In Vitro Activity of Aztreonam-Avibactam against Enterobacteriaceae and Pseudomonas aeruginosa Isolated by Clinical Laboratories in 40 Countries from 2012 to 2015

Multicenter evaluation of activity of aztreonam in combination with avibactam, relebactam, and vaborbactam against metallo-β-lactamase-producing carbapenem-resistant gram-negative bacilli

Treatment options for carbapenem-resistant gram-negative bacilli (CR-GNB), especially metallo-β-lactamase (MBL)-producing CR-GNB, are limited. Aztreonam (ATM) in combination with avibactam (AVI) has shown potential for treating MBL-producing carbapenem-resistant Enterobacterales (CREs) and Stenotrophomonas maltophilia. However, data on ATM in combination with other β-lactamase inhibitors (BLIs) are limited. We performed a multicenter study to evaluate the in vitro activities of ATM in combination with AVI, vaborbactam (VAB), relebactam (REL), tazobactam (TAZ) as well as with their commercially available formulations against CREs and S. maltophilia using broth microdilution. AVI restored ATM activity for MBL-producing CREs (ATM: 9.8% vs ATM-AVI: 78.0%) and S. maltophilia (ATM: 0% vs ATM-AVI: 93.3%). REL also moderately restored activity of ATM in MBL-producing CREs (ATM: 9.8% vs ATM-REL: 42.7%) and S. maltophilia (ATM: 0% vs ATM-REL: 68.9%). VAB and TAZ demonstrated very limited effect on the activity of ATM against CR-GNB evaluated. The combination of ATM with ceftazidime-AVI (CAZ-AVI) demonstrated maximum activity against CREs. Although ATM-CAZ-AVI is the most potent regimen available for CREs and S. maltophilia, ATM-IMI-REL might be a reasonable alternative.

Evolving resistance landscape in gram-negative pathogens: An update on β-lactam and β-lactam-inhibitor treatment combinations for carbapenem-resistant organisms

Antibiotic resistance has become a global threat as it is continuously growing due to the evolution of β-lactamases diminishing the activity of classic β-lactam (BL) antibiotics. Recent antibiotic discovery and development efforts have led to the availability of β-lactamase inhibitors (BLIs) with activity against extended-spectrum β-lactamases as well as Klebsiella pneumoniae carbapenemase (KPC)-producing carbapenem-resistant organisms (CRO). Nevertheless, there is still a lack of drugs that target metallo-β-lactamases (MBL), which hydrolyze carbapenems efficiently, and oxacillinases (OXA) often present in carbapenem-resistant Acinetobacter baumannii. This review aims to provide a snapshot of microbiology, pharmacology, and clinical data for currently available BL/BLI treatment options as well as agents in late stage development for CRO harboring various β-lactamases including MBL and OXA-enzymes.

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.

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.

In vitro and in vivo activity of ceftazidime/avibactam and aztreonam alone or in combination against mcr-9, serine- and metallo-β-lactamases-co-producing carbapenem-resistant Enterobacter cloacae complex

PURPOSE

Enterobacteriaceae carrying mcr-9, in particularly those also co-containing metallo-β-lactamase (MBL) and TEM type β-lactamase, present potential transmission risks and lack adequate clinical response methods, thereby posing a major threat to global public health. The aim of this study was to assess the antimicrobial efficacy of a combined ceftazidime/avibactam (CZA) and aztreonam (ATM) regimen against carbapenem-resistant Enterobacter cloacae complex (CRECC) co-producing mcr-9, MBL and TEM.

METHODS

The in vitro antibacterial activity of CZA plus ATM was evaluated using a time-kill curve assay. Furthermore, the in vivo interaction between CZA plus ATM was confirmed using a Galleria mellonella (G. mellonella) infection model.

RESULTS

All eight clinical strains of CRECC, co-carrying mcr-9, MBL and TEM, exhibited high resistance to CZA and ATM. In vitro time-kill curve analysis demonstrated that the combination therapy of CZA + ATM exerted significant bactericidal activity against mcr-9, MBL and TEM-co-producing Enterobacter cloacae complex (ECC) isolates with a 100% synergy rate observed in our study. Furthermore, in vivo survival assay using Galleria mellonella larvae infected with CRECC strains co-harboring mcr-9, MBL and TEM revealed that the CZA + ATM combination significantly improved the survival rate compared to the drug-treatment alone and untreated control groups.

CONCLUSION

To our knowledge, this study represents the first report on the in vitro and in vivo antibacterial activity of CZA plus ATM against CRECC isolates co-harboring mcr-9, MBL and TEM. Our findings suggest that the combination regimen of CZA + ATM provides a valuable reference for clinicians to address the increasingly complex antibiotic resistance situation observed in clinical microorganisms.

Synergistic Combination of Aztreonam and Ceftazidime-Avibactam-A Promising Defense Strategy against OXA-48 + NDM Klebsiella pneumoniae in Romania

With the increasing burden of carbapenem-resistant Klebsiella pneumoniae (CR-Kp), including high rates of healthcare-associated infections, treatment failure, and mortality, a good therapeutic strategy for attacking this multi-resistant pathogen is one of the main goals in current medical practice and necessitates the use of novel antibiotics or new drug combinations.

OBJECTIVES

We reviewed the clinical and microbiological outcomes of seven patients treated at the "Agrippa Ionescu" Clinical Emergency Hospital between October 2023 and January 2024, aiming to demonstrate the synergistic activity of the ceftazidime-avibactam (C/A) plus aztreonam (ATM) combination against the co-producers of blaNDM + blaOXA-48-like CR-Kp.

MATERIAL AND METHODS

Seven CR-Kp with blaNDM and blaOXA-48 as resistance mechanisms were tested. Seven patients treated with C/A + ATM were included. The synergistic activity of C/A + ATM was proven through double-disk diffusion in all seven isolates. Resistance mechanisms like KPC, VIM, OXA-48, NDM, IMP, and CTX-M were assessed through immunochromatography.

RESULTS

With a mean of nine days of treatment with the synergistic combination C/A + ATM, all patients achieved clinical recovery, and five achieved microbiological recovery.

CONCLUSIONS

With the emerging co-occurrence of blaOXA-48 and blaNDM among Kp in Romania, the combination of C/A and ATM could be a promising therapeutic option.

Comparison of testing methods assessing the in vitro efficacy of the combination of aztreonam with avibactam on multidrug-resistant Gram-negative bacilli

BACKGROUND

Aztreonam-avibactam (ATM-AVI) combination shows promising effectiveness on most carbapenemase-producing Gram-negatives, yet standardized antibiotic susceptibility testing (AST) methods for evaluating the combination in clinical laboratories is lacking. We aimed to evaluate different ATM-AVI AST approaches.

METHODS

96 characterized carbapenem-resistant clinical isolates belonging to 9 Enterobacterales (EB; n = 80) and P. aeruginosa (PA; n = 16) species, including 90 carbapenemase producers and 72 strains resistant to both CAZ-AVI and ATM, were tested. Paper disk elution (DE; Bio-Rad) and E-test gradient strips stacking (SS; bioMérieux) were performed for the ATM + CAZ-AVI combination. MIC Test Strip (MTS; Liofilchem) was evaluated for ATM-AVI MIC determination. Results were interpreted applying ATM clinical breakpoints of the EUCAST guidelines and compared to the broth microdilution method (Sensititre, Thermofisher).

RESULTS

According to broth microdilution method, 93% of EB and 69% of PA were tested susceptible to ATM-AVI. The synergistic effect of ATM-AVI was of 95% for EB, but of only 17% for PA. The MTS method yielded higher categorical and essential agreement (CA/EA) rates for both EB (89%/91%) and PA (94%/94%) compared to SS, where the rates were 87%/83% for EB and 81%/81% for PA. MTS and SS yielded 2 and 3 major discrepancies, respectively, while 3 very major discrepancies each were observed for both methods. Concerning the DE method, CA reached 91% for EB and 81% for PA, but high number of very major discrepancies were observed for EB (n = 6; 8%) and for PA (n = 3; 19%).

CONCLUSIONS

The ATM-AVI association displayed excellent in vitro activity against highly resistant clinical Enterobacterales strains. MTS method offers accurate ATM-AVI AST results, while the SS method might serve as better alternative then DE method in assessing the efficacy of ATM + CAZ-AVI combination. However, further investigation is needed to confirm the methods' ability to detect ATM-AVI resistance.

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.

Evaluation of the MTS™ aztreonam-avibactam strip (Liofilchem) on New Delhi metallo-β-lactamase-producing Enterobacterales

The combination of ceftazidime-avibactam (CAZ-AVI) and aztreonam (ATM) is used to treat MBL-producing Enterobacterales-related infections. The new combination aztreonam-avibactam (AZA) is currently in development. We compared results obtained with the new MIC test strip (MTS) AZA (Liofilchem) with broth microdilution method (BMD) on 41 MBL-producing Enterobacterales from 41 clinical samples. The MTS AZA was also compared to combination testing method using CAZ-AVI and ATM strips. Compared to BMD, categorical agreement (CA) was 100%. Compared with combination testing method, CA was 97.6%. The MTS AZA can be used to determine MICs levels of AZA or CAZ-AVI/ATM combinations.

Role of β-Lactamase Inhibitors as Potentiators in Antimicrobial Chemotherapy Targeting Gram-Negative Bacteria

Since the discovery of penicillin, β-lactam antibiotics have commonly been used to treat bacterial infections. Unfortunately, at the same time, pathogens can develop resistance to β-lactam antibiotics such as penicillins, cephalosporins, monobactams, and carbapenems by producing β-lactamases. Therefore, a combination of β-lactam antibiotics with β-lactamase inhibitors has been a promising approach to controlling β-lactam-resistant bacteria. The discovery of novel β-lactamase inhibitors (BLIs) is essential for effectively treating antibiotic-resistant bacterial infections. Therefore, this review discusses the development of innovative inhibitors meant to enhance the activity of β-lactam antibiotics. Specifically, this review describes the classification and characteristics of different classes of β-lactamases and the synergistic mechanisms of β-lactams and BLIs. In addition, we introduce potential sources of compounds for use as novel BLIs. This provides insights into overcoming current challenges in β-lactamase-producing bacteria and designing effective treatment options in combination with BLIs.

Activities of aztreonam in combination with several novel β-lactam-β-lactamase inhibitor combinations against carbapenem-resistant Klebsiella pneumoniae strains coproducing KPC and NDM

Isolates coproducing serine/metallo-carbapenems are a serious emerging public health threat, given their rapid dissemination and the limited number of treatment options. The purposes of this study were to evaluate the in vitro antibacterial activity of novel β-lactam-β-lactamase inhibitor combinations (BLBLIs) against carbapenem-resistant Klebsiella pneumoniae (CRKP) coproducing metallo-β-lactamase and serine-β-lactamase, and to explore their effects in combination with aztreonam, meropenem, or polymyxin in order to identify the best therapeutic options. Four CRKP isolates coproducing K. pneumoniae carbapenemase (KPC) and New Delhi metallo-β-lactamase (NDM) were selected, and a microdilution broth method was used to determine their susceptibility to antibiotics. Time-kill assay was used to detect the bactericidal effects of the combinations of antibiotics. The minimum inhibitory concentration (MIC) values for imipenem and meropenem in three isolates did not decrease after the addition of relebactam or varbobactam, but the addition of avibactam to aztreonam reduced the MIC by more than 64-fold. Time-kill assay demonstrated that imipenem-cilastatin/relebactam (ICR) alone exerted a bacteriostatic effect against three isolates (average reduction: 1.88 log10 CFU/mL) and ICR combined with aztreonam exerted an additive effect. Aztreonam combined with meropenem/varbobactam (MEV) or ceftazidime/avibactam (CZA) showed synergistic effects, while the effect of aztreonam combined with CZA was inferior to that of MEV. Compared with the same concentration of aztreonam plus CZA combination, aztreonam/avibactam had a better bactericidal effect (24 h bacterial count reduction >3 log10CFU/mL). These data indicate that the combination of ATM with several new BLBLIs exerts powerful bactericidal activity, which suggests that these double β-lactam combinations might provide potential alternative treatments for infections caused by pathogens coproducing-serine/metallo-carbapenems.

The burden of antibiotic resistance of the main microorganisms causing infections in humans - review of the literature

One of the biggest threats to human well-being and public health is antibiotic resistance. If allowed to spread unchecked, it might become a major health risk and trigger another pandemic. This proves the need to develop antibiotic resistance-related global health solutions that take into consideration microdata from various global locations. Establishing positive social norms, guiding individual and group behavioral habits that support global human health, and ultimately raising public awareness of the need for such action could all have a positive impact. Antibiotic resistance is not just a growing clinical concern but also complicates therapy, making adherence to current guidelines for managing antibiotic resistance extremely difficult. Numerous genetic components have been connected to the development of resistance; some of these components have intricate paths of transfer between microorganisms. Beyond this, the subject of antibiotic resistance is becoming increasingly significant in medical microbiology as new mechanisms underpinning its development are identified. In addition to genetic factors, behaviors such as misdiagnosis, exposure to broad-spectrum antibiotics, and delayed diagnosis contribute to the development of resistance. However, advancements in bioinformatics and DNA sequencing technology have completely transformed the diagnostic sector, enabling real-time identification of the components and causes of antibiotic resistance. This information is crucial for developing effective control and prevention strategies to counter the threat.

Molecular analysis of metallo-beta-lactamase-producing Pseudomonas aeruginosa in Switzerland 2022-2023

OBJECTIVES

The occurrence of metallo-beta-lactamase-producing Pseudomonas aeruginosa (MBL-PA) isolates is increasing globally, including in Switzerland. The aim of this study was to characterise, phenotypically and genotypically, the MBL-PA isolates submitted to the Swiss National Reference Center for Emerging Antibiotic Resistance (NARA) reference laboratory over a 12-month period from July 2022 to July 2023.

METHODS

Thirty-nine non-duplicate MBL-PA Isolates were submitted to NARA over the study period from across Switzerland. Susceptibility was determined by broth microdilution according to EUCAST methodology. Whole-genome sequencing was performed on 34 isolates. Sequence types (STs) and resistance genes were ascertained using the Centre for Genomic Epidemiology platform. MBL genes, blaNDM-1, blaIMP-1, and blaVIM-2, were cloned into vector pUCP24 and transformed into P. aeruginosa PA14.

RESULTS

The most prevalent MBL types identified in this study were VIM (21/39; 53.8%) followed by NDM (11/39; 28.2%), IMP (6/39; 15.4%), and a single isolate produced both VIM and NDM enzymes. WGS identified 13 different STs types among the 39 isolates. They all exhibited resistance to cephalosporins, carbapenems, and the beta-lactam-beta-lactamase inhibitor combinations, ceftolozane-tazobactam, ceftazidime-avibactam, imipenem-relebactam, and meropenem-vaborbactam, and 8 isolates were cefiderocol (FDC) resistant. Recombinant P. aeruginosa strains producing blaNDM-1, blaIMP-1, and blaVIM-2 exhibited FDC MICs of 16, 8, and 1 mg/L, respectively.

CONCLUSIONS

This study showed that the MBL-PA in Switzerland could be attributed to the wide dissemination of high-risk clones that accounted for most isolates in this study. Although FDC resistance was only found in 8 isolates, MBL carriage was shown to be a major contributor to this phenotype.

Next generation antibiotic combinations to combat pan-drug resistant Klebsiella pneumoniae

Antimicrobial resistance has emerged as one of the leading public health threats of the twenty-first century. Gram-negative pathogens have been a major contributor to the declining efficacy of antibiotics through both acquired resistance and tolerance. In this study, a pan-drug resistant (PDR), NDM-1 and CTX-M-15 co-producing isolate of K. pneumoniae, CDC Nevada, (Kp Nevada) was exposed to the clinical combination of aztreonam + ceftazidime/avibactam (ATM/CAZ/AVI) to overcome metallo-β-lactamases. Unexpectedly, the β-lactam combination resulted in long filamentous cell formation induced by PBP3 inhibition over 168 h in the hollow fiber infection model experiments with eventual reversion of the total population upon drug removal. However, the addition of imipenem to the two drug β-lactam combination was highly synergistic with suppression of all drug resistant subpopulations over 5 days. Scanning electron microscopy and fluorescence microscopy for all imipenem combinations in time kill studies suggested a role for imipenem in suppression of long filamentous persisters, via the formation of metabolically active spheroplasts. To complement the imaging studies, salient transcriptomic changes were quantified using RT-PCR and novel cassette assay evaluated β-lactam permeability. This showed significant upregulation of both spheroplast protein Y (SPY), a periplasmic chaperone protein that has been shown to be related to spheroplast formation, and penicillin binding proteins (PBP1, PBP2, PBP3) for all combinations involving imipenem. However, with aztreonam alone, pbp1, pbp3 and spy remained unchanged while pbp2 levels were downregulated by > 25%. Imipenem displayed 207-fold higher permeability as compared with aztreonam (mean permeability coefficient of 17,200 nm/s). Although the clinical combination of aztreonam/avibactam and ceftazidime has been proposed as an important treatment of MBL Gram-negatives, we report the first occurrence of long filamentous persister formation. To our knowledge, this is the first study that defines novel β-lactam combinations involving imipenem via maximal suppression of filamentous persisters to combat PDR CDC Nevada K. pneumoniae.

Approach to multidrug resistant infections in pediatric transplant recipients

Introduction

There is increasing recognition of infections due to multidrug-resistant Gram negative (MDRGN) bacterial infections among children undergoing solid organ and hematopoietic cell transplantation, which may be associated with morbidity and mortality.

Methods

We present two vignettes that highlight the clinical challenges of evaluation, management, and prevention of MDRGN bacterial infections in children prior to and after transplantation. The goal of this discussion is to provide a framework to help develop an approach to evaluation and management of these infections.

Results

Source control remains the utmost priority in management of MDR infections and is paired with antibiotic selection guided by in vitro susceptibilities, adverse effect profiles, and clinical response. Identification and confirmation of resistance can be challenging and often requires additional testing for recognition of complex mechanisms. Current antimicrobial approaches to MDRGN infections include use of novel agents, prolonged infusion, and/or combination therapy. We also discuss preventative efforts including infection control, antimicrobial stewardship, targeted pre-emptive or prophylactic treatment, and decolonization.

Discussion

The impact of MDRGN infections on patient and graft survival highlights the need to optimize treatment and prevention strategies.

Management strategies for severe Pseudomonas aeruginosa infections

PURPOSE OF REVIEW

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

RECENT FINDINGS

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

SUMMARY

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

Antimicrobial Activities of Aztreonam-Avibactam and Comparator Agents against Enterobacterales Analyzed by ICU and Non-ICU Wards, Infection Sources, and Geographic Regions: ATLAS Program 2016-2020

Increasing antimicrobial resistance among multidrug-resistant (MDR), extended-spectrum β-lactamase (ESBL)- and carbapenemase-producing Enterobacterales (CPE), in particular metallo-β-lactamase (MBL)-positive strains, has led to limited treatment options in these isolates. This study evaluated the activity of aztreonam-avibactam (ATM-AVI) and comparator antimicrobials against Enterobacterales isolates and key resistance phenotypes stratified by wards, infection sources and geographic regions as part of the ATLAS program between 2016 and 2020. Minimum inhibitory concentrations (MICs) were determined per Clinical and Laboratory Standards Institute (CLSI) guidelines. The susceptibility of antimicrobials were interpreted using CLSI and European Committee on Antimicrobial Susceptibility Testing (EUCAST) breakpoints. A tentative pharmacokinetic/pharmacodynamic breakpoint of 8 µg/mL was considered for ATM-AVI activity. ATM-AVI inhibited ≥99.2% of Enterobacterales isolates across wards and ≥99.7% isolates across infection sources globally and in all regions at ≤8 µg/mL. For resistance phenotypes, ATM-AVI demonstrated sustained activity across wards and infection sources by inhibiting ≥98.5% and ≥99.1% of multidrug-resistant (MDR) isolates, ≥98.6% and ≥99.1% of ESBL-positive isolates, ≥96.8% and ≥90.9% of carbapenem-resistant (CR) isolates, and ≥96.8% and ≥97.4% of MBL-positive isolates, respectively, at ≤8 µg/mL globally and across regions. Overall, our study demonstrated that ATM-AVI represents an important therapeutic option for infections caused by Enterobacterales, including key resistance phenotypes across different wards and infection sources.

Clinical outcomes in elderly patients with infections caused by NDM-producing Klebsiella pneumoniae: results from a real-life retrospective single center study in an endemic area

Real-life outcomes data for elderly patients with infections caused by Klebsiella pneumoniae producing New Delhi metallo-beta-lactamase (NDM-Kp) are lacking. We conducted a retrospective cohort study enrolling 33 consecutive adult patients (mean age 77.4 years; 48.5% males; mean Charlson Comorbidity Index-CCI 5.9) hospitalized for NDM-Kp infections during a 24-month period in an Italian highly endemic area. 78.8% were admitted to Internal Medicine ward. 45.4% of patients had bloodstream infections (BSI), 39.4% urinary tract infections (UTI) without BSI, 9.1% respiratory tract infections and 6.1% intra-abdominal infections. 93.9% had rectal colonization.Adequate definitive antibiotic therapy (mainly represented by aztreonam plus ceftazidime/avibactam) was provided to 36.4% of cases. Mean age and CCI of patients adequately treated were significantly lower than those inadequately treated (71.2 vs 80.9 years, p = 0.041, and 4.6 vs 6.7, p = 0.040, respectively). Patients adequately treated had a mean hospitalization length significantly higher (28 vs 15 days, p = 0.016). The overall 30-day survival rate of patients adequately and inadequately treated was 83.3% and 57.1%, respectively: this difference was not statistically significant. Mean age and CCI of 22 patients who survived at 30 days were lower than those of 11 patients who died (73.7 vs 84.8 years, p = 0.003, and 5.3 vs 7.2, p = 0.049, respectively). Twelve survivors received an inadequate therapy: 8/12 had UTI. Six of nine patients inadequately treated who died within 30 days, died before microbiological diagnosis. Our study provides real-life data on outcomes of elderly and multimorbid patients hospitalized for infections caused by NDM-Kp. Further studies with larger sample size are warranted.

In vitro, in vivo and clinical studies comparing the efficacy of ceftazidime-avibactam monotherapy with ceftazidime-avibactam-containing combination regimens against carbapenem-resistant Enterobacterales and multidrug-resistant Pseudomonas aeruginosa isolates or infections: a scoping review

Introduction

Carbapenem-resistant Enterobacterales (CRE) and multidrug-resistant Pseudomonas aeruginosa (MDR-PA) infections are associated with a high risk of morbidity, mortality, and treatment costs. We aimed to evaluate in vitro, in vivo and clinical studies comparing the efficacy of ceftazidime-avibactam (CZA) combination regimens with CZA alone against CRE and/or MDR-PA isolates or infections.

Methods

We systematically reviewed the relevant literature in CINAHL/MEDLINE, Pubmed, Cochrane, Web of Science, Embase, and Scopus until December 1, 2022. Review articles, grey literature, abstracts, comments, editorials, non-peer reviewed articles, non-English articles, and in vitro synergy studies conducted on single isolates were excluded.

Results

22 in vitro, 7 in vivo and 20 clinical studies were evaluated. In vitro studies showed reliable synergy between CZA and aztreonam against metallo-β-lactamase (MBL)-producing isolates. Some studies indicated good in vitro synergy between CZA and amikacin, meropenem, fosfomycin and polymyxins against CRE isolates. For MDR-PA isolates, there are comparatively fewer in vitro or in vivo studies. In observational clinical studies, mortality, clinical cure, adverse events, and development of CZA resistance after exposure were generally similar in monotherapy and combination therapy groups. However, antibiotic-related nephrotoxicity and infection relapses were higher in patients receiving CZA combination therapies.

Discussion

The benefit, if any, of CZA combination regimens in MDR-PA infections is elusive, as very few clinical studies have included these infections. There is no currently documented clinical benefit for the use of CZA combination regimens rather than CZA monotherapy. CZA combined with aztreonam for serious infections due to MBL producers should be evaluated by randomized controlled trials.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=278552, CRD42021278552.

In vitro activity of aztreonam-avibactam against Enterobacterales isolates collected in Latin America, Africa/Middle East, Asia, and Eurasia for the ATLAS Global Surveillance Program in 2019-2021

This study aimed to report reference method antimicrobial susceptibility results for 24,937 recent (2019-2021) clinical isolates of Enterobacterales from 27 countries in Latin America, Eurasia, Africa/Middle East, and Asia with a focus on the investigational combination aztreonam-avibactam against metallo-β-lactamase (MBL) isolates. Antimicrobial susceptibility testing was performed by the CLSI broth microdilution methodology. Minimum inhibitory concentrations (MICs) were interpreted using the CLSI (2022) breakpoints for all agents except aztreonam-avibactam (provisional pharmacokinetic/pharmacodynamic susceptible breakpoint, ≤ 8 mg/L) and tigecycline (US-FDA). Molecular testing for β-lactamase genes was performed on isolates with meropenem MICs ≥ 2 mg/L, ceftazidime-avibactam MICs ≥ 16 mg/L, and/or aztreonam-avibactam MICs ≥ 16 mg/L, and 50% of isolates of Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, Klebsiella variicola, and Proteus mirabilis testing with ceftazidime and/or aztreonam MICs ≥ 2 mg/L. Aztreonam-avibactam inhibited 99.8% of all Enterobacterales at ≤ 8 mg/L (MIC90, 0.25 mg/L) and maintained activity against phenotypically resistant subsets of multidrug-resistant (MDR) (99.5% susceptible), extensively drug-resistant (XDR) (98.7%), and carbapenem-resistant Enterobacterales (CRE) (99.1%) isolates. At ≤ 8 mg/L, aztreonam-avibactam inhibited 100%, 99.6%, 99.6%, and 98.8% of KPC-, OXA-48-like-, ESBL-, and MBL-carrying isolates, respectively. MBL-positive isolates were most prevalent in India (20.5%), Guatemala (13.8%), and Jordan (13.2%). No differences in the activity of aztreonam-avibactam were observed across the global regions evaluated. At a concentration of ≤ 8 mg/L, aztreonam-avibactam inhibited almost all Enterobacterales collected from developing countries, including MBL-producing isolates. The widespread dissemination of MBLs among Enterobacterales highlights the unmet need for new agents such as aztreonam-avibactam for the treatment of CRE infections.

Case report: Continuous infusions of ceftazidime-avibactam and aztreonam in combination through elastomeric infusors for 12 weeks for the treatment of bone and joint infections due to metallo-β-lactamase producing Enterobacterales

Among carbapenem-resistant Enterobacterales, metallo-beta-lactamase producing strains represent a growing therapeutic challenge. While the association of aztreonam and ceftazidime-avibactam has been investigated in recent years for the treatment of infections involving these strains, little to no clinical data support the use of this association for the treatment of bone and joint infections. We report two cases of complex bone and joint infections involving metallo-beta-lactamase-producing Enterobacterales, successfully treated at our referral center with aztreonam and ceftazidime-avibactam for 12 weeks in continuous infusions through elastomeric infusors.

Case Commentary: When Voldemort Meets Sauron: Treatment Considerations for Emerging Dual-Carbapenemase-Producing Extensively Drug-Resistant Pseudomonas aeruginosa

Infections caused by extensively drug-resistant Pseudomonas aeruginosa are difficult to treat due to limited effective treatment options. In this issue, a patient with a corneal infection caused by a Verona integron-encoded metallo-β-lactamase (VIM)- and Guiana extended-spectrum β-lactamase (GES)-coproducing P. aeruginosa strain associated with the recent artificial tears-related outbreak in the United States is described. This resistance genotype/phenotype further compromises therapeutic options, and this report provides insights into diagnostic and treatment approaches for clinicians dealing with infections due to this highly resistant P. aeruginosa.

Metallo-β-lactamase-mediated antimicrobial resistance and progress in inhibitor discovery

Resistance to β-lactam antibiotics is rapidly growing, substantially due to the spread of serine-β-lactamases (SBLs) and metallo-β-lactamases (MBLs), which efficiently catalyse β-lactam hydrolysis. Combinations of a β-lactam antibiotic with an SBL inhibitor have been clinically successful; however, no MBL inhibitors have been developed for clinical use. MBLs are a worrying resistance vector because they catalyse hydrolysis of all β-lactam antibiotic classes, except the monobactams, and they are being disseminated across many bacterial species worldwide. Here we review the classification, structures, substrate profiles, and inhibition mechanisms of MBLs, highlighting current clinical problems due to MBL-mediated resistance and progress in understanding and combating MBL-mediated resistance.

Synthesis and biological evaluation of novel β-lactam-metallo β-lactamase inhibitors

β-lactamases are enzymes that deactivate β-lactam antibiotics through a hydrolysis mechanism. There are two known types of β-lactamases: serine β-lactamases (SBLs) and metallo β-lactamases (MBLs). The two existing strategies to overcome β-lactamase-mediated resistance are (a) to develop novel β-lactam antibiotics that are not susceptible to hydrolysis by these enzymes; or (b) to develop β-lactamase inhibitors that deactivate the enzyme and thereby restore the efficacy of the co-administered antibiotics. Many commercially available SBL inhibitors are used in combination therapy with antibiotics to treat antimicrobial resistant infections; however, there are only a handful of MBL inhibitors undergoing clinical trials. In this study, we present 11 novel potential MBL inhibitors (via multi-step chemical synthesis), that have shown to completely restore the efficacy of meropenem (≤2 mg L^-1) against New Delhi metallo-β-lactamase (NDM) producing Klebsiella pneumoniae in vitro. These compounds contain a cyclic amino acid zinc chelator conjugated to various commercially available β-lactam antibiotic scaffolds with the aim to improve the overall drug transport, lipophilicity, and pharmacokinetic/pharmacodynamic properties as compared to the chelator alone. Biological evaluation of compounds 24b and 24c has further highlighted the downstream application of these MBLs, since they are non-toxic at the selected doses. Time-kill assays indicate that compounds 24b and 24c exhibit sterilizing activity towards NDM producing Klebsiella pneumoniae in vitro using minimal concentrations of meropenem. Furthermore, 24b and 24c proved to be promising inhibitors of VIM-2 (K_i = 0.85 and 1.87, respectively). This study has revealed a novel series of β-lactam MBLIs that are potent, efficacious, and safe leads with the potential to develop into therapeutic MBLIs.

Treatment options for multidrug-resistant Gram-negatives in urinary tract infections

PURPOSE OF REVIEW

Infections due to multidrug-resistant (MDR) Gram-negative bacteria are challenging to treat because of limited treatment options and potential side effects of less frequently used anti-infectives. In the past few years, several new antimicrobial agents effective against MDR Gram-negatives have become available. This review focuses on the treatment options for complicated urinary tract infections (cUTIs) caused by MDR Gram-negatives.

RECENT FINDINGS

The novel combinations, betalactam or carbapenem and betalactamase inhibitor, ceftazidime/avibactam and meropenem/vaborbactam, are effective for infections caused by KPC-carbapenemase-producing pathogens. Imipenem/relebactam, another carbapenem/betalactamase inhibitor combination, has been approved for the treatment of cUTI. However, data on the efficacy of imipenem/relebactam against carbapenem-resistant pathogens is still limited. Ceftolozane/tazobactam is mainly used for the treatment of MDR Pseudomonas aeruginosa infections. For the treatment of cUTI caused by extended-spectrum betalactamases producing Enterobacterales aminoglycosides or intravenous fosfomycin should be considered.

SUMMARY

To ensure prudent use and to avoid the development of resistance to novel anti-infective substances, an interdisciplinary approach, including urologists, microbiologists, and infectious disease physicians, is strongly advised.

Dissemination of Metallo-β-Lactamase-Producing Pseudomonas aeruginosa in Serbian Hospital Settings: Expansion of ST235 and ST654 Clones

This nationwide study aimed to investigate the molecular characteristics of metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa in Serbia, underlying resistance mechanisms, the genetic context of detected MBL genes, and the clonal relationship between isolates harboring genes-encoding MBL. Overall, 320/5334 isolates collected from 2018 to 2021 were identified as P. aeruginosa. Carbapenem-resistant P. aeruginosa (CRPA) were screened for the presence of bla_VIM, bla_IMP, and bla_NDM, genes whereas MBL-positive isolates were tested for the presence of the bla_CTX-M-2, bla_PER, bla_TEM, bla_SHV, bla_VEB, and bla_GES. Multilocus sequence typing and phylogenomic analysis were performed for P. aeruginosa-producing MBL. The majority of the P. aeruginosa isolates were recovered from the lower respiratory tract (n = 120; 37.5%) and wound specimens (n = 108; 33.75%). CRPA isolates accounted for 43.1% (n = 138) of the tested isolates, 31 out of them being bla_NDM-1-positive (22.5%). The colistin resistance rate was 0.3%. MLST analysis revealed the occurrence of ST235 (n = 25) and ST654 (n = 6), mostly confined to Serbia. The distribution of beta-lactamase-encoding genes in these isolates suggested clonal dissemination and possible recombination: ST235/bla_NDM-1, ST235/bla_NDM-1/bla_PER-1, ST654/bla_NDM-1, ST654/bla_NDM-1/bla_PER-1, and ST654/bla_NDM-1/bla_GES-5. High-risk clones ST235 and ST654 identified for the first time in Serbia, are important vectors of acquired MBL and ESBL and their associated multidrug resistance phenotypes represent a cause for considerable concern.

Molecular Profiling of a Multi-Strain Hypervirulent Klebsiella pneumoniae Infection Within a Single Patient

Background

The rising prevalence of infections caused by carbapenem-resistant and hypervirulent Klebsiella pneumoniae (CR-hvKP) has outpaced our understanding of their evolutionary diversity. By straining the antimicrobial options and constant horizontal gene transfer of various pathogenic elements, CR-hvKP poses a global health threat.

Methods

Six KP isolates (KP1~KP6) from urine, sputum and groin infection secretion of a single patient were characterized phenotypically and genotypically. The antimicrobial susceptibility, carbapenemase production, hypermucoviscosity, serum resistance, virulence factors, MLST and serotypes were profiled. Genomic variations were identified by whole-genome sequencing and the phylogenetic differentiation was analyzed by Enterobacterial repetitive intergenic consensus (ERIC)-PCR.

Results

All KP strains were multi-drug resistant. Four of them (KP1, KP3, KP5 and KP6) belonged to ST11-K64, with high genetic closeness (relatedness coefficient above 0.96), sharing most resistance and virulence genes. Compared with KP1, the later isolates KP3, KP5 and KP6 acquired bla _KPC-1 and lost bla _SHV-182 genes. KP2 and KP4 had the same clonal origin of ST35-K16 (relatedness coefficient 0.98), containing almost identical genes for resistance and virulence. They were non-mucoid and carried bla _NDM-5 gene.

Conclusion

A co-infection with two types of CR-hvKP affiliated with different clades within a single patient amplified the treatment difficulties. In addition to source control and epidemiological surveillance, investigation of the in-host interactions between CR-hvKP variants may provide valuable treatment solutions.

Pharmacokinetics of Ceftazidime-Avibactam in Combination with Aztreonam (COMBINE) in a Phase 1, Open-Label Study of Healthy Adults

Scant pharmacokinetic (PK) data are available on ceftazidime-avibactam (CZA) and aztreonam (ATM) in combination, and it is unknown if CZA-ATM exacerbates alanine aminotransferase (ALT)/aspartate aminotransferase (AST) elevations relative to ATM alone. This phase 1 study sought to describe the PK of CZA-ATM and assess the associations between ATM exposures and ALT/AST elevations. Subjects (n = 48) were assigned to one of six cohorts (intermittent infusion [II] CZA, continuous infusion [CI] CZA, II ATM, CI ATM [8 g/daily], II CZA with II ATM [6 g/daily], and II CZA with II ATM [8 g/daily]), and study product(s) were administered for 7 days. A total of 19 subjects (40%) had ALT/AST elevations, and most (89%) occurred in the ATM/CZA-ATM cohorts. Two subjects in the CI ATM cohort experienced severe ALT/AST elevations, which halted the study. All subjects with ALT/AST elevations were asymptomatic with no other signs of liver injury, and all ALT/AST elevations resolved without sequalae after cessation of dosing. In the population PK (PopPK) analyses, CZA-ATM administration reduced total ATM clearance by 16%, had a negligible effect on total ceftazidime clearance, and was not a covariate in the avibactam PopPK model. In the exposure-response analyses, coadministration of CZA-ATM was not found to augment ALT/AST elevations. Modest associations were observed between ATM exposure (maximum concentration of drug in serum [Cmax] and area under the concentration-time curve [AUC]) and ALT/AST elevations in the analysis of subjects in the II ATM/CZA-ATM cohorts. The findings suggest that administration of CZA-ATM reduces ATM clearance but does not exacerbate AST/ALT elevations relative to ATM alone. The results also indicate that CI ATM should be used with caution.

Safety of Ceftazidime-Avibactam in Combination with Aztreonam (COMBINE) in a Phase I, Open-Label Study in Healthy Adult Volunteers

This phase I study evaluated the safety of the optimal ceftazidime-avibactam (CZA) with aztreonam (ATM) regimens identified in hollow fiber infection models of MBL-producing Enterobacterales. Eligible healthy subjects aged 18 to 45 years were assigned to one of six cohorts: 2.5 g CZA over 2 h every 8 h (approved dose), CZA continuous infusion (CI) (7.5 g daily), 2 g ATM over 2 h every 6 h, ATM CI (8 g daily), CZA (approved dose) with 1.5 g ATM over 2 h every 6 h, and CZA (approved dose) with 2 g ATM over 2 h every 6 h. Study drug(s) were administered for 7 days. The most frequently observed adverse events (AEs) were hepatic aminotransferase (ALT/AST) elevations (n = 19 subjects). Seventeen of the 19 subjects with ALT/AST elevations received ATM alone or CZA-ATM. The incidence of ALT/AST elevations was comparable between the ATM-alone and CZA-ATM cohorts. Two subjects in the ATM CI cohort experienced severe ALT/AST elevation AEs. All subjects with ALT/AST elevations were asymptomatic with no other findings suggestive of liver injury. Most other AEs were of mild to moderate severity and were similar across cohorts, except for prolonged prothrombin time (more frequent in CZA-ATM cohorts). These results suggest that CZA-ATM administered as 2-h intermittent infusions is safe and that some caution should be exercised with the use of ATM CI at an ATM dose of 8 g daily. If CZA-ATM is prescribed, clinicians are advised to monitor liver function, hematologic, and coagulation parameters. Future controlled studies are required to better define the safety and efficacy of the CZA-ATM regimens evaluated in this phase I study.

Computational and data mining studies to understand the distribution and dynamics of Temoneria (TEM) β-lactamase and their interaction with β-lactam and β-lactamase inhibitors

β-lactams are large group of antibiotics widely used to suppress the bacterial growth by inhibiting cell wall synthesis. Bacterial resistance against β-lactam antibiotics is primarily mediated through the production of Temoneria (TEM) β-lactamase (BLs), with almost 474 variants identified in Lactamase Engineering Database (LacED). The present study aims to develop a model to track the evolution of TEM BLs and their interactions with β-lactam and BLs inhibitors through data mining and computational approaches. Further, the model will be used to predict the effective combinations of β-lactam and BLs inhibitors to treat the bacterial infection harbouring emerging variants of β-lactamase. The molecular docking study results demonstrated that most TEM mutants recorded the least binding energy to penicillin and cephalosporin (I/II/III/IV/V generations) class of antibiotics. On the contrary, the same mutants recorded higher binding energy to carbapenem and Monobactam class of antibiotics. Among the BLs inhibitors, tazobactam recorded the least binding energy against most of the TEM mutants, indicating that it can lower the catalytic activity of TEM BLs, thereby potentiating antibiotic action. Similarly, data mining work has assisted us in creating a database of TEM mutants that has comprehensive data on mutations, bacterial diversity, Km, MIC, and IRT types. It has been noted that earlier released antibiotics like amoxicillin and ampicillin had lower Km and higher MIC values, which indicates the prevalence of bacterial resistance. By analysing the differential binding energy (ΔBE) of the selected TEM mutants against β-lactam and BLs inhibitors, the most effective combination of β-lactam (carbapenem and monobactam class of antibiotics) and BLs inhibitors (tazobactam) was identified, to cure bacterial diseases/infections and to prevent similar antibiotic resistance outbreaks. Therefore, our study opens a new avenue in developing strategies to manage antibiotic resistance in bacteria.

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.

Cefiderocol for the Treatment of Infections Due to Metallo-B-lactamase-Producing Pathogens in the CREDIBLE-CR and APEKS-NP Phase 3 Randomized Studies

In the CREDIBLE-CR and APEKS-NP studies, cefiderocol treatment was effective against gram-negative bacteria producing metallo-B-lactamases; rates of clinical cure (70.8% [17/24]), microbiological eradication (58.3% [14/24]), and day 28 all-cause mortality (12.5% [3/24]) compared favorably with comparators of best-available therapy and high-dose meropenem (40.0% [4/10], 30.0% [3/10], and 50.0% [5/10], respectively).

Drug development concerning metallo-β-lactamases in gram-negative bacteria

β-Lactams have been a clinical focus since their emergence and indeed act as a powerful tool to combat severe bacterial infections, but their effectiveness is threatened by drug resistance in bacteria, primarily by the production of serine- and metallo-β-lactamases. Although once of less clinical relevance, metallo-β-lactamases are now increasingly threatening. The rapid dissemination of resistance mediated by metallo-β-lactamases poses an increasing challenge to public health worldwide and comprises most existing antibacterial chemotherapies. Regrettably, there have been no clinically available inhibitors of metallo-β-lactamases until now. To cope with this unique challenge, researchers are exploring multidimensional strategies to combat metallo-β-lactamases. Several studies have been conducted to develop new drug candidates or calibrate already available drugs against metallo-β-lactamases. To provide an overview of this field and inspire more researchers to explore it further, we outline some promising candidates targeting metallo-β-lactamase producers, with a focus on Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Acinetobacter baumannii. Promising candidates in this review are composed of new antibacterial drugs, non-antibacterial drugs, antimicrobial peptides, natural products, and zinc chelators, as well as their combinations with existing antibiotics. This review may provide ideas and insight for others to explore candidate metallo-β-lactamases as well as promote the improvement of existing data to obtain further convincing evidence.

A Case of New Delhi Metallo-β-Lactamases (NDM) Citrobacter sedlakii Osteomyelitis Successfully Treated With Ceftazidime-Avibactam and Aztreonam

There have been an increase in multi-drug resistant (MDR) organisms causing infections with high mortality and morbidity. Bacteria that carry metallo-β-lactamases (MBLs) are particularly dangerous. Novel antibiotic combinations, such as ceftazidime-avibactam with aztreonam, are in clinical trials for the treatment of MBL-harboring bacteria. We discuss the case of a 39-year-old patient who presented with tibial osteomyelitis growing MBL-producing Citrobacter sedlakii. He was successfully treated with ceftazidime-avibactam and aztreonam combination therapy. We discuss the importance of developing new antibiotic regimens for the growing threat of MDR organisms with special consideration of MBL.

Treatment of MDR Gram-Negative Bacteria Infections: Ongoing and Prospective

Antimicrobial resistance is a serious public health concern across the world. Gram-negative resistance has propagated over the globe via various methods, the most challenging of which include extended-spectrum β-lactamases, carbapenemases, and AmpC enzymes. Gram-negative bacterial infections are difficult to treat in critically extremely sick persons. Resistance to different antibiotic treatments nearly always lowers the probability of proper empirical coverage, sometimes resulting in severe outcomes. Multidrug resistance can be combated with varying degrees of success using a combination of older drugs with high toxicity levels and novel therapeutics. The current therapies for multidrug-resistant Gram-negative bacteria are discussed in this review, which includes innovative medications, older pharmaceuticals, creative combinations of the two, and therapeutic targets.

Mutation of PA4292 in Pseudomonas aeruginosa Increases β-Lactam Resistance through Upregulating Pyocyanin Production

Metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa is increasingly reported worldwide and usually causes infections with high mortality rates. Aztreonam/avibactam is a β-lactam/β-lactamase inhibitor (BLBLI) combination that is under clinical trials. The advantage of aztreonam/avibactam over the currently used BLBLIs lies in its effectiveness against MBL-producing pathogens, making it one of the few drugs that can be used to treat infections caused by MBL-producing P. aeruginosa. However, the molecular mechanisms underlying aztreonam/avibactam resistance development remain unexplored. Here, in this study, we performed an in vitro evolution assay by using a previously identified MBL-producing P. aeruginosa clinical isolate, NKPa-71, and found mutations in a novel gene, PA4292, in the aztreonam/avibactam-resistant mutants. By mutation of PA4292 in the reference strain PA14, we verified the role of PA4292 in the resistance to aztreonam/avibactam and β-lactams. Transcriptomic analyses revealed upregulation of pyocyanin biosynthesis genes among the most overexpressed in the PA4292 mutant. We further demonstrated that pyocyanin overproduction in the PA4292 mutant increased the bacterial resistance to β-lactams by reducing drug influx. These data revealed a novel mechanism that might lead to the development of resistance to aztreonam/avibactam and β-lactams.

In-vitro susceptibility testing methods for the combination of ceftazidime-avibactam with aztreonam in metallobeta-lactamase producing organisms: Role of combination drugs in antibiotic resistance era

Resistance in Gram-negative organisms has become one of the leading threats in recent years. Of the different mechanisms described in the literature, resistance due to beta-lactamases genes have been overcomed by the use of a beta-lactamase inhibitor in combination with a beta-lactam antibiotic. When this combination is insufficient to counter metallo-beta-lactamases, a third antibiotic, has been added to restore susceptibility. One such recent combination is ceftazidime-avibactam with aztreonam. In this study, 60 isolates of multidrug-resistant organisms producing metallo-beta-lactamases were included to perform in-vitro antibiotic susceptibility testing against ceftazidime-avibactam and aztreonam alone and in combination using three different methods. Individual testing revealed 100% (60/60) resistance to both ceftazidime-avibactam and aztreonam in all the isolates. The disk diffusion method showed an inhibition zone size of 21 mm in all the isolates, with 16 isolates showing an increase in inhibition zone size of >16 mm. In the E-test fixed ratio method, MICs of ceftazidime-avibactam and aztreonam when used alone ranged from 8/4 µg l⁻¹ to ≥256/4 µg l⁻¹ and 16 µg l⁻¹ to 256 µg l⁻¹, respectively, but in combination, these MICs were reduced to 0.016/4 µg l⁻¹ to 2/4 µg l⁻¹ with FIC < 0.5 in all the isolates. Similar results were obtained with the E-test agar dilution method with more than a 16-fold reduction in MIC in all the isolates when avibactam concentration was fixed at 4 µg l⁻¹. All three methods showed a 100% correlation with each other. The current study depicted the usefulness of combining ceftazidime-avibactam with aztreonam against organisms producing metallo-beta-lactamases and that disk diffusion methods can be used as a method for performing in-vitro antibiotic susceptibility testing of this combination.

Efficacy and In Vitro Activity of Novel Antibiotics for Infections With Carbapenem-Resistant Gram-Negative Pathogens

Infections by Gram-negative multi-drug resistant (MDR) bacterial species are difficult to treat using available antibiotics. Overuse of carbapenems has contributed to widespread resistance to these antibiotics; as a result, carbapenem-resistant Enterobacterales (CRE), A. baumannii (CRAB), and P. aeruginosa (CRPA) have become common causes of healthcare-associated infections. Carbapenems, tigecycline, and colistin are the last resource antibiotics currently used; however, multiple reports of resistance to these antimicrobial agents have been documented worldwide. Recently, new antibiotics have been evaluated against Gram-negatives, including plazomicin (a new aminoglycoside) to treat CRE infection, eravacycline (a novel tetracycline) with in vitro activity against CRAB, and cefiderocol (a synthetic conjugate) for the treatment of nosocomial pneumonia by carbapenem-non-susceptible Gram-negative isolates. Furthermore, combinations of known β-lactams with recently developed β-lactam inhibitors, such as ceftazidime-avibactam, ceftolozane-tazobactam, ceftazidime-tazobactam, and meropenem-vaborbactam, has been suggested for the treatment of infections by extended-spectrum β-lactamases, carbapenemases, and AmpC producer bacteria. Nonetheless, they are not active against all carbapenemases, and there are reports of resistance to these combinations in clinical isolates.This review summarizes and discusses the in vitro and clinical evidence of the recently approved antibiotics, β-lactam inhibitors, and those in advanced phases of development for treating MDR infections caused by Gram-negative multi-drug resistant (MDR) bacterial species.

In vitro activity of imipenem/relebactam plus aztreonam against metallo-β-lactamase producing, OprD-deficient Pseudomonas aeruginosa with varying levels of Pseudomonas-derived cephalosporinase production

BACKGROUND

Limited treatment options exist for metallo-β-lactamase (MBL)-producing Pseudomonas aeruginosa infections. Imipenem/relebactam plus aztreonam may be an option.

METHODS

Ten OprD(-) P. aeruginosa isolates (3 parent strains; 7 MBL-producers) were evaluated using checkerboard methodology and Fractional Inhibitory Concentration Index (FICI). Isolates exhibiting synergy in checkerboard studies (FICI ≤0.5) were evaluated using 24-hour static concentration time-kill. Bacteria in late log-phase growth were diluted to 1 × 10⁶ cfu/mL and incubated at 37°C for 24 hours. Samples were drawn at 0, 2, 4, 6 and 24 hours. Physiologic fC_max, fC_ss,avg and fC_min of imipenem (26.7, 5.6, 0.5 mg/L), relebactam (13.1, 4, 0.8 mg/L) and aztreonam (62, 29, 8 mg/L) were used. Synergy in time-kill studies was defined as >2 log₁₀ cfu/mL reduction compared to the most active individual agent.

RESULTS

Synergy was observed in five isolates in checkerboard studies, including three of seven MBL-producing isolates. Isolates which were OprD(-) and harboured inducible Pseudomonas-derived cephalosporinases (PDCs) did not show synergy as defined by FICI, however aztreonam MICs were significantly reduced with the combination. In time-kill studies, ATM alone was as active as combination regimens for MBL-producing isolates with deleted or inducible PDC production. For strains exhibiting constitutive PDC production, I/R plus ATM was synergistic at fC_ss,avg concentrations but exhibited similar activity to ATM at fC_min and fC_max concentrations.

CONCLUSIONS

Imipenem/relebactam plus aztreonam appears to exhibit synergy for some MBL-producing P. aeruginosa at physiologic concentrations. Further study of the effect of dynamic concentrations is needed to understand fully the utility of this combination.

Infectious Diseases Society of America 2022 Guidance on the Treatment of Extended-Spectrum β-lactamase Producing Enterobacterales (ESBL-E), Carbapenem-Resistant Enterobacterales (CRE), and Pseudomonas aeruginosa with Difficult-to-Treat Resistance (DTR-P. aeruginosa)

BACKGROUND

The Infectious Diseases Society of America (IDSA) is committed to providing up-to-date guidance on the treatment of antimicrobial-resistant infections. The initial guidance document on infections caused by extended-spectrum β-lactamase producing Enterobacterales (ESBL-E), carbapenem-resistant Enterobacterales (CRE), and Pseudomonas aeruginosa with difficult-to-treat resistance (DTR-P. aeruginosa) was published on 17 September 2020. Over the past year, there have been a number of important publications furthering our understanding of the management of ESBL-E, CRE, and DTR-P. aeruginosa infections, prompting a rereview of the literature and this updated guidance document.

METHODS

A panel of 6 infectious diseases specialists with expertise in managing antimicrobial-resistant infections reviewed, updated, and expanded previously developed questions and recommendations about the treatment of ESBL-E, CRE, and DTR-P. aeruginosa infections. Because of differences in the epidemiology of resistance and availability of specific anti-infectives internationally, this document focuses on the treatment of infections in the United States.

RESULTS

Preferred and alternative treatment recommendations are provided with accompanying rationales, assuming the causative organism has been identified and antibiotic susceptibility results are known. Approaches to empiric treatment, duration of therapy, and other management considerations are also discussed briefly. Recommendations apply for both adult and pediatric populations.

CONCLUSIONS

The field of antimicrobial resistance is highly dynamic. Consultation with an infectious diseases specialist is recommended for the treatment of antimicrobial-resistant infections. This document is current as of 24 October 2021. The most current versions of IDSA documents, including dates of publication, are available at www.idsociety.org/practice-guideline/amr-guidance/.

β-Lactam Antibiotics and β-Lactamase Enzymes Inhibitors, Part 2: Our Limited Resources

β-lactam antibiotics (BLAs) are crucial molecules among antibacterial drugs, but the increasing emergence of resistance to them, developed by bacteria producing β-lactamase enzymes (BLEs), is becoming one of the major warnings to the global public health. Since only a small number of novel antibiotics are in development, a current clinical approach to limit this phenomenon consists of administering proper combinations of β-lactam antibiotics (BLAs) and β-lactamase inhibitors (BLEsIs). Unfortunately, while few clinically approved BLEsIs are capable of inhibiting most class-A and -C serine β-lactamases (SBLEs) and some carbapenemases of class D, they are unable to inhibit most part of the carbapenem hydrolyzing enzymes of class D and the worrying metallo-β-lactamases (MBLEs) of class B. Particularly, MBLEs are a set of enzymes that catalyzes the hydrolysis of a broad range of BLAs by a zinc-mediated mechanism, and currently no clinically available molecule capable of inhibiting MBLEs exists. Additionally, new types of alarming "superbugs", were found to produce the New Delhi metallo-β-lactamases (NDMs) encoded by increasing variants of a plasmid-mediated gene capable of rapidly spreading among bacteria of the same species and even among different species. Particularly, NDM-1 possesses a flexible hydrolysis mechanism that inactivates all BLAs, except for aztreonam. The present review provides first an overview of existing BLAs and the most clinically relevant BLEs detected so far. Then, the BLEsIs and their most common associations with BLAs already clinically applied and those still in development are reviewed.

Occurrence of multi-carbapenemases producers among carbapenemase-producing Enterobacterales and in vitro activity of combinations including cefiderocol, ceftazidime-avibactam, meropenem-vaborbactam, and aztreonam in the COVID-19 era

PURPOSE

To evaluate the prevalence of multi-carbapenemase-producing Enterobacterales (EB) and the activity of cefiderocol (CFDC), meropenem-vaborbactam (MEV), ceftazidime-avibactam (CZA), and combinations of CZA plus aztreonam (ATM), MEV plus ATM and CFDC plus CZA against them.

METHODS

A collection of carbapenemase-producing EB clinical isolates (n = 1242) was investigated by lateral flow immunoassay NG-Test CARBA-5 and molecular testing. Cefiderocol MICs were determined using broth microdilution SensititreTM panel. MICs of CZA and MEV were determined by the gradient diffusion method. Antimicrobial synergy testing was performed using gradient diffusion strip crossing.

RESULTS

KPC were the most frequent carbapenemases (83.2%), followed by VIM (9.2 %), OXA-48-like (4.3 %) and NDM enzymes (4.1%). Multi-carbapenemase producers were found in 10 (0.8%) isolates. Three combinations of two different carbapenemases were observed: KPC+VIM (n = 4), NDM+OXA-48-like (n = 4), and VIM+OXA-48-like (n = 2). CFDC showed potent activity against eight out of ten dual-carbapenemases producers, while resistance or reduced susceptibility was shown towards CZA and MEV. CFDC in combination with CZA showed no synergistic effects and only two additive effects on seven (87.5%) of the CFDC-susceptible strains. Conversely, CZA plus ATM and MEV plus ATM combinations were synergistic against all ATM-resistant strains regardless of dual-carbapenemases phenotype.

CONCLUSIONS

The occurrence of multi-carbapenemase producers is not uncommon in Northern Italy area. MEV in combination with ATM might be considered as a potential therapeutic option, alternative to CZA plus ATM. CFDC susceptibility testing and synergy evaluation of ATM-based combinations should be performed in the lab routine to evaluate the most in vitro active antimicrobial regimen.

Recommendations to Synthetize Old and New β-Lactamases Inhibitors: A Review to Encourage Further Production

The increasing emergence of bacteria producing β-lactamases enzymes (BLEs), able to inactivate the available β-lactam antibiotics (BLAs), causing the hydrolytic opening of their β-lactam ring, is one of the global major warnings. According to Ambler classification, BLEs are grouped in serine-BLEs (SBLEs) of class A, C, and D, and metal-BLEs (MBLEs) of class B. A current strategy to restore no longer functioning BLAs consists of associating them to β-lactamase enzymes inhibitors (BLEsIs), which, interacting with BLEs, prevent them hydrolyzing to the associated antibiotic. Worryingly, the inhibitors that are clinically approved are very few and inhibit only most of class A and C SBLEs, leaving several class D and all MBLEs of class B untouched. Numerous non-clinically approved new molecules are in development, which have shown broad and ultra-broad spectrum of action, some of them also being active on the New Delhi metal-β-lactamase-1 (NDM-1), which can hydrolyze all available BLAs except for aztreonam. To not duplicate the existing review concerning this topic, we have herein examined BLEsIs by a chemistry approach. To this end, we have reviewed both the long-established synthesis adopted to prepare the old BLEsIs, those proposed to achieve the BLEsIs that are newly approved, and those recently reported to prepare the most relevant molecules yet in development, which have shown high potency, providing for each synthesis the related reaction scheme.

Global Threat of Carbapenem-Resistant Gram-Negative Bacteria

Infections caused by multidrug-resistant (MDR) and extensively drug-resistant (XDR) Gram-negative bacteria (GNB), including carbapenem-resistant (CR) Enterobacterales (CRE; harboring mainly bla_KPC, bla_NDM, and bla_OXA-48-like genes), CR- or MDR/XDR-Pseudomonas aeruginosa (production of VIM, IMP, or NDM carbapenemases combined with porin alteration), and Acinetobacter baumannii complex (producing mainly OXA-23, OXA-58-like carbapenemases), have gradually worsened and become a major challenge to public health because of limited antibiotic choice and high case-fatality rates. Diverse MDR/XDR-GNB isolates have been predominantly cultured from inpatients and hospital equipment/settings, but CRE has also been identified in community settings and long-term care facilities. Several CRE outbreaks cost hospitals and healthcare institutions huge economic burdens for disinfection and containment of their disseminations. Parenteral polymyxin B/E has been observed to have a poor pharmacokinetic profile for the treatment of CR- and XDR-GNB. It has been determined that tigecycline is suitable for the treatment of bloodstream infections owing to GNB, with a minimum inhibitory concentration of ≤ 0.5 mg/L. Ceftazidime-avibactam is a last-resort antibiotic against GNB of Ambler class A/C/D enzyme-producers and a majority of CR-P. aeruginosa isolates. Furthermore, ceftolozane-tazobactam is shown to exhibit excellent in vitro activity against CR- and XDR-P. aeruginosa isolates. Several pharmaceuticals have devoted to exploring novel antibiotics to combat these troublesome XDR-GNBs. Nevertheless, only few antibiotics are shown to be effective in vitro against CR/XDR-A. baumannii complex isolates. In this era of antibiotic pipelines, strict implementation of antibiotic stewardship is as important as in-time isolation cohorts in limiting the spread of CR/XDR-GNB and alleviating the worsening trends of resistance.

The Role of Colistin in the Era of New β-Lactam/β-Lactamase Inhibitor Combinations

With the current crisis related to the emergence of carbapenem-resistant Gram-negative bacteria (CR-GNB), classical treatment approaches with so-called “old-fashion antibiotics” are generally unsatisfactory. Newly approved β-lactam/β-lactamase inhibitors (BLBLIs) should be considered as the first-line treatment options for carbapenem-resistant Enterobacterales (CRE) and carbapenem-resistant Pseudomonas aeruginosa (CRPA) infections. However, colistin can be prescribed for uncomplicated lower urinary tract infections caused by CR-GNB by relying on its pharmacokinetic and pharmacodynamic properties. Similarly, colistin can still be regarded as an alternative therapy for infections caused by carbapenem-resistant Acinetobacter baumannii (CRAB) until new and effective agents are approved. Using colistin in combination regimens (i.e., including at least two in vitro active agents) can be considered in CRAB infections, and CRE infections with high risk of mortality. In conclusion, new BLBLIs have largely replaced colistin for the treatment of CR-GNB infections. Nevertheless, colistin may be needed for the treatment of CRAB infections and in the setting where the new BLBLIs are currently unavailable. In addition, with the advent of rapid diagnostic methods and novel antimicrobials, the application of personalized medicine has gained significant importance in the treatment of CRE infections.

New Antibiotics for Hospital-Acquired Pneumonia and Ventilator-Associated Pneumonia

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) represent one of the most common hospital-acquired infections, carrying a significant morbidity and risk of mortality. Increasing antibiotic resistance among the common bacterial pathogens associated with HAP and VAP, especially Enterobacterales and nonfermenting gram-negative bacteria, has made the choice of empiric treatment of these infections increasingly challenging. Moreover, failure of initial empiric therapy to cover the causative agents associated with HAP and VAP has been associated with worse clinical outcomes. This review provides an overview of antibiotics newly approved or in development for the treatment of HAP and VAP. The approved antibiotics include ceftobiprole, ceftolozane-tazobactam, ceftazidime-avibactam, meropenem-vaborbactam, imipenem-relebactam, and cefiderocol. Their major advantages include their high activity against multidrug-resistant gram-negative pathogens.

European Society of clinical microbiology and infectious diseases (ESCMID) guidelines for the treatment of infections caused by Multidrug-resistant Gram-negative bacilli (endorsed by ESICM -European Society of intensive care Medicine)

SCOPE

These ESCMID guidelines address the targeted antibiotic treatment of 3^rd generation cephalosporin-resistant Enterobacterales (3GCephRE) and carbapenem-resistant Gram-negative bacteria, focusing on the effectiveness of individual antibiotics and on combination vs. monotherapy.

METHODS

An expert panel was convened by ESCMID. A systematic review was performed including randomized controlled trials and observational studies, examining different antibiotic treatment regimens for the targeted treatment of infections caused by the 3GCephRE, carbapenem-resistant Enterobacterales (CRE), carbapenem-resistant Pseudomonas aeruginosa (CRPA) and carbapenem-resistant Acinetobacter baumanni (CRAB). Treatments were classified as head-to-head comparisons between individual antibiotics and monotherapy vs. combination therapy regimens, including defined monotherapy and combination regimens only. The primary outcome was all-cause mortality, preferably at 30 days and secondary outcomes included clinical failure, microbiological failure, development of resistance, relapse/recurrence, adverse events and length of hospital stay. The last search of all databases was conducted in December 2019, followed by a focused search for relevant studies up until ECCMID 2021. Data were summarized narratively. The certainty of the evidence for each comparison between antibiotics and between monotherapy vs. combination therapy regimens was classified by the GRADE recommendations. The strength of the recommendations for or against treatments was classified as strong or conditional (weak).

RECOMMENDATIONS

The guideline panel reviewed the evidence per pathogen, preferably per site of infection, critically appraising the existing studies. Many of the comparisons were addressed in small observational studies at high risk of bias only. Notably, there was very little evidence on the effects of the new, recently approved, beta-lactam beta-lactamase inhibitors on infections caused by carbapenem-resistant Gram-negative bacteria. Most recommendations are based on very-low and low certainty evidence. A high value was placed on antibiotic stewardship considerations in all recommendations, searching for carbapenem-sparing options for 3GCephRE and limiting the recommendations of the new antibiotics for severe infections, as defined by the sepsis-3 criteria. Research needs are addressed.