is rarely reported. Here we presented the case of a 66-year-old man with CRAB meningitis and purulent ventriculitis successfully treated with a combination antibiotic therapy including cefiderocol. Cerebrospinal fluid (CSF) analysis revealed normalization of glucose, chloride, protein, and lactate levels. CRAB cultures turned negative by Day 7, and metagenomics next generation sequencing (mNGS) results were negative by Day 25. The cefiderocol-contained regimen was continued for 41 days, with no recurrence of CRAB infection and no cefiderocol-associated adverse effects were observed. This case highlighted the potential of cefiderocol as a promising therapeutic option in treating CRAB CNS infections.

A randomised crossover clinical trial of the efficacy of an ultrasonic cleaner combined with a denture cleanser on the microbiome on removable dentures among community-dwelling older adults

OBJECTIVE

To evaluate and characterise the microbial compositional changes of removable dentures after interventions by comparing the efficacy of the test arm (a portable self-operated ultrasonic cleaner combined with an enzymatic peroxide-based denture cleanser solution) to the control arm (immersion of the denture in the same cleanser solution followed by conventional brushing).

MATERIALS AND METHODS

A prospective, single-blind, block-randomised, two-period crossover, controlled clinical trial was conducted, involving 56 community-dwelling older adults wearing removable acrylic dentures. They were block-randomized into the test/control or control/test denture cleaning sequence. Type IIB Restriction-site Associated DNA for Microbiome metagenomic sequencing was adopted to characterize the species-resolved microbial composition for denture biofilm.

RESULTS

For the intervention effect, the overall microbial richness in both arms was not significantly different based on the Chao 1 index (P = 0.343). However, Beta diversity analysis (Jaccard qualitative distance matrix) demonstrated significant differences in the microbial community structures between the Test and Control arms after interventions, confirmed by the Permanova test (R2 = 0.01118, P = 0.034). Among the opportunistic pathogenic bacteria, Pseudomonas aeruginosa was detected as one of the top 30 species by relative abundance at the end of the clinical trial, and Enterobacter kobei was significantly enriched in the control arm, as determined by LEfSe analysis.

CONCLUSIONS

The microbial community of denture biofilm samples after both interventions were significantly 'shifted' and had limited numbers of opportunistic pathogens, suggesting the interventions equally effective in mitigating the overall number of pathogenic bacteria.

CLINICAL SIGNIFICANCE

Denture cleaning intervention using ultrasonic cleaner combined with immersion in denture cleanser solution appears to be effective in shifting the denture microbiome with reduced pathogenic bacteria among community-dwelling denture wearers.

Novel Antibacterial Approaches and Therapeutic Strategies

The increase in multidrug-resistant organisms worldwide is a major public health threat driven by antibiotic overuse, horizontal gene transfer (HGT), environmental drivers, and deficient infection control in hospitals. In this article, we discuss these factors and summarize the new drugs and treatment strategies suggested to combat the increasing challenges of multidrug-resistant (MDR) bacteria. New treatments recently developed involve targeting key processes involved in bacterial growth, such as riboswitches and proteolysis, and combination therapies to improve efficacy and minimize adverse effects. It also tackles the challenges of the Gram-negative bacterial outer membrane, stressing that novel strategies are needed to evade permeability barriers, efflux pumps, and resistance mechanisms. Other approaches, including phage therapy, AMPs, and AI in drug discovery, are also discussed as potential alternatives. Finally, this review points out the urgency for continued research and development (R&D), industry-academic partnerships, and financial engines to ensure that MDR microbes do not exceed the value of antibacterial therapies.

The global resistance problem and the clinical antibacterial pipeline

A comprehensive analysis of the clinical antibacterial pipeline demonstrates that there is a limited range of strategies that are primarily focused on modified versions of widely used chemical classes. These modifications aim to circumvent class-specific resistance mechanisms and reduce resistance rates in certain multidrug-resistant pathogens. Owing to the great variation in resistance rates and mechanisms, the clinical success of current approaches varies substantially across different countries, regions, and economic and environmental conditions, which affects the global societal value of these antibiotics that remain vulnerable to cross-resistance. Although there has been some progress in developing urgently needed antibiotics with novel targets and chemical structures, some of which have advanced to phase I/II trials, further breakthroughs are required. Additionally, adjunctive agents designed to enhance the outcome of conventional antibiotic therapies, along with bacteriophages that offer targeted and personalized treatments, are also under investigation. However, the potential of adjunctive therapeutics, such as antivirulence agents, and bacteriophages has yet to be realized in terms of feasibility and global societal impact.

Global health perspectives on antibacterial drug discovery and the preclinical pipeline

Antibacterial resistance is a global challenge that requires a coordinated international response. The current clinical pipeline largely consists of derivatives of established antibiotic classes, whereas the discovery and preclinical pipeline is diverse and innovative including new direct-acting agents with no cross-resistance with existing antibiotics. These novel compounds target pathways such as lipoprotein synthesis, lipopolysaccharide biosynthesis and transport, outer membrane assembly, peptidoglycan biosynthesis, fatty acid biosynthesis and isoprenoid biosynthesis. If these agents can be developed into safe, effective and affordable drugs, they could address a broad range of infections worldwide, benefiting large patient populations without geographical limitations. However, strategies such as indirect-acting or pathogen-specific treatments are likely to benefit small patient groups, primarily in high-income countries that have advanced health-care systems and diagnostic infrastructure. Although encouraging, the discovery and preclinical pipeline remains insufficiently robust to offset the high attrition rates typical of early-stage drug innovation and to meet global health needs.

Antimicrobial activity of peptoids against Metallo-β-lactamase-producing Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and other WHO priority pathogens, including Candida auris

AIMS

The World Health Organization has identified ESKAPE bacteria and Candida auris as priority pathogens, emphasizing an urgent need for novel antimicrobials to combat them. This study aimed to explore the therapeutic potential of antimicrobial peptidomimetics, specifically peptoids with sequence-specific N-substituted glycines, against ESKAPEE pathogens, including metallo-β-lactamase (MBL) producers, as well as C. auris strains.

METHODS AND RESULTS

This study evaluated activity of the peptoids against the multidrug-resistant priority pathogens. The peptoid TM8 (with an N-decyl alkyl chain) demonstrated a geometric mean minimum inhibitory concentration (MIC) of 7.8 μg ml-1 against MBL-producing bacteria, and 5.5 μg ml-1 against C. auris. TM8 showed synergy with ciprofloxacin, enhancing its effectiveness 4-fold against NDM-1-producing Klebsiella pneumoniae. No antagonism was seen when TM8 was used with either conventional antibiotics or antifungals. Peptoids that had therapeutic indices below 3 were generally more hydrophobic, due to either alkyl chains or bromine. Scanning electron microscopy and live-dead staining assay on peptoid-treated C. auris confirmed morphological changes and killing activity, respectively. Furthermore, the peptoid could effectively inhibit biofilm formation by C. auris.

CONCLUSION

Peptoids demonstrated antibacterial activity against ESKAPEE, particularly against MBL-producing Gram-negative bacteria. Additionally, they exhibited antifungal and anti-biofilm activities against C. auris strains.

Cefiderocol for the Treatment of Nosocomial Bloodstream Infections Caused by Stenotrophomonas maltophilia: A Case Series and Literature Review

INTRODUCTION

The treatment of Stenotrophomonas maltophilia bloodstream infections (BSI) remains challenging due to the organism's intrinsic multidrug resistance and the potential side effects of commonly used first-line antibiotics.

METHODS

Here, we describe four cases of S. maltophilia BSI treated with cefiderocol (≥ 72 h) in different Italian hospitals. Additionally, we conducted a PubMed search to identify other studies reporting cases of S. maltophilia BSI managed with cefiderocol.

RESULTS

We reviewed a total of 8 cases of S. maltophilia BSI [median age 52.5 years (Q1-Q3 27.5-61.0), 50% males] treated with cefiderocol, including ours. BSI sources were mainly central venous catheters (62.5%) and the lower respiratory tract (25.0%). Cefiderocol was used as first-line therapy in 87.5% of patients (7/8), with a median treatment duration of 14 days (IQR 6.2-16.0). Combination therapy was administered in 62.5% of cases. Infection source control was required in 75.0% and achieved in 40.0%. Clinical success was observed in 62.5% of patients, with microbiological eradication in 87.5%. In-hospital mortality occurred in 37.5% of cases, with one death directly attributable to S. maltophilia. No significant differences were observed in terms of outcomes between cefiderocol monotherapy and combination therapy.

CONCLUSIONS

Based on our findings and a review of the literature, cefiderocol-based regimens show promise as an effective treatment option for S. maltophilia BSI, warranting further investigation in larger studies.

The hidden threat: Klebsiella pneumoniae may develop co-resistance to colistin and cefiderocol under pressure of colistin

OBJECTIVES

Carbapenem-resistant Klebsiella pneumoniae (CRKP) has become a global concern owing to its difficult treatment. This study aimed to determine the impact of colistin resistance on susceptibility to cefiderocol.

METHODS

The colistin-susceptible clinical strain CRKP12-130 (colistin minimum inhibitory concentration [MIC] 0.5 mg/L) was cultured in medium containing 4× and 8× the MIC of colistin. Eight colistin-resistant derivatives were randomly selected for susceptibility testing of cefiderocol and zeta potential changes. To compare the impact of colistin resistance on bacterial uptake of iron, growth curve experiments were conducted in cation-adjusted Mueller-Hinton broth (CAMHB) and iron-depleted CAMHB (ID-CAMHB). Resistant strains and the original strain CRKP12-130 were subjected to next-generation sequencing.

RESULTS

Colistin MICs ranged from 16 to 128 mg/L for the eight colistin-resistant derivatives. The key genetic variants identified in colistin-resistant strains involved insertions and deletions in mgrB, and missense mutations in pmrB and phoQ. The colistin-resistant derivatives also exhibited reduced susceptibility to cefiderocol, with MICs increasing from 1 mg/L to 2-8 mg/L. Additionally, colistin-resistant strains demonstrated higher zeta potentials, ranging from -45.2 mV to levels between -32.8 mV and -14.2 mV. Resistant strains showed a more significant decrease in growth rate when cultivated in ID-CAMHB medium.

CONCLUSION

This study investigated the phenomenon of co-resistance to colistin and cefiderocol in CRKP under pressure of colistin. The simultaneous decrease in susceptibility poses a potential threat to the efficacy of clinical treatment of CRKP infections.

In Vitro Interactions Between Bacteriophages and Antibacterial Agents of Various Classes Against Multidrug-Resistant Metallo-β-Lactamase-Producing Pseudomonas aeruginosa Clinical Isolates

Background: Combination therapy with antibiotics and phages has been suggested to increase the antibacterial activity of both antibiotics and phages. We tested the in vitro activity of five antibiotics belonging to different classes in combination with lytic bacteriophages against multidrug-resistant metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa isolates. Material/Methods: A total of 10 non-repetitive well-characterized MBL-producing P. aeruginosa isolates (5 NDM, 5 VIM) co-resistant to aminoglycosides and quinolones were used. Phage-antibiotic interactions were assessed using an ISO-20776-based broth microdilution checkerboard assay in 96-well microtitration plates. Two-fold dilutions of colistin (8-0.125 mg/L), ciprofloxacin, meropenem, aztreonam, and amikacin (256-4 mg/L) were combined with ten-fold dilutions of five different phages (5 × 109-5 × 100 PFU/mL) belonging to Pakpunavirus, Phikzvirus, Pbunavirus, and Phikmvvirus genus. Plates were incubated at 35 ± 2 °C for 24 h, and the minimum inhibitory concentration of antibiotics (MICA) and phages (MICP) were determined as the lowest drug and phage concentration, resulting in <10% growth based on photometric reading at 550 nm. Interactions were assessed based on the fractional inhibitory concentration index (FICi) of three independent replicates and clinical relevance based on the reversal of phenotypic resistance. The statistical significance of each drug alone and in combination with phages was assessed using GraphPad Prism 8.0. Results: Synergistic and additive interactions were found for 60-80% of isolates for all drugs. FICis were statistically significantly lower than 0.5 for colistin (p = 0.005), ciprofloxacin (p = 0.02), meropenem (p = 0.003), and amikacin (p = 0.002). Interactions were found at clinically achievable concentrations for colistin, meropenem, and amikacin, and a reversal of phenotypic resistance was observed for most strains (63-64%) for amikacin and meropenem. Antagonism was found for few isolates with all antibiotics tested. Phage vB_PaerM_AttikonH10 and vB_PaerP_AttikonH4 belonging to Phikzvirus and Phikmvvirus genus, respectively, showed either synergistic (FICi ≤ 0.35) or additive effects with most antibiotics tested. Conclusions: Synergy was observed for most drugs and phages with amikacin, showing strong synergy and reversal of phenotypic resistance against most isolates. Taking into account the wide utility of jumbo phages obtained, the findings of vB_PaerM_AttikonH10 in combination with different classes of antibiotics can enhance the activity of currently ineffective antibiotics against MBL-producing P. aeruginosa isolates.

Characterization of Klebsiella pneumoniae Isolates Resistant to Cefiderocol from Hospitals and Outpatient Settings in Croatia

BACKGROUND/OBJECTIVES

We conducted this study to evaluate the genotypic and phenotypic profiles of carbapenem-resistant Klebsiella pneumoniae (CRKP) isolates, exhibiting resistance to cefiderocol (FDC), focusing on antibiotic susceptibility, β-lactamase production, the genetic environment of blaCARB and blaESBL genes and molecular epidemiology. FDC is now a last-line antibiotic for severe infections due to CRKP.

METHODS

Susceptibility to a wide range of antibiotics was determined by the disk diffusion and broth microdilution method. Carbapenemases were screened by a modified Hodge test while carbapenem hydrolysis was investigated using mCIM and eCIM tests. The screening for β-lactamase and fluoroquinolone cluster resistance genes was carried out by PCR. Plasmids were characterized by PCR-based replicon typing (PBRT). An inter-array genotyping CarbaResist test and whole genome sequencing (WGS) were applied on selected isolates.

RESULTS

All of the 31 isolates studied exhibited high-level resistance to amoxicillin-clavulanate, piperacillin-tazobactam, cefuroxime, expanded-spectrum cephalosporins (ESC), cefepime, ceftolozan-tazobactam and ciprofloxacin and the majority to gentamicin, and amikacin. Colistin and ceftazidime-avibactam preserved activity against 71% and 87% of the isolates, respectively. The combined disk method with clavulanic acid was positive in all but one isolate, indicating the production of an ESBL. Twenty-eight isolates carried one single carbapenemase-encoding gene, whereas three harbored double blaCARB genes. Among the studied isolates, 61% carried blaOXA-48, 29% blaKPC and 12.9% blaNDM genes. The inter-array genotyping CarbaResist test and WGS identified additional aminoglycoside-, sulphonamide- and trimethoprim-resistance genes.

CONCLUSION

To our knowledge, this is the first study on FDC resistance in Croatia. The diffusion of FDC-resistant isolates was detected in both hospital and outpatient settings, emphasizing the need for a "One Health" approach.

Early Predictive Value of Infectious Markers for Ventilator-associated Pneumonia after Stanford Type A Aortic Dissection Surgery

Background

This study investigates the early predictive value of infectious markers for ventilator-associated pneumonia (VAP) after Stanford type A aortic dissection surgery.

Methods

A retrospective review of the medical records of all patients with Stanford type A aortic dissection admitted to Shanghai General Hospital from July 2020 to July 2023 who received mechanical ventilation after surgery was performed. Patients were divided into infection and non-infection groups according to the presence of VAP. The clinical data of the two groups were compared. The early predictive values of procalcitonin (PCT), C-reactive protein (CRP), the neutrophil/lymphocyte ratio (NLR) and sputum smears for VAP were evaluated by receiver operating characteristic (ROC) curve analysis.

Results

A total of 139 patients with Stanford type A aortic dissection were included in this study. There were 35 cases of VAP infection, and the VAP incidence rate was 25.18%. The CRP, PCT, and NLR levels in the infection group were more significant than those in the non-infection group (p < 0.05). The percentage of positive sputum smears was 80.00% in the infected group and 77.88% in the non-infected group. The ROC curve analysis revealed that the areas under the curve (AUCs) of PCT, the NLR, CRP and sputum smear were 0.835, 0.763, 0.820 and 0.745, respectively, and the AUC for the combined diagnosis was 0.923. The pathogenic bacteria associated with VAP, after Stanford type A aortic dissection, was mainly gram-negative bacteria.

Conclusions

The combined application of the NLR, CRP, PCT and sputum smear is helpful for the early diagnosis of VAP after Stanford type A aortic dissection surgery to help clinicians make decisions about treating VAP quickly.

Activity of cefiderocol in combination with tetracycline analogues against carbapenem-resistant Acinetobacter baumannii

Therapeutic options for carbapenem-resistant Acinetobacter baumannii (CA-AB) are quite limited. Cefiderocol, a novel siderophore cephalosporin, has shown potent in vitro activity against CR-AB, and new tetracycline analogues such as eravacycline and omadacycline have been available in recent years. However, the synergism of cefiderocol with tetracycline analogues against CR-AB has not been well investigated. In this study, we evaluated the in vitro synergistic activity of cefiderocol in combination with tetracycline analogues (minocycline, tigecycline, eravacycline and omadacycline) against 48 clinical isolates of CR-AB by checkerboard methods and time-kill assays. Then we further verified the in vitro results with neutropenic murine thigh-infection models. Among 48 tested isolates tested with checkerboard methods, 35.4%, 33.3%, 50.0% and 37.5% showed synergistic interactions (FICI ≤ 0.5) in cefiderocol-minocycline combination, cefiderocol-tigecycline combination, cefiderocol-eravacycline combination and cefiderocol-omadacycline combination, respectively. None of the combinations exhibited any antagonistic interactions. In the time-kill assays, cefiderocol combined with tetracycline analogues showed synergistic effects in most isolates. Animal models found that combination therapy could reduce cell counts by nearly 2 log10 CFU/thigh compared with the monotherapy in the AB-2 isolate who was susceptible to minocycline (MIC = 4 mg/l). But for the AB-26 who was resistant to minocycline, the decrease of bacterial cell counts was less than 1 log10 CFU/thigh compared with cefiderocol monotherapy in the cefiderocol-minocycline, cefiderocol-tigecycline and cefiderocol-omadacycline therapies; while the cefiderocol-eravacycline combination could still reduce the bacterial cell counts nearly 2 log10 CFU/thigh compared with the monotherapy. In summary, the cefiderocol-eravacycline combination seems to be a promising therapeutic strategy for treating CR-AB infections.

Current developments and prospects of the antibiotic delivery systems

Antibiotics have remained the cornerstone for the treatment of bacterial infections ever since their discovery in the twentieth century. The uproar over antibiotic resistance among bacteria arising from genome plasticity and biofilm development has rendered current antibiotic therapies ineffective, urging the development of innovative therapeutic approaches. The development of antibiotic resistance among bacteria has further heightened the clinical failure of antibiotic therapy, which is often linked to its low bioavailability, side effects, and poor penetration and accumulation at the site of infection. In this review, we highlight the potential use of siderophores, antibodies, cell-penetrating peptides, antimicrobial peptides, bacteriophages, and nanoparticles to smuggle antibiotics across impermeable biological membranes to achieve therapeutically relevant concentrations of antibiotics and combat antimicrobial resistance (AMR). We will discuss the general mechanisms via which each delivery system functions and how it can be tailored to deliver antibiotics against the paradigm of mechanisms underlying antibiotic resistance.

Multidrug-resistant Gram-negative bacterial infections

Multidrug-resistant Gram-negative bacterial infections cause significant morbidity and mortality globally. These pathogens easily acquire antimicrobial resistance (AMR), further highlighting their clinical significance. Third-generation cephalosporin-resistant and carbapenem-resistant Enterobacterales (eg, Escherichia coli and Klebsiella spp), multidrug-resistant Pseudomonas aeruginosa, and carbapenem-resistant Acinetobacter baumannii are the most problematic and have been identified as priority pathogens. In response, several new diagnostic technologies aimed at rapidly detecting AMR have been developed, including biochemical, molecular, genomic, and proteomic techniques. The last decade has also seen the licensing of multiple antibiotics that have changed the treatment landscape for these challenging infections.

Microbial Colonization and Antibiotic Resistance Profiles in Chronic Wounds: A Comparative Study of Hidradenitis Suppurativa and Venous Ulcers

Background/Objectives: Chronic wounds, including hidradenitis suppurativa (HS) and venous ulcers (VU), are commonly associated with complex microbial communities that may influence wound healing and treatment outcomes. Understanding microbial diversity and antibiotic resistance patterns is essential in order to optimize therapeutic strategies. This study aimed to investigate the microbial populations and antibiotic resistance profiles in HS and VU patients, comparing the prevalence of common pathogens and their antimicrobial resistance profiles. Methods: We conducted a cross-sectional analysis that included a total of 112 individuals (24 with the diagnosis of hidradenitis suppurativa and 88 diagnosed with venous ulcer). Wound swabs were cultured to identify bacterial species, and antibiotic resistance was assessed using a standard panel of antibiotics. Prevalence rates of key pathogens, such as Staphylococcus aureus, Pseudomonas aeruginosa, and Enterococcus faecalis, were compared between the two groups. Resistance patterns were analyzed using statistical methods to identify significant differences. Results: Staphylococcus aureus was the most common pathogen in both groups (45.8% in HS; 38.6% in VU), with a notable prevalence of methicillin-resistant S. aureus (MRSA). Pseudomonas aeruginosa was exclusively identified in VU patients (27.3%), while beta-hemolytic Streptococcus and Corynebacterium amycolatum were identified in HS cases only. Antibiotic resistance was moderate, notably in S. aureus and Proteus mirabilis, while one case of multidrug-resistant Pseudomonas aeruginosa was identified. Conclusions: This study highlights the distinctive microbial profiles and antibiotic resistance patterns in HS and VU chronic wounds. The predominance of S. aureus in both groups underscores the need for targeted therapies, while the absence of P. aeruginosa in HS wounds and the higher prevalence of other species emphasizes wound-specific microbial variations. These findings underscore the importance of personalized treatment strategies and continuous surveillance of antimicrobial resistance.

Resistance profiles of carbapenemase-producing Enterobacterales in a large centre in England: are we already losing cefiderocol?

BACKGROUND

Carbapenemase-producing Enterobacterales (CPE) pose difficult therapeutic challenges. We aimed to characterize antimicrobial resistance profiles of CPE in our centre.

METHODS

All non-duplicate CPE isolates between 1 August 2020 and 31 August 2023 in a large teaching trust in England were retrospectively studied. Cefiderocol antimicrobial susceptibility testing (AST) was performed using disc diffusion, ceftazidime/avibactam using disc diffusion and gradient diffusion, and ceftazidime/avibactam aztreonam synergy using the double disc diffusion method. EUCAST version 14.0 breakpoints were used.

RESULTS

A total of 158 CPE from 136 patients were isolated. Most patients were colonized with CPE, but only 16.9% had active infections. Thirty-day all-cause mortality was 10.3%, increasing to 13% for patients with infections and to 18.2% for bacteraemias. OXA-48 was the most prevalent carbapenemase (48.1%), followed by NDM (38%). All isolates exhibited MDR profiles, with high levels of resistance to meropenem (41.1%). Resistance to cefiderocol was found in 69.7% of NDM-producing isolates, with a further 18.2% in the area of technical uncertainty. Ceftazidime/avibactam and aztreonam synergy was seen in 87.5% of isolates, whereas colistin and fosfomycin susceptibility remained high (98.1% and 97.2%, respectively). All OXA-48-producing isolates were susceptible to ceftazidime/avibactam, and 15.3% were resistant to cefiderocol. No patients had been exposed to cefiderocol beforehand, whereas three had been exposed to ceftazidime/avibactam. The most common risk factor for CPE isolation was travel and receiving healthcare abroad, especially in Asia.

CONCLUSIONS

We found high rates of resistance to cefiderocol in CPE isolates without prior cefiderocol exposure. Our results prohibit empirical use of cefiderocol for the treatment of CPE infections in our setting.

Updates on the Activity, Efficacy and Emerging Mechanisms of Resistance to Cefiderocol

In recent years, novel antimicrobials have been developed to counter the emergence of antimicrobial resistance and provide effective therapeutic options against multidrug-resistant (MDR) Gram-negative bacilli (GNB). Cefiderocol, a siderophore cephalosporin, represents a novel valuable antimicrobial drug for the treatment of infections caused by MDR-GNB. The mechanism of cefiderocol to penetrate through the outer membrane of bacterial cells, termed "Trojan horse", makes this antimicrobial drug unique and immune to the various resistance strategies adopted by GNB. Its broad spectrum of action, potent antibacterial activity, pharmacokinetics properties, safety, and tolerability make cefiderocol a key drug for the treatment of infections due to MDR strains. Although this novel antimicrobial molecule contributed to revolutionizing the therapeutic armamentarium against MDR-GNB, the recent emergence of cefiderocol-resistant strains has redefined its role in clinical practice and required new strategies to preserve its antibacterial activity. In this review, we provide an updated discussion regarding the mechanism of action, emerging mechanisms of resistance, pharmacokinetic/pharmacodynamic (PK/PD) properties, and efficacy data of cefiderocol against the major Gram-negative bacteria and future prospects.

Cefiderocol susceptibility of 146 Stenotrophomonas maltophilia strains clinically isolated from blood in two Japanese hospitals over a 10-year period

Previous reports focusing on cefiderocol susceptibility against Stenotrophomonas maltophilia have included a large number of noninvasive or colonized isolates, and data focusing on invasive S. maltophilia strains are still lacking. We retrospectively investigated the cefiderocol susceptibility of stored S. maltophilia strains that caused bacteremia at two Japanese hospitals. The MIC50 and MIC90 were 0.06 μg/mL and 0.25 μg/mL, respectively, while the susceptibility rate was 99.3% (current CLSI breakpoint criteria). Our results provide the MIC distribution of bacteremic S. maltophilia isolates in Japan and show the preserved cefiderocol susceptibility of S. maltophilia among clinically invasive pathogenic strains.

Recent updates in treating carbapenem-resistant infections in patients with hematological malignancies

INTRODUCTION

Patients with hematological malignancies (PHMs) are at increased risk for infections caused by carbapenem-resistant organisms (CROs) due to frequent exposure to broad-spectrum antibiotics and prolonged hospital stays. These infections result in high mortality and morbidity rates along with delays in chemotherapy, longer hospitalizations, and increased health care costs.

AREAS COVERED

Treatment alternatives for CRO infections in PHMs.

EXPERT OPINION

The best available treatment option for KPC and OXA-48 producers is ceftazidime/avibactam. Imipenem/cilastatin/relebactam and meropenem/vaborbactam remain as the alternative options. They can also be used as salvage therapy in KPC-positive Enterobacterales infections resistant to ceftazidime/avibactam, if in vitro susceptibility is shown. Treatment of metallo-β-lactamase producers is an unmet need. Ceftazidime/avibactam plus aztreonam or aztreonam/avibactam seems to be the most reliable option for metallo-β-lactamase producers. As a first-line option for carbapenem-resistant Pseudomonas aeruginosa infections, ceftolozane/tazobactam is preferable and ceftazidime/avibactam and imipenem/cilastatin/relebactam constitute alternative regimens. Although sulbactam/durlobactam is the most reliable option against carbapenem-resistant Acinetobacter baumannii infections, its utility as monotherapy and in PHMs is not yet known. Cefiderocol can be selected as a 'last-resort' option for CRO infections. New risk score models supported by artificial intelligence algorithms can be used to predict the exact risk of infections in previously colonized patients.

National Multicenter Study on the Prevalence of Carbapenemase-Producing Enterobacteriaceae in the Post-COVID-19 Era in Argentina: The RECAPT-AR Study

The COVID-19 pandemic has exacerbated the global antimicrobial resistance (AMR) crisis. Consequently, it is more urgent than ever to prioritize AMR containment and support countries in improving the detection, characterization, and rapid response to emerging AMR threats. We conducted a prospective, multicenter study to assess the prevalence of carbapenemase-producing Enterobacterales in infectious processes in Argentina during the post-COVID-19 pandemic period and explore therapeutic alternatives for their treatment (RECAPT-AR study).

METHODS

A total of 182 hospitals participated by submitting Enterobacterales clinical isolates to the National Reference Laboratory (NRL) during the first three weeks of November 2021. Inclusion criteria were defined as an ertapenem MIC ≥ 0.5 mg/L, a zone diameter ≤ 22 mm. Carbapenemase genes and those coding for major extended-spectrum β-lactamases were molecularly characterized using multiplex PCR at the NRL. Antibiotic susceptibility testing followed international standards (CLSI and EUCAST).

RESULTS

The NRL analyzed 821 Enterobacterales isolates. Metallo-β-lactamase (MBL, 42.0%) and KPC (39.8%) accounted for 81.8% of carbapenemases, followed by OXA-163 (7.4%), a variant of OXA-48 with additional activity against extended-spectrum cephalosporins, and enzyme combinations (8.3%). These combinations included NDM plus KPC (3.4%), OXA-163 plus KPC (2.4%), and OXA-163 plus NDM (2.1%). Klebsiella pneumoniae was the main species recovered, representing 76% of the isolates. According to the carbapenemase classes or combinations, tigecycline exhibited a susceptibility range of 33-83%, fosfomycin 59-81%, colistin 27-78%, and amikacin 17-81%. Ceftazidime-avibactam (CZA) and imipenem-relebactam (IMR) showed 92% and 98% susceptibility against serine carbapenemases, respectively. Meanwhile, aztreonam-avibactam (AZA) exhibited 96-98% susceptibility against all carbapenemase classes.

CONCLUSIONS

A new epidemiological landscape has emerged, characterized by the equivalent circulation of NDM and KPC. K. pneumoniae remains the primary species responsible for their dissemination. The co-production of carbapenemase combinations, particularly KPC plus NDM, was confirmed, mainly in K. pneumoniae. High activity was observed for AZA against MBLs and for CZA and IMR against KPC and OXA-163 carbapenemases.

Navigating the Current Treatment Landscape of Metallo-β-Lactamase-Producing Gram-Negative Infections: What are the Limitations?

The spread of carbapenemase-producing gram-negative pathogens, especially those producing metallo-β-lactamases (MBLs), has become a major health concern. MBLs are molecularly the most diverse carbapenemases, produced by a wide spectrum of gram-negative organisms, including the Enterobacterales, Pseudomonas spp., Acinetobacter baumannii, and Stenotrophomonas maltophilia, and can hydrolyze most β-lactams using metal ion cofactors in their active sites. Over the years, the prevalence of MBL-carrying isolates has increased globally, particularly in Asia. MBL infections are associated with adverse clinical outcomes including longer length of hospital stay, ICU admission, and increased mortality across the globe. The optimal treatment for MBL infections not only depends on the pathogen but also on the underlying resistance mechanisms. Currently, there are only few drugs or drug combinations that can efficiently offset MBL-mediated resistance, which makes the treatment of MBL infections challenging. The rising concern of MBLs along with the limited treatment options has led to the need and development of drugs that are specifically targeted towards MBLs. This review discusses the prevalence of MBLs, their clinical impact, and the current treatment options for MBL infections and their limitations. Furthermore, this review will discuss agents currently in the pipeline for treatment of MBL infections.

Sulbactam-durlobactam for the treatment of Acinetobacter baumannii-calcoaceticus complex

INTRODUCTION

Infections with Acinetobacter baumannii-calcoaceticus complex (ABC) pose difficulty for clinicians given a limited arsenal of effective antimicrobials. Sulbactam/durlobactam provides a novel treatment option for patients experiencing hospital- or ventilator-acquired pneumonia with susceptible strains.

AREAS COVERED

This review provides a comprehensive discussion of sulbactam/durlobactam, including basic characteristics, in vitro activity, and clinical trial data supporting its use for the treatment of ABC. Manufacturer's data, published literature to date, and conference data are utilized in this review.

EXPERT OPINION

Sulbactam/durlobactam offers clinicians a new and effective treatment option for resistant ABC infection. Sulbactam, when combined with durlobactam, displays enhanced potency against ABC isolates, which has translated into positive clinical outcomes observed in clinical trials and post-marketing case studies. Although overall treatment indications and clinical experience are limited to date, sulbactam/durlobactam offers a familiar and favorable safety profile in comparison with alternative agents. Factors associated with use of combination antibiotic therapy, availability of commercial drug susceptibility testing, and cost-effectiveness are all currently key considerations for sulbactam/durlobactam use.

Successful therapy of a newborn with Stenotrophomonas maltophilia nosocomial pneumonia with cefiderocol

Cefiderocol is a new siderophore-beta-lactam antibiotic used for the treatment of severe multidrug-resistant infections like sepsis, hospital-acquired and ventilator-associated pneumonia in adults, but there are only single reports on its use in the neonatal population. We describe the successful cefiderocol treatment of a newborn with pneumogenic sepsis due to Stenotrophomonas maltophilia.

Evaluation of the quickmic system in the rapid diagnosis of Gram-negative bacilli bacteremia

Rapid microbiological diagnosis of the antibiotic susceptibility of Gram-negative bacilli is a priority in clinical microbiology, especially in cases of bacteremia. The rapid advancement of antimicrobial resistance proposes a challenge for empirical antibiotic therapy and shows the need for fast antibiotic susceptibility diagnostics to guide treatments. The QuickMIC System (Gradientech AB, Uppsala, Sweden) is a recently developed rapid diagnostic tool for antibiotic susceptibility testing. Our study evaluates a rapid phenotypic system (QuickMIC) that provides information on the susceptibility of 12 antibiotics against Escherichia coli, Klebsiella spp., Pseudomonas aeruginosa, Acinetobacter baumannii, Enterobacter cloacae, Proteus spp., Citrobacter spp., and Serratia marcescens. A total of 816 antibiotic/microorganism combinations were tested, resulting in eight discrepancies. The concordance between the antibiotics offered by QuickMIC and reference methods (MicroScan WalkAway plus system, Beckman Coulter; Etest (BioMerieux microdilution system (Bruker); Real-time PCR (GeneXpert, Cepheid); and immunochromatography (Biotech) was 99.02%. Time elapsed to obtain a valid minimal inhibitory concentration (MIC) was between 2 and 4 h. The QuickMIC system allows for the early adjustment of antibiotic treatment in these infections. Given the existing limitations of currently available rapid methods, its clinical utility is particularly relevant in the management of P. aeruginosa infections and AmpC-producing Enterobacterales. The use of rapid methods can help diversify antibiotic use and reduce carbapenem consumption.

IMPORTANCE

The rapid diagnosis of antibiotic sensitivity in Gram-negative bacilli is of paramount importance in clinical microbiology, particularly in cases of bacteremia. The escalating challenge of antimicrobial resistance underscores the need for expeditious antibiotic susceptibility diagnostics to guide empirical antibiotic therapy effectively. In light of this, we present our study that evaluates the QuickMIC System, a recently developed rapid diagnostic antibiogram. QuickMIC System, offers a novel approach to phenotypic testing, providing information on the activity of 12 antibiotics against key pathogens, including Escherichia coli, Klebsiella spp., Pseudomonas aeruginosa, Acinetobacter baumannii, Enterobacter cloacae, Proteus spp., Citrobacter spp., and Serratia marcescens. Our investigation involved testing a total of 816 antibiotic/microorganism combinations. The study demonstrated an impressive 99.02% concordance between the QuickMIC System and the reference methods, with only eight discrepancies observed. The time to actionable minimum inhibitory concentration (MIC) ranged between 2 and 4 h, highlighting the system's efficiency in providing rapid results.

RESIST ACINETO test for the rapid detection of NDM and OXA acquired carbapenemases directly from blood culture in Acinetobacter species

Carbapenem-resistant Acinetobacter baumannii (CRAB) are increasingly reported worldwide and a leading cause of mortality associated with antimicrobial resistance. Their early detection, particularly in the cases of bloodstream infections, is crucial in attempting to initiate effective antibiotic treatment. The immunochromatographic assay RESIST ACINETO (Coris BioConcept) is a new test developed for the detection of OXA-23, OXA-40/58, and New-Delhi Metallo-beta-lactamase (NDM) carbapenemases in Acinetobacter spp. We evaluated this test on a collection of 121 Acinetobacter spp. clinical isolates, including 104 carbapenemase producers (97 carbapenemases targeted by the test) and 17 non-carbapenemase producers. The performance of the RESIST ACINETO test was evaluated according to the manufacturer's recommendations from bacterial and blood cultures. The strains producing the carbapenemases OXA-23, -40, -58, or/and NDM were accurately detected from bacterial cultures and directly from blood cultures, with the exception of one OXA-23/NDM-1-positive Acinetobacter radioresistens isolate (only detected through standard culture). None of the non-carbapenemase producers tested positive. The RESIST ACINETO test demonstrated sensitivity/specificity of 100%/100% and 99%/100% on bacterial and blood cultures, respectively.

IMPORTANCE

The incidence of bloodstream infections with carbapenem-resistant Acinetobacter baumannii (CRAB) could be very high in some countries such as the Balkans or Southeast Asia. In case of positive blood cultures with Gram-negative bacteria, the use of the RESIST ACINETO test could prove highly beneficial for the rapid identification of these imipenem-resistant bacteria and their antibiotic resistance mechanisms. In addition, it is now well established that New-Delhi Metallo-beta-lactamase (NDM) carbapenemase-producing isolates can have increased MICs of cefiderocol, which is an alternative treatment for these infections. This test may also allow the optimization of treatment based on the type of carbapenemase present. Finally, the RESIST ACINETO test is a rapid, easy-to-use, and cost-effective assay that demonstrates excellent performance in detecting the major acquired carbapenemases present in the Acinetobacter species.

Real-world performance of susceptibility testing for cefiderocol: insights from a prospective multicentre study on Gram-negative bacteria

Objectives

Cefiderocol is a novel siderophore-conjugated cephalosporin developed for the treatment of multidrug-resistant Gram-negative bacterial (GNB) infections. However, the current gold standard for cefiderocol susceptibility testing, broth microdilution (BMD) using iron-depleted cation-adjusted Mueller-Hinton broth, presents challenges for many microbiology laboratories. In this study, we evaluate the real-world performance of disc diffusion (DD) and a commercial BMD method (ComASP®) to test cefiderocol susceptibility in a series of isolates collected prospectively from severely ill patients in a multicentre study.

Methods

The susceptibilities of 1472 isolates (632 Enterobacterales, 532 Pseudomonas aeruginosa, 84 Acinetobacter spp. and 224 Stenotrophomonas maltophilia) collected in 60 Spanish hospitals were analysed following the EUCAST 2023 and 2024 criteria. We assessed the performance of DD (cefiderocol 30 μg disc, Liofilchem) and a commercial BMD method (ComASP® Cefiderocol, Liofilchem).

Results

A total of 1408 and 1450 isolates were susceptible by DD and ComASP® BMD, respectively. Overall, the agreement between both methods was 96.9%. Forty-four isolates were resistant by DD but susceptible by ComASP® BMD, and two were susceptible by DD but resistant by ComASP® BMD (Acinetobacter baumannii isolates). Adoption of the updated 2024 EUCAST DD breakpoints and areas of technical uncertainty (ATUs) led to a decrease in susceptibility among Enterobacterales (95.3% versus 92.6%).

Conclusions

DD is a straightforward, rapid and accessible method for routine determination of cefiderocol susceptibility in real-world practice. ComASP® BMD shows a high agreement with DD in susceptible isolates and may help to resolve DD interpretability concerns in isolates with susceptibility results within the ATU, but caution is warranted when testing resistant isolates.

Use of Cefiderocol in Adult Patients: Descriptive Analysis from a Prospective, Multicenter, Cohort Study

INTRODUCTION

Cefiderocol is a siderophore cephalosporin showing activity against various carbapenem-resistant Gram-negative bacteria (CR-GNB). No data currently exist about real-world use of cefiderocol in terms of types of therapy (e.g., empirical or targeted, monotherapy or combined regimens), indications, and patient characteristics.

METHODS

In this multicenter, prospective study, we aimed at describing the use of cefiderocol in terms of types of therapy, indications, and patient characteristics.

RESULTS

Cefiderocol was administered as empirical and targeted therapy in 27.5% (55/200) and 72.5% (145/200) of cases, respectively. Overall, it was administered as monotherapy in 101/200 cases (50.5%) and as part of a combined regimen for CR-GNB infections in the remaining 99/200 cases (49.5%). In multivariable analysis, previous isolation of carbapenem-resistant Acinetobacter baumannii odds ratio (OR) 2.56, with 95% confidence interval (95% CI) 1.01-6.46, p = 0.047] and previous hematopoietic stem cell transplantation (OR 8.73, 95% CI 1.05-72.54, p = 0.045) were associated with administration of cefiderocol as part of a combined regimen, whereas chronic kidney disease was associated with cefiderocol monotherapy (OR 0.38 for combined regimen, 95% CI 0.16-0.91, p = 0.029). Cumulative 30-day mortality was 19.8%, 45.0%, 20.7%, and 22.7% in patients receiving targeted cefiderocol for infections by Enterobacterales, A. baumannii, Pseudomonas aeruginosa, and any metallo-β-lactamase producers, respectively.

CONCLUSIONS

Cefiderocol is mainly used for targeted treatment, although empirical therapies account for more than 25% of prescriptions, thus requiring dedicated standardization and guidance. The almost equal distribution of cefiderocol monotherapy and cefiderocol-based combination therapies underlines the need for further study to ascertain possible differences in efficacy between the two approaches.

Genomic Insights into Vietnamese Extended-Spectrum β-Lactamase-9-Producing Extensively Drug-Resistant Pseudomonas aeruginosa Isolates Belonging to the High-Risk Clone ST357 Obtained from Bulgarian Intensive Care Unit Patients

Extensively drug-resistant P. aeruginosa (XDR-PA) has been highlighted as a serious public health threat. The present study aimed to explore the genomic characteristics of two Vietnamese extended-spectrum β-lactamase-9 (VEB-9)-producing XDR-PA isolates from Bulgaria in comparison to all blaVEB-9-positive strains with available genomes. The isolates designated Pae51 and Pae52 were obtained from tracheobronchial aspirates of intensive care unit (ICU) patients. Antimicrobial susceptibility testing, whole-genome sequencing, RT-qPCR, and phylogenomic analysis were performed. Pae51 and Pae52 were resistant to most antipseudomonal β-lactams including carbapenems, aminoglycosides, and fluoroquinolones but remained susceptible to colistin and cefiderocol. Numerous resistance determinants were detected: blaVEB-9, blaPDC-3, blaOXA-10, blaOXA-50, aac(6')-II, ant(2″)-Ia, ant(3″)-IIa, aph(3')-IIb, cprP, catB7, dfrB2, sul1, fosA, and tet(A). Both isolates carried complex integrons with blaVEB-9 and tet(A) embedded next to the conservative 3' end sequences. A variety of virulence factors were also identified, including the type III secretion system exotoxin U. Pae51 and Pae52 differed by only four SNPs and belonged to the high-risk clone ST357. To our knowledge, this is the first report of blaVEB-9-positive XDR-PA isolates in Bulgaria presenting a detailed genomic analysis. The development of novel antimicrobial strategies for such pathogens should be an essential part of infection control stewardship practices in ICU wards.

Challenges Facing Two Outbreaks of Carbapenem-Resistant Acinetobacter baumannii: From Cefiderocol Susceptibility Testing to the Emergence of Cefiderocol-Resistant Mutants

Carbapenem-resistant Acinetobacter baumannii (CRAB) infections are associated with poor outcomes depending on patient's conditions, clinical severity and type of infection, and treatment is challenging given the limited therapeutic options available. The aim of this study was to describe the clinical and microbiological characteristics of two outbreaks caused by CRAB in an intensive care unit (ICU). In addition, the mechanisms of resistance detected in these strains and the treatment chosen according to the available therapeutic options were analyzed. Overall, 28 patients were included. Ten patients (35.71%) had ventilator-associated pneumonia (VAP), ten (35.71%) had a bloodstream infection (BSI), and eight (28.57%) were only colonized. Recurrent infection occurred in 25% (5/20) of infected patients. Two different strains of A. baumannii were isolated from the index patient of the first outbreak. The first strain belonged to the ST85 and carried the blaNDM-1 carbapenemase gene, while the second belonged to the ST2 and carried blaOXA-23, and blaOXA-66 carbapenemase genes. The phylogenetic analysis revealed that the ST2 strain was the cause of the major outbreak, and mutations in the AmpC gene were related to progressive increasing minimum inhibitory concentration (MIC) and finally, cefiderocol-resistance in one strain. The CRAB isolates from the second outbreak were also identified as ST2. Cefiderocol-resistant strains tests identified by the disc diffusion method were involved in 24% (6/25) of nosocomial infections. Using broth microdilution (BMD) ComASP® only, 33.3% (2/6) of these strains were cefiderocol-resistant. All-cause ICU mortality was 21.4%. Conclusions: Cefiderocol is the first approved siderophore cephalosporin for the treatment of CRAB infections. Cefiderocol-resistant strains were related with blaNDM-1 carbapenemase and mutations in the AmpC gene. Cefiderocol-resistant strains or that cannot be properly interpreted by disk diffusion, should be retested using BMD for definitive categorization.

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.

Comparison of Different Methods for Assaying the In Vitro Activity of Cefiderocol against Carbapenem-Resistant Pseudomonas aeruginosa Strains: Influence of Bacterial Inoculum

Carbapenem-resistant Pseudomonas aeruginosa infections represent a critical public health concern, highlighting the need for the development of effective antibiotics. Cefiderocol demonstrated potent in vitro activity against Pseudomonas aeruginosa, particularly in strains that are resistant to other drugs. However, concerns regarding the emergence of drug-resistant strains persist. This study, conducted with 109 carbapenem-resistant Pseudomonas aeruginosa strains from the Spanish Hospital (Dr. Balmis, Alicante). The study evaluated susceptibility to cefiderocol in comparison to alternative antibiotics and including their susceptibility to bacterial inoculum, while assessing various testing methods. Our findings revealed high susceptibility to cefiderocol against carbapenem-resistant strains, with only 2 of 109 strains exhibiting resistance. Comparative analysis demonstrated superiority of cefiderocol towards alternative antibiotics. Both the E-test and disk-diffusion methods showed 100% concordance with the microdilution method in classifying strains as susceptible or resistant. However, 4.6% (5/109) of disc zone diameters fell within the technical uncertainty zone, so the E-test technique was found to be more useful in routine clinical practice. Additionally, escalating bacterial inoculum correlated with decreases in vitro activity, so this parameter should be adjusted very carefully in in vivo studies. This study underscores cefiderocol's potential as a therapeutic option for carbapenem-resistant Pseudomonas aeruginosa infections. However, the emergence of drug-resistant strains emphasizes the critical need for a wise use of antibiotics and a continuous monitoring of resistance to antibiotics. Based on our in vitro data, further investigation concerning the impact of bacterial inoculum on drug efficacy is warranted in order to detect resistance mechanisms and optimize treatment strategies, thereby mitigating the risk of resistance.

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.

Treatment Strategies of Colistin Resistance Acinetobacter baumannii Infections

Acinetobacter baumannii has emerged as a pressing challenge in clinical practice, mainly due to the development of resistance to multiple antibiotics, including colistin, one of the last-resort treatments. This review highlights all the possible mechanisms of colistin resistance and the genetic basis contributing to this resistance, such as modifications to lipopolysaccharide or lipid A structures, alterations in outer membrane permeability via porins and heteroresistance. In light of this escalating threat, the review also evaluates available treatment options. The development of new antibiotics (cefiderocol, sulbactam/durlobactam) although not available everywhere, and the use of various combinations and synergistic drug combinations (including two or more of the following: a polymyxin, ampicillin/sulbactam, carbapenems, fosfomycin, tigecycline/minocycline, a rifamycin, and aminoglycosides) are discussed in the context of overcoming colistin resistance of A. baumannii infections. Although most studied combinations are polymyxin-based combinations, non-polymyxin-based combinations have been emerging as promising options. However, clinical data remain limited and continued investigation is essential to determine optimal therapeutic strategies against colistin-resistant A. baumannii.

Performance evaluation of Bruker UMIC® microdilution panel and disc diffusion to determine cefiderocol susceptibility in Enterobacterales, Acinetobacter baumannii, Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Achromobacter xylosoxidans and Burkolderia species

PURPOSE

Cefiderocol susceptibility testing (AST) represents an open challenge for clinical microbiology. Herein, we evaluated the performance of the UMIC® Cefiderocol broth microdilution (BMD) test and disc diffusion on Gram-negative species.

METHODS

UMIC® Cefiderocol BMD test, disc diffusion and reference BMD were in parallel performed on a collection of 256 clinical isolates. Categorical agreement (CA), essential agreement (EA), bias, major errors (MEs) and very major errors (VMEs) were calculated for both AST methods.

RESULTS

The UMIC® Cefiderocol BMD strip exhibited an EA < 90% (85.5%), a CA higher than 90% (93.7%) and a low number of VMEs (n = 4, 4.2%) and MEs (n = 12, 7.4%). UMIC® Cefiderocol identified 96.2% of the resistant isolates [Enterobacterales, (39/40); P. aeruginosa (19/19); A. xylosoxidans (5/6); S. maltophilia (5/6); Burkholderia spp. (8/8)]. Disc diffusion showed a high CA (from 94.9 to 100%) regardless of disc manufacturer in Enterobacterales, P. aeuroginosa, A. baumannii and S. maltophilia. However, high rates of results falling in the area of technical uncertainty (ATU) were observed in Enterobacterales (34/90, 37.8%) and P. aeruginosa (16/40, 40%). Disc diffusion showed a poor performance in A. xylosoxidans and Burkholderia spp. if PK/PD breakpoint was used (overall, 5/9 VMEs; in contrast, the use of P. aeruginosa-specific breakpoints resulted in 100% of CA with 24.6% of results in the ATU).

CONCLUSION

In conclusion, disc diffusion and UMIC® Cefiderocol are valid methods for the determination of cefiderocol susceptibility. Given the high number of results in the ATU by disc diffusion, a combined use of both AST methods may represent a solution to overcome the challenge of cefiderocol susceptibility testing in routine microbiology laboratories.

Carbapenem-resistant Klebsiella pneumoniae: the role of plasmids in emergence, dissemination, and evolution of a major clinical challenge

INTRODUCTION

Klebsiella pneumoniae is a major agent of healthcare-associated infections and a cause of some community-acquired infections, including severe bacteremic infections associated with metastatic abscesses in liver and other organs. Clinical relevance is compounded by its outstanding propensity to evolve antibiotic resistance. In particular, the emergence and dissemination of carbapenem resistance in K. pneumoniae has posed a major challenge due to the few residual treatment options, which have only recently been expanded by some new agents. The epidemiological success of carbapenem-resistant K. pneumoniae (CR-Kp) is mainly linked with clonal lineages that produce carbapenem-hydrolyzing enzymes (carbapenemases) encoded by plasmids.

AREAS COVERED

Here, we provide an updated overview on the mechanisms underlying the emergence and dissemination of CR-Kp, focusing on the role that plasmids have played in this phenomenon and in the co-evolution of resistance and virulence in K. pneumoniae.

EXPERT OPINION

CR-Kp have disseminated on a global scale, representing one of the most important contemporary public health issues. These strains are almost invariably associated with complex multi-drug resistance (MDR) phenotypes, which can also include recently approved antibiotics. The heterogeneity of the molecular bases responsible for these phenotypes poses significant hurdles for therapeutic and diagnostic purposes.

Bacterial Pathogenesis and Antimicrobial Strategy

Antimicrobial resistance and multidrug resistance are major global health concerns [...].

Approaches to Testing Novel β-Lactam and β-Lactam Combination Agents in the Clinical Laboratory

The rapid emergence of multi-drug resistant Gram-negative pathogens has driven the introduction of novel β-lactam combination agents (BLCs) to the antibiotic market: ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, cefiderocol, and sulbactam-durlobactam. These agents are equipped with innovative mechanisms that confer broad Gram-negative activity, notably against certain challenging carbapenemases. While their introduction offers a beacon of hope, clinical microbiology laboratories must navigate the complexities of susceptibility testing for these agents due to their diverse activity profiles against specific β-lactamases and the possibility of acquired resistance mechanisms in some bacterial isolates. This review explores the complexities of these novel antimicrobial agents detailing the intricacies of their application, providing guidance on the nuances of susceptibility testing, interpretation, and result reporting in clinical microbiology laboratories.