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

Cefepime-Enmetazobactam: A Drug Review of a Novel Beta-Lactam/Beta-Lactamase Inhibitor

OBJECTIVE

To describe and analyze the pharmacodynamic and pharmacokinetic properties and clinical evidence supporting the efficacy and use of cefepime-enmetazobactam (FEP-EMT).

DATA SOURCES

A literature search was conducted using MEDLINE and EMBASE databases (January 2015 to May 2024). Search terms included: "cefepime-enmetazobactam" or "cefepime" or "enmetazobactam" or "cefepime" or "novel beta-lactamase inhibitor" and "complicated urinary tract infection" or "cUTI." Conference abstracts, bibliographies, clinical trials, and drug monographs were included for review.

STUDY SELECTION AND DATA EXTRACTION

Relevant studies in English and clinical trials conducted in humans were reviewed.

DATA SYNTHESIS

In February 2024, the Food and Drug Administration (FDA) approved the combination beta-lactam/beta-lactamase inhibitor (BL/BLI) FEP-EMT for the treatment of complicated urinary tract infections (cUTIs) and acute pyelonephritis following the completion of the Phase III ALLIUM trial comparing it to piperacillin-tazobactam (TZP). The trial resulted in 79.1% of the FEP-EMT group versus 58.9% of the TZP group meeting the primary outcome of clinical cure and microbiological eradication (95% CI 21.2 [14.3 to 27.9]).

RELEVANCE TO PATIENT CARE AND CLINICAL PRACTICE IN COMPARISON TO EXISTING AGENTS

This review describes the use of FEP-EMT for the treatment of cUTI and compares its use to other novel BL/BLI combinations including utility in drug-resistant infections.

CONCLUSIONS

FEP-EMT provides an antimicrobial option to reduce overuse of carbapenems for extended spectrum beta-lactamase (ESBL) producing Enterobacteriaceae. However, unlike other novel BL/BLI combinations, its limited spectrum of antibacterial effect for more difficult-to-treat pathogens and cost may also impact its overall utilization.

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.

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.

Resistance to ceftazidime-avibactam and other new β-lactams in Pseudomonas aeruginosa clinical isolates: a multi-center surveillance study

New β-lactam-β-lactamase inhibitor combinations represent last-resort antibiotics to treat infections caused by multidrug-resistant Pseudomonas aeruginosa. Carbapenemase gene acquisition can limit their spectrum of activity, and reports of resistance toward these new molecules are increasing. In this multi-center study, we evaluated the prevalence of resistance to ceftazidime-avibactam (CZA) and comparators among P. aeruginosa clinical isolates from bloodstream infections, hospital-acquired or ventilator-associated pneumonia, and urinary tract infections, circulating in Southern Italy. We also investigated the clonality and content of relevant β-lactam resistance mechanisms of CZA-resistant (CZAR) isolates. A total of 120 P. aeruginosa isolates were collected. CZA was among the most active β-lactams, retaining susceptibility in the 81.7% of cases, preceded by cefiderocol (95.8%) and followed by ceftolozane-tazobactam (79.2%), meropenem-vaborbactam (76.1%), imipenem-relebactam (75%), and aztreonam (69.6%). Among non-β-lactams, colistin and amikacin were active against 100% and 85.8% of isolates respectively. In CZAR strains subjected to whole-genome sequencing (n = 18), resistance was mainly due to the expression of metallo-β-lactamases (66.6% VIM-type and 5.5% FIM-1), followed by PER-1 (16.6%) and GES-1 (5.5%) extended-spectrum β-lactamases, mostly carried by international high-risk clones (ST111 and ST235). Of note, two strains producing the PER-1 enzyme were resistant to all β-lactams, including cefiderocol. In conclusion, the CZA resistance rate among P. aeruginosa clinical isolates in Southern Italy remained low. CZAR isolates were mostly metallo-β-lactamases producers and belonging to ST111 and ST253 epidemic clones. It is important to implement robust surveillance systems to monitor emergence of new resistance mechanisms and to limit the spread of P. aeruginosa high-risk clones.

IMPORTANCE

Multidrug-resistant Pseudomonas aeruginosa infections are a growing threat due to the limited therapeutic options available. Ceftazidime-avibactam (CZA) is among the last-resort antibiotics for the treatment of difficult-to-treat P. aeruginosa infections, although resistance due to the acquisition of transferable β-lactamase genes is increasing. With this work, we report that CZA represents a highly active antipseudomonal β-lactam compound (after cefiderocol), and that metallo-β-lactamases (VIM-type) and extended-spectrum β-lactamases (GES and PER-type) production is the major factor underlying CZA resistance in isolates from Southern Italian hospitals. In addition, we reported that such resistance mechanisms were mainly carried by the international high-risk clones ST111 and ST235.

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

The impact of chromosomally encoded wild-type or extended-spectrum (ESAC) AmpC β-lactamases of Escherichia coli on susceptibility to ceftazidime, cefepime, and cefiderocol was evaluated in different genetic backgrounds, including wild-type, PBP3-modified, and porin-deficient E. coli strains. Recombinant E. coli strains possessing the different backgrounds and producing variable ESACs were evaluated. Although ESAC enzymes conferred resistance to ceftazidime and decreased susceptibility to cefepime as expected, we showed here that cefiderocol was also a substrate of ESAC enzymes.

IMPORTANCE

We showed here that chromosomally encoded intrinsic extended-spectrum cephalosporinases of Escherichia coli may impact susceptibility not only to ceftazidime and cefepime but also to cefiderocol.

Effect of modification of penicillin-binding protein 3 on susceptibility to ceftazidime-avibactam, imipenem-relebactam, meropenem-vaborbactam, aztreonam-avibactam, cefepime-taniborbactam, and cefiderocol of Escherichia coli strains producing broad-spectrum β-lactamases

The impact of penicillin-binding protein 3 (PBP3) modifications that may be identified in Escherichia coli was evaluated with respect to susceptibility to β-lactam/β-lactamase inhibitor combinations including ceftazidime-avibactam, imipenem-relebactam, meropenem-vaborbactam, aztreonam-avibactam, cefepime-taniborbactam, and to cefiderocol. A large series of E. coli recombinant strains producing broad-spectrum β-lactamases was evaluated. While imipenem-relebactam showed a similar activity regardless of the PBP3 background, susceptibility to other molecules tested was affected at various levels. This was particularly the case for ceftazidime-avibactam, aztreonam-avibactam, and cefepime-taniborbactam.

In vitro activity of cefepime/taniborbactam and comparator agents against Gram-negative bacterial bloodstream pathogens recovered from patients with cancer

Background

Taniborbactam is a β-lactamase inhibitor that, when combined with cefepime, may offer a potential treatment option for patients with serious and resistant Gram-negative bacterial (GNB) pathogens.

Objectives

This study evaluated in vitro activity of cefepime/taniborbactam and comparator agents against GNB pathogens isolated from patients with cancer at our institution.

Methods

A total of 270 GNB pathogens (2019-23) isolated from patients with cancer were tested against cefepime/taniborbactam and comparator agents commonly used for these patients. CLSI-approved broth microdilution methods were used. MIC50, MIC90, MIC range and percentage of susceptibility calculations were made using FDA breakpoints when available.

Results

Cefepime/taniborbactam showed highly potent activity against tested Enterobacterales, including isolates producing ESBLs and carbapenem-resistant Enterobacterales. At a provisional breakpoint of ≤16/4 mg/L, cefepime/taniborbactam inhibited most tested species of GNB pathogens, with overall 98.9% susceptibility, which was significantly (P < 0.0001) higher than the susceptibility of the GNB isolates to all other tested comparator agents, ranging from 39.6% for cefepime to 86.3% for ceftazidime/avibactam.

Conclusions

Our results showed that taniborbactam in combination with cefepime improved in vitro activity against GNB pathogens isolated from patients with cancer, including MDR Pseudomonas aeruginosa, carbapenem-resistant Enterobacterales, ESBL-producing Enterobacterales and Stenotrophomonas maltophilia isolates, with highest activity compared with all tested comparator agents, including other β-lactam/β-lactamase inhibitor combinations. Further studies are warranted to explore the efficacy of cefepime/taniborbactam for empirical initial treatment of GNB infections in cancer patients with high rates of febrile neutropenia requiring hospitalization.

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.

Relative inhibitory activities of the broad-spectrum β-lactamase inhibitor taniborbactam against metallo-β-lactamases

Taniborbactam (TAN) is a novel broad-spectrum β-lactamase inhibitor with significant activity against subclass B1 metallo-β-lactamases (MBLs). Here, we showed that TAN exhibited an overall excellent activity against B1 MBLs including most NDM- and VIM-like as well as SPM-1, GIM-1, and DIM-1 enzymes, but not against SIM-1. Noteworthy, VIM-1-like enzymes (particularly VIM-83) were less inhibited by TAN than VIM-2-like. Like NDM-9, NDM-30 (also differing from NDM-1 by a single amino acid substitution) was resistant to TAN.

Reduced susceptibility to aztreonam-avibactam conferred by acquired AmpC-type β-lactamases in PBP3-modified Escherichia coli

PURPOSE

Carbapenemase-producing Enterobacterales are a growing threat, and very few therapeutic options remain active against those multidrug resistant bacteria. Aztreonam is the molecule of choice against metallo-beta-lactamases (MBL) producers since it is not hydrolyzed by those enzymes, but the co-production of acquired plasmidic cephalosporinases or extended-spectrum β-lactamases leading to aztreonam resistance may reduce the efficacy of this molecule. Hence, the development of the aztreonam-avibactam (AZA) combination provides an interesting therapeutic alternative since avibactam inhibits the activity of both cephalosporinases and extended-spectrum β-lactamases. However, structural modifications of penicillin binding protein PBP3, the target of aztreonam, may lead to reduced susceptibility to aztreonam-avibactam.

METHODS

Here the impact of various plasmid-encoded AmpC-type β-lactamases (ACC-1, ACT-7, ACT-17, CMY-2, CMY-42, DHA-1, FOX-1, and FOX-5) on susceptibility to aztreonam-avibactam was evaluated using isogenic E. coli MG1655 strains harboring insertions in PBP3 (YRIN and YRIK). The inhibitory activity of various β-lactamase inhibitors (clavulanic acid, tazobactam, avibactam, relebactam, and vaborbactam) were also compared against these enzymes.

RESULTS

Hence, we showed that reduced susceptibility to AZA was due to the combined effect of both AmpC production and amino acid insertions in PBP3. The highest resistance level was achieved in strains possessing the insertions in PBP3 in association with the production of ACT-7, ACC-1, or CMY-42.

CONCLUSION

Although none of the recombinant strains tested displayed clinical resistance to aztreonam-avibactam, our data emphasize that the occurrence of such profile might be of clinical relevance for MBL-producing strains.

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.

Impact of acquired broad-spectrum β-lactamases on susceptibility to oral penems/carbapenems (tebipenem, sulopenem, and faropenem) alone or in combination with avibactam and taniborbactam β-lactamase inhibitors in Escherichia coli

The impact of β-lactamases on susceptibility to oral penems/carbapenems (tebipenem, sulopenem, and faropenem) and other carbapenem molecules was evaluated in Escherichia coli, alone and in combination with avibactam or taniborbactam β-lactamase inhibitors. Tebipenem and sulopenem exhibited a similar spectrum of activity compared to the intravenous carbapenems and displayed lower MIC values than ceftibuten-avibactam against E. coli producing extended-spectrum β-lactamases or AmpC enzymes. Combined with taniborbactam, tebipenem and sulopenem exhibited low MIC values against almost all tested recombinant E. coli, including metallo-β-lactamase producers.

In Vitro Susceptibility of Aztreonam-Vaborbactam, Aztreonam-Relebactam and Aztreonam-Avibactam Associations against Metallo-β-Lactamase-Producing Gram-Negative Bacteria

BACKGROUND

Despite the availability of new options (ceftazidime-avibactam, imipenem-relebactam, meropenem-vaborbactam and cefiderocol), it is still very difficult to treat infections caused by metallo-β-lactamase (MBLs)-producers resistant to aztreonam. The in vitro efficacy of aztreonam in association with avibactam, vaborbactam or relebactam was evaluated on a collection of MBL-producing Enterobacterales, MBL-producing P. aeruginosa and highly drug-resistant S. maltophilia.

METHODS

A total of fifty-two non-duplicate MBL-producing Enterobacterales, five MBL-producing P. aeruginosa and five multidrug-resistant S. maltophila isolates were used in this study. The minimum inhibitory concentrations (MICs) of aztreonam, meropenem-vaborbactam and imipenem-relebactam were determined by Etest® (bioMérieux, La Balme-les-Grottes) according to EUCAST recommendations. For aztreonam-avibactam, aztreonam-vaborbactam and aztreonam-relebactam associations, the MICs were determined using Etest® on Mueller-Hinton (MH) agar supplemented with 8 mg/L of avibactam, 8 mg/L of vaborbactam and 4 mg/L of relebactam. The MICs were interpreted according to EUCAST guidelines.

RESULTS

The susceptibility rates of aztreonam-avibactam, aztreonam-vaborbactam and aztreonam-relebactam with a standard exposure of aztreonam (1g × 3, IV) were 84.6% (44/52), 55.8% and 34.6% for Enterobacterales and 0% for all combinations for P. aeruginosa and S. maltophila. The susceptibility rates of aztreonam-avibactam, aztreonam-vaborbactam and aztreonam-relebactam with a high exposure of aztreonam (2g × 4, IV) were 92.3%, 78.9% and 57.7% for Enterobacterales, 75%, 60% and 60% for P. aeruginosa and 100%, 100% and 40% for S. maltophila.

CONCLUSIONS

As previously demonstrated for an aztreonam/ceftazidime-avibactam combination, aztreonam plus imipenem-relebactam and aztreonam plus meropenem-vaborbactam might be useful options, but with potentially lower efficiency, to treat infections caused by aztreonam-non-susceptible MBL-producing Gram-negative strains.