Bonomo, Robert A.

ABSTRACT Beta‐lactam antibiotics (beta‐lactams) are first‐line treatments for most major infectious syndromes in acutely ill patients, with in vitro activity against common pathogens, demonstrated efficacy in trials, and a perceived low risk of adverse effects. The current dosing approach, informed by population‐level data, tends to be simplistically reduced to a “one size fits all” dosing method which only accounts for body weight (i.e., in pediatrics) and end organ function to estimate drug clearance (e.g., estimated glomerular filtration rate); this approach results in substantial variability in observed serum concentrations in acutely ill patients, which can compromise real‐world effectiveness and safety. Beta‐lactam dose individualization, therefore, defined as a dosing regimen for one patient informed by measured concentrations from that patient, has been recommended in international clinical guidelines. Comprehensive guidance on best practices for beta‐lactam dose individualization is lacking. To address this knowledge gap and develop guidance, a multidisciplinary panel of international experts was assembled from the disciplines of infectious diseases, critical care, pharmacometrics, and laboratory medicine, representing both adults and pediatrics. The panel systematically evaluated the literature, using the GRADE approach where feasible, to address broad thematic questions pertaining to whether beta‐lactam dose individualization should be pursued, for what indications beta‐lactam dose individualization is warranted, and the most critical considerations and best practices for implementation of beta‐lactam individualization. The resultant consensus recommendations will equip healthcare professionals caring for acutely ill patients treated with beta‐lactam therapy with the evidence and tools necessary to guide optimal use of beta‐lactam dose individualization.

ABSTRACT Novel β-lactam/β-lactamase inhibitors (βL/βLIs) are important therapies for carbapenem-resistant Pseudomonas aeruginosa (CRPA). However, the global extent of resistance to these agents and the impact of resistance on patient outcomes are unclear. We therefore evaluated patients with CRPA isolates at 35 hospitals (nine countries) from December 2018 to November 2019. Antimicrobial susceptibility testing was performed at a central laboratory by agar dilution for ceftolozane-tazobactam (C/T) and ceftazidime-avibactam (CZA) and by broth microdilution for imipenem-relebactam (I/R). Characteristics and outcomes, including desirability of outcome rankings (DOOR), were compared between patients infected with isolates not susceptible vs susceptible to each agent. Of 800 CRPA isolates, susceptibility to C/T, CZA, and I/R was 69%, 67%, and 33%, respectively. USA isolates ( n = 526) were more frequently susceptible to these agents than isolates from other countries ( n = 274; C/T: 83% vs 42%; CZA: 77% vs 47%; I/R: 37% vs 23%; P < 0.001 for each comparison) and isolates with carbapenemases ( n = 157) were less frequently susceptible than isolates without carbapenemases ( n = 643; C/T: 7% vs 84%; CZA: 24% vs 77%; I/R: 6% vs 39%; P < 0.001 for each comparison). Thirty-day mortality and DOOR were similar overall in patients infected with isolates not susceptible vs susceptible to each βL/βLI. However, the adjusted probability of a better DOOR outcome for a randomly selected patient with bacteremia due to a C/T-not susceptible vs -susceptible isolate was 38.2% (95% confidence interval, 25.6%–52.7%). Resistance to novel βL/βLIs, especially I/R, is common in CRPA, particularly outside the USA and in carbapenemase-producing isolates. Additional treatment options are needed for CRPA infections.

ABSTRACT Intrinsic Acinetobacter -derived cephalosporinases (ADCs) in Acinetobacter baumannii are AmpC-type β-lactamases that confer resistance to β-lactam agents, typically through insertion sequence (IS) element-driven overexpression. However, the contribution of ADCs to resistance against advanced β-lactam agents has not been systematically investigated. Given the increasing clinical use of these agents, including cefiderocol, we analyzed the diversity and function of ADC variants in a global collection of carbapenem-resistant A. baumannii (CRAb) isolates. We identified 52 distinct ADC variants in a collection of 428 CRAb clinical isolates from the United States. Among these, variants carrying both a valine substitution at position 292 in the R2 loop and an alanine duplication (ADUP) in the Ω loop consistently conferred stable resistance to cefiderocol. Biochemical and crystallographic analyses demonstrated that ADC-227, which harbors a V292W substitution with an ADUP at position 218a in the Ω loop, exhibits enhanced catalytic efficiencies for ceftazidime and cefiderocol and moderately reduced inhibition by avibactam, leading to resistance not only to cefiderocol but also to ceftazidime–avibactam. Structural studies revealed conformational flexibility of the R2 loop, allowing dynamic accommodation of substrates. Collectively, the findings identify Val292, in combination with an ADUP in the Ω loop, as a mutational “hot spot” for ADCs evolution that may undermine the efficacy of newer β-lactams, including cefiderocol. These results underscore the need for ongoing molecular surveillance of A. baumannii isolates to detect and track the emergence of such variants in clinical settings. IMPORTANCE Carbapenem-resistant Acinetobacter baumannii (CRAb) has been designated as a critical priority pathogen by the World Health Organization (WHO). Cefiderocol has been introduced as a novel therapy against CRAb; however, recent clinical data highlight concerning treatment failures and excess mortality. Understanding resistance mechanisms is therefore essential to preserve the clinical utility of this agent. This study addresses a critical knowledge gap by investigating the role of intrinsic Acinetobacter -derived cephalosporinases (ADCs), which are ubiquitous in A. baumannii and diverse in sequence. By defining specific mutational patterns that endanger cefiderocol activity, this work highlights how chromosomally encoded enzymes can evolve to erode the effectiveness of newer β-lactams such as cefiderocol. These insights underscore the importance of integrating molecular surveillance into clinical practice and antimicrobial stewardship to ensure timely detection of emerging resistance in clinical A. baumannii isolates, ultimately informing treatment strategies and guiding future drug development.

ABSTRACT Ledaborbactam (formerly VNRX-5236), a bicyclic boronate β-lactamase inhibitor with activity against class A, C, and D β-lactamases, is under development as an orally bioavailable etzadroxil prodrug (VNRX-7145) in combination with ceftibuten for the treatment of urinary tract infections. At ceftibuten breakpoints of ≤1 mg/L (EUCAST) and ≤8 mg/L (CLSI), 92.5% and 99.0%, respectively, of 200 carbapenem-resistant Klebsiella pneumoniae isolates, predominantly K. pneumoniae carbapenemase producing, were susceptible to ceftibuten-ledaborbactam (ledaborbactam tested at a fixed concentration of 4 mg/L) compared to 4.5% and 30.5%, respectively, to ceftibuten alone.

Abstract Background The CDC reported a 35% increase in hospital-onset (HO) carbapenem-resistant Enterobacterales (CRE) infections during the COVID-19 pandemic. We evaluated patient outcomes following HO and community-onset (CO) CRE bloodstream infections (BSI). Methods Patients prospectively enrolled in CRACKLE-2 from 56 hospitals in 10 countries between 30 April 2016 and 30 November 2019 with a CRE BSI were eligible. Infections were defined as CO or HO by CDC guidelines, and clinical characteristics and outcomes were compared. The primary outcome was desirability of outcome ranking (DOOR) 30 days after index culture. Difference in 30-day mortality was calculated with 95% CI. Results Among 891 patients with CRE BSI, 65% were HO (582/891). Compared to those with CO CRE, patients with HO CRE were younger [median 60 (Q1 42, Q3 70) years versus 65 (52, 74); P &lt; 0.001], had fewer comorbidities [median Charlson comorbidity index 2 (1, 4) versus 3 (1, 5); P = 0.002] and were more acutely ill (Pitt bacteraemia score ≥4: 47% versus 32%; P &lt; 0.001). The probability of a better DOOR outcome in a randomly selected patient with CO BSI compared to a patient with HO BSI was 60.6% (95% CI: 56.8%–64.3%). Mortality at 30-days was 12% higher in HO BSI (192/582; 33%) than CO BSI [66/309 (21%); P &lt; 0.001]. Conclusion We found a disproportionately greater impact on patient outcomes with HO compared to CO CRE BSIs; thus, the recently reported increases in HO CRE infections by CDC requires rigorous surveillance and infection prevention methods to prevent added mortality.

ABSTRACT Taniborbactam, a bicyclic boronate β-lactamase inhibitor with activity against Klebsiella pneumoniae carbapenemase (KPC), Verona integron–encoded metallo-β-lactamase (VIM), New Delhi metallo-β-lactamase (NDM), extended-spectrum beta-lactamases (ESBLs), OXA-48, and AmpC β-lactamases, is under clinical development in combination with cefepime. Susceptibility of 200 previously characterized carbapenem-resistant K. pneumoniae and 197 multidrug-resistant (MDR) Pseudomonas aeruginosa to cefepime-taniborbactam and comparators was determined by broth microdilution. For K. pneumoniae (192 KPC; 7 OXA-48-related), MIC 90 values of β-lactam components for cefepime-taniborbactam, ceftazidime-avibactam, and meropenem-vaborbactam were 2, 2, and 1 mg/L, respectively. For cefepime-taniborbactam, 100% and 99.5% of isolates of K. pneumoniae were inhibited at ≤16 mg/L and ≤8 mg/L, respectively, while 98.0% and 95.5% of isolates were susceptible to ceftazidime-avibactam and meropenem-vaborbactam, respectively. For P. aeruginosa , MIC 90 values of β-lactam components of cefepime-taniborbactam, ceftazidime-avibactam, ceftolozane-tazobactam, and meropenem-vaborbactam were 16, >8, >8, and >4 mg/L, respectively. Of 89 carbapenem-susceptible isolates, 100% were susceptible to ceftolozane-tazobactam, ceftazidime-avibactam, and cefepime-taniborbactam at ≤8 mg/L. Of 73 carbapenem-intermediate/resistant P. aeruginosa isolates without carbapenemases, 87.7% were susceptible to ceftolozane-tazobactam, 79.5% to ceftazidime-avibactam, and 95.9% and 83.6% to cefepime-taniborbactam at ≤16 mg/L and ≤8 mg/L, respectively. Cefepime-taniborbactam at ≤16 mg/L and ≤8 mg/L, respectively, was active against 73.3% and 46.7% of 15 VIM- and 60.0% and 35.0% of 20 KPC-producing P. aeruginosa isolates. Of all 108 carbapenem-intermediate/resistant P. aeruginosa isolates, cefepime-taniborbactam was active against 86.1% and 69.4% at ≤16 mg/L and ≤8 mg/L, respectively, compared to 59.3% for ceftolozane-tazobactam and 63.0% for ceftazidime-avibactam. Cefepime-taniborbactam had in vitro activity comparable to ceftazidime-avibactam and greater than meropenem-vaborbactam against carbapenem-resistant K. pneumoniae and carbapenem-intermediate/resistant MDR P. aeruginosa .

ABSTRACT 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 MIC 50 /MIC 90 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.

AbstractIn this overview, we describe important contributions from the Antibacterial Resistance Leadership Group (ARLG) to patient care, clinical trials design, and mentorship while outlining future priorities. The ARLG research agenda is focused on 3 key areas: gram-positive infections, gram-negative infections, and diagnostics. The ARLG has developed an innovative approach to clinical trials design, the desirability of outcome ranking (DOOR), which uses an ordinal measure of global outcome to assess both benefits and harms. DOOR was initially applied to observational studies to determine optimal dosing of vancomycin for methicillin-resistant Staphylcococcus aureus bacteremia and the efficacy of ceftazidime-avibactam versus colistin for the treatment of carbapenem-resistant Enterobacterales infection. DOOR is being successfully applied to the analysis of interventional trials and, in collaboration with the US Food and Drug Administration (FDA), for use in registrational trials. In the area of diagnostics, the ARLG developed Master Protocol for Evaluating Multiple Infection Diagnostics (MASTERMIND), an innovative design that allows simultaneous testing of multiple diagnostic platforms in a single study. This approach will be used to compare molecular assays for the identification of fluoroquinolone-resistant Neisseria gonorrhoeae (MASTER GC) and to compare rapid diagnostic tests for bloodstream infections. The ARLG has initiated a first-in-kind randomized, double-blind, placebo-controlled trial in participants with cystic fibrosis who are chronically colonized with Pseudomonas aeruginosa to assess the pharmacokinetics and antimicrobial activity of bacteriophage therapy. Finally, an engaged and highly trained workforce is critical for continued and future success against antimicrobial drug resistance. Thus, the ARLG has developed a robust mentoring program targeted to each stage of research training to attract and retain investigators in the field of antimicrobial resistance research.

Abstract Addressing the treatment and prevention of antibacterial-resistant gram-negative bacterial infections is a priority area of the Antibacterial Resistance Leadership Group (ARLG). The ARLG has conducted a series of observational studies to define the clinical and molecular global epidemiology of carbapenem-resistant and ceftriaxone-resistant Enterobacterales, carbapenem-resistant Pseudomonas aeruginosa, and carbapenem-resistant Acinetobacter baumannii, with the goal of optimizing the design and execution of interventional studies. One ongoing ARLG study aims to better understand the impact of fluoroquinolone-resistant gram-negative gut bacteria in neutropenic patients, which threatens to undermine the effectiveness of fluoroquinolone prophylaxis in these vulnerable patients. The ARLG has conducted pharmacokinetic studies to inform the optimal dosing of antibiotics that are important in the treatment of drug-resistant gram-negative bacteria, including oral fosfomycin, intravenous minocycline, and a combination of intravenous ceftazidime-avibactam and aztreonam. In addition, randomized clinical trials have assessed the safety and efficacy of step-down oral fosfomycin for complicated urinary tract infections and single-dose intravenous phage therapy for adult patients with cystic fibrosis who are chronically colonized with P. aeruginosa in their respiratory tract. Thus, the focus of investigation in the ARLG has evolved from improving understanding of drug-resistant gram-negative bacterial infections to positively affecting clinical care for affected patients through a combination of interventional pharmacokinetic and clinical studies, a focus that will be maintained moving forward.

Abstract Background Carbapenem-resistant Acinetobacter baumannii (CRAb) is 1 of the most problematic antimicrobial-resistant bacteria. We sought to elucidate the international epidemiology and clinical impact of CRAb. Methods In a prospective observational cohort study, 842 hospitalized patients with a clinical CRAb culture were enrolled at 46 hospitals in five global regions between 2017 and 2019. The primary outcome was all-cause mortality at 30 days from the index culture. The strains underwent whole-genome analysis. Results Of 842 cases, 536 (64%) represented infection. By 30 days, 128 (24%) of the infected patients died, ranging from 1 (6%) of 18 in Australia-Singapore to 54 (25%) of 216 in the United States and 24 (49%) of 49 in South-Central America, whereas 42 (14%) of non-infected patients died. Bacteremia was associated with a higher risk of death compared with other types of infection (40 [42%] of 96 vs 88 [20%] of 440). In a multivariable logistic regression analysis, bloodstream infection and higher age-adjusted Charlson comorbidity index were independently associated with 30-day mortality. Clonal group 2 (CG2) strains predominated except in South-Central America, ranging from 216 (59%) of 369 in the United States to 282 (97%) of 291 in China. Acquired carbapenemase genes were carried by 769 (91%) of the 842 isolates. CG2 strains were significantly associated with higher levels of meropenem resistance, yet non-CG2 cases were over-represented among the deaths compared with CG2 cases. Conclusions CRAb infection types and clinical outcomes differed significantly across regions. Although CG2 strains remained predominant, non-CG2 strains were associated with higher mortality. Clinical Trials Registration. NCT03646227.