Β-lactamase Inhibitor Combinations Research Articles

Genomic and Functional Characterization of CTX-M-15-Producing Klebsiella pneumoniae ST307 Isolated from Imported Leopard Tortoises in Germany

The Klebsiella pneumoniae ST307 clone, identified in the mid-1990s, has emerged as a global antimicrobial-resistant (AMR) high-risk clone, significantly contributing to the global health challenge also posed by other AMR K. pneumoniae lineages. The acquisition of a blaCTX-M-15-carrying plasmid has facilitated its widespread dissemination. At Europe’s major transport hub for the movement of live animals, Frankfurt Airport, a shipment of 20 live leopard tortoises was sampled during German border control in 2014. Phylogenetic analysis (MLST) identified a K. pneumoniae ST307 strain, prompting further investigation. Our analysis revealed the presence of a ~193 kb plasmid carrying a broad range of AMR genes, including blaCTX-M-15, blaTEM-1B, blaOXA-1, aac(3)-IIa, aac(6′)-Ib-cr, aph(3″)-Ib, aph(6)-Id, and qnrB1. Additionally, mutations in the quinolone resistance-determining region in gyrA (S83I) and parC (S80I) were detected. Phenotypic testing demonstrated resistance of the isolate to the most common antimicrobials used in both human and veterinary medicine; exceptions included carbapenems and newer β-lactamase inhibitor combinations. Because the role of imported exotic animals in the dissemination of AMR genes is largely deficient, the present study fills yet missing mosaic pieces in the complete picture of extended-spectrum β-lactamase (ESBL)-producing Enterobacterales.

Revisiting the Checkerboard to Inform Development of β-Lactam/β-Lactamase Inhibitor Combinations.

A two-dimensional "checkerboard" array employing systematic titration (e.g., serial two-fold dilutions) is a well-established in vitro method for exploring the antibacterial effects of novel drug combinations. Minimum inhibitory concentrations (MICs) on the checkerboard are isoeffective points at which the antibiotic potency is the same. Representations of checkerboard MIC curves for a β-lactam and β-lactamase inhibitor combination are used in hypothetical "thought experiments" and reveal the ways in which current practices can be improved. Because different types of response (i.e., independence vs. additivity vs. one effective agent; interaction vs. noninteraction) produce different MIC curves, data from different strains/isolates should not be pooled indiscriminately, as the composition of a pooled dataset will influence any derived pharmacokinetic/pharmacodynamic (PK/PD) index. Because the β-lactamase inhibitor threshold concentration (CT) parameter is a function of the β-lactam partner dosing regimen, it is not possible to derive a universal PK/PD index target based on CT. Alternative susceptibility testing methods represent different planes through the checkerboard; a fixed ratio method is less prone to bias for all β-lactam and β-lactamase inhibitor combinations. Susceptibility test MICs will often not reflect the sensitivity of the strain/isolate to the β-lactamase inhibitor, so the use of these MICs to normalize PK/PD indices is inappropriate.

Epidemiology and antimicrobial susceptibility profiles of Enterobacterales causing bloodstream infections before and during COVID-19 pandemic: Results of the Study for Monitoring Antimicrobial Resistance Trends (SMART) in Taiwan, 2018–2021

BackgroundThe coronavirus disease 2019 (COVID-19) pandemic has contributed to the spread of antimicrobial resistance, including carbapenem-resistant Enterobacterales. MethodsThis study utilized data from the Study for Monitoring Antimicrobial Resistance Trends (SMART) surveillance program in Taiwan. Enterobacterales from patients with bloodstream infections (BSIs) were collected and subjected to antimicrobial susceptibility testing and β-lactamase gene detection using a multiplex PCR assay. Statistical analysis was conducted to compare susceptibility rates and resistance genes between time periods before (2018–2019) and during the COVID-19 pandemic (2020–2021). ResultsA total of 1231 Enterobacterales isolates were collected, predominantly Escherichia coli (55.6%) and Klebsiella pneumoniae (29.2%). The proportion of nosocomial BSIs increased during the COVID-19 pandemic (55.5% vs. 61.7%, p < 0.05). Overall, susceptibility rates for most antimicrobial agents decreased, with Enterobacterales from nosocomial BSIs showing significantly lower susceptibility rates than those from community-acquired BSIs. Among 123 Enterobacterales isolates that underwent molecular resistance mechanism detection, ESBL, AmpC β-lactamase, and carbapenemase genes were detected in 43.1%, 48.8% and 16.3% of the tested isolates, respectively. The prevalence of carbapenemase genes among carbapenem-resistant Enterobacterales increased during the pandemic, although the difference was not statistically significant. Two novel β-lactamase inhibitor combinations, imipenem-relebactam and meropenem-vaborbactam, preserved good efficacy against Enterobacterales. However, imipenem-relebactam showed lower in vitro activity against imipenem-non-susceptible Enterobacterales than that of meropenem-vaborbactam. ConclusionsThe COVID-19 pandemic appears to be associated with a general decrease in antimicrobial susceptibility rates among Enterobacterales causing BSIs in Taiwan. Continuous surveillance is crucial to monitor antimicrobial resistance during the pandemic and in the future.

Structure Guided Discovery of Novel Pan Metallo-β-Lactamase Inhibitors with Improved Gram-Negative Bacterial Cell Penetration.

The use of β-lactam (BL) and β-lactamase inhibitor combination to overcome BL antibiotic resistance has been validated through clinically approved drug products. However, unmet medical needs still exist for the treatment of infections caused by Gram-negative (GN) bacteria expressing metallo-β-lactamases. Previously, we reported our effort to discover pan inhibitors of three main families in this class: IMP, VIM, and NDM. Herein, we describe our work to improve the GN coverage spectrum in combination with imipenem and relebactam. This was achieved through structure- and property-based optimization to tackle the GN cell penetration and efflux challenges. A significant discovery was made that inhibition of both VIM alleles, VIM-1 and VIM-2, is essential for broad GN coverage, especially against VIM-producing P. aeruginosa. In addition, pharmacokinetics and nonclinical safety profiles were investigated for select compounds. Key findings from this drug discovery campaign laid the foundation for further lead optimization toward identification of preclinical candidates.

Cefepime–Taniborbactam in Complicated Urinary Tract Infection

BackgroundCarbapenem-resistant Enterobacterales species and multidrug-resistant Pseudomonas aeruginosa are global health threats. Cefepime–taniborbactam is an investigational β-lactam and β-lactamase inhibitor combination with activity against Enterobacterales species and P. aeruginosa expressing serine and metallo-β-lactamases.MethodsIn this phase 3, double-blind, randomized trial, we assigned hospitalized adults with complicated urinary tract infection (UTI), including acute pyelonephritis, in a 2:1 ratio to receive intravenous cefepime–taniborbactam (2.5 g) or meropenem (1 g) every 8 hours for 7 days; this duration could be extended up to 14 days in case of bacteremia. The primary outcome was both microbiologic and clinical success (composite success) on trial days 19 to 23 in the microbiologic intention-to-treat (microITT) population (patients who had a qualifying gram-negative pathogen against which both study drugs were active). A prespecified superiority analysis of the primary outcome was performed after confirmation of noninferiority.ResultsOf the 661 patients who underwent randomization, 436 (66.0%) were included in the microITT population. The mean age of the patients was 56.2 years, and 38.1% were 65 years of age or older. In the microITT population, 57.8% of the patients had complicated UTI, 42.2% had acute pyelonephritis, and 13.1% had bacteremia. Composite success occurred in 207 of 293 patients (70.6%) in the cefepime–taniborbactam group and in 83 of 143 patients (58.0%) in the meropenem group. Cefepime–taniborbactam was superior to meropenem regarding the primary outcome (treatment difference, 12.6 percentage points; 95% confidence interval, 3.1 to 22.2; P=0.009). Differences in treatment response were sustained at late follow-up (trial days 28 to 35), when cefepime–taniborbactam had higher composite success and clinical success. Adverse events occurred in 35.5% and 29.0% of patients in the cefepime–taniborbactam group and the meropenem group, respectively, with headache, diarrhea, constipation, hypertension, and nausea the most frequently reported; the frequency of serious adverse events was similar in the two groups.ConclusionsCefepime–taniborbactam was superior to meropenem for the treatment of complicated UTI that included acute pyelonephritis, with a safety profile similar to that of meropenem. (Funded by Venatorx Pharmaceuticals and others; CERTAIN-1 ClinicalTrials.gov number, NCT03840148.)

Activity of aztreonam-avibactam against Enterobacterales resistant to recently approved beta-lactamase inhibitor combinations collected in Europe, Latin America, and the Asia-Pacific Region (2020–2022)

BackgroundAztreonam-avibactam is under clinical development for treatment of infections caused by carbapenem-resistant Enterobacterales (CRE), especially those resistant to recently approved β-lactamase inhibitor combinations (BLICs). ObjectivesTo evaluate a large collection of CRE isolates, including those non-susceptible to ceftazidime-avibactam, meropenem-vaborbactam, and/or imipenem-relebactam. MethodsOverall, 24 580 Enterobacterales isolates were consecutively collected (1/patient) in 2020–2022 from 64 medical centres located in Western Europe (W-EU), Eastern Europe (E-EU), Latin America (LATAM), and the Asia-Pacific region (APAC). Of those, 1016 (4.1%) were CRE. Isolates were susceptibility tested by broth microdilution. CRE isolates were screened for carbapenemase genes by whole genome sequencing. ResultsAztreonam-avibactam inhibited 99.6% of CREs at ≤8 mg/L. Ceftazidime-avibactam, meropenem-vaborbactam, and imipenem-relebactam were active against 64.6%, 57.4%, and 50.7% of CRE isolates, respectively; most of the non-susceptible isolates carried metallo-beta-lactamases. Aztreonam-avibactam was active against ≥98.9% of isolates non-susceptible to these BLICs. The activity of these BLICs varied by region, with highest susceptibility rates observed in W-EU (76.9% for ceftazidime-avibactam, 72.5% for meropenem-vaborbactam, 63.8% for imipenem-relebactam) and the lowest susceptibility rates identified in the APAC region (39.9% for ceftazidime-avibactam, 37.8% for meropenem-vaborbactam, and 27.5% for imipenem-relebactam). The most common carbapenemase types overall were KPC (44.6% of CREs), NDM (29.9%), and OXA-48–like (16.0%). KPC predominated in LATAM (64.1% of CREs in the region) and W-EU (61.1%). MBL occurrence was highest in APAC (59.5% of CREs in the region), followed by LATAM (34.0%), E-EU (28.9%), and W-EU (23.6%). ConclusionsAztreonam-avibactam demonstrated potent activity against CRE isolates resistant to ceftazidime-avibactam, meropenem-vaborbactam, and/or imipenem-relebactam independent of the carbapenemase produced.

In vitro activity of sulbactam-durlobactam against colistin-resistant and/or cefiderocol-non-susceptible, carbapenem-resistant Acinetobacter baumannii collected in U.S. hospitals.

The activity of a novel β-lactamase inhibitor combination, sulbactam-durlobactam (SUL-DUR), was tested against 87 colistin-resistant and/or cefiderocol-non-susceptible carbapenem-resistant Acinetobacter baumannii clinical isolates collected from U.S. hospitals between 2017 and 2019. Among them, 89% and 97% were susceptible to SUL-DUR and imipenem plus SUL-DUR, with MIC50/MIC90 values of 2 µg/mL/8 µg/mL and 1 µg/mL/4 µg/mL, respectively. The presence of amino acid substitutions in penicillin-binding protein 3, including previously reported A515V or T526S, was associated with SUL-DUR non-susceptibility.

Clarithromycin for early anti-inflammatory responses in community-acquired pneumonia in Greece (ACCESS): a randomised, double-blind, placebo-controlled trial

Addition of macrolide antibiotics to β-lactam antibiotics for the treatment of patients in hospital with community-acquired pneumonia is based on results from observational studies and meta-analyses rather than randomised clinical trials. We investigated if addition of the macrolide clarithromycin to treatment with a β-lactam antibiotic in this population could improve early clinical response-the new regulatory endpoint for community-acquired pneumonia-and explored the possible contribution of modulation of the inflammatory host response to that outcome. The ACCESS trial was a phase 3 prospective, double-blind, randomised controlled trial, in which adults in hospital with community-acquired pneumonia who had systemic inflammatory response syndrome, Sequential Organ Failure Assessment (SOFA) score of 2 or more, and procalcitonin 0·25 ng/mL or more were enrolled in 18 internal medicine departments of public Greek hospitals. Patients were randomly assigned (1:1) by computer-generated block randomisation to standard of care medication (including intravenous administration of a third-generation cephalosporin or intravenous administration of β-lactam plus β-lactamase inhibitor combination) plus either oral placebo or oral clarithromycin 500 mg twice daily for 7 days. Investigators, staff, and patients were masked to group allocation. The primary composite endpoint required that patients fulfilled both of the following conditions after 72 hours (ie, day 4 of treatment): (1) decrease in respiratory symptom severity score of 50% or more as an indicator of early clinical response and (2) decrease in SOFA score of at least 30% or favourable procalcitonin kinetics (defined as ≥80% decrease from baseline or procalcitonin <0·25 ng/mL), or both, as an indicator of early inflammatory response. Participants who were randomly assigned and received allocated treatment were included in the primary analysis population. This trial is complete and is registered with the EU Clinical Trials Register (2020-004452-15) and ClinicalTrials.gov (NCT04724044). Patients were enrolled between Jan 25, 2021, and April 11, 2023, and 278 individuals were randomly allocated to receive standard of care in combination with either clarithromycin (n=139) or placebo (n=139). 134 patients in the clarithromycin group (five withdrew consent) and 133 patients in the placebo group (six withdrew consent) were included in the analysis of the primary endpoint. The primary endpoint was met in 91 (68%) patients in the clarithromycin group and 51 (38%) patients in the placebo group (difference 29·6% [95% CI 17·7-40·3]; odds ratio [OR] 3·40 [95% CI 2·06-5·63]; p<0·0001). Serious treatment-emergent adverse events (TEAEs) occurred in 58 (43%) patients in the clarithromycin group and 70 (53%) patients in the placebo group (difference 9·4% [95% CI -2·6 to 20·9]; OR 0·67 [95% CI 0·42 to 1·11]; p=0·14). None of the serious TEAEs was judged to be related to treatment assignment. Addition of clarithromycin to standard of care enhances early clinical response and attenuates the inflammatory burden of community-acquired pneumonia. The mechanism of benefit is associated with changes in the immune response. These findings suggest the importance of adding clarithromycin to β-lactams for treatment of patients in hospital with community-acquired pneumonia to achieve early clinical response and early decrease of the inflammatory burden. Hellenic Institute for the Study of Sepsis and Abbott Products Operations.

Efficacy and safety of novel carbapenem-β-lactamase inhibitor combinations: imipenem-cilastatin/relebactam results from randomized controlled trials.

Gram-negative bacteria is a global public health problem. Treatment options include novel beta-lactamase inhibitors. The objective of this study was to collect information on the efficacy and safety of novel β-lactamase inhibitor combinations such as imipenem-cilastatin/relebactam (IMI/REL). In order to comprehensively evaluate the clinical, microbiological, and adverse events outcomes, a meta-analysis was conducted on clinical trials comparing novel β-lactamase inhibitor combinations with existing comparator therapies. Four studies comprising 948 patients were included in the analysis. IMI/REL therapy demonstrated similar clinical responses to comparators across various treatment visits, including discontinuation of intravenously administered therapy visits [DCIV, RR = 1.00 (0.88, 1.12)], early follow-up visits [EFU, RR = 1.00 (0.89, 1.14)], late follow-up visits [LFU, RR = 1.00 (0.88, 1.13)]. Moreover, no significant difference in the microbiologic response of MITT patients was observed between IMI/REL and comparators across DCIV [RR = 0.99 (0.89, 1.11)], EFU [RR = 1.01 (0.95, 1.07)], and LFU visits [RR = 1.00 (90.94, 1.07)]. In terms of safety, therapy with IMI/REL and comparators exhibited similar risks of at least one adverse event (AE), drug-related AEs, and discontinuation due to AEs. The incidence of serious AEs (SAEs) was significantly lower in the IMI/REL group compared to the comparison groups. The predominant AEs were gastrointestinal disorders, with no significant difference observed between the IMI/REL group and comparators. The clinical and microbiologic response to IMI/REL in the treatment of bacterial infection was comparable to that of the comparator. Furthermore, the incidence of AEs and the tolerability of IMI/REL were similar among the comparators. Based on these findings, IMI/REL can be considered as a viable alternative treatment option.

2598. Activity of Aztreonam-Avibactam and Other β-Lactamase Inhibitor Combinations against Gram-negative Bacteria Isolated from Patients Hospitalized with Pneumonia in US Medical Centers (2020–2022)

Abstract Background Resistance to recently approved β-lactamase inhibitor combinations, such as ceftazidime-avibactam (CAZ-AVI) and meropenem-vaborbactam (MEM-VAB), appears to be increasing among carbapenem-resistant Enterobacterales (CRE) in some US hospitals. We evaluated the frequency and antimicrobial susceptibility of Gram-negative bacteria (GNB) causing pneumonia in US hospitals. Methods Bacterial isolates were consecutively collected (1/patient) from patients hospitalized with pneumonia and the susceptibility of GNBs (3,911 Enterobacterales [ENT] and 2,753 non-fermenters) was evaluated by broth microdilution. Isolates were collected in 69 medical centers in 2020–2022. Susceptibility testing was performed by CLSI broth microdilution in a monitoring laboratory. Aztreonam-avibactam (ATM-AVI) was tested with AVI at fixed 4 mg/L and a pharmacokinetic/pharmacodynamic susceptible (S) breakpoint of ≤ 8 mg/L was applied for comparison. CRE isolates were screened for carbapenemases (CPE) by whole genome sequencing. Results GNB represented 71.1% of organisms. The most common GNB species were P. aeruginosa (22.4% of organisms), K. pneumoniae (8.6%), E. coli (6.6%), S. marcescens (6.2%), S. maltophilia (4.9%), and E. cloacae complex (4.8%). ATM-AVI inhibited 100.0% of ENT at ≤ 8 mg/L and 99.9% at ≤ 4 mg/L and showed potent activity against CRE (MIC50/90, 0.25/1 mg/L; Table). CAZ-AVI and MEM-VAB were active against 89.4% and 88.5% of CREs, respectively. ATM-AVI retained activity against ENT non-S to CAZ-AVI and/or MEM-VAB (n=19; MIC50/90, 0.25/4 mg/L). The most common CPEs were KPC (69.2% of CREs), NDM (9.6%), and SME (4.8%). A CPE gene was not observed in 16.3% of CREs. CAZ-AVI and MEM-VAB were highly active against KPC and SME producers but showed limited activity against MBL producers. The most active comparators against CRE were tigecycline (95.2%S), amikacin (73.1%S), and gentamicin (60.6%S). Among P. aeruginosa, 79.1% were inhibited at ≤8 mg/L of ATM-AVI, 77.2% were MEM-S, and 77.2% were piperacillin-tazobactam-S. ATM-AVI was highly active against S. maltophilia, inhibiting 99.5% of isolates at ≤ 8 mg/L. Conclusion ATM-AVI demonstrated potent in vitro activity against the GNB most isolated from patients with pneumonia in US hospitals. Disclosures Helio S. Sader, MD, PhD, FIDSA, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|Cipla: Grant/Research Support|Paratek: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support Rodrigo E. Mendes, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|Cipla: Grant/Research Support|Entasis: Grant/Research Support|GSK: Grant/Research Support|Paratek: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support Leonard R. Duncan, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|CorMedix: Grant/Research Support|Melinta: Grant/Research Support|Pfizer: Grant/Research Support Timothy Doyle, MS, AbbVie: Grant/Research Support Mariana Castanheira, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|bioMerieux: Grant/Research Support|Cipla: Grant/Research Support|CorMedix: Grant/Research Support|Entasis: Grant/Research Support|Melinta: Grant/Research Support|Paratek: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support

1949. Activity of Aztreonam-Avibactam against Enterobacterales Resistant to Recently Approved Beta-Lactamase Inhibitor Combinations Collected Worldwide (ex-US; 2020–2022)

Abstract Background Aztreonam-avibactam (ATM-AVI) is under clinical development. Aztreonam is a monobactam stable to hydrolysis by metallo-β-lactamases (MBLs). ATM-AVI has shown activity against MBL-producing, carbapenem-resistant Enterobacterales (CRE) that are resistant to recently approved β-lactamase inhibitor combinations (BLIs) such as ceftazidime-avibactam (CAZ-AVI), meropenem-vaborbactam (MEM-VAB), and imipenem-relebactam (IMI-REL). We evaluated a large collection of CRE isolates nonsusceptible (NS) to these BLIs. Methods 24,580 Enterobacterales isolates were consecutively collected (1/patient) in 2020–2022 from 64 medical centers located in Western Europe (W-EU; 27 centers in 10 countries), Eastern Europe (E-EU; 13 centers in 9 countries), Latin America (LATMA; 8 centers in 6 countries), and the Asia-Pacific region (APAC; 16 centers in 8 countries). Among these isolates, 1,016 (4.1%) were CRE. Isolates were susceptibility tested by CLSI broth microdilution. CRE isolates were screened for carbapenemase (CPE) genes by whole genome sequencing. Results ATM-AVI inhibited 99.6% of CREs (MIC50/90, 0.25/0.5 mg/L) and ≥ 98.9% of CRE isolates NS to CAZ-AVI, MEM-VAB, and/or IMI-REL at ≤8 mg/L (Table). The most active comparators against CREs were CAZ-AVI (64.6%S), MEM-VAB (57.4%S), and IMI-REL (50.7%S). The activity of these BLIs varied widely among region, with highest susceptibility rates observed in W-EU (76.9% for CAZ-AVI, 72.5% for MEM-VAB, 63.8% for IMI-REL), followed by LATAM (65.1% for CAZ-AVI, 70.6% for MEM-VAB, 62.8% for IMI-REL), E-EU (66.6% for CAZ-AVI, 46.7% for MEM-VAB, 43.5% for IMI-REL), and APAC (39.9% for CAZ-AVI, 37.8% for MEM-VAB, 27.7% for IMI-REL). The most common CPE types overall were KPC (44.5% of CREs), NDM (29.8%), and OXA-48-like (16.0%). KPC predominated in LATAM (64.1%) and W-EU (61.1% of CREs). MBL occurrence was highest in APAC (59.5% of CREs), followed by LATAM (34.0%), E-EU (28.9%), and W-EU (23.6%). NDM represented 85.4% of MBLs. Conclusion ATM-AVI demonstrated potent activity against CRE isolates resistant to CAZ-AVI, MEM-VAB, and/or IMI-REL independent of the CPE produced. The activity of recently approved BLIs varied broadly among regions and were very limited in E-EU and APAC. Disclosures Helio S. Sader, MD, PhD, FIDSA, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|Cipla: Grant/Research Support|Paratek: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support Mariana Castanheira, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|bioMerieux: Grant/Research Support|Cipla: Grant/Research Support|CorMedix: Grant/Research Support|Entasis: Grant/Research Support|Melinta: Grant/Research Support|Paratek: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support Leonard R. Duncan, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|CorMedix: Grant/Research Support|Melinta: Grant/Research Support|Pfizer: Grant/Research Support John H. Kimbrough, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support Cecilia G. Carvalhaes, MD, PhD, AbbVie: Grant/Research Support|bioMerieux: Grant/Research Support|Cipla: Grant/Research Support|CorMedix: Grant/Research Support|Melinta: Grant/Research Support|Pfizer: Grant/Research Support Rodrigo E. Mendes, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|Cipla: Grant/Research Support|Entasis: Grant/Research Support|GSK: Grant/Research Support|Paratek: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support

2149. In vitro Activity of Aztreonam-avibactam and Comparator Agents Against Carbapenem-Resistant Enterobacterales With and Without Carbapenemases, ATLAS Global Surveillance Program, 2017–2021

Abstract Background The investigational β-lactam/non-β-lactam β-lactamase inhibitor combination aztreonam-avibactam (ATM-AVI) is active in vitro against CRE isolates, including MBL-producers, as well as those co-producing serine β-lactamases of Class A, C, and some class D types. This study evaluated the in vitro activity of ATM-AVI and comparators against carbapenemase- and non-carbapenemase-producing CRE collected globally from 2017−2021 as part of the ATLAS surveillance program. Methods 85,990 non-duplicate, clinically relevant Enterobacterales isolates were collected from 258 medical centers located in 56 countries worldwide (excluding N. America and China). Susceptibility testing was performed by CLSI broth microdilution and interpreted using CLSI 2023 breakpoints. ATM-AVI was tested at a fixed concentration of 4 mg/L avibactam. A tentative ATM-AVI pharmacokinetic/pharmacodynamic (PK/PD) susceptible MIC breakpoint of ≤ 8 mg/L was applied for comparison purposes. Organisms with meropenem MIC &amp;gt;1 mg/L and Escherichia coli, Klebsiella pneumoniae, Klebsiella oxytoca, and Proteus mirabilis with aztreonam or ceftazidime MIC &amp;gt;1 mg/L were screened for β-lactamase genes by PCR and Sanger sequencing. Results In total, 5,473 isolates were identified as CRE based on resistance to meropenem. ATM-AVI demonstrated potent in vitro activity against the CRE, with 99.3% of isolates (MIC90, 1 mg/L) inhibited at ≤8 mg/L (Table). ATM-AVI inhibited 99.5% of the carbapenemase-positive CRE, including 99.1% of the MBL-carriers (n=2,375) and 99.8% of serine-carbapenemase carriers (n=2,675) at ≤8 mg/L. Activity was somewhat reduced against the 441 CRE without detected carbapenemases as 96.3% (MIC90, 4 mg/L) of the isolates were inhibited at ≤8 mg/L aztreonam-avibactam. Amikacin was the most active comparator, although &amp;lt; 50% of each subgroup was susceptible at the CLSI breakpoint. Conclusion Based on MIC90 values and the preliminary PK/PD breakpoint, ATM-AVI demonstrated potent in vitro activity against CRE, including MBL- and serine carbapenemase-carrying isolates. As limited therapeutic options presently exist for treating infections caused by CRE, further development of this agent appears warranted. Disclosures Mark G Wise, PhD, Merck &amp; Co., Inc.: Honoraria|Pfizer Inc.: Honoraria|Venatorx: Paid fees for conducting the study and abstract preparation Daniel F. Sahm, PhD, Merck &amp; Co., Inc.: Honoraria|Pfizer Inc.: Honoraria|Venatorx: Paid fees for conducting the study and abstract preparation

2146. Antimicrobial Activity of Aztreonam-avibactam, Ceftazidime-avibactam, and Meropenem-vaborbactam against Enterobacterales causing Bloodstream Infection in US Medical Centers (2020–2022)

Abstract Background As the frequency of Enterobacterales (ENT) producing metallo-β-lactamase (MBL) and/or OXA-48 is increasing in some US medical centers, effective antimicrobials to treat the infections caused by these organisms are urgently needed. Aztreonam-avibactam (ATM-AVI) is under clinical development for treatment of infections caused by Gram-negative bacteria, including MBL producers. We evaluated the activities of ATM-AVI, ceftazidime-avibactam (CAZ-AVI), meropenem-vaborbactam (MEM-VAB), and comparators against ENT isolated from patients with bloodstream infections (BSIs). Methods 4,802 ENT were consecutively collected (1/patient) from 72 US medical centers in 2020–2022 and susceptibility tested by CLSI broth microdilution method. ATM-AVI was tested with AVI at a fixed 4 mg/L. A pharmacokinetic/pharmacodynamic susceptible (S) breakpoint of ≤ 8 mg/L was applied for comparison. Carbapenem-resistant ENT (CRE) isolates were screened for carbapenemase (CPE) by whole genome sequencing. Results ATM-AVI was highly active against ENT (Table); only 2 isolates showed ATM-AVI MICs &amp;gt; 8 mg/L: 1 MEM-S E. coli and 1 E. aerogenes (CRE). All CPE producers and 98.0% of CREs were inhibited at an ATM-AVI MIC of ≤ 8 mg/L. CAZ-AVI and MEM-VAB were active against 81.6% and 65.3% of CREs, respectively. Ceftolozane-tazobactam (TOL-TAZ) was active against only 72.6% of ceftriaxone (CRO)-nonsusceptible (NS) isolates. ATM-AVI retained activity (MIC, ≤8 mg/L) against all MEM-VAB-NS and 90.0% of CAZ-AVI-NS isolates. The most common CPEs were KPC-2/3 (57.1% of CREs), OXA-48–like (16.3%), and NDM (12.2%). A CPE gene was not observed in 14.3% of CREs. CAZ-AVI and MEM-VAB were active against 100.0% of KPC producers, but CAZ-AVI showed limited activity against MBL producers and MEM-VAB showed limited activity against OXA-48–like and MBL producers. The most active comparators against CRE were tigecycline (95.9%S), gentamicin (49.0%S), and amikacin (44.9%S). Conclusion ATM-AVI demonstrated potent activity against a large collection ENT isolated from patients with BSI in US hospitals, including CREs and isolates resistant to recently approved β-lactamase inhibitor combinations. These results support further clinical development of ATM-AVI. Disclosures Helio S. Sader, MD, PhD, FIDSA, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|Cipla: Grant/Research Support|Paratek: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support Cecilia G. Carvalhaes, MD, PhD, AbbVie: Grant/Research Support|bioMerieux: Grant/Research Support|Cipla: Grant/Research Support|CorMedix: Grant/Research Support|Melinta: Grant/Research Support|Pfizer: Grant/Research Support John H. Kimbrough, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support Rodrigo E. Mendes, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|Cipla: Grant/Research Support|Entasis: Grant/Research Support|GSK: Grant/Research Support|Paratek: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support Mariana Castanheira, PhD, AbbVie: Grant/Research Support|Basilea: Grant/Research Support|bioMerieux: Grant/Research Support|Cipla: Grant/Research Support|CorMedix: Grant/Research Support|Entasis: Grant/Research Support|Melinta: Grant/Research Support|Paratek: Grant/Research Support|Pfizer: Grant/Research Support|Shionogi: Grant/Research Support

Functional features of KPC-109, a novel 270-loop KPC-3 mutant mediating resistance to avibactam-based β-lactamase inhibitor combinations and cefiderocol

To investigate a ceftazidime/avibactam (CZA)-resistant Klebsiella pneumoniae (NE368), isolated from a patient exposed to CZA, expressing a novel K. pneumoniae carbapenemase (KPC)-3 variant (KPC-109). Antimicrobial susceptibility testing was performed by reference broth microdilution. Whole-genome sequencing (WGS) analysis of NE368 was performed combining a short- and long-reads approach (Illumina and Oxford Nanopore Technologies). Functional characterization of KPC-109 was performed to investigate the impact of KPC-109 production on the β-lactam resistance phenotype of various Escherichia coli and Klebsiella pneumoniae strains, including derivatives of K. pneumoniae with OmpK35 and OmpK36 porin alterations. Horizontal transfer of the KPC-109-encoding plasmid was investigated by conjugation and transformation experiments. K. pneumoniae NE368 was isolated from a patient after repeated CZA exposure, and showed resistance to CZA, fluoroquinolones, piperacillin/tazobactam, expanded-spectrum cephalosporins, amikacin, carbapenems and cefiderocol. WGS revealed the presence of a large chimeric plasmid of original structure (pKPN-NE368), encoding a novel 270-loop mutated KPC-3 variant (KPC-109; ins_270_KYNKDD). KPC-109 production mediated resistance/decreased susceptibility to avibactam-based combinations (with ceftazidime, cefepime and aztreonam) and cefiderocol, with a trade-off on carbapenem resistance. However, in the presence of porin alterations commonly encountered in high-risk clonal lineages of K. pneumoniae, KPC-109 was also able to confer clinical-level resistance to carbapenems. Resistance of NE368 to cefiderocol was likely contributed by KPC-109 production acting in concert with a mutated EnvZ sensor kinase. The KPC-109-encoding plasmid did not appear to be conjugative. These findings expand current knowledge about the diversity of emerging KPC enzyme variants with 270-loop alterations that can be encountered in the clinical setting.

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

Multi-drug resistant (MDR) Pseudomonas aeruginosa harbor a complex array of β-lactamases and non-enzymatic resistance mechanisms. In this study, the activity of a β-lactam/β-lactam-enhancer, cefepime/zidebactam, and novel β-lactam/β-lactamase inhibitor combinations was determined against an MDR phenotype-enriched, challenge panel of P. aeruginosa (n = 108). Isolates were multi-clonal as they belonged to at least 29 distinct sequence types (STs) and harbored metallo-β-lactamases, serine β-lactamases, penicillin binding protein (PBP) mutations, and other non-enzymatic resistance mechanisms. Ceftazidime/avibactam, ceftolozane/tazobactam, imipenem/relebactam, and cefepime/taniborbactam demonstrated MIC90s of >128 mg/L, while cefepime/zidebactam MIC90 was 16 mg/L. In a neutropenic-murine lung infection model, a cefepime/zidebactam human epithelial-lining fluid-simulated regimen achieved or exceeded a translational end point of 1-log10 kill for the isolates with elevated cefepime/zidebactam MICs (16-32 mg/L), harboring VIM-2 or KPC-2 and alterations in PBP2 and PBP3. In the same model, to assess the impact of zidebactam on the pharmacodynamic (PD) requirement of cefepime, dose-fractionation studies were undertaken employing cefepime-susceptible P. aeruginosa isolates. Administered alone, cefepime required 47%-68% fT >MIC for stasis to ~1 log10 kill effect, while cefepime in the presence of zidebactam required just 8%-16% for >2 log10 kill effect, thus, providing the pharmacokinetic/PD basis for in vivo efficacy of cefepime/zidebactam against isolates with MICs up to 32 mg/L. Unlike β-lactam/β-lactamase inhibitors, β-lactam enhancer mechanism-based cefepime/zidebactam shows a potential to transcend the challenge of ever-evolving resistance mechanisms by targeting multiple PBPs and overcoming diverse β-lactamases including carbapenemases in P. aeruginosa.IMPORTANCECompared to other genera of Gram-negative pathogens, Pseudomonas is adept in acquiring complex non-enzymatic and enzymatic resistance mechanisms thus remaining a challenge to even novel antibiotics including recently developed β-lactam and β-lactamase inhibitor combinations. This study shows that the novel β-lactam enhancer approach enables cefepime/zidebactam to overcome both non-enzymatic and enzymatic resistance mechanisms associated with a challenging panel of P. aeruginosa. This study highlights that the β-lactam enhancer mechanism is a promising alternative to the conventional β-lactam/β-lactamase inhibitor approach in combating ever-evolving MDR P. aeruginosa.

In vitro potency of xeruborbactam in combination with multiple β-lactam antibiotics in comparison with other β-lactam/β-lactamase inhibitor (BLI) combinations against carbapenem-resistant and extended-spectrum β-lactamase-producing Enterobacterales.

Recently, several β-lactam (BL)/β-lactamase inhibitor (BLI) combinations have entered clinical testing or have been marketed for use, but limited direct comparative studies of their in vitro activity exist. Xeruborbactam (XER, also known as QPX7728), which is undergoing clinical development, is a cyclic boronate BLI with potent inhibitory activity against serine (serine β-lactamase) and metallo-β-lactamases (MBLs). The objectives of this study were (i) to compare the potency and spectrum of β-lactamase inhibition by various BLIs in biochemical assays using purified β-lactamases and in microbiological assays using the panel of laboratory strains expressing diverse serine and metallo-β-lactamases and (ii) to compare the in vitro potency of XER in combination with multiple β-lactam antibiotics to that of other BL/BLI combinations in head-to-head testing against recent isolates of carbapenem-resistant Enterobacterales (CRE). Minimal inhibitory concentrations (MICs) of XER combinations were tested with XER at fixed 4 or 8 µg/mL, and MIC testing was conducted in a blinded fashion using Clinical and Laboratory Standards Institute reference methods. Xeruborbactam and taniborbactam (TAN) were the only BLIs that inhibited clinically important MBLs. The spectrum of activity of xeruborbactam included several MBLs identified in Enterobacterales, e.g., and various IMP enzymes and NDM-9 that were not inhibited by taniborbactam. Xeruborbactam potency against the majority of purified β-lactamases was the highest in comparison with other BLIs. Meropenem-xeruborbactam (MEM-XER, fixed 8 µg/mL) was the most potent combination against MBL-negative CRE with MIC90 values of 0.125 µg/mL. MEM-XER and cefepime-taniborbactam (FEP-TAN) were the only BL/BLIs with activity against MBL-producing CREs; with MEM-XER (MIC90 of 1 µg/mL) being at least 16-fold more potent than FEP-TAN (MIC90 of 16 µg/mL). MEM-XER MIC values were ≤8 µg/mL for >90% of CRE, including both MBL-negative and MBL-positive isolates, with FEP-TAN MIC of >8 µg/mL. Xeruborbactam also significantly enhanced potency of other β-lactam antibiotics, including cefepime, ceftolozane, ceftriaxone, aztreonam, piperacillin, and ertapenem, against clinical isolates of Enterobacterales that carried various class A, class C, and class D extended-spectrum β-lactamases and carbapenem-resistant Enterobacterales, including metallo-β-lactamase-producing isolates. These results strongly support further clinical development of xeruborbactam combinations.

Citrobacter freundii resistant to novel β-lactamase inhibitor combinations and cefiderocol, co-producing class A, B and D carbapenemases encoded by transferable plasmids.

To characterize a carbapenem-resistant Citrobacter freundii (Cf-Emp) co-producing class A, B and D carbapenemases, resistant to novel β-lactamase inhibitor combinations (BLICs) and cefiderocol. Carbapenemase production was tested by an immunochromatography assay. Antibiotic susceptibility testing (AST) was performed by broth microdilution. WGS was performed using short- and long-read sequencing. Transfer of carbapenemase-encoding plasmids was assessed by conjugation experiments. Cf-Emp was isolated on selective medium for carbapenem-resistant Enterobacterales from the surveillance rectal swab taken at hospital admission from a patient of Moroccan origin. Cf-Emp produced three different carbapenemases, including KPC-2, OXA-181 and VIM-1, and was resistant to all β-lactams including carbapenems, novel BLICs (ceftazidime/avibactam, meropenem/vaborbactam and imipenem/relebactam) and cefiderocol. MIC of aztreonam/avibactam was 0.25 mg/L. The strain belonged to ST22, one of the C. freundii lineages of global diffusion, known to be associated with carbapenemase production. Each carbapenemase gene was located aboard a different plasmid (named pCf-KPC, pCf-OXA and pCf-VIM, respectively), which also carried other clinically relevant resistance genes, such as armA (pCf-KPC), blaSHV-12 (pCf-VIM) and qnrS1 (pCf-OXA). Transferability to Escherichia coli J53 by conjugation was observed for all plasmids. The finding of enterobacterial strains carrying multiple carbapenemase genes on transferable plasmids is alarming, because similar strains could provide an important reservoir for disseminating these clinically relevant resistance determinants.

Comparison of In Vitro Activity of Ceftazidime-Avibactam and Imipenem-Relebactam against Clinical Isolates of Pseudomonas aeruginosa.

The role of novel β-lactam/β-lactamase inhibitor combinations in ceftazidime-nonsusceptible (CAZ-NS) and imipenem-nonsusceptible (IPM-NS) Pseudomonas aeruginosa has not been fully elucidated. This study evaluated the in vitro activity of novel β-lactam/β-lactamase inhibitor combinations against Pseudomonas aeruginosa clinical isolates, determined how avibactam restored ceftazidime activity, and compared the activity of ceftazidime-avibactam (CZA) and imipenem-relebactam (IMR) against KPC-producing P. aeruginosa. Similar high susceptibility rates for CZA, IMR, and ceftolozane-tazobactam (88.9% to 89.8%) were found for 596 P. aeruginosa clinical isolates from 11 hospitals in China, and a higher susceptibility rate to ceftazidime than imipenem was observed (73.5% versus 63.1%). For CAZ-NS and IPM-NS isolates, susceptibility rates for CZA, ceftolozane-tazobactam, and IMR were 61.5% (75/122), 54.9% (67/122), and 51.6% (63/122), respectively. For CAZ-NS, IPM-NS but CZA-susceptible isolates, 34.7% (26/75) harbored acquired β-lactamases with KPC-2 predominant (n = 19), and 45.3% (34/75) presented overexpression of chromosomal β-lactamase ampC. Among 22 isolates carrying KPC-2 carbapenemase alone, susceptibility rates to CZA and IMR were 86.4% (19/22) and 9.1% (2/22), respectively. Notably, 95% (19/20) of IMR-nonsusceptible isolates had an inactivating mutation of oprD gene. In conclusion, CZA, ceftolozane-tazobactam, and IMR exhibit high activity against P. aeruginosa, and CZA is more active than IMR against CAZ-NS and IPM-NS isolates as well as KPC-producing P. aeruginosa. Avibactam overcomes ceftazidime resistance engendered by KPC-2 enzyme and overexpressed AmpC. IMPORTANCE The emergence of antimicrobial resistance poses a particular challenge globally, and the concept of P. aeruginosa with "difficult-to-treat" resistance (DTR-P. aeruginosa) was proposed. Here, P. aeruginosa clinical isolates were highly susceptible to three β-lactamase inhibitor combinations, CZA, IMR, and ceftolozane-tazobactam. The combination of KPC-2 enzyme and nonfunctional porin OprD contributed to IMR resistance in P. aeruginosa, and CZA was more active than IMR in fighting against KPC-2-producing P. aeruginosa. CZA also showed good activity against CAZ-NS and IPM-NS P. aeruginosa, primarily by inhibiting KPC-2 enzyme and overproduced AmpC, supporting the clinical use of CZA in the treatment of infections caused by DTR-P. aeruginosa.

Sulbactam-durlobactam: A Step Forward in Treating Carbapenem-Resistant Acinetobacter baumannii (CRAB) Infections.

Antimicrobial resistance in gram-negative pathogens, such as Acinetobacter baumannii, is a serious threat to human health. Sulbactam-durlobactam, a unique β-lactam and a β-lactamase inhibitor combination, is a novel agent targeted against carbapenem-resistant A. baumannii. This supplement provides a summary of the development of SUL-DUR, discussing its unique features and role in treating infections caused by CRAB pathogens.

Ceftazidime-avibactam, meropenem-vaborbactam, and imipenem-relebactam activities against multidrug-resistant Enterobacterales from United States Medical Centers (2018–2022)

A total of 35,360 Enterobacterales isolates were consecutively collected from 75 US medical centers in 2018–2022. Among these isolates, 2612 (7.4%) were categorized as multidrug-resistant (MDR). Isolates were susceptibility tested by reference broth microdilution methods. Carbapenem-resistant Enterobacterales (CRE) were screened for carbapenemase (CPE) genes by whole genome sequencing. The highest MDR rates was observed among Klebsiella pneumoniae (12.2%), followed by Raoultella spp. (10.9%) and Providencia stuartii (9.8%). Ceftazidime-avibactam and meropenem-vaborbactam were very active and showed identical susceptibility rates against MDR isolates (97.9%). Imipenem-relebactam (93.5% susceptible [S]) exhibited slightly lower susceptibility rates due to its limited activity against Morganellaceae family. The most active β-lactamase inhibitor combination (BLI) against CRE isolates (n = 310) was ceftazidime-avibactam (84.2%S), followed by meropenem-vaborbactam (81.9%S) and imipenem-relebactam (74.8%S). All 3 BLIs were very active against KPC producers and none were active against MBL producers. Ceftazidime-avibactam exhibited greater activity against OXA-48–type producers than meropenem-vaborbactam and imipenem-vaborbactam.