Activity of cefiderocol, imipenem/relebactam, cefepime/taniborbactam and cefepime/zidebactam against ceftolozane/tazobactam- and ceftazidime/avibactam-resistant Pseudomonas aeruginosa

Rapid prediction of carbapenemases in Pseudomonas aeruginosa by imipenem/relebactam and MALDI-TOF MS

Pseudomonas aeruginosa is a major nosocomial pathogen commonly involved in multidrug-resistant (MDR) infections that are very difficult to treat. Imipenem/relebactam is a new carbapenem/β-lactamase inhibitor combination with robust activity against P. aeruginosa. However, resistance is increasingly reported, and rapid detection is, therefore, crucial so that appropriate treatments can be prescribed. We have developed a rapid MALDI TOF-MS-based method that can accurately predict the presence of carbapenemases in P. aeruginosa using imipenem/relebactam. The method was developed using a retrospective and a prospective collection of 419 P. aeruginosa isolates (including recombinant isolates and WGS-characterized clinical strains) encompassing the most important β-lactam resistance mechanisms. The MALDI TOF-MS method is based on the detection of the hydrolysis of imipenem in the presence or absence of relebactam, measuring modifications in the mass spectra of imipenem after incubation with bacteria. The method was evaluated against a retrospective collection and then validated against 250 prospectively collected clinical isolates, showing a 98% (246/250) agreement between the phenotype and the MALDI-TOF MS hydrolysis result and a 100% accordance with the β-lactam resistance genotype. Some errors in detecting GES-producing isolates and in detecting different mutational resistance mechanisms associated with imipenem/relebactam resistance (MICs ranging from 4 to 8 mg/L) were observed. All results were obtained within 1 hour, positioning the MALDI-TOF-based test as a rapid and easy-to-perform method for detection of carbapenemases (except GES enzymes) in P. aeruginosa. Besides, implementation of the method in routine laboratory screening would facilitate the correct use of imipenem/relebactam to treat P. aeruginosa infections.IMPORTANCEWhile several rapid diagnostic methods have been developed for the detection of ESBLs and carbapenemases to improve treatment decision-making in Enterobacterales, there is a lack of approaches to rapidly identify resistance mechanisms and predict β-lactam susceptibility in Pseudomonas aeruginosa. Taking advantage of the mechanism of action and the high efficacy of the newly developed β-lactam/β-lactamase inhibitor combination imipenem/relebactam against P. aeruginosa, we developed a WGS-guided, MALDI-TOF-based algorithm that accurately predicts the presence of carbapenemase enzymes in this bacterium and aids in forecasting the imipenem/relebactam susceptibility profile. The implementation of this method in routine laboratory testing would provide significant support in the rapid decision-making for the use of imipenem/relebactam in severe P. aeruginosa infections.

Spectrum of cefepime-taniborbactam coverage against 190 β-lactamases defined in engineered isogenic Escherichia coli strains

Cefepime-taniborbactam is a β-lactam/β-lactamase inhibitor combination in clinical development for the treatment of Enterobacterales and Pseudomonas infections, including carbapenem-resistant Enterobacterales and multidrug-resistant Pseudomonas aeruginosa. Taniborbactam is a novel cyclic boronate with direct inhibitory activity against clinically relevant Ambler class A, B, C, and D β-lactamases. To further characterize the spectrum of β-lactamase coverage by cefepime-taniborbactam, we constructed 190 isogenic strains of Escherichia coli that constitutively expressed a different β-lactamase. Synthetic codon-optimized genes encoding the mature periplasmic protein linked to the TEM-1 signal sequence were used for optimized expression and periplasmic localization of the β-lactamase. The repertoire of β-lactamases consisted of 50 Ambler class A, 34 class B (metallo), 48 class C, and 58 class D enzymes known to mediate β-lactam resistance in the clinical isolates of Enterobacterales and P. aeruginosa. Overall, in the 190 isogenic strains, the MIC50/MIC90 values were 8/128 µg/mL for cefepime and >128/>128 µg/mL for ceftazidime. Cefepime-taniborbactam (MIC50/MIC90 of 0.25/8 µg/mL) showed greater activity than ceftazidime-avibactam (MIC50/MIC90 of 4/>128 µg/mL) and similar activity to aztreonam-avibactam (MIC50/MIC90 of 0.5/4 µg/mL). Cefepime-taniborbactam inhibited strains overproducing metallo-β-lactamases, including clinically important NDM and VIM enzymes, whereas ceftazidime-avibactam showed no coverage. Among the 129 β-lactamase-overproducing strains with increased cefepime MIC ≥16-fold relative to the control strain, taniborbactam potentiated cefepime MIC by ≥8-fold for 113 strains overexpressing β-lactamases (42 Ambler class A, 24 B, 23 C, and 24 D). Cefepime-taniborbactam demonstrated broader activity relative to ceftazidime-avibactam and comparable activity with aztreonam-avibactam in the overall coverage of both serine- and metallo-β-lactamases from all four Ambler classes.

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.

Antimicrobial activity of new anti-Pseudomonas beta-lactam-beta-lactamase inhibitors against Pseudomonas aeruginosa respiratory isolates recovered during the study for Monitoring Antimicrobial Resistance Trends (SMART) program in France (2016-2022)

OBJECTIVES

To assess the susceptibility of ceftolozane/tazobactam (C/T) and comparators to Pseudomonas aeruginosa isolates recovered from respiratory-tract-infections (RTI) between 2016-2022 in the French SMART study.

METHODS

Antibiotic susceptibility testing and minimum inhibitory concentrations (MICs) of 717 P.aeruginosa isolates collected in five French hospitals were determined and interpreted according to the EUCAST-2022 guidelines. P. aeruginosa isolates resistant (R) to imipenem and/or C/T were screened by PCR for extended-spectrum-β-lactamases (ESBLs), AmpC and carbapenemase genes. The identified genes were sequenced and the variants determined.

RESULTS

All in all, 96.5 % of P. aeruginosa isolates were susceptible to C/T, comparable to the susceptibilities of meropenem-vaborbactam (MVB = 96.5 %), imipenem/relebactam (IMI/REL = 96.9 %) and ceftazidime-avibactam (C/A = 97.0 %). MIC50 and MIC90 for C/T were 0.5 and 2 mg/L respectively against the 717 isolates. Among the 242 isolates (33.7 %) resistant to at least one anti-Pseudomonas β-lactam, close to 90 % were susceptible to C/T, C/A, MVB and IMI/REL. Among the 80 isolates resistant to piperacillin-tazobactam, cefepime and ceftazidime, 76.3 % were susceptible to C/T and only IMI/REL and amikacin reached susceptibility exceeding 80 %. Among the 32 isolates resistant to imipenem and meropenem, susceptibility exceeding 60 % was observed only for IMI/REL, C/T, and C/A. For these strains, the MIC50 of C/T was 2 mg/L, while that of C/A was at the resistance threshold (8 mg/L). IMI/REL had the strongest activity (72 %) against the 25 isolates resistant to C/T. Lastly, 53 imipenem and/or C/T-R isolates harbored a class C β-lactam (blaPDC) variant, and one of them also carried the blaPER-1 gene and another, the blaVIM-2 gene.

CONCLUSION

C/T is a reliable treatment option in RTI caused by P. aeruginosa.

In-vitro activity of the novel β-lactam/β-lactamase inhibitor combinations and cefiderocol against carbapenem-resistant Pseudomonas spp. clinical isolates collected in Switzerland in 2022

To evaluate the in-vitro activity of the novel commercially-available drugs, including meropenem-vaborbactam (MEV), ceftazidime-avibactam (CZA), ceftolozane-tazobactam (C/T), imipenem-relebactam (IPR) as well as cefiderocol (FDC), against carbapenem-resistant Pseudomonas spp. (CRP) isolates. All CRP isolates collected at the Swiss National Reference Laboratory (NARA) over the year 2022 (n = 170) have been included. Most of these isolates (n = 121) were non-carbapenemase producers. Among the 49 carbapenemase producers, 47 isolates produced metallo-β-lactamases (MBL) including NDM-1 (n = 11), VIM-like (n = 28), IMP-like (n = 7), and both NDM-1 and VIM-2 (n = 1) and two isolates produced the class A carbapenemase GES-5. Susceptibility testing was determined by broth microdilution method (BMD), or disk diffusion test, and results interpreted following EUCAST guidelines. The susceptibility rates for MEV, CZA, C/T and IPR were found to be 41%, 45%, 59% and 58%, respectively, for the whole set of isolates tested. Among non-carbapenemase producers, susceptibility rates for these β-lactam/β-lactamase inhibitors (BL/BLI) combinations were higher, determined at 55%, 61%, 83%, and 82%, respectively. The overall susceptibility of carbapenemase-producing Pseudomonas spp. to novel BL/BLI was relatively low, while 80% of these isolates demonstrated susceptibility to FDC, with a similar proportion (79%) observed among MBL producers. A total of 10 MBL-producing isolates (6%), mainly NDM-1, were found to exhibit resistance to all drugs tested, with the exception of colistin. FDC exhibited an excellent in-vitro activity against this collection of CRP recovered from Switzerland in 2022, including MBL producers. The new BL/BLI combinations displayed significant activity against non-carbapenemase CRP, with IPR and C/T showing the highest susceptibility rates.

Advancements in the fight against globally distributed OXA-48 carbapenemase: evaluating the new generation of carbapenemase inhibitors

Carbapenemase OXA-48 and its variants pose a serious threat to the development of effective treatments for bacterial infections. OXA-48-producing Enterobacterales are the most prevalent carbapenemase-producing bacteria in large parts of the world. Although these bacteria exhibit low-level carbapenem resistance in vitro, the infections they cause are challenging to treat with conventional therapies, owing to their spread and complex detection in clinical settings. However, numerous β-lactamase inhibitors (BLIs) are currently in the pipeline or late clinical stages. To assess the potential of these compounds, this study compared the efficacy against OXA-48 of novel β-lactamase inhibitors, specifically the 1,6-diazabicyclo[3,2,1]octanes (DBOs) avibactam, relebactam, zidebactam, nacubactam, and durlobactam, along with the cyclic and bicyclic boronates vaborbactam, taniborbactam, and xeruborbactam. The extensive kinetics assays identified xeruborbactam, taniborbactam, and durlobactam, together with the already established avibactam, as BLIs with superior biochemical performance. Susceptibility testing further validated these findings but also demonstrated significantly improved bacterial killing by the DBOs zidebactam, nacubactam, and durlobactam. On the other hand, binding studies demonstrated the superior inhibitory capacity of the BLIs durlobactam and xeruborbactam. Combinations, such as cefepime/zidebactam, meropenem/nacubactam, and sulbactam/durlobactam, show promising activity against OXA-48-producing Enterobacterales, while ceftazidime/avibactam, cefepime/taniborbactam, and meropenem/xeruborbactam combinations also appear highly active, largely due to the excellent kinetics of these new inhibitors. Overall, this comprehensive analysis provides important insights into the effectiveness of new BLIs against OXA-48-producing Enterobacterales, highlighting xeruborbactam, durlobactam, and avibactam as leading candidates. Additionally, BLIs like zidebactam, nacubactam, and taniborbactam also showed potential in addressing the clinical challenges posed by OXA-48-mediated antimicrobial resistance.

Difficult-to-Treat Pseudomonas aeruginosa Infections in Critically Ill Patients: A Comprehensive Review and Treatment Proposal

The management of infections caused by difficult-to-treat Pseudomonas aeruginosa in critically ill patients poses a significant challenge. Optimal antibiotic therapy is crucial for patient prognosis, yet the numerous resistance mechanisms of P. aeruginosa, which may even combine, complicate the selection of an appropriate antibiotic. In this review, we examine the epidemiology, resistance mechanisms, risk factors, and available and future therapeutic options, as well as strategies for treatment optimization. Finally, we propose a treatment algorithm to facilitate decision making based on the resistance patterns specific to each Intensive Care Unit.

Cefepime-taniborbactam activity against antimicrobial-resistant clinical isolates of Enterobacterales and Pseudomonas aeruginosa: GEARS global surveillance programme 2018-22

OBJECTIVES

Taniborbactam is a boronate-based β-lactamase inhibitor in clinical development in combination with cefepime.

METHODS

Cefepime-taniborbactam and comparator broth microdilution MICs were determined for patient isolates of Enterobacterales (n = 20 725) and Pseudomonas aeruginosa (n = 7919) collected in 59 countries from 2018 to 2022. Taniborbactam was tested at a fixed concentration of 4 mg/L. Isolates with cefepime-taniborbactam MICs ≥ 16 mg/L underwent WGS. β-Lactamase genes were identified in additional meropenem-resistant isolates by PCR/Sanger sequencing.

RESULTS

Taniborbactam reduced the cefepime MIC90 value for all Enterobacterales from >16 to 0.25 mg/L (>64-fold). At ≤16 mg/L, cefepime-taniborbactam inhibited 99.5% of all Enterobacterales isolates; >95% of isolates with MDR and ceftolozane-tazobactam-resistant phenotypes;  ≥ 89% of isolates with meropenem-resistant and difficult-to-treat-resistant (DTR) phenotypes; >80% of isolates with meropenem-vaborbactam-resistant and ceftazidime-avibactam-resistant phenotypes; 100% of KPC-positive, 99% of OXA-48-like-positive, 99% of ESBL-positive, 97% of acquired AmpC-positive, 95% of VIM-positive and 76% of NDM-positive isolates. Against P. aeruginosa, taniborbactam reduced the cefepime MIC90 value from 32 to 8 mg/L (4-fold). At ≤16 mg/L, cefepime-taniborbactam inhibited 96.5% of all P. aeruginosa isolates; 85% of meropenem-resistant phenotype isolates; 80% of isolates with MDR and meropenem-vaborbactam-resistant phenotypes; >70% of isolates with DTR, ceftazidime-avibactam-resistant and ceftolozane-tazobactam-resistant phenotypes; and 82% of VIM-positive isolates. Multiple potential mechanisms of resistance, including carriage of IMP, or alterations in PBP3 (ftsI), porins (decreased permeability) and efflux (up-regulation) were present in most isolates with cefepime-taniborbactam MICs ≥ 16 mg/L.

CONCLUSIONS

Cefepime-taniborbactam exhibited potent in vitro activity against Enterobacterales and P. aeruginosa, and inhibited most carbapenem-resistant isolates, including those carrying serine carbapenemases or NDM/VIM MBLs.

Integrative and conjugative elements of Pasteurella multocida: Prevalence and signatures in population evolution

Pasteurella multocida (P. multocida) is a bacterial pathogen responsible for a range of infections in humans and various animal hosts, causing significant economic losses in farming. Integrative and conjugative elements (ICEs) are important horizontal gene transfer elements, potentially enabling host bacteria to enhance adaptability by acquiring multiple functional genes. However, the understanding of ICEs in P. multocida and their impact on the transmission of this pathogen remains limited. In this study, 42 poultry-sourced P. multocida genomes obtained by high-throughput sequencing together with 393 publicly available P. multocida genomes were used to analyse the horizontal transfer of ICEs. Eighty-two ICEs were identified in P. multocida, including SXT/R391 and Tn916 subtypes, as well as three subtypes of ICEHin1056 family, with the latter being widely prevalent in P. multocida and carrying multiple resistance genes. The correlations between insertion sequences and resistant genes in ICEs were also identified, and some ICEs introduced the carbapenem gene blaOXA-2 and the bleomycin gene bleO to P. multocida. Phylogenetic and collinearity analyses of these bioinformatics found that ICEs in P. multocida were transmitted vertically and horizontally and have evolved with host specialization. These findings provide insight into the transmission and evolution mode of ICEs in P. multocida and highlight the importance of understanding these elements for controlling the spread of antibiotic resistance.

The Challenge of Treating Infections Caused by Metallo-β-Lactamase-Producing Gram-Negative Bacteria: A Narrative Review

Gram-negative multidrug-resistant (MDR) bacteria, including Enterobacterales, Acinetobacter baumannii, and Pseudomonas aeruginosa, pose a significant challenge in clinical practice. Infections caused by metallo-β-lactamase (MBL)-producing Gram-negative organisms, in particular, require careful consideration due to their complexity and varied prevalence, given that the microbiological diagnosis of these pathogens is intricate and compounded by challenges in assessing the efficacy of anti-MBL antimicrobials. We discuss both established and new approaches in the treatment of MBL-producing Gram-negative infections, focusing on 3 strategies: colistin; the recently approved combination of aztreonam with avibactam (or with ceftazidime/avibactam); and cefiderocol. Despite its significant activity against various Gram-negative pathogens, the efficacy of colistin is limited by resistance mechanisms, while nephrotoxicity and acute renal injury call for careful dosing and monitoring in clinical practice. Aztreonam combined with avibactam (or with avibactam/ceftazidime if aztreonam plus avibactam is not available) exhibits potent activity against MBL-producing Gram-negative pathogens. Cefiderocol in monotherapy is effective against a wide range of multidrug-resistant organisms, including MBL producers, and favorable clinical outcomes have been observed in various clinical trials and case series. After examining scientific evidence in the management of infections caused by MBL-producing Gram-negative bacteria, we have developed a comprehensive clinical algorithm to guide therapeutic decision making. We recommend reserving colistin as a last-resort option for MDR Gram-negative infections. Cefiderocol and aztreonam/avibactam represent favorable options against MBL-producing pathogens. In the case of P. aeruginosa with MBL-producing enzymes and with difficult-to-treat resistance, cefiderocol is the preferred option. Further research is needed to optimize treatment strategies and minimize resistance.

Rapid detection of imipenem/relebactam susceptibility/resistance in Pseudomonas aeruginosa

OBJECTIVES

Imipenem-relebactam (IPR) has been reported to exhibit a good activity against non-metallo-ß-lactamase carbapenem-resistant Pseudomonas aeruginosa (CRPA), and the rapid detection of susceptibility/resistance to this new therapeutic alternative may be crucial. Therefore, the Rapid IPR Pseudomonas NP test was developed to quickly identify IPR susceptibility/resistance among multidrug-resistant P. aeruginosa.

METHODS

The principle of the Rapid IPR Pseudomonas NP test is based on visually detecting glucose metabolization by observing (or not) a color change from yellow to red or orange of the red phenol pH indicator in the presence of imipenem at 2 mg/L and relebactam at 4 mg/L A total of 80 clinical Pseudomonas aeruginosa isolates were analyzed, among which 42 isolates were IPR resistant according to EUCAST guidelines (MICs, susceptible ≤2 mg/L, resistant >2 mg/L). Results obtained with the Rapid IPR Pseudomonas NP test were compared with the reference broth microdilution (BMD).

RESULTS

The sensitivity, specificity and accuracy of the test were found to be 100 %, 89.5 % and 95 %, respectively, using the BMD reference method as a comparator. Moreover, five out of the IPR-susceptible isolates (n = 38) exhibiting an MIC of IPR close to the breakpoint (MIC = 1 mg/L, n = 2; MIC = 2 mg/L, n = 3) yielded to a major error result, namely a positive result with the rapid IPR Pseudomonas NP test (resistance). By contrast, all IPR-resistant isolates (n = 42) were all correctly categorized.

CONCLUSIONS

The Rapid IPR Pseudomonas NP test is sensitive, specific, and easy to perform and interpret. Therefore, it is suitable for implementation in routine clinical laboratories.

Not all carbapenem-resistant Pseudomonas aeruginosa strains are alike: tailoring antibiotic therapy based on resistance mechanisms

PURPOSE OF REVIEW

To correlate the resistance mechanisms and the susceptibility to new antibiotics in Pseudomonas aeruginosa .

RECENT FINDINGS

Definition of antibiotic resistance in Pseudomonas aeruginosa is still debated. Carbapenem-resistant Pseudomonas aeruginosa (CRPA) and difficult-to-treat resistant Pseudomonas aeruginosa (DTR-PA) are used but which of them better correlate with the risk of mortality remains debated. Mechanisms underlying resistance in Pseudomonas aeruginosa are complex and may be combined, resulting in unpredictable phenotype and cross-resistance. Thus, not all CRPA are alike and tailoring antibiotic therapy on resistance mechanisms is challenging.

SUMMARY

Current guidelines recommend the use of new antipseudomonal agents for CRPA or DTR-PA infections but they don't provide specific information on how tailoring antibiotic therapy on underlying resistance mechanisms. This review may be useful to understand which mechanisms are involved in CRPA and may have practical implications helping clinicians to select an appropriate antibiotic regimen. Several antibiotics are now available for Pseudomonas aeruginosa but their rational use is important to avoid development of future resistance. The knowledge of local epidemiology and most common resistance mechanisms may guide empirical therapy, but targeted antibiotic therapy should be re-evaluated as soon as susceptibility testing profile is available and selected according to Pseudomonas aeruginosa phenotype.

Impact of transferable β-lactamases and intrinsic AmpC amino acid substitutions on the activity of cefiderocol against wild-type and iron uptake-deficient mutants of Pseudomonas aeruginosa

OBJECTIVES

We aimed to analyse the interplay between impaired iron uptake and β-lactamases on cefiderocol resistance in Pseudomonas aeruginosa.

METHODS

Thirty-one transferable β-lactamases and 16 intrinsic P. aeruginosa AmpC (PDC) variants were cloned and expressed in wild-type (PAO1) and iron uptake-deficient (PAO ΔpiuC) P. aeruginosa backgrounds. MICs of cefiderocol and antipseudomonal β-lactams were determined by reference broth microdilution.

RESULTS

Relative to PAO1, deletion of piuC caused a specific 16-fold decrease in cefiderocol activity but negligible effects on the activity of other β-lactams. Among transferable β-lactamases, SHV-12, KPC Ω-loop mutants, NDMs and OXA-15 showed cefiderocol MIC values above the clinical breakpoint (2 mg/L) when expressed in PAO1. When expressed in PAO ΔpiuC, these and the transformants harbouring PER-1, VEB-1, KPC-2, KPC-3, VIM-1, CMY-2, OXA-2 and OXA-14 showed increased MIC values from 16 to >256 mg/L. The PDC variants carrying the Ω-loop changes ΔP215-G222 (PDC-577), E219K (PDC-221 and PDC-558) and the H10 helix change L293P (PDC-219) had the greatest impact on cefiderocol resistance, with MICs of 2-4 mg/L in PAO1 and of up to 32-64 mg/L in PAO ΔpiuC. Widespread enzymes such as GES, CTX-M-9, CTX-M-15, VIM-2-like enzymes, IMPs, DHA-1, FOX-4, OXA-10, OXA-48 and the other PDC variants tested had weaker effects on cefiderocol resistance.

CONCLUSION

We add evidence about the effect of the interplay between iron uptake and β-lactamases on the acquisition of cefiderocol resistance in P. aeruginosa. These findings may help to anticipate the emergence of resistance and optimize the use of cefiderocol against P. aeruginosa infections.

Cefepime-Taniborbactam: A Novel Cephalosporin/β-Lactamase Inhibitor Combination

Taniborbactam (formerly known as VNRX-5133) is a novel bicyclic boronate β-lactamase inhibitor of serine β-lactamases (SBLs) [Ambler classes A, C, and D] and metallo-β-lactamases (MBLs) [Ambler class B], including NDM and VIM, but not IMP. Cefepime-taniborbactam is active in vitro against most isolates of carbapenem-resistant Enterobacterales (CRE) and carbapenem-resistant Pseudomonas aeruginosa (CRPA), including both carbapenemase-producing and carbapenemase-non-producing CRE and CRPA, as well as against multidrug-resistant (MDR), ceftazidime-avibactam-resistant, meropenem-vaborbactam-resistant, and ceftolozane-tazobactam-resistant Enterobacterales and P. aeruginosa. The addition of taniborbactam to cefepime resulted in a > 64-fold reduction in MIC90 compared with cefepime alone for a 2018-2021 global collection of > 13,000 clinical isolates of Enterobacterales. In the same study, against > 4600 P. aeruginosa, a fourfold MIC reduction was observed with cefepime-taniborbactam, compared with cefepime alone. Whole genome sequencing studies have shown that resistance towards cefepime-taniborbactam in Enterobacterales arises due to the presence of multiple resistance mechanisms, often in concert, including production of IMP, PBP3 alterations, permeability (porin) defects, and upregulation of efflux pumps. In P. aeruginosa, elevated cefepime-taniborbactam MICs are also associated with the presence of multiple, concurrent mechanisms, most frequently IMP, PBP3 mutations, and upregulation of efflux pumps, as well as AmpC (PDC) overexpression. The pharmacokinetics of taniborbactam are dose proportional, follow a linear model, and do not appear to be affected when combined with cefepime. Taniborbactam's approximate volume of distribution (Vd) at steady state is 20 L and the approximate elimination half-life (t½) is 2.3 h, which are similar to cefepime. Furthermore, like cefepime, taniborbactam is primarily cleared renally, and clearance corresponds with renal function. Pharmacodynamic studies (in vitro and in vivo) have reported that cefepime-taniborbactam has bactericidal activity against various β-lactamase-producing Gram-negative bacilli that are not susceptible to cefepime alone. It has been reported that antimicrobial activity best correlated with taniborbactam exposure (area under the curve). A phase III clinical trial showed that cefepime-taniborbactam (2 g/0.5 g administered as an intravenous infusion over 2 h) was superior to meropenem for the treatment of complicated urinary tract infection (cUTI), including acute pyelonephritis, caused by Enterobacterales species and P. aeruginosa while demonstrating similar safety compared with meropenem. The safety and tolerability of taniborbactam and cefepime-taniborbactam has been reported in one pharmacokinetic trial, and in two pharmacokinetic trials and one phase III clinical trial, respectively. Cefepime-taniborbactam appears to be well tolerated in both healthy subjects and patients. Headache and gastrointestinal upset are the most common drug-related adverse effects associated with cefepime-taniborbactam use. Cefepime-taniborbactam will likely have a role in the treatment of infections proven or suspected to be caused by MDR Gram-negative bacteria, including Enterobacterales and P. aeruginosa. In particular, it may be useful in the treatment of infections caused by isolates that harbor an MBL (NDM, VIM) enzyme, although further clinical data are needed. Additional safety and efficacy studies may support indications for cefepime-taniborbactam beyond cUTI.

Impact of chromosomally encoded resistance mechanisms and transferable β-lactamases on the activity of cefiderocol and innovative β-lactam/β-lactamase inhibitor combinations against Pseudomonas aeruginosa

OBJECTIVES

We aimed to compare the stability of the newly developed β-lactams (cefiderocol) and β-lactam/β-lactamase inhibitor combinations (ceftazidime/avibactam, ceftolozane/tazobactam, aztreonam/avibactam, cefepime/taniborbactam, cefepime/zidebactam, imipenem/relebactam, meropenem/vaborbactam, meropenem/nacubactam and meropenem/xeruborbactam) against the most clinically relevant mechanisms of mutational and transferable β-lactam resistance in Pseudomonas aeruginosa.

METHODS

We screened a collection of 61 P. aeruginosa PAO1 derivatives. Eighteen isolates displayed the most relevant mechanisms of mutational resistance to β-lactams. The other 43 constructs expressed transferable β-lactamases from genes cloned in pUCP-24. MICs were determined by reference broth microdilution.

RESULTS

Cefiderocol and imipenem/relebactam exhibited excellent in vitro activity against all of the mutational resistance mechanisms studied. Aztreonam/avibactam, cefepime/taniborbactam, cefepime/zidebactam, meropenem/vaborbactam, meropenem/nacubactam and meropenem/xeruborbactam proved to be more vulnerable to mutational events, especially to overexpression of efflux operons. The agents exhibiting the widest spectrum of activity against transferable β-lactamases were aztreonam/avibactam and cefepime/zidebactam, followed by cefepime/taniborbactam, cefiderocol, meropenem/xeruborbactam and meropenem/nacubactam. However, some MBLs, particularly NDM enzymes, may affect their activity. Combined production of certain enzymes (e.g. NDM-1) with increased MexAB-OprM-mediated efflux and OprD deficiency results in resistance to almost all agents tested, including last options such as aztreonam/avibactam and cefiderocol.

CONCLUSIONS

Cefiderocol and new β-lactam/β-lactamase inhibitor combinations show promising and complementary in vitro activity against mutational and transferable P. aeruginosa β-lactam resistance. However, the combined effects of efflux pumps, OprD deficiency and efficient β-lactamases could still result in the loss of all therapeutic options. Resistance surveillance, judicious use of new agents and continued drug development efforts are encouraged.

Structural basis of Pseudomonas aeruginosa penicillin binding protein 3 inhibition by the siderophore-antibiotic cefiderocol

The breakthrough cephalosporin cefiderocol, approved for clinical use in 2019, has activity against many Gram-negative bacteria. The catechol group of cefiderocol enables it to efficiently enter bacterial cells via the iron/siderophore transport system thereby reducing resistance due to porin channel mutations and efflux pump upregulation. Limited information is reported regarding the binding of cefiderocol to its key proposed target, the transpeptidase penicillin binding protein 3 (PBP3). We report studies on the reaction of cefiderocol and the related cephalosporins ceftazidime and cefepime with Pseudomonas aeruginosa PBP3, including inhibition measurements, protein observed mass spectrometry, and X-ray crystallography. The three cephalosporins form analogous 3-exomethylene products with P. aeruginosa PBP3 following elimination of the C3' side chain. pIC50 and k inact/K i measurements with isolated PBP3 imply ceftazidime and cefiderocol react less efficiently than cefepime and, in particular, meropenem with P. aeruginosa PBP3. Crystal structures inform on conserved and different interactions involved in binding of the three cephalosporins and meropenem to P. aeruginosa PBP3. The results will aid development of cephalosporins with improved PBP3 inhibition properties.

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

OBJECTIVES

Despite the introduction of cystic fibrosis transmembrane conductance regulator (CFTR) modulators, Pseudomonas aeruginosa is still a major pathogen in people with cystic fibrosis (pwCF). We determine the activity of cefiderocol and comparators in a collection of 154 P. aeruginosa isolates recovered from pwCF during three multicentre studies performed in 17 Spanish hospitals in 2013, 2017 and 2021.

METHODS

ISO broth microdilution was performed and MICs were interpreted with CLSI and EUCAST criteria. Mutation frequency and WGS were also performed.

RESULTS

Overall, 21.4% were MDR, 20.8% XDR and 1.3% pandrug-resistant (PDR). Up to 17% of the isolates showed a hypermutator phenotype. Cefiderocol demonstrated excellent activity; only 13 isolates (8.4%) were cefiderocol resistant by EUCAST (none using CLSI). A high proportion of the isolates resistant to ceftolozane/tazobactam (71.4%), meropenem/vaborbactam (70.0%), imipenem/relebactam (68.0%) and ceftazidime/avibactam (55.6%) were susceptible to cefiderocol. Nine out of 13 cefiderocol-resistant isolates were hypermutators (P < 0.001). Eighty-three STs were detected, with ST98 being the most frequent. Only one isolate belonging to the ST175 high-risk clone carried blaVIM-2. Exclusive mutations affecting genes involved in membrane permeability, AmpC overexpression (L320P-AmpC) and efflux pump up-regulation were found in cefiderocol-resistant isolates (MIC = 4-8 mg/L). Cefiderocol resistance could also be associated with mutations in genes related to iron uptake (tonB-dependent receptors and pyochelin/pyoverdine biosynthesis).

CONCLUSIONS

Our results position cefiderocol as a therapeutic option in pwCF infected with P. aeruginosa resistant to most recent β-lactam/β-lactamase inhibitor combinations.

Intravenous fosfomycin in combination regimens as a treatment option for difficult-to-treat infections due to multi-drug-resistant Gram-negative organisms: A real-life experience

AIM

To investigate the efficacy of intravenous (IV) fosfomycin as combination therapy for treatment of difficult-to-treat (DTT) acute and subacute infections with multi-drug-resistant (MDR) Gram-negative bacteria (GNB), and risk factors associated with 90-day mortality.

METHODS

A retrospective, observational, monocentric study enrolled patients treated with IV fosfomycin in combination regimens (≥72 h) for proven DTT-MDR-GNB infection. Multi-variate regression analysis identified independent risk factors for 90-day mortality. A propensity score for receiving fosfomycin was performed to control for confounding factors.

RESULTS

In total, 70 patients were included in this study: 54.3% had carbapenem-resistant isolates, 31.4% had ceftazidime/avibactam-resistant isolates and 28.6% had ceftolozane/tazobactam-resistant isolates. The main pathogens were Pseudomonas aeruginosa (57.1%) and Klebsiella pneumoniae (22.9%). The most prevalent infections were nosocomial pneumonia (42.9%), osteomyelitis (17.1%) and intra-abdominal infections. All-cause 30- and 90-day mortality were 15.7% and 31.4%, respectively (18.9% and 50% considering acute DTT-MDR-GNB infections alone). Relapse at 30 days occurred in 22.9% of cases (29% with emergence of fosfomycin resistance). Mortality at 90 days was independently associated with septic shock and ceftolozane/tazobactam resistance. The relationship between resistance to ceftolozane/tazobactam and 90-day mortality was confirmed to be significant after adjustment by propensity score analysis (hazard ratio 5.84, 95% confidence interval 1.65-20.68; P=0.006).

CONCLUSIONS

Fosfomycin seems to be a promising salvage, combination treatment in DTT-MDR-GNB infections. Resistance to ceftolozane/tazobactam seems to be independently associated with treatment failure. Randomized clinical trials focusing on pathogen and infection sites are needed urgently to demonstrate the superiority of fosfomycin in combination with other agents for the resolution of DTT-MDR-GNB infections.

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.

Pseudomonasaeruginosa antimicrobial susceptibility profiles, resistance mechanisms and international clonal lineages: update from ESGARS-ESCMID/ISARPAE Group

SCOPE

Pseudomonas aeruginosa, a ubiquitous opportunistic pathogen considered one of the paradigms of antimicrobial resistance, is among the main causes of hospital-acquired and chronic infections associated with significant morbidity and mortality. This growing threat results from the extraordinary capacity of P. aeruginosa to develop antimicrobial resistance through chromosomal mutations, the increasing prevalence of transferable resistance determinants (such as the carbapenemases and the extended-spectrum β-lactamases), and the global expansion of epidemic lineages. The general objective of this initiative is to provide a comprehensive update of P. aeruginosa resistance mechanisms, especially for the extensively drug-resistant (XDR)/difficult-to-treat resistance (DTR) international high-risk epidemic lineages, and how the recently approved β-lactams and β-lactam/β-lactamase inhibitor combinations may affect resistance mechanisms and the definition of susceptibility profiles.

METHODS

To address this challenge, the European Study Group for Antimicrobial Resistance Surveillance (ESGARS) from the European Society of Clinical Microbiology and Infectious Diseases launched the 'Improving Surveillance of Antibiotic-Resistant Pseudomonas aeruginosa in Europe (ISARPAE)' initiative in 2022, supported by the Joint programming initiative on antimicrobial resistance network call and included a panel of over 40 researchers from 18 European Countries. Thus, a ESGARS-ISARPAE position paper was designed and the final version agreed after four rounds of revision and discussion by all panel members.

QUESTIONS ADDRESSED IN THE POSITION PAPER

To provide an update on (a) the emerging resistance mechanisms to classical and novel anti-pseudomonal agents, with a particular focus on β-lactams, (b) the susceptibility profiles associated with the most relevant β-lactam resistance mechanisms, (c) the impact of the novel agents and resistance mechanisms on the definitions of resistance profiles, and (d) the globally expanding XDR/DTR high-risk lineages and their association with transferable resistance mechanisms.

IMPLICATION

The evidence presented herein can be used for coordinated epidemiological surveillance and decision making at the European and global level.

Cefepime-Taniborbactam in Complicated Urinary Tract Infection

BACKGROUND

Carbapenem-resistant Enterobacterales species and multidrug-resistant Pseudomonas aeruginosa are global health threats. Cefepime-taniborbactam is an investigational β-lactam and β-lactamase inhibitor combination with activity against Enterobacterales species and P. aeruginosa expressing serine and metallo-β-lactamases.

METHODS

In this phase 3, double-blind, randomized trial, we assigned hospitalized adults with complicated urinary tract infection (UTI), including acute pyelonephritis, in a 2:1 ratio to receive intravenous cefepime-taniborbactam (2.5 g) or meropenem (1 g) every 8 hours for 7 days; this duration could be extended up to 14 days in case of bacteremia. The primary outcome was both microbiologic and clinical success (composite success) on trial days 19 to 23 in the microbiologic intention-to-treat (microITT) population (patients who had a qualifying gram-negative pathogen against which both study drugs were active). A prespecified superiority analysis of the primary outcome was performed after confirmation of noninferiority.

RESULTS

Of the 661 patients who underwent randomization, 436 (66.0%) were included in the microITT population. The mean age of the patients was 56.2 years, and 38.1% were 65 years of age or older. In the microITT population, 57.8% of the patients had complicated UTI, 42.2% had acute pyelonephritis, and 13.1% had bacteremia. Composite success occurred in 207 of 293 patients (70.6%) in the cefepime-taniborbactam group and in 83 of 143 patients (58.0%) in the meropenem group. Cefepime-taniborbactam was superior to meropenem regarding the primary outcome (treatment difference, 12.6 percentage points; 95% confidence interval, 3.1 to 22.2; P = 0.009). Differences in treatment response were sustained at late follow-up (trial days 28 to 35), when cefepime-taniborbactam had higher composite success and clinical success. Adverse events occurred in 35.5% and 29.0% of patients in the cefepime-taniborbactam group and the meropenem group, respectively, with headache, diarrhea, constipation, hypertension, and nausea the most frequently reported; the frequency of serious adverse events was similar in the two groups.

CONCLUSIONS

Cefepime-taniborbactam was superior to meropenem for the treatment of complicated UTI that included acute pyelonephritis, with a safety profile similar to that of meropenem. (Funded by Venatorx Pharmaceuticals and others; CERTAIN-1 ClinicalTrials.gov number, NCT03840148.).

Structural role of K224 in taniborbactam inhibition of NDM-1

Taniborbactam (TAN; VNRX-5133) is a novel bicyclic boronic acid β-lactamase inhibitor (BLI) being developed in combination with cefepime (FEP). TAN inhibits both serine and some metallo-β-lactamases. Previously, the substitution R228L in VIM-24 was shown to increase activity against oxyimino-cephalosporins like FEP and ceftazidime (CAZ). We hypothesized that substitutions at K224, the homologous position in NDM-1, could impact FEP/TAN resistance. To evaluate this, a library of codon-optimized NDM K224X clones for minimum inhibitory concentration (MIC) measurements was constructed; steady-state kinetics and molecular docking simulations were next performed. Surprisingly, our investigation revealed that the addition of TAN restored FEP susceptibility only for NDM-1, as the MICs for the other 19 K224X variants remained comparable to those of FEP alone. Moreover, compared to NDM-1, all K224X variants displayed significantly lower MICs for imipenem, tebipenem, and cefiderocol (32-, 133-, and 33-fold lower, respectively). In contrast, susceptibility to CAZ was mostly unaffected. Kinetic assays with the K224I variant, the only variant with hydrolytic activity to FEP comparable to NDM-1, confirmed that the inhibitory capacity of TAN was modestly compromised (IC50 0.01 µM vs 0.14 µM for NDM-1). Lastly, structural modeling and docking simulations of TAN in NDM-1 and in the K224I variant revealed that the hydrogen bond between TAN's carboxylate with K224 is essential for the productive binding of TAN to the NDM-1 active site. In addition to the report of NDM-9 (E149K) as FEP/TAN resistant, this study demonstrates the fundamental role of single amino acid substitutions in the inhibition of NDM-1 by TAN.

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.

Deciphering mechanisms affecting cefepime-taniborbactam in vitro activity in carbapenemase-producing Enterobacterales and carbapenem-resistant Pseudomonas spp. isolates recovered during a surveillance study in Spain

PURPOSE

To characterize the resistance mechanisms affecting the cefepime-taniborbactam combination in a collection of carbapenemase-producing Enterobacterales (CPE) and carbapenem-resistant Pseudomonas spp. (predominantly P. aeruginosa; CRPA) clinical isolates.

METHODS

CPE (n = 247) and CRPA (n = 170) isolates were prospectively collected from patients admitted to 8 Spanish hospitals. Susceptibility to cefepime-taniborbactam and comparators was determined by broth microdilution. Cefepime-taniborbactam was the most active agent, inhibiting 97.6% of CPE and 67.1% of CRPA (MICs ≤ 8/4 mg/L). All isolates with cefepime-taniborbactam MIC > 8/4 mg/L (5 CPE and 52 CRPA) and a subset with MIC ≤ 8/4 mg/L (23 CPE and 24 CRPA) were characterized by whole genome sequencing.

RESULTS

A reduced cefepime-taniborbactam activity was found in two KPC-ST307-Klebsiella pneumoniae isolates with altered porins [KPC-62-K. pneumoniae (OmpA, OmpR/EnvZ), KPC-150-K. pneumoniae (OmpK35, OmpK36)] and one each ST133-VIM-1-Enterobacter hormaechei with altered OmpD, OmpR, and OmpC; IMP-8-ST24-Enterobacter asburiae; and NDM-5-Escherichia coli with an YRIN-inserted PBP3 and a mutated PBP2. Among the P. aeruginosa (68/76), elevated cefepime-taniborbactam MICs were mostly associated with GES-5-ST235, OXA-2+VIM-2-ST235, and OXA-2+VIM-20-ST175 isolates also carrying mutations in PBP3, efflux pump (mexR, mexZ) and AmpC (mpl) regulators, and non-carbapenemase-ST175 isolates with AmpD-T139M and PBP3-R504C mutations. Overall, accumulation of these mutations was frequently detected among non-carbapenemase producers.

CONCLUSIONS

The reduced cefepime-taniborbactam activity among the minority of isolates with elevated cefepime-taniborbactam MICs is not only due to IMP carbapenemases but also to the accumulation of multiple resistance mechanisms, including PBP and porin mutations in CPE and chromosomal mutations leading to efflux pumps up-regulation, AmpC overexpression, and PBP modifications in P. aeruginosa.

Multidrug-resistant Gram-negative clinical isolates with reduced susceptibility/resistance to cefiderocol: which are the best present and future therapeutic alternatives?

PURPOSE

To evaluate the different present and future therapeutic β-lactam/β-lactamase inhibitor (BL/BLI) alternatives, namely aztreonam-avibactam, imipenem-relebactam, meropenem-vaborbactam, cefepime-zidebactam, cefepime-taniborbactam, meropenem-nacubactam, and sulbactam-durlobactam against clinical isolates showing reduced susceptibility or resistance to cefiderocol in Enterobacterales, Acinetobacter baumannii, and Pseudomonas aeruginosa.

METHODS

MIC values of aztreonam, aztreonam-avibactam, cefepime, cefepime-taniborbactam, cefepime-zidebactam, imipenem, imipenem-relebactam, meropenem, meropenem-vaborbactam, meropenem-nacubactam, sulbactam-durlobactam, and cefiderocol combined with a BLI were determined for 67, 9, and 11 clinical Enterobacterales, P. aeruginosa or A. baumannii isolates, respectively, showing MIC values of cefiderocol being ≥1 mg/L. If unavailable, the respective β-lactam breakpoints according to EUCAST were used for BL/BLI combinations.

RESULTS

For Enterobacterales, the susceptibility rates for aztreonam, cefepime, imipenem, and meropenem were 7.5%, 0%, 10.4%, and 10.4%, respectively, while they were much higher for cefepime-zidebactam (91%), cefiderocol-zidebactam (91%), meropenem-nacubactam (71.6%), cefiderocol-nacubactam (74.6%), and cefiderocol-taniborbactam (76.1%), as expected. For P. aeruginosa isolates, the higher susceptibility rates were observed for imipenem-relebactam, cefiderocol-zidebactam, and meropenem-vaborbactam (56% for all combinations). For A. baumannii isolates, lower susceptibility rates were observed with commercially or under development BL/BLI combos; however, a high susceptibility rate (70%) was found for sulbactam-durlobactam and when cefiderocol was associated to some BLIs.

CONCLUSIONS

Zidebactam- and nacubactam-containing combinations showed a significant in vitro activity against multidrug-resistant Enterobacterales clinical isolates with reduced susceptibility to cefiderocol. On the other hand, imipenem-relebactam and meropenem-vaborbactam showed the highest susceptibility rates against P. aeruginosa isolates. Finally, sulbactam-durlobactam and cefiderocol combined with a BLI were the only effective options against A. baumannii tested isolates.

Transcending the challenge of evolving resistance mechanisms in Pseudomonas aeruginosa through β-lactam-enhancer-mechanism-based cefepime/zidebactam

Compared to other genera of Gram-negative pathogens, Pseudomonas is adept in acquiring complex non-enzymatic and enzymatic resistance mechanisms thus remaining a challenge to even novel antibiotics including recently developed β-lactam and β-lactamase inhibitor combinations. This study shows that the novel β-lactam enhancer approach enables cefepime/zidebactam to overcome both non-enzymatic and enzymatic resistance mechanisms associated with a challenging panel of P. aeruginosa. This study highlights that the β-lactam enhancer mechanism is a promising alternative to the conventional β-lactam/β-lactamase inhibitor approach in combating ever-evolving MDR P. aeruginosa.

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.

MDR/XDR/PDR or DTR? Which definition best fits the resistance profile of Pseudomonas aeruginosa?

PURPOSE OF REVIEW

The aim of this narrative review is to compare the prognostic utility of the new definition of difficult-to-treat resistance (DTR) vs. established definitions in patients with Pseudomonas aeruginosa infection to understand the therapeutic implications of resistance classification and its impact on clinical outcome.

RECENT FINDINGS

Among Gram-negative bacteria (GNB), P. aeruginosa (PA) is associated with high rates of morbidity and mortality, mostly related to its intrinsic capacity of developing antibiotic resistance. Several classifications of antibiotic resistance have been proposed in the last 15 years. The most common used is that from Magiorakos et al. including multidrug resistance (MDR), extensively drug-resistant (XDR) and pan drug resistance (PDR) according to the number of antibiotic classes showing in vitro activity. A further classification based on the resistance to specific antibiotic classes (i.e. fluoroquinolones, cephalosporins, carbapenem resistance) was also proposed. However, both of them have been criticized because of limited usefulness in clinical practice and for poor correlation with patient outcome, mainly in infections due to PA. More recently the new definition of difficult-to-treat resistance (DTR) has been proposed referring to nonsusceptibility to all first-line agents showing high-efficacy and low-toxicity (i.e. carbapenems, β-lactam-β-lactamase inhibitor combinations, and fluoroquinolones). Studies including large cohorts of patients with GNB bloodstream infections have confirmed the prognostic value of DTR classification and its clinical usefulness mainly in infections due to PA. Indeed, in the recent documents from the Infectious Diseases Society of America (IDSA) on the management of antibiotic resistant GNB infections, the DTR classification was applied to PA.

SUMMARY

DTR definition seems to identify better than MDR/XDR/PDR and single class resistant categories the cases of PA with limited treatment options. It requires periodic revision in order to remain up-to-date with the introduction of new antibiotics and the evolving pattern of resistance.

Resistance in Pseudomonas aeruginosa: A Narrative Review of Antibiogram Interpretation and Emerging Treatments

Pseudomonas aeruginosa is a ubiquitous Gram-negative bacterium renowned for its resilience and adaptability across diverse environments, including clinical settings, where it emerges as a formidable pathogen. Notorious for causing nosocomial infections, P. aeruginosa presents a significant challenge due to its intrinsic and acquired resistance mechanisms. This comprehensive review aims to delve into the intricate resistance mechanisms employed by P. aeruginosa and to discern how these mechanisms can be inferred by analyzing sensitivity patterns displayed in antibiograms, emphasizing the complexities encountered in clinical management. Traditional monotherapies are increasingly overshadowed by the emergence of multidrug-resistant strains, necessitating a paradigm shift towards innovative combination therapies and the exploration of novel antibiotics. The review accentuates the critical role of accurate antibiogram interpretation in guiding judicious antibiotic use, optimizing therapeutic outcomes, and mitigating the propagation of antibiotic resistance. Misinterpretations, it cautions, can inadvertently foster resistance, jeopardizing patient health and amplifying global antibiotic resistance challenges. This paper advocates for enhanced clinician proficiency in interpreting antibiograms, facilitating informed and strategic antibiotic deployment, thereby improving patient prognosis and contributing to global antibiotic stewardship efforts.

The balance between antibiotic resistance and fitness/virulence in Pseudomonas aeruginosa: an update on basic knowledge and fundamental research

The interplay between antibiotic resistance and bacterial fitness/virulence has attracted the interest of researchers for decades because of its therapeutic implications, since it is classically assumed that resistance usually entails certain biological costs. Reviews on this topic revise the published data from a general point of view, including studies based on clinical strains or in vitro-evolved mutants in which the resistance phenotype is seen as a final outcome, i.e., a combination of mechanisms. However, a review analyzing the resistance/fitness balance from the basic research perspective, compiling studies in which the different resistance pathways and respective biological costs are individually approached, was missing. Here we cover this gap, specifically focusing on Pseudomonas aeruginosa, a pathogen that stands out because of its extraordinary capacity for resistance development and for which a considerable number of recent and particular data on the interplay with fitness/virulence have been released. The revised information, split into horizontally-acquired vs. mutation-driven resistance, suggests a great complexity and even controversy in the resistance-fitness/virulence balance in the acute infection context, with results ranging from high costs linked to certain pathways to others that are seemingly cost-free or even cases of resistance mechanisms contributing to increased pathogenic capacities. The elusive mechanistic basis for some enigmatic data, knowledge gaps, and possibilities for therapeutic exploitation are discussed. The information gathered suggests that resistance-fitness/virulence interplay may be a source of potential antipseudomonal targets and thus, this review poses the elementary first step for the future development of these strategies harnessing certain resistance-associated biological burdens.

Cefiderocol activity is compromised by acquired extended-spectrum oxacillinases in Pseudomonas aeruginosa

OBJECTIVES

Cefiderocol has an excellent in vitro activity on clinical strains of Pseudomonas aeruginosa (P. aeruginosa). However, the resistance of some isolates has been associated with the production of some β-lactamases. Whether some acquired extended-spectrum oxacillinases (ES-OXA) common in this species may compromise the susceptibility of P. aeruginosa to cefiderocol has not been evaluated so far.

METHODS

Eighteen genes encoding OXA belonging to the major subgroups identified in P. aeruginosa OXA-1 (n = 3); - 2 (n = 5); - 10 (n = 8), and - 46 (n = 2) were cloned into pUCP24 shuttle vector and transferred into reference strain PAO1.

RESULTS

Although production of the OXA-1 subgroup enzymes did not alter cefiderocol MICs, the β-lactamases of OXA-2, OXA-46, and four variants of the OXA-10 subgroup resulted in an 8-fold to 32-fold decrease in susceptibility in the PAO1 background. Interestingly, point mutations Ala149Pro and Asp150Gly in OXA-2 subgroup, Trp154Cys and Gly157Asp in OXA-10 subgroup (all located in the Ω loop), and the duplication of a Thr206 and a Gly207 in the β5-β6 loop of OXA-10 subgroup were related to decreased susceptibility to cefiderocol. We also showed that some ES-OXA, including the most frequent ES-OXA in P. aeruginosa strains, OXA-19 (derived from OXA-10 subgroup), significantly compromised activity of cefiderocol in addition to ceftazidime, ceftolozane/tazobactam, and ceftazidime/avibactam in clinical strains.

CONCLUSION

This work shows that several ES-OXA have a significant effect on cefiderocol susceptibility. Of concern are the Trp154Cys and Gly157Asp mutations that occur in some of these β-lactamases, as they are associated with a decreased activity of the most recent cephalosporins introduced to combat P. aeruginosa infections.

Case Commentary: Successful Use of Cefepime/Zidebactam (WCK 5222) as a Salvage Therapy for the Treatment of Disseminated Extensively Drug-Resistant New Delhi Metallo-β-Lactamase-Producing Pseudomonas aeruginosa Infection in an Adult Patient with Acute T-Cell Leukemia

Multidrug-resistant/extensively drug-resistant (MDR/XDR) Pseudomonas aeruginosa (PA) are critical antimicrobial resistance threats. Despite their increasing prevalence, treatment options for metallo-β-lactamase (MBL)-producing PA are limited, especially for New Delhi metallo-β-lactamase (NDM) producers. Pending further clinical studies, this case provides support for limited-scope use of cefepime-zidebactam for treating disseminated infections secondary to NDM-producing XDR PA. Susceptibilities should be tested and/or alternative regimens considered when treating isolates with alternative MBLs or increased efflux pump expression because some in vitro data suggest associated loss of cefepime-zidebactam susceptibility.

Impact of Acquired Broad Spectrum β-Lactamases on Susceptibility to Novel Combinations Made of β-Lactams (Aztreonam, Cefepime, Meropenem, and Imipenem) and Novel β-Lactamase Inhibitors in Escherichia coli and Pseudomonas aeruginosa

The impact of broad-spectrum β-lactamases on the susceptibility to novel β-lactamase/β-lactamase inhibitor combinations was evaluated both in Pseudomonas aeruginosa and Escherichia coli using isogenic backgrounds. Cefepime-zidebactam displayed low MICs, mainly due to the significant intrinsic antibacterial activity of zidebactam. Cefepime-taniborbactam showed excellent activity against recombinant E. coli strains, including metallo-β-lactamase producers, whereas aztreonam-avibactam remained the best therapeutic option against class B β-lactamase-producing P. aeruginosa.

Novel Antimicrobial Agents for Gram-Negative Pathogens

Gram-negative bacterial resistance to antimicrobials has had an exponential increase at a global level during the last decades and represent an everyday challenge, especially for the hospital practice of our era. Concerted efforts from the researchers and the industry have recently provided several novel promising antimicrobials, resilient to various bacterial resistance mechanisms. There are new antimicrobials that became commercially available during the last five years, namely, cefiderocol, imipenem-cilastatin-relebactam, eravacycline, omadacycline, and plazomicin. Furthermore, other agents are in advanced development, having reached phase 3 clinical trials, namely, aztreonam-avibactam, cefepime-enmetazobactam, cefepime-taniborbactam, cefepime-zidebactam, sulopenem, tebipenem, and benapenem. In this present review, we critically discuss the characteristics of the above-mentioned antimicrobials, their pharmacokinetic/pharmacodynamic properties and the current clinical data.

Antimicrobial Treatment of Pseudomonas aeruginosa Severe Sepsis

Pseudomonas aeruginosa is a pathogen often encountered in a healthcare setting. It has consistently ranked among the most frequent pathogens seen in nosocomial infections, particularly bloodstream and respiratory tract infections. Aside from having intrinsic resistance to many antibiotics, it rapidly acquires resistance to novel agents. Given the high mortality of pseudomonal infections generally, and pseudomonal sepsis particularly, and with the rise of resistant strains, treatment can be very challenging for the clinician. In this paper, we will review the latest evidence for the optimal treatment of P. aeruginosa sepsis caused by susceptible as well as multidrug-resistant strains including the difficult to treat pathogens. We will also discuss the mode of drug infusion, indications for combination therapy, along with the proper dosing and duration of treatment for various conditions with a brief discussion of the use of non-antimicrobial agents.