In Vitro Activity of Cefiderocol against U.S. and European Gram-Negative Clinical Isolates Collected in 2020 as Part of the SENTRY Antimicrobial Surveillance Program

Navigating the network: a narrative overview of AMR surveillance and data flow in the United States

The antimicrobial resistance (AMR) surveillance landscape in the United States consists of a data flow that starts in the clinical setting and is maintained by a network of national and state public health laboratories. These organizations are well established, with robust methodologies to test and confirm antimicrobial susceptibility. Still, the bridge that guides the flow of data is often one directional and caught in a constant state of rush hour that can only be refined with improvements to infrastructure and automation in the data flow. Moreover, there is an absence of information in the literature explaining the processes clinical laboratories use to coalesce and share susceptibility test data for AMR surveillance, further complicated by variability in testing procedures. This knowledge gap limits our understanding of what is needed to improve and streamline data sharing from clinical to public health laboratories. Successful models of AMR surveillance display attributes like 2-way communication between clinical and public health laboratories, centralized databases, standardized data, and the use of electronic health records or data systems, highlighting areas of opportunity and improvement. This article explores the roles and processes of the organizations involved in AMR surveillance in the United States and identifies current knowledge gaps and opportunities to improve communication between them through standardization, communication, and modernization of data flow.

Unitary Tract Infection Treatment: When to Use What Agents including Beta-lactam Combination Agents

In this study, the authors review antibiotic treatment options for both acute uncomplicated and complicated urinary tract infection (UTI). In addition, they also review regimens used in the setting of drug-resistant pathogens including vancomycin resistant Enterococcus, extended spectrum beta-lactamase (ESBL) producing Enterobacterals, carbapenem-resistant Enterobacterals and carbapenem-resistant Pseudomonas, which are encountered with increasing frequency.

How New Regulation of Laboratory-Developed Antimicrobial Susceptibility Tests Will Affect Infectious Diseases Clinical Practice

Antimicrobial resistance (AMR) affects 2.8 million Americans annually. AMR is identified through antimicrobial susceptibility testing (AST), but current and proposed regulatory policies from the United States Food and Drug Administration (FDA) jeopardize the future availability of AST for many microorganisms. Devices that perform AST must be cleared by the FDA using their susceptibility test interpretive criteria, also known as breakpoints. The FDA list of breakpoints is relatively short. Today, laboratories supplement FDA breakpoints using breakpoints published by the Clinical and Laboratory Standards Institute, using legacy devices and laboratory-developed tests (LDTs). FDA proposes to regulate LDTs, and with no FDA breakpoints for many drug-bug combinations, the risk is loss of AST for key clinical indications and stifling innovation in technology development. Effective solutions require collaboration between manufacturers, infectious diseases clinicians, pharmacists, laboratories, and the FDA.

In vitro activity of cefiderocol against European Pseudomonas aeruginosa and Acinetobacter spp., including isolates resistant to meropenem and recent β-lactam/β-lactamase inhibitor combinations

Carbapenem-resistant Pseudomonas aeruginosa and Acinetobacter spp. represent major threats and have few approved therapeutic options. Non-‍fermenting Gram-negative isolates were collected from hospitalized inpatients from 49 sites in 6 European countries between 01 January 2020 and 31 December 2020 and underwent susceptibility testing against cefiderocol and β-lactam/β-lactamase inhibitor combinations. Meropenem-resistant (MIC >8 mg/L), cefiderocol-susceptible isolates were analyzed by PCR, and cefiderocol-resistant isolates were analyzed by whole-genome sequencing to identify resistance mechanisms. Overall, 1,451 (950 P. aeruginosa; 501 Acinetobacter spp.) isolates were collected, commonly from the respiratory tract (42.0% and 39.3%, respectively). Cefiderocol susceptibility was higher than ‍β‍-‍l‍a‍c‍t‍a‍m‍/‍β‍-‍l‍a‍c‍t‍a‍mase‍ inhibitor combinations against P. aeruginosa (98.9% vs 83.3%-91.4%), and P. ‍aeruginosa resistant to meropenem (n = 139; 97.8% vs 12.2%-59.7%), β-lactam/β-lactamase inhibitor combinations (93.6%-98.1% vs 10.7%-71.8%), and both meropenem and ceftazidime-avibactam (96.7% vs 5.0%-‍‍45.0%) or ‍ceftolozane-tazobactam (98.4% vs 8.1%-54.8%), respectively. Cefiderocol and sulbactam-durlobactam susceptibilities were high against Acinetobacter spp. (92.4% and 97.0%) and meropenem-resistant Acineto‍bacter ‍spp. (n = 227; 85.0% and 93.8%) but lower against sulbactam-durlobactam- (n ‍= 15; 13.3%) and cefiderocol- (n = 38; 65.8%) resistant isolates, respectively. Among meropenem-resistant P. aeruginosa and Acinetobacter spp., the most common β-‍‍lactamase genes were metallo-β-lactamases [30/139; blaVIM-2 (15/139)] and oxacillinases [215/227; blaOXA-23 (194/227)], respectively. Acquired β-lactamase genes were identified in 1/10 and 32/38 of cefiderocol-resistant P. aeruginosa and Acinetobacter spp., and pirA-like or piuA mutations in 10/10 and 37/38, respectively. Conclusion: cefiderocol susceptibility was high against P. aeruginosa and Acinetobacter spp., including meropenem-resistant isolates and those resistant to recent β-lactam/β-lactamase inhibitor combinations common in first-line treatment of European non-fermenters.

IMPORTANCE

This was the first study in which the in vitro activity of cefiderocol and non-licensed β-lactam/β-lactamase inhibitor combinations were directly compared against Pseudomonas aeruginosa and Acinetobacter spp., including meropenem- and β-lactam/β-lactamase inhibitor combination-resistant isolates. A notably large number of European isolates were collected. Meropenem resistance was defined according to the MIC breakpoint for high-dose meropenem, ensuring that data reflect antibiotic activity against isolates that would remain meropenem resistant in the clinic. Cefiderocol susceptibility was high against non-fermenters, and there was no apparent cross resistance between cefiderocol and β-lactam/β-lactamase inhibitor combinations, with the exception of sulbactam-durlobactam. These results provide insights into therapeutic options for infections due to resistant P. aeruginosa and Acinetobacter spp. and indicate how early susceptibility testing of cefiderocol in parallel with β-lactam/β-lactamase inhibitor combinations will allow clinicians to choose the effective treatment(s) from all available options. This is particularly important as current treatment options against non-fermenters are limited.

Global mapping of antibiotic resistance rates among clinical isolates of Stenotrophomonas maltophilia: a systematic review and meta-analysis

INTRODUCTION

Infections caused by Stenotrophomonas maltophilia are clinically important due to its intrinsic resistance to a broad range of antibiotics. Therefore, selecting the most appropriate antibiotic to treat S. maltophilia infection is a major challenge.

AIM

The current meta-analysis aimed to investigate the global prevalence of antibiotic resistance among S. maltophilia isolates to the develop more effective therapeutic strategies.

METHOD

A systematic literature search was performed using the appropriate search syntax after searching Pubmed, Embase, Web of Science and Scopus databases (May 2023). Statistical analysis was performed using Pooled and the random effects model in R and the metafor package. A total of 11,438 articles were retrieved. After a thorough evaluation, 289 studies were finally eligible for inclusion in this systematic review and meta-analysis.

RESULT

Present analysis indicated that the highest incidences of resistance were associated with doripenem (97%), cefoxitin (96%), imipenem and cefuroxime (95%), ampicillin (94%), ceftriaxone (92%), aztreonam (91%) and meropenem (90%) which resistance to Carbapenems is intrinsic. The lowest resistance rates were documented for minocycline (3%), cefiderocol (4%). The global resistance rate to TMP-SMX remained constant in two periods before and after 2010 (14.4% vs. 14.6%). A significant increase in resistance to tigecycline and ceftolozane/tazobactam was observed before and after 2010.

CONCLUSIONS

Minocycline and cefiderocol can be considered the preferred treatment options due to low resistance rates, although regional differences in resistance rates to other antibiotics should be considered. The low global prevalence of resistance to TMP-SMX as a first-line treatment for S. maltophilia suggests that it remains an effective treatment option.

Current Therapeutic Approaches for Multidrug-Resistant and Extensively Drug-Resistant Acinetobacter baumannii Infections

The treatment of Acinetobacter baumannii infections remains a challenge for physicians worldwide in the 21st century. The bacterium possesses a multitude of mechanisms to escape the human immune system. The consequences of A. baumannii infections on morbidity and mortality, as well on financial resources, remain dire. Furthermore, A. baumannii superinfections have also occurred during the COVID-19 pandemic. While prevention is important, the antibiotic armamentarium remains the most essential factor for the treatment of these infections. The main problem is the notorious resistance profile (including resistance to carbapenems and colistin) that this bacterium exhibits. While newer beta lactam/beta-lactamase inhibitors have entered clinical practice, with excellent results against various infections due to Enterobacteriaceae, their contribution against A. baumannii infections is almost absent. Hence, we have to resort to at least one of the following, sulbactam, polymyxins E or B, tigecycline or aminoglycosides, against multidrug-resistant (MDR) and extensively drug-resistant (XDR) A. baumannii infections. Furthermore, the notable addition of cefiderocol in the fight against A. baumannii infections represents a useful addition. We present herein the existing information from the last decade regarding therapeutic advances against MDR/XDR A. baumannii infections.

Dynamic within-host cefiderocol heteroresistance caused by blaSHV-12 amplification in pandrug-resistant and hypervirulent Klebsiella pneumoniae sequence type 11

AIMS

Although cefiderocol (FDC) is not prescribed in China, FDC-resistant pandrug-resistant hypervirulent Klebsiella pneumoniae (PDR-hvKp) is emerging. In this study, we performed FDC susceptibility testing of clinical Kp isolates to explore the prevalence of FDC-resistant isolates and the mechanism of FDC-resistance.

METHODS

We retrospectively selected 151 carbapenem-resistant Kp isolates to assess FDC susceptibility. Seven isolates harboring blaSHV-12 from two patients were enrolled for whole-genome sequencing. The antimicrobial resistance, virulence, blaSHV-12 expression, and fitness costs in different media were examined. The amplification of blaSHV-12 was further investigated by qPCR and long-read sequencing.

RESULTS

The 151 isolates showed a low MIC50/MIC90 (1/4 mg/L) of FDC. The seven isolates were ST11 PDR-hvKp, and two represented FDC-resistance (MIC=32 mg/L). The IncR/IncFII plasmids of two FDC-resistant isolates harbored 6 and 15 copies of blaSHV-12, whereas four FDC-susceptible isolates carried one copy and one harbored three copies. These blaSHV-12 genes concatenated together and were located within the same 7.3 kb fragment flanked by IS26, which contributed to the increased expression and FDC resistance without fitness costs. The amplification of blaSHV-12 and FDC resistance could be induced by FDC in vitro and reversed during continuous passage.

CONCLUSIONS

The amplification of blaSHV-12 and the consequent dynamic within-host heteroresistance are important concerns for the rational application of antibiotics. Long-read sequencing might be a superior way to detect resistance gene amplification rapidly and accurately.

A FtsZ Inhibitor That Can Utilize Siderophore-Ferric Iron Uptake Transporter Systems for Activity against Gram-Negative Bacterial Pathogens

The global threat of multidrug-resistant Gram-negative bacterial pathogens necessitates the development of new and effective antibiotics. FtsZ is an essential and highly conserved cytoskeletal protein that is an appealing antibacterial target for new antimicrobial therapeutics. However, the effectiveness of FtsZ inhibitors against Gram-negative species has been limited due in part to poor intracellular accumulation. To address this limitation, we have designed a FtsZ inhibitor (RUP4) that incorporates a chlorocatechol siderophore functionality that can chelate ferric iron (Fe3+) and utilizes endogenous siderophore uptake pathways to facilitate entry into Gram-negative pathogens. We show that RUP4 is active against both Klebsiella pneumoniae and Acinetobacter baumannii, with this activity being dependent on direct Fe3+ chelation and enhanced under Fe3+-limiting conditions. Genetic deletion studies in K. pneumoniae reveal that RUP4 gains entry through the FepA and CirA outer membrane transporters and the FhuBC inner membrane transporter. We also show that RUP4 exhibits bactericidal synergy against K. pneumoniae when combined with select antibiotics, with the strongest synergy observed with PBP2-targeting β-lactams or MreB inhibitors. In the aggregate, our studies indicate that incorporation of Fe3+-chelating moieties into FtsZ inhibitors is an appealing design strategy for enhancing activity against Gram-negative pathogens of global clinical significance.

Cefiderocol: early clinical experience for multi-drug resistant gram-negative infections

Multi-drug resistant gram-negative bacteria present a significant global health threat. Cefiderocol (CFDC), a siderophore cephalosporin, has shown potential in combating this threat, but with the currently available data, its role in therapy remains poorly defined. This multi-center, retrospective cohort study evaluated the real-world application of CFDC across six U.S. medical centers from January 2018 to May 2023. Patients aged ≥18 years and who had received ≥72 hours of CFDC were included. The primary outcome was a composite of clinical success: survival at 30 days, absence of symptomatic microbiologic recurrence at 30 days following CFDC treatment initiation, and resolution of signs and symptoms. Secondary outcomes included time to CFDC therapy and on-treatment non-susceptibility to CFDC. A total of 112 patients were included, with median (interquartile range [IQR]) APACHE II scores of 15 (19-18). Clinical success was observed in 68.8% of patients, with a mortality rate of 16.1% and comparable success rates across patients infected with carbapenem-resistant gram-negative infections. The most common isolated organisms were Pseudomonas aeruginosa (61/112, 54.5%, of which 55/61 were carbapenem-resistant) and carbapenem-resistant Acinetobacter baumannii (32/112, 28.6%). Median (IQR) time to CFDC therapy was 77 (14-141) hours. Two patients experienced a non-anaphylactic rash as an adverse drug reaction. On-treatment non-susceptibility to CFDC was found in six patients, notably due to P. aeruginosa and A. baumannii.IMPORTANCECFDC was safe and clinically effective as a monotherapy or in combination in treating a variety of carbapenem-resistant gram-negative infections. Further prospective studies are warranted to confirm these findings.

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

BACKGROUND

Cefiderocol is a last resort option for carbapenem-resistant (CR) Gram-negative bacteria, especially metallo-β-lactamase-producing Pseudomonas aeruginosa and CR Acinetobacter baumannii. Monitoring global levels of cefiderocol non-susceptibility (CFDC-NS) is important.

OBJECTIVES

To systematically collate and examine studies investigating in vitro CFDC-NS and estimate the global prevalence of CFDC-NS against major Gram-negative pathogens.

DATA SOURCES

PubMed and Scopus, up to May 2023.

STUDY ELIGIBILITY CRITERIA

Eligible were studies reporting CFDC-NS in Enterobacterales, P. aeruginosa, A. baumannii, or Stenotrophomonas maltophilia clinical isolates.

RISK-OF-BIAS ASSESSMENT

Two independent reviewers extracted study data and assessed the risk of bias on the population, setting, and measurement (susceptibility testing) domains.

DATA SYNTHESIS

Binomial-Normal mixed-effects models were applied to estimate CFDC-NS prevalence by species, coresistance phenotype, and breakpoint definition (EUCAST, CLSI, and FDA). Sources of heterogeneity were investigated by subgroup and meta-regression analyses.

RESULTS

In all, 78 studies reporting 82 035 clinical isolates were analysed (87% published between 2020 and 2023). CFDC-NS prevalence (EUCAST breakpoints) was low overall but varied by species (S. maltophilia 0.4% [95% CI 0.2-0.7%], Enterobacterales 3.0% [95% CI 1.5-6.0%], P. aeruginosa 1.4% [95% CI 0.5-4.0%]) and was highest for A. baumannii (8.8%, 95% CI 4.9-15.2%). CFDC-NS was much higher in CR Enterobacterales (12.4%, 95% CI 7.3-20.0%) and CR A. baumannii (13.2%, 95% CI 7.8-21.5%), but relatively low for CR P. aeruginosa (3.5%, 95% CI 1.6-7.8%). CFDC-NS was exceedingly high in New Delhi metallo-β-lactamase-producing Enterobacterales (38.8%, 95% CI 22.6-58.0%), New Delhi metallo-β-lactamase-producing A. baumannii (44.7%, 95% CI 34.5-55.4%), and ceftazidime/avibactam-resistant Enterobacterales (36.6%, 95% CI 22.7-53.1%). CFDC-NS varied considerably with breakpoint definition, predominantly among CR bacteria. Additional sources of heterogeneity were single-centre investigations and geographical regions.

CONCLUSIONS

CFDC-NS prevalence is low overall, but alarmingly high for specific CR phenotypes circulating in some institutions or regions. Continuous surveillance and updating of global CFDC-NS estimates are imperative while cefiderocol is increasingly introduced into clinical practice. The need to harmonize EUCAST and CLSI breakpoints was evident.

Cefiderocol: Clinical application and emergence of resistance

Antibacterial drug resistance of gram-negative bacteria (GNB) results in high morbidity and mortality of GNB infection, seriously threaten human health globally. Developing new antibiotics has become the critical need for dealing with drug-resistant bacterial infections. Cefiderocol is an iron carrier cephalosporin that achieves drug accumulation through a unique "Trojan horse" strategy into the bacterial periplasm. It shows high antibacterial activity against multidrug-resistant (MDR) Enterobacteriaceae and MDR non-fermentative bacteria. The application of cefiderocol offers new hope for treating clinical drug-resistant bacterial infections. However, limited clinical data and uncertainties about its resistance mechanisms constrain the choice of its therapeutic use. This review aimed to summarize the clinical applications, drug resistance mechanisms, and co-administration of cefiderocol.

Cefiderocol and Sulbactam-Durlobactam against Carbapenem-Resistant Acinetobacter baumannii

Infections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) remain a clinical challenge due to limited treatment options. Recently, cefiderocol, a novel siderophore cephalosporin, and sulbactam-durlobactam, a bactericidal β-lactam-β-lactamase inhibitor combination, have been approved by the Food and Drug Administration for the treatment of A. baumannii infections. In this review, we discuss the mechanisms of action of and resistance to cefiderocol and sulbactam-durlobactam, the antimicrobial susceptibility of A. baumannii isolates to these drugs, as well as the clinical effectiveness of cefiderocol and sulbactam/durlobactam-based regimens against CRAB. Overall, cefiderocol and sulbactam-durlobactam show an excellent antimicrobial activity against CRAB. The review of clinical studies evaluating the efficacy of cefiderocol therapy against CRAB indicates it is non-inferior to colistin/other treatments for CRAB infections, with a better safety profile. Combination treatment is not associated with improved outcomes compared to monotherapy. Higher mortality rates are often associated with prior patient comorbidities and the severity of the underlying infection. Regarding sulbactam-durlobactam, current data from the pivotal clinical trial and case reports suggest this antibiotic combination could be a valuable option in critically ill patients affected by CRAB infections, in particular where no other antibiotic appears to be effective.

Management strategies for severe Pseudomonas aeruginosa infections

PURPOSE OF REVIEW

This review focuses on the management of severe Pseudomonas aeruginosa infections in critically ill patients.

RECENT FINDINGS

Pseudomonas aeruginosa is the most common pathogen in intensive care; the main related infections are nosocomial pneumonias, then bloodstream infections. Antimicrobial resistance is common; despite new antibiotics, it is associated with increased mortality, and can lead to a therapeutic deadlock.

SUMMARY

Carbapenem resistance in difficult-to-treat P. aeruginosa (DTR-PA) strains is primarily mediated by loss or reduction of the OprD porin, overexpression of the cephalosporinase AmpC, and/or overexpression of efflux pumps. However, the role of carbapenemases, particularly metallo-β-lactamases, has become more important. Ceftolozane-tazobactam, ceftazidime-avibactam and imipenem-relebactam are useful against DTR phenotypes (noncarbapenemase producers). Other new agents, such as aztreonam-ceftazidime-avibactam or cefiderocol, or colistin, might be effective for carbapenemase producers. Regarding nonantibiotic agents, only phages might be considered, pending further clinical trials. Combination therapy does not reduce mortality, but may be necessary for empirical treatment. Short-term treatment of severe P. aeruginosa infections should be preferred when it is expected that the clinical situation resolves rapidly.

Emerging infections in vulnerable hosts: Stenotrophomonas maltophilia and Elizabethkingia anophelis

PURPOSE OF REVIEW

This systematic review aimed to explore the recent trends in the epidemiology, risk factors, and antimicrobial susceptibility of two emerging opportunistic pathogens, Stenotrophomonas maltophilia and Elizabethkingia anophelis .

RECENT FINDINGS

Since 2020, numerous outbreaks of S. maltophilia and E. anophelis have been reported worldwide. Most of these outbreaks have been associated with healthcare facilities, although one outbreak caused by E. anophelis in France was considered a community-associated infection. In terms of antimicrobial susceptibility, trimethoprim/sulfamethoxazole (TMP-SMZ), levofloxacin, and minocycline have exhibited good efficacy against S. maltophilia . Additionally, cefiderocol and a combination of aztreonam and avibactam have shown promising results in in vitro susceptibility testing. For E. anophelis , there is currently no consensus on the optimal treatment. Although some studies have reported good efficacy with rifampin, TMP-SMZ, piperacillin/tazobactam, and cefoperazone/sulbactam, minocycline had the most favourable in vitro susceptibility rates. Cefiderocol may serve as an alternative due to its low minimum inhibitory concentration (MIC) against E. anophelis . The role of vancomycin in treatment is still uncertain, although several successful cases with vancomycin treatment, even with high MIC values, have been reported.

SUMMARY

Immunocompromised patients are particularly vulnerable to infections caused by S. maltophilia and E. anophelis , but the optimal treatment strategy remains inconclusive. Further research is necessary to determine the most effective use of conventional and novel antimicrobial agents in combatting these multidrug-resistant pathogens.

In vitro activity of cefiderocol against comparators (ceftazidime-avibactam, ceftazidime-avibactam/ aztreonam combination, and colistin) against clinical isolates of meropenem-resistant Klebsiella pneumoniae from India

Cefiderocol (FDC), a novel siderophore drug, is active against Gram-negative bacteria producing carbapenemases, including metallo-beta-lactamases. The objective of this study is to compare the in vitro activity of FDC with ceftazidime-avibactam (CZA), CZA/aztreonam (AT) combination, and colistin (CST), in clinical isolates of meropenem-resistant (MER-R) Klebsiella pneumoniae. From the 2,052 clinical specimens submitted for culture testing, 245 K. pneumoniae isolates were recovered within a 6-month period in 2021. One hundred three non-duplicate, non-outbreak, MER-R (minimum inhibitory concentration, MIC >4 µg/mL) strains were included in the study. Identification and susceptibility were performed using VITEK-2 (bioMérieux). Meropenem-susceptible isolates (n = 10) served as controls. For FDC, broth microdilution (BMD) was performed after in-house standardization. Disk diffusion (Liofilchem, Italy) and broth microdilution (ComASP, STC, Liofilchem, Italy) were used for susceptibility testing of CZA and CST, respectively. Synergy testing for CZA and AT was performed using disk approximation method. CLSI breakpoints were used for the interpretation of the results. For FDC, MIC50 and MIC90 were 2 and 8 µg/mL, respectively. A total of 80% of isolates were susceptible to FDC, 26.2% of isolates were susceptible to CZA, synergy testing with CZA/AT was positive for 74 (72%) of the isolates, and 89.3% were intermediate to CST. Nine (8.7%) were susceptible only to FDC. FDC is active in vitro against MER-R K. pneumoniae >CZA/AT > CZA > CST, as observed in this study, applying CLSI criteria. Clinico-microbiological studies should be performed to assess the clinical efficacy of this novel drug in this region with a high prevalence of carbapenem resistance among Gram-negative organisms. IMPORTANCE Management of infections with multi-drug resistant Klebsiella pneumoniae is a major challenge in hospital settings, with few treatment options. In this study, the authors aim to assess the in vitro susceptibility of these clinical isolates to cefiderocol, a novel siderophore. Comparators are colistin, ceftazidime-avibactam, and ceftazidime-avibactam/aztreonam synergy, which are currently available options for treatment in this region. Baseline-resistance rates against cefiderocol are higher than those in the previously published studies, with MIC50 and MIC90 at 2 and 8 µg/mL, respectively.

Antibiotic Therapy Strategies for Treating Gram-Negative Severe Infections in the Critically Ill: A Narrative Review

INTRODUCTION

Not enough data exist to inform the optimal duration and type of antimicrobial therapy against GN infections in critically ill patients.

METHODS

Narrative review based on a literature search through PubMed and Cochrane using the following keywords: "multi-drug resistant (MDR)", "extensively drug resistant (XDR)", "pan-drug-resistant (PDR)", "difficult-to-treat (DTR) Gram-negative infection," "antibiotic duration therapy", "antibiotic combination therapy" "antibiotic monotherapy" "Gram-negative bacteremia", "Gram-negative pneumonia", and "Gram-negative intra-abdominal infection".

RESULTS

Current literature data suggest adopting longer (≥10-14 days) courses of synergistic combination therapy due to the high global prevalence of ESBL-producing (45-50%), MDR (35%), XDR (15-20%), PDR (5.9-6.2%), and carbapenemases (CP)/metallo-β-lactamases (MBL)-producing (12.5-20%) Gram-negative (GN) microorganisms (i.e., Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumanii). On the other hand, shorter courses (≤5-7 days) of monotherapy should be limited to treating infections caused by GN with higher (≥3 antibiotic classes) antibiotic susceptibility. A general approach should be based on (i) third or further generation cephalosporins ± quinolones/aminoglycosides in the case of MDR-GN; (ii) carbapenems ± fosfomycin/aminoglycosides for extended-spectrum β-lactamases (ESBLs); and (iii) the association of old drugs with new expanded-spectrum β-lactamase inhibitors for XDR, PDR, and CP microorganisms. Therapeutic drug monitoring (TDM) in combination with minimum inhibitory concentration (MIC), bactericidal vs. bacteriostatic antibiotics, and the presence of resistance risk predictors (linked to patient, antibiotic, and microorganism) should represent variables affecting the antimicrobial strategies for treating GN infections.

CONCLUSIONS

Despite the strategies of therapy described in the results, clinicians must remember that all treatment decisions are dynamic, requiring frequent reassessments depending on both the clinical and microbiological responses of the patient.

Cefiderocol Treatment for Patients with Multidrug- and Carbapenem-Resistant Pseudomonas aeruginosa Infections in the Compassionate Use Program

Cefiderocol is an option for infections caused by multidrug-resistant Pseudomonas aeruginosa, but its in vitro activity against these isolates and its clinical effectiveness for isolates with MICs of >1 μg/mL is unclear. We investigated the in vitro activity of cefiderocol against P. aeruginosa isolates collected from patients treated with cefiderocol through the compassionate use program and assessed physician-reported clinical response and 28-day all-cause mortality by cefiderocol MIC values. P. aeruginosa isolates underwent susceptibility testing to cefiderocol and comparator agents by using reference broth microdilution. U.S. Food and Drug Administration (FDA; susceptible, ≤1 μg/mL) and Clinical and Laboratory Standards Institute (CLSI; susceptible, ≤4 μg/mL) cefiderocol breakpoints were applied. Additionally, molecular characterization of β-lactamase genes was performed. Clinical response and vital status were reported by treating physicians. Forty-six patients with P. aeruginosa infections were evaluated. Twenty-nine (63%) and 42 (91%) isolates were susceptible to cefiderocol using FDA and CLSI breakpoints, respectively. Thirty-seven (80%) and 32 (70%) isolates were not susceptible to ceftolozane-tazobactam and ceftazidime-avibactam, respectively. The clinical response rate was 69% (20/29) with a cefiderocol MIC of ≤1 μg/mL, 69% (9/13) with a cefiderocol MIC of 2 to 4 μg/mL, and 100% (4/4) with an MIC of ≥8 μg/mL, while day 28 all-cause mortality rates were 23% (6/26; MIC ≤ 1 μg/mL), 33% (4/12; MIC, 2 to 4 μg/mL), and 0% (0/4; MIC ≥8 μg/mL), respectively. Cefiderocol was active in vitro against most P. aeruginosa isolated from patients with limited or no alternative therapies. Patients with cefiderocol MICs of 2 to 4 μg/mL did not have significantly worse outcomes than those with MICs of ≤1 μg/mL.

In Vitro Activity of Cefiderocol against a Global Collection of Carbapenem-Resistant Acinetobacter baumannii Isolates

Background: Cefiderocol is a novel siderophore cephalosporin with potent activity against multi-drug-resistant Gram-negative pathogens including carbapenem-resistant Acinetobacter baumannii (CRAB). Methods: The susceptibility of 313 non-duplicate CRAB isolates with defined carbapenem resistance mechanisms from a global collection to cefiderocol, ceftazidime, ceftazidime/avibactam, ceftolozane/tazobactam, ciprofloxacin, colistin, imipenem/relebactam, meropenem, meropenem/vaborbactam, minocycline, and piperacillin/tazobactam was determined using the broth microdilution method. Isolates were obtained from various body sites from patients in 47 countries in five world regions between 2012 and 2016. The identification of carbapenem resistance mechanisms and assignment to A. baumannii international clonal lineages were based on whole genome sequencing. Results: Cefiderocol showed greater activity than comparator antimicrobials of the β-lactam class, including novel β-lactams combined with β-lactamase inhibitors, ciprofloxacin, and minocycline. Cefiderocol MIC₅₀ and MIC₉₀ values were 0.5 mg/L and 4 mg/L, respectively, while colistin had comparable activity with a higher MIC₅₀ at 1 mg/L and a lower MIC₉₀ value of 2 mg/L. Many isolates with elevated cefiderocol MICs ≥ 4 mg/L represented A. baumannii international clone (IC) 1 and harbored a metallo-β-lactamase. Conclusions: While cefiderocol is a useful addition to the limited armamentarium of drugs targeting this problematic pathogen, a considerable part of CRAB isolates had elevated MIC values in a range of 4 -> 32 mg/L, including all isolates with a metallo-β-lactamase.

In vitro activities of antimicrobial combinations against planktonic and biofilm forms of Stenotrophomonas maltophilia

Objectives

To investigate the in vitro activity of antibiotic combinations against Stenotrophomonas maltophilia isolates and their associated biofilms.

Methods

Thirty-two S. maltophilia clinical isolates with at least twenty-five different pulsotypes were tested. The antibacterial activity of various antibiotic combinations against seven randomly selected planktonic and biofilm-embedded S. maltophilia strains with strong biofilm formation was assessed using broth methods. Extraction of bacterial genomic DNA and PCR detection of antibiotic resistance and biofilm-related genes were also performed.

Results

The susceptibility rates of levofloxacin (LVX), fosfomycin (FOS), tigecycline (TGC) and sulfamethoxazole-trimethoprim (SXT) against 32 S. maltophilia isolates were 56.3, 71.9, 71.9 and 90.6%, respectively. Twenty-eight isolates were detected with strong biofilm formation. Antibiotic combinations, including aztreonam-clavulanic (ATM-CLA) with LVX, ceftazidime-avibactam (CZA) with LVX and SXT with TGC, exhibited potent inhibitory activity against these isolates with strong biofilm formation. The antibiotic resistance phenotype might not be fully caused by the common antibiotic-resistance or biofilm-formation gene.

Conclusion

S. maltophilia remained resistant to most antibiotics, including LVX and β-lactam/β-lactamases; however, TGC, FOS and SXT still exhibited potent activity. Although all tested S. maltophilia isolates exhibited moderate-to-strong biofilm formation, combination therapies, especially ATM-CLA with LVX, CZA with LVX and SXT with TGC, exhibited a higher inhibitory activity for these isolates.

Use of Newer and Repurposed Antibiotics against Gram-Negative Bacteria in Neonates

Antimicrobial resistance has become a significant public health problem globally with multidrug resistant Gram negative (MDR-GN) bacteria being the main representatives. The emergence of these pathogens in neonatal settings threatens the well-being of the vulnerable neonatal population given the dearth of safe and effective therapeutic options. Evidence from studies mainly in adults is now available for several novel antimicrobial compounds, such as new β-lactam/β-lactamase inhibitors (e.g., ceftazidime-avibactam, meropenem-vaborbactam, imipenem/cilastatin-relebactam), although old antibiotics such as colistin, tigecycline, and fosfomycin are also encompassed in the fight against MDR-GN infections that remain challenging. Data in the neonatal population are scarce, with few clinical trials enrolling neonates for the evaluation of the efficacy, safety, and dosing of new antibiotics, while the majority of old antibiotics are used off-label. In this article we review data about some novel and old antibiotics that are active against MDR-GN bacteria causing sepsis and are of interest to be used in the neonatal population.

Treatment of critically ill patients with cefiderocol for infections caused by multidrug-resistant pathogens: review of the evidence

Appropriate antibiotic treatment for critically ill patients with serious Gram-negative infections in the intensive care unit is crucial to minimize morbidity and mortality. Several new antibiotics have shown in vitro activity against carbapenem-resistant Enterobacterales (CRE) and difficult-to-treat resistant Pseudomonas aeruginosa. Cefiderocol is the first approved siderophore beta-lactam antibiotic with potent activity against multidrug-resistant, carbapenem-resistant, difficult-to-treat or extensively drug-resistant Gram-negative pathogens, which have limited treatment options. The spectrum of activity of cefiderocol includes drug-resistant strains of Acinetobacter baumannii, P. aeruginosa, Stenotrophomonas maltophilia, Achromobacter spp. and Burkholderia spp. and CRE that produce serine- and/or metallo-carbapenemases. Phase 1 studies established that cefiderocol achieves adequate concentration in the epithelial lining fluid in the lung and requires dosing adjustment for renal function, including patients with augmented renal clearance and continuous renal-replacement therapy (CRRT); no clinically significant drug-drug interactions are expected. The non-inferiority of cefiderocol versus high-dose, extended-infusion meropenem in all-cause mortality (ACM) rates at day 14 was demonstrated in the randomized, double-blind APEKS-NP Phase 3 clinical study in patients with nosocomial pneumonia caused by suspected or confirmed Gram-negative bacteria. Furthermore, the efficacy of cefiderocol was investigated in the randomized, open-label, pathogen-focused, descriptive CREDIBLE-CR Phase 3 clinical study in its target patient population with serious carbapenem-resistant Gram-negative infections, including hospitalized patients with nosocomial pneumonia, bloodstream infection/sepsis, or complicated urinary tract infections. However, a numerically greater ACM rate with cefiderocol compared with BAT led to the inclusion of a warning in US and European prescribing information. Cefiderocol susceptibility results obtained with commercial tests should be carefully evaluated due to current issues regarding their accuracy and reliability. Since its approval, real-world evidence in patients with multidrug-resistant and carbapenem-resistant Gram-negative bacterial infections suggests that cefiderocol can be efficacious in certain critically ill patient groups, such as those requiring mechanical ventilation for COVID-19 pneumonia with subsequently acquired Gram-negative bacterial superinfection, and patients with CRRT and/or extracorporeal membrane oxygenation. In this article, we review the microbiological spectrum, pharmacokinetics/pharmacodynamics, efficacy and safety profiles and real-world evidence for cefiderocol, and look at future considerations for its role in the treatment of critically ill patients with challenging Gram-negative bacterial infections.

In Vitro Activity of Cefiderocol Compared to Other Antimicrobials against a Collection of Metallo-Beta-Lactamase-Producing Gram-Negative Bacilli from Southern Spain

In this study, we aimed to comparatively evaluate the in vitro activity of cefiderocol versus other antimicrobials against a well-characterized collection of metallo-beta-lactamase (MBL)-producing Gram-negative bacilli (MBL-GNB) isolates from hospitals in Andalusia, Spain. We recovered 232 MBL-GNB from Andalusian hospitals, including 160 Enterobacterales and 72 nonfermenting Gram-negative bacilli belonging to 44 different clones (2015 to 2020). Cefiderocol and comparator MICs were determined with commercial methods (UMIC [Bruker] and EUMDROXF [Sensititre; Thermo Fisher], respectively). EUCAST breakpoints were used for all antimicrobials tested, and CLSI also was used for cefiderocol. Control strains used were E. coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853. Cefiderocol showed potent in vitro activity against isolates tested, regardless of breakpoint (susceptibility rates, 85.3% for EUCAST versus 96.6% for CLSI, P < 0.001). MIC ranges for Enterobacterales and nonfermenting Gram-negative bacilli (NF-GNB) were ≤0.03 to 1 mg/L and 0.06 to 2 (IMP), 0.06 to 8 mg/L and 0.06 to 16 (VIM), 0.25 to 16 mg/L and 2 to 16 mg/L (NDM), respectively, and 0.25 to 8 mg/L for double MBL-producing Enterobacterales. By species, all cefiderocol-susceptible rates were over 90%, except Klebsiella oxytoca, Enterobacter cloacae, Escherichia coli, and Acinetobacter spp. Significant differences were observed comparing resistant isolates between Enterobacterales and NF-GNB by EUCAST (19.4% versus 4.2%, P < 0.01), but not by CLSI (4.4% versus 1.4%, P = 0.2). Cefiderocol was the most active antimicrobial tested. Cefiderocol showed excellent in vitro activity against MBL-GNB, especially NF-GNB; almost all isolates resistant to comparators were susceptible. IMPORTANCE This article demonstrates the efficacy of cefiderocol against a large collection of well-characterized metallo-beta-lactamase-producing isolates, some of them even producing double carbapenemases. Furthermore, cefiderocol activity is compared to other novel broad-spectrum antimicrobials with activity against carbapenemases.

Cefiderocol Treatment for Severe Infections due to Difficult-to-Treat-Resistant Non-Fermentative Gram-Negative Bacilli in ICU Patients: A Case Series and Narrative Literature Review

Cefiderocol (FDC) is a siderophore cephalosporin now recognized as a new weapon in the treatment of difficult-to-treat-resistant (DTR) Gram-negative pathogens, including carbapenemase-producing enterobacterales and non-fermentative Gram-negative bacilli (GNB). This article reports our experience with an FDC-based regimen in the treatment of 16 extremely severe patients (invasive mechanical ventilation, 15/16; extracorporeal membrane oxygenation, 9/16; and renal replacement therapy, 8/16) infected with DTR GNB. Our case series provides detailed insight into the pharmacokinetic profile and the microbiological data in real-life conditions. In the narrative review, we discuss the interest of FDC in the treatment of non-fermentative GNB in critically ill patients. We reviewed the microbiological spectrum, resistance mechanisms, pharmacokinetics/pharmacodynamics, efficacy and safety profiles, and real-world evidence for FDC. On the basis of our experience and the available literature, we discuss the optimal FDC-based regimen, FDC dosage, and duration of therapy in critically ill patients with DTR non-fermentative GNB infections.

In Vitro Activity of Cefiderocol against Clinical Gram-Negative Isolates Originating from Germany in 2016/17

Antimicrobial resistance poses a global threat to public health. Of great concern are Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacterales with resistance to carbapenems or third-generation cephalosporins. The aim of the present study was to investigate the in vitro activity of the novel siderophore cephaloporin cefiderocol (CID) and four comparator β-lactam-β-lactamase-inhibitor combinations and to give insights into the genetic background of CID-resistant isolates. In total, 301 clinical Enterobacterales and non-fermenting bacterial isolates were selected for this study, including randomly chosen isolates (set I, n = 195) and challenge isolates (set II, n = 106; enriched with ESBL and carbapenemase producers, as well as colistin-resistant isolates). Isolates displayed CID MIC_50/90 values of 0.12/0.5 mg/L (set I) and 0.5/1 mg/L (set II). Overall, the CID activity was superior to the comparators against A. baumannii, Stenotrophomonas maltophilia and set II isolates of P. aeruginosa. There were eight CID-resistant isolates detected (MIC > 2 mg/L): A. baumannii (n = 1), E. cloacae complex (n = 5) and P. aeruginosa (n = 2). Sequencing analyses of these isolates detected the acquired β-lactamase (bla) genes bla_NDM-1,bla_SHV-12 and naturally occurring bla_OXA-396, bla_ACT-type and bla_CMH-3. In conclusion, CID revealed potent activity against clinically relevant organisms of multidrug-resistant Enterobacterales and non-fermenters.

What to Do with the New Antibiotics?

Multidrug-resistant Gram-negative bacteria-related infections have become a real public health problem and have exposed the risk of a therapeutic impasse. In recent years, many new antibiotics have been introduced to enrich the therapeutic armamentarium. Among these new molecules, some are mainly of interest for the treatment of the multidrug-resistant infections associated with Pseudomonas aeruginosa (ceftolozane/tazobactam and imipenem/relebactam); others are for carbapenem-resistant infections associated with Enterobacterales (ceftazidime/avibactam, meropenem/vaborbactam); and finally, there are others that are effective on the majority of multidrug-resistant Gram-negative bacilli (cefiderocol). Most international guidelines recommend these new antibiotics in the treatment of microbiologically documented infections. However, given the significant morbidity and mortality of these infections, particularly in the case of inadequate therapy, it is important to consider the place of these antibiotics in probabilistic treatment. Knowledge of the risk factors for multidrug-resistant Gram-negative bacilli (local ecology, prior colonization, failure of prior antibiotic therapy, and source of infection) seems necessary in order to optimize antibiotic prescriptions. In this review, we will assess these different antibiotics according to the epidemiological data.

Cefiderocol, a Siderophore Cephalosporin, as a Treatment Option for Infections Caused by Carbapenem-Resistant Enterobacterales

Carbapenem-resistant Enterobacterales (CRE) remain a significant public health threat, and, despite recent approvals, new antibiotics are needed. Severe infections caused by CRE, such as nosocomial pneumonia and bloodstream infections, are associated with a relatively high risk of morbidity and mortality. The recent approval of ceftazidime-avibactam, imipenem-relebactam, meropenem-vaborbactam, plazomicin, eravacycline and cefiderocol has broadened the armamentarium for the treatment of patients with CRE infections. Cefiderocol is a siderophore cephalosporin with overall potent in vitro activity against CRE. It is taken up via iron transport channels through active transport, with some entry into bacteria through traditional porin channels. Cefiderocol is relatively stable against hydrolysis by most serine- and metallo-beta-lactamases, including KPC, NDM, VIM, IMP and OXA carbapenemases-the most frequent carbapenemases detected in CRE. The efficacy and safety of cefiderocol has been demonstrated in three randomised, prospective, parallel group or controlled clinical studies in patients at risk of being infected by multidrug-resistant or carbapenem-resistant Gram-negative bacteria. This paper reviews the in vitro activity, emergence of resistance, preclinical effectiveness, and clinical experience for cefiderocol, and its role in the management of patients with CRE infections.

Real-world experience with cefiderocol therapy for Pseudomonas aeruginosa and other multidrug resistant gram-negative infections within the Veterans Health Administration, 2019-2022

Objective

Single-center and regional studies have reported outcomes after treatment with cefiderocol, a novel siderophore cephalosporin. We report on real-world use, clinical outcomes, and microbiological outcomes with cefiderocol therapy within the Veterans' Health Administration (VHA).

Design

Prospective, observational descriptive study.

Setting

Veterans' Health Administration, 132 sites across the United States, during 2019-2022.

Patients

This study included patients admitted to any VHA medical center who received cefiderocol for ≥2 days.

Methods

Data were obtained from the VHA Corporate Data Warehouse and through manual chart review. We extracted clinical and microbiologic characteristics and outcomes.

Results

In total, 8,763,652 patients received 1,142,940,842 prescriptions during the study period. Of these, 48 unique individuals received cefiderocol. The median age of this cohort was 70.5 years (IQR, 60.5-74), and the median Charlson comorbidity score was 6 (IQR, 3-9). The most common infectious syndromes were lower respiratory tract infection in 23 patients (47.9%) and urinary tract infection in 14 patients (29.2%). The most common pathogen cultured was P. aeruginosa in 30 patients (62.5%). The clinical failure rate was 35.4% (17 of 48), and 15 (88.2%) of these 17 patients died within 3 days of clinical failure. The 30-day and 90-day all-cause mortality rates were 27.1% (13 of 48) and 45.8% (22 of 48), respectively. The 30-day and 90-day microbiologic failure rates were 29.2% (14 of 48) and 41.7% (20 of 48), respectively.

Conclusions

In this nationwide VHA cohort clinical and microbiologic failure occurred in >30% of patients treated with cefiderocol, and >40% of these died within 90 days. Cefiderocol is not widely used, and many of the patients who received it had substantial comorbidities.

Alternatives Therapeutic Approaches to Conventional Antibiotics: Advantages, Limitations and Potential Application in Medicine

Resistance to antimicrobials and particularly multidrug resistance is one of the greatest challenges in the health system nowadays. The continual increase in the rates of antimicrobial resistance worldwide boosted by the ongoing COVID-19 pandemic poses a major public health threat. Different approaches have been employed to minimize the effect of resistance and control this threat, but the question still lingers as to their safety and efficiency. In this context, new anti-infectious approaches against multidrug resistance are being examined. Use of new antibiotics and their combination with new β-lactamase inhibitors, phage therapy, antimicrobial peptides, nanoparticles, and antisense antimicrobial therapeutics are considered as one such promising approach for overcoming bacterial resistance. In this review, we provide insights into these emerging alternative therapies that are currently being evaluated and which may be developed in the future to break the progression of antimicrobial resistance. We focus on their advantages and limitations and potential application in medicine. We further highlight the importance of the combination therapy approach, wherein two or more therapies are used in combination in order to more effectively combat infectious disease and increasing access to quality healthcare. These advances could give an alternate solution to overcome antimicrobial drug resistance. We eventually hope to provide useful information for clinicians who are seeking solutions to the problems caused by antimicrobial resistance.

How to use new antibiotics in the therapy of serious multidrug resistant Gram-negative infections?

PURPOSE OF REVIEW

Multidrug resistant Gram-negative infections are becoming more common and pose a serious threat to both individual patients and the population as a whole. Treatment of these infections can be difficult and result in significant morbidity and mortality. The purpose of this review is to discuss information and strategies for using new antibiotics to combat these infections.

RECENT FINDINGS

Eight new antibiotics represent possible means to treat multidrug resistant Gram-negative infections. Although no new mechanisms of action are present amongst these new antibiotics, novel additions to previously utilized mechanisms have been shown to be viable options for treatment of highly resistant organisms.

SUMMARY

The novel antibiotics considered in this review have varying data on their use as empiric treatment of patients at high risk for multidrug resistant organisms and as final therapy for identified multidrug resistant organisms. Cefiderocol, ceftazidime-avibactam, ceftolozane-tazobactam, meropenem-vaborbactam, and imipenem-relabactam have the best support evidence for use in this patient population.

Clinical evidence supporting cefiderol for serious Acinetobacter baumannii infections

PURPOSE OF REVIEW

Nosocomial infections caused by Acinetobacter baumannii currently represent a serious challenge for clinicians because treatment options are limited and frequently associated with significant toxicity. Cefiderocol is a first-in-class siderophore cephalosporin that has a proven efficacy for the treatment of multidrug-resistant Gram-negative infections, including carbapenem-resistant A. baumannii. The aim of this review is to evaluate the current evidence for the role of cefiderocol in the management of A. baumannii infections.

RECENT FINDINGS

In this review, we briefly summarize the available data on the efficacy (from randomized controlled trials) and on effectiveness and cure rates (from observational studies), pertaining to the use of cefiderocol for treatment of serious A. baumannii infections.

SUMMARY

Cefiderocol represents a promising and safe antibiotic option for treating patients with carbapenem-resistant A. baumannii infections. Due to conflicting mortality data from available experience, well-designed future randomized controlled trials and real-life studies are needed.

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

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

Antibacterial spectrum of cefiderocol

Cefiderocol, a siderophore catechol cephalosporin, recently introduced in the market has been developed to enhance the in vitro activity of extended spectrum cephalosporins and to avoid resistance mechanisms affecting cephalosporins and carbapenems. The in vitro study of cefiderocol in the laboratory requires iron depleted media when MIC values are determined by broth microdilution. Disk diffusion presents good correlation with MIC values. In surveillance studies and in clinical trials it has been demonstrated excellent activity against Gram-negatives, including carbapenemase producers and non-fermenters such as Pseudomonas aeruginosa, Acinetobacter baumannii and Stenotrophomonas maltophilia. Few cefiderocol resistant isolates have been found in surveillance studies. Resistance mechanisms are not directly associated with porin deficiency and or efflux pumps. On the contrary, they are related with gene mutations affecting iron transporters, AmpC mutations in the omega loop and with certain beta-lactamases such us KPC-variants determining also ceftazidime-avibactam resistance, certain infrequent extended-spectrum betalactamases (PER, BEL) and metallo-beta-lactamases (certain NDM variants and SPM enzyme).

In Vitro Antioxidant, Antibacterial and Mechanisms of Action of Ethanolic Extracts of Five Tunisian Plants against Bacteria

Pistacia lentiscus, Rosmarinus officinalis, Erica multiflora, Calicotome villosa, and Phillyrea latifolia were considered important medicinal herbs and were used to treat various ailments. The present study was designed to evaluate the antioxidant and antimicrobial activities of ethanolic extracts (EEs). P. lentiscus and R. officinalis were the richest species in phenolic compounds. Similarly, both species showed the highest values of flavonoids. While the EEs of P. lentiscus, E. multiflora, and C. villosa had higher amounts of tannins. These phenolic compounds were evaluated by two different tests, namely diphenyl picrylhydrazyl (DPPH) and ferric iron-reducing power (FRAP). The IC50 values were found to be significant (p < 0.05) for P. lentiscus and E. multiflora. Similarly, both plants showed the highest ferric-reducing antioxidant power (FRAP). This study has been conducted to evaluate the antibacterial potential of EEs against selected bacteria—Gram-positive bacteria (Staphylococcus aureus ATCC 29213, Listeria monocytogenes ATCC 7644) and Gram-negative bacteria (Escherichia coli ATCC 8739, Salmonella typhimurium NCTC 6017)—and determine their modes of action. The ethanolic extracts inhibited bacterial growth by producing concentration-dependent zones of inhibition. Treatment with these extracts at their minimum inhibitory concentrations (MICs) showed a significant reduction (p < 0.05) in the viability of bacteria. The extracts did not induce total lysis. Bacteria organisms treated with EEs at MICs showed a significant (p < 0.05) loss of tolerance to NaCl (5%). Our results highlighted the use of plant extracts as natural antibacterials that can be safely used in health care and led to the understanding of the antibacterial mechanism of plant extracts.

New Drugs for the Treatment of Pseudomonas aeruginosa Infections with Limited Treatment Options: A Narrative Review

P. aeruginosa is still one of the most threatening pathogens responsible for serious hospital-acquired infections. It is intrinsically resistant to many antimicrobial agents and additional acquired resistance further complicates the management of such infections. High rates of combined antimicrobial resistance persist in many countries, especially in the eastern and south-eastern parts of Europe. The aim of this narrative review is to provide a comprehensive assessment of the epidemiology, latest data, and clinical evidence on the current and new available drugs active against P. aeruginosa isolates with limited treatment options. The latest evidence and recommendations supporting the use of ceftolozane-tazobactam and ceftazidime-avibactam, characterized by targeted clinical activity against a significant proportion of P. aeruginosa strains with limited treatment options, are described based on a review of the latest microbiological and clinical studies. Cefiderocol, with excellent in vitro activity against P. aeruginosa isolates, good stability to all β-lactamases and against porin and efflux pumps mutations, is also examined. New carbapenem combinations are explored, reviewing the latest experimental and initial clinical evidence. One section is devoted to a review of new anti-pseudomonal antibiotics in the pipeline, such as cefepime-taniborbactam and cefepime-zidebactam. Finally, other “old” antimicrobials, mainly fosfomycin, that can be used as combination strategies, are described.