INTRODUCTION:Expanded multiplex PCR gastrointestinal panels (GIPs) are routinely ordered to diagnose infectious diarrhea. However, recommendations for repeat GIP testing are limited, resulting in variable testing practices. We evaluated the diagnostic yield of repeat GIP testing within 14 days. METHODS:We conducted a retrospective cohort study of adults (age ≥ 18 years) tested with GIPs across 12 hospitals and outpatient centers (2019-2024). We analyzed the first diarrheal episode per patient, excluding cases with invalid/missing results and C. difficile results. Repeat testing was defined as a GIP completed within 14 days of an index GIP, excluding confirmatory testing using the same stool sample. The primary outcome was diagnostic yield (new pathogen detection), and the secondary outcome was pathogen persistence (same pathogen detection). RESULTS:Among 16,502 patients, 507 (3.1%) underwent repeat GIP testing within 14 days (median interval: 6.3 days; IQR: 2.7-9.8). Only 4.6% [19/415] index-negative patients and 2.2% [2/92] index-positive patients detected new pathogens on repeat testing, with 51% [47/92] index-positive patients demonstrating persistence of at least one pathogen from their initial test. The number needed to test (NNT) to identify one new pathogen was 24 (95% CI: 16-39) tests overall, and 127 (95% CI: 50-455) tests to identify one new pathogen warranting antimicrobial treatment. Most repeat testing (86% [436/507]) was ordered by a different clinician. DISCUSSION:Repeat GIP testing within 14 days rarely provided new diagnostic information, highlighting the limited utility of early repeat testing. Institutional policies discouraging repeat GIPs within 14 days may improve diagnostic stewardship.

Commercial antimicrobial susceptibility testing (AST) systems for gram-negative bacteria provide operational advantages over reference broth microdilution (BMD) testing, but the results produced by commercial AST systems might not be as accurate as the reference method. Assessing and comparing the performance of AST systems can be informative for clinical microbiology practice. In total, 280 clinical isolates and 100 isolates from the U.S. Centers for Disease Control and Prevention Antimicrobial Resistance Isolate Bank, including Enterobacterales and Pseudomonas aeruginosa, were intended to be tested using disk diffusion (DD) and automated commercial AST systems, such as Selux AST System (Selux Diagnostics), MicroScan (Beckman Coulter), Phoenix (Becton, Dickinson and Company), and Vitek 2 (bioMérieux). These results were compared to BMD as the reference standard. In total, 372 isolates were assessed. For Enterobacterales, the greatest frequency of very major errors was identified with cefepime by Vitek 2 (29.0%) and ertapenem by DD (9.1%); essential agreement less than 90% was identified with the following combinations: aztreonam by MicroScan (86.4%), aztreonam by Vitek 2 (88.9%), cefepime by Selux (86.3%), cefepime by Vitek 2 (76.8%), ceftazidime by Vitek 2 (89.9%), and levofloxacin by MicroScan (83.4%). For P. aeruginosa, essential agreement less than 90% was identified with the following combinations: gentamicin by Selux (87.2%), tobramycin by Selux (86.6%), and ciprofloxacin by Phoenix (88.4%). Overall, antimicrobials that had low demonstrable bias across all automated commercial AST systems included ampicillin, amoxicillin-clavulanate, ceftazidime-avibactam, ertapenem, and trimethoprim-sulfamethoxazole. Comparing commercial testing systems head-to-head against a reference standard provides insight into the strengths and weaknesses of the performance of these test systems, and these insights can subsequently inform local decisions regarding further investigations and potential operational mitigation strategies.IMPORTANCEThis study assessed and compared the performance of multiple commercial antimicrobial susceptibility testing (AST) systems and disk diffusion methods. The accuracy of determining minimum inhibitory concentrations or zone diameters of antimicrobials and the associated interpretive categories were studied for 372 isolates of Enterobacterales and Pseudomonas aeruginosa. Performance of the evaluated systems revealed that multiple antimicrobial-organism combinations were below the standards typically required by regulatory agencies and clinical laboratories. These deficiencies varied across the commercial platforms and disk diffusion methods, highlighting the importance of benchmarking studies that compare the performance using identical isolates. These identified performance weaknesses may warrant further study and/or the implementation of mitigation strategies in clinical laboratory operations to prevent the reporting of errant results.

Congenital cytomegalovirus (cCMV) infection is the most common congenital infection. Cleveland Clinic (CC) recognized a substantial underdiagnosis of cCMV compared to the expected incidence. A multidisciplinary team at CC developed and implemented an active cCMV screening program for infants beginning Jan 2022 with a goal of improving detection and follow-up. This report highlights cohort outcomes and key challenges encountered during program execution.cCMV Screening algorithmHybrid screening algorithm for congenital CMV (cCMV) at Cleveland Clinic: universal screening in NICU infants and targeted screening in newborn nurseries based on clinical signs or abnormal newborn hearing screen. Guides audiology follow-up and identifies candidates for antiviral therapy.cCMV Screenings and Detections by YearAnnual cCMV (congenital cytomegalovirus) screening volumes and corresponding detections are shown for the years 2020 through March 31, 2025. Both the number of screenings and the number of confirmed detections increased substantially over time. This analysis highlights the benefits of active newborn screening. With input from caregivers in Laboratory Medicine, Infectious Disease, Otolaryngology, Audiology, Newborn Nursery and Intensive Care, a standardized saliva screening program was developed and implemented. This protocol involves universal screening of newborns admitted to NICU and targeted screening in healthy newborn nurseries (clinical suspicion or abnormal newborn hearing screen (NHS)). Positive saliva screens were confirmed with urine PCR testing. Over 12,000 deliveries occur annually across Ohio and Florida. From 1/1/2022 through 3/31/2025, there was a 1223% increase in screening compared to 2020-21. Of 5513 saliva screens that occurred across 16 newborn wards (9 NICU, 7 nursery) at 8 hospitals in 2 states, 918 were targeted and 4595 were universal. In total, 33 infants were identified by saliva screening and confirmed with urine testing (10 symptomatic with 2 deaths, 23 asymptomatic) nearly tripling the relative rate of identification. Of asymptomatic infants, 15 (65%) passed their NHS. Incidence of cCMV was 0.58% (1.42% targeted, 0.41% universal). The newborn nursery and ICU quickly adapted to using the program without a disruption in workflows. Substantial false-positive saliva results early in the program catalyzed changes in sample testing workflows and ultimately the testing platform. Infectious Disease and Audiology were instrumental in accommodating capacity for longitudinal follow-up and 1-3-6 benchmark auditory screening. Early multidisciplinary involvement and coordination are essential for successful implementation of cCMV screening. This program significantly increased the detection of cCMV in newborns despite many being asymptomatic with normal NHS, highlighting the importance of active screening programs. Samantha Anne, MD, Cochlear: Grant/Research Support|Eli Lilly: Advisor/Consultant|Plural publishing: royalties Daniel D. Rhoads, MD, Abbott: Grant/Research Support|Altona: Grant/Research Support|BD: Grant/Research Support|bioMerieux: Grant/Research Support|Cepheid: Grant/Research Support|Cleveland Diagnostics: Grant/Research Support|HelixBind: Grant/Research Support|Hologic: Grant/Research Support|Luminex/Diasorin: Grant/Research Support|Meridian: Grant/Research Support|Next Gen Diagnostics: Board Member|Next Gen Diagnostics: Ownership Interest|Pattern Bio: Grant/Research Support|Qiagen: Grant/Research Support|Q-Linea: Grant/Research Support|Rapid Diagnostics: Grant/Research Support|Renascent Diagnostics: Advisor/Consultant|Renascent Diagnostics: Financial payments|Renascent Diagnostics: Ownership Interest|Roche: Grant/Research Support|Selux Diagnostics: Grant/Research Support|Thermo Fisher: Grant/Research Support|Vela Diagnostics: Grant/Research Support Hannah Wang, MD, Cepheid: Grant/Research Support|Hologic: Advisor/Consultant|Hologic: Grant/Research Support|Moderna: Honoraria

Context.—:Clinical laboratory tests in the United States have been subject to dichotomous regulatory oversight, encompassing both laboratory-developed tests (LDTs) and US Food and Drug Administration (FDA)-approved or FDA-cleared in vitro diagnostic products (IVDs). Objective.—:To assess the factors and preferences that are important for the selection of tests by clinical laboratories. Design.—:A questionnaire was sent to laboratories participating in College of American Pathologists proficiency testing programs for 5 molecular analytes across molecular oncology, infectious disease, and germline genetics. The questionnaire asked about the factors that influenced the decision to implement an LDT or an FDA IVD. Results.—:For all laboratories providing analyte responses, including those using LDTs and FDA IVDs, the factors most rated as very important were assay coverage of specific variants and/or positions of interest (95.1%; 656 of 690) and assay performance (eg, analytical sensitivity and specificity) (92.8%; 666 of 718). Laboratories using LDTs preferentially rated flexibility to modify the assay and already possessing the testing platform/equipment as very important. Laboratories using FDA IVDs preferentially rated the reputation of the assay manufacturer and support and customer service as very important. Conclusions.—:This study highlights the primacy of performance for laboratories' selection of assays. The variability of laboratory preferences for LDTs and FDA IVDs illustrates the need for a regulatory approach that minimizes burdens and is flexible so that laboratories can best adapt to their unique clinical environments. These preferences should be considered to reduce impact on laboratories and on patient care as the FDA and other agencies assess regulatory oversight.

Context.—:The Becton Dickinson BACTEC blood culture media bottle shortage led hospitals to create a mitigation strategy to conserve bottles while ensuring a high quality of care. Objective.—:To describe how our existing framework of teams was able to quickly pivot to implement conservation strategies without negatively impacting patient care. Design.—:A team implemented various mitigation measures based on current inventory, which included education, leveraging electronic medical record guidance and alerts with evidence-based information on appropriate ordering, alternative sources of supply, and real-time dashboards to inform next steps. Results.—:Implementation of educational efforts and alerts resulted in more than 22 000 blood cultures avoided in 6 months, with an increase in blood culture positivity rates by 25%. We did not see any adverse events that impacted the quality of patient care. We observed cost savings of nearly $200 000 in 2024 with these measures. Conclusions.—:Handling widespread shortages in situations of single suppliers requires rapid assembly of key stakeholders with decision-making authority and support of executive leadership. Existing frameworks of experienced teams quickly assessed the situation, worked on mitigation measures, predicted future challenges, and implemented alternatives to ensure patient care was not disrupted.

Taxonomy classifies organisms based on shared traits, while nomenclature assigns formal names using distinct rules for bacteria, fungi, parasites, and viruses. Advances in genomic sequencing have refined microbial classification, often prompting name changes that can inadvertently impact clinical practice, including patient diagnosis, treatment, and communication among healthcare providers. Various organizations govern taxonomy and nomenclature differently across pathogen domains, and implementation of new nomenclature in clinical settings poses challenges. The College of American Pathologists has introduced requirements for laboratories to maintain consistent nomenclature across testing platforms and to consider use of contemporary nomenclature. While scientific accuracy is important, practical considerations must guide the adoption of new names to avoid confusion and ensure high-quality patient care.

Automated continuous monitoring blood culture instruments identify metabolism byproducts and flag blood culture bottles as "positive." A Gram stain is used to visualize and characterize the microbial growth in the broth and initiate additional testing. When no organisms are seen (NOS) on Gram stain, in our laboratory, bottles are reevaluated with a Wayson stain, a rapid one-step stain that provides contrast between organisms and the background, especially in Gram-negative organisms. In this study, we assess the performance of the Wayson stain on reevaluation of Gram stain NOS blood culture bottles. The study period, August 2022 to July 2023, includes blood cultures that were flagged as positive by the automated blood culture instrument (BACTEC) with accompanying Gram and Wayson stain interpretations and organism identification. 133,463 blood cultures were performed during the study period, and 20,129 cultures were flagged as positive by BACTEC. 601 NOS Gram stain cultures were identified of which 76 had a positive Wayson. The Wayson stain procedure increased the sensitivity of direct organism visualization from 99.32% to 99.71% by identifying 55% (76 of 137) of NOS Gram stain blood culture bottles. Of blood cultures that were positive by BACTEC with NOS Gram and Wayson stains (475), 414 were finalized as no growth and 61 had an isolate (false negatives) of which 49% (30) were yeasts. The Wayson stain aided in detecting gram-negative genera such as Capnocytophaga, Campylobacter, and Fusobacterium species and other rarely identified species. IMPORTANCE The Wayson stain, a rapid one-step stain that provides contrast between microorganisms and the background, was historically used for the presumptive diagnosis of Yersinia pestis from bubo specimen. In our laboratory, the Wayson stain has long been used to reevaluate blood culture Gram-stained smears from bottles that were flagged as positive by the automated continuous monitoring instrument but where no organisms are seen. In this study, we show that the Wayson stain provides an easily implemented and interpreted technique, other than a repeat Gram stain or acridine orange, to increase the sensitivity of direct organism visualization from blood culture bottles, particularly for Gram-negative organisms.

OBJECTIVES:Infectious diarrhoea remains a significant cause of morbidity and mortality in immunocompromised and high-risk populations. However, pathogen-specific epidemiology and diagnostic utility of molecular gastrointestinal panels (GIPs) in these groups remain poorly defined. Our objective was to describe diarrhoeal pathogen distribution across 10 high-risk conditions and evaluate the diagnostic yield of GIPs in these populations to inform the development of improved diagnostic algorithms. METHODS:We conducted a retrospective observational study analysing all adults (age ≥18 years) tested with a BioFire FilmArray GIP at 12 U.S. hospitals from 2019-2024. We reported observed organism detection rates overall, risk status, and by each of 10 high-risk conditions identified by International Classification of Diseases 10 (ICD-10) codes. Mixed-effects multivariable logistic regression estimated the independent effect of each high-risk condition on organism detection, controlling for sex, location, setting, year, season, and 10 high-risk conditions. RESULTS:Among 16 570 patients, (median age 66 years; 65% [10 752/16 570] with ≥1 high-risk condition), pathogens were detected in 22% [3591/16 570]. Enteropathogenic Escherichia coli (EPEC) and norovirus were the most common organisms detected (6.4% [1059/16 570] and 6.1% [1006/16 570], respectively). The third most common organism varied based on high-risk comorbidity, typically Salmonella or Campylobacter. High-risk patients had significantly lower odds of detecting any pathogen compared with low-risk patients (19% [1996/10 752] vs. 27% [1595/5818]) (OR 0.60; 95% CI, 0.56-0.65). Patients with HIV had higher bacterial (adjusted OR 1.61; 95% CI, 1.05-2.38) and parasitic detection (2.94; 95% CI, 1.11-6.46), while transplant recipients had higher viral detection (adjusted OR 1.50; 95% CI, 1.08-2.07). Codetections most commonly involved EPEC with other organisms. DISCUSSION:Most GIP testing in high-risk patients did not identify a causative pathogen. When the GIP did detect an organism, EPEC and norovirus were the most common, with distinct pathogen profiles by comorbidity. Our findings support risk-stratified testing and highlight GIP limitations, including potential false positives.

Context.— Laboratory testing practices for diagnosis of Clostridioides difficile infection (CDI) have evolved in response to published guidelines, availability of highly sensitive nucleic acid amplification tests (NAATs), perceived problems with the specificity of NAATs, and CDI reporting requirements. Objective.— To assess the current state of laboratory practice for diagnostic CDI testing. Design.— An optional 8-item supplemental questionnaire was distributed in December 2019 to the 1374 laboratories participating in the College of American Pathologists C difficile Detection (CDF) proficiency testing program challenge CDF-C. Results.— Of 1374 CDF-C participants, 1160 (84.4%) responded, predominantly representing laboratories based in the United States (1077 of 1160; 92.8%). The majority reported using a multistep testing algorithm (684 of 1159; 59.0%). Initial testing with a glutamate dehydrogenase and toxin A/B combination test followed by NAAT for discrepant results was the most common testing method (360 of 1146; 31.4%). NAAT alone (299 of 1146; 26.1%) was next, then NAAT followed by an assay that included toxin A/B enzyme immunoassay if NAAT is positive (258 of 1146; 22.5%). Only 5.4% (62 of 1146) reported using toxin A/B immunoassay alone. Most respondents (1093 of 1131; 96.6%) reported rejecting CDI tests on formed stool, but rejection of CDI testing in pediatric patients was uncommon (211 of 1131; 18.7%). Rejection of CDI testing in patients using laxatives was reported more often by US-based respondents (379 of 1054 [36.0%] versus 9 of 77 [11.7%], P < .001). Conclusions.— Multistep algorithms for CDI diagnosis are widely used in line with published recommendations. Most respondents reported rejection of formed stool for CDI testing, but few reported rejection of testing in infants and patients taking laxatives, suggesting these may be areas of opportunity for laboratories to pursue in improving CDI testing practices.

The QIAstat-Dx Gastrointestinal Panel 2 (GI2 Panel) is a sample-to-answer multiplex PCR instrument that can detect 17 targets in a run time of about 80 minutes. The performance of the QIAstat-Dx GI2 Panel was evaluated by testing 1,939 prospective, 119 prospectively collected and then archived positive clinical samples and 750 retrospective clinical specimens across 13 sites in Europe and the United States. Specimens tested included bulk stool samples preserved in modified Cary-Blair transport medium. For most targets, results were compared to those of the FilmArray GI panel (13/17), and discordant results were adjudicated with a third assay. For the remaining targets (4/17), a composite comparator method was used, which included three comparator assays for each target. Before discordant resolution, the QIAstat-Dx GI2 Panel positive percent agreement (PPA) was 95% or greater for 5/17 targets (Campylobacter, E. coli O157, Cryptosporidium, Cyclospora cayetanensis, and Giardia lamblia) and 90% or greater for 11/17 targets: adenovirus F40/F41, astrovirus, norovirus GI/GII, rotavirus A, Plesiomonas shigelloides, enteropathogenic Escherichia coli, enterotoxigenic E. coli, Salmonella, Yersinia enterocolitica, Shiga-like toxin E. coli (STEC) stx1/stx2, and Shigella/enteroinvasive E. coli. No cases of Entamoeba histolytica were encountered during the clinical study. The negative percent agreement (NPA) was >98.9% for all QIAstat-Dx GI2 Panel targets. The three most common pathogens identified in single and co-infections were enteropathogenic E. coli (9.9%), Campylobacter (5.2%), and norovirus GI/GII (3.1%). In summary, this clinical study examined more than 2,800 samples from Europe and the U.S. using the QIAstat-Dx GI2 Panel and identified 90%-100% PPA and 99% NPA for its 17 targets.IMPORTANCEThe manuscript highlights the significance and impact of the QIAstat-Dx GI2 Panel, a sample-to-answer multiplex PCR instrument capable of detecting 17 targets in approximately 80 minutes. This comprehensive clinical study, conducted across 13 sites in Europe and the United States, evaluated the performance of the panel using over 2,800 clinical samples. The results demonstrate a high accuracy of the QIAstat-Dx GI2 panel, with a PPA equal to or higher than 90% for all targets and an NPA greater than 98.9% for all targets. These findings underscore the reliability and effectiveness of the GI2 panel in the rapid and precise detection of gastrointestinal pathogens, which is crucial for timely diagnosis and treatment of infections.

Improving the rapidity of identification of bacteria causing bacteremia continues to be a focus for quality improvement within the discipline of clinical microbiology. This multicenter study was used to obtain In Vitro Diagnostic Regulation Conformite Europeenne (CE) mark in Europe and describes the performance of the VITEK MITUBE to matrix-assisted laser desorption/ionization (MALDI) workflow for identification of 10 species of gram-negative bacteria directly from positive blood culture broth without subculture. One hundred twenty-five (125) prospective clinical samples, including Escherichia coli (69), Klebsiella aerogenes (4), Klebsiella oxytoca (3), Klebsiella pneumoniae (29), Proteus mirabilis (9), Pseudomonas aeruginosa (10), and Serratia marcescens (1), were included; and 123 (98.4%) were accurately identified using the VITEK MITUBE workflow. None were misidentified, and two (1.6%) K. pneumoniae were not identified. Contrived samples were also tested and reported in this study. When considering both the prospective clinical samples and the contrived samples, the workflow was able to identify the species 95% of the time. Proteus vulgaris accounted for 81% (13/16) of the samples that were unable to achieve an identification. A single misidentification error is reported in the contrived sample testing. The VITEK MITUBE to MALDI workflow enables accurate and reliable identification of commonly encountered gram-negative bacteria directly from positive blood culture broth.IMPORTANCEMITUBE is a new in vitro diagnostic device designed to meet a need in the clinical microbiology community for a simple, rapid, accurate, and inexpensive system to identify bacteria detected in blood cultures using MALDI-TOF and without the need for subculture.

Anaerobic bacteria are an important but understudied cause of bacteremia. The objective of this study was to evaluate the impact of using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) to rapidly identify obligate anaerobic gram-negative bacteria directly from positive blood culture broth (PBCB) samples. This retrospective pre- and post-intervention study included patients with blood cultures positive for anaerobic gram-negative organisms, comparing outcomes before and after the implementation of a direct-from-PBCB MALDI-TOF MS workflow. The primary outcome was the time from Gram stain to organism identification. A secondary outcome was the time to first antibiotic modification (escalation or de-escalation). In monomicrobial anaerobic bloodstream infections, the median (interquartile range [IQR]) time from Gram stain to pathogen identification was significantly reduced in the post-intervention group compared to the pre-intervention group (15.0 hours [IQR: 7.8-47.8] vs 45.3 hours [IQR: 41.5-49.3]; P < 0.001). Similarly, the median (IQR) time to the first antibiotic de-escalation was significantly shorter following implementation of directly-from-PBCB MALDI-TOF MS (21.1 hours [IQR: 7.9-51.6] vs 52.0 hours [IQR: 24.0-64.5]; P = 0.014). This study demonstrates that the rapid identification of gram-negative obligate anaerobes from PBCB can help to significantly expedite antibiotic therapy de-escalation.IMPORTANCEObligate anaerobic gram-negative organisms are a significant but understudied cause of bloodstream infections. This study demonstrates that rapid identification of anaerobic gram-negative bacteria directly-from-positive blood culture broth by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry can substantially reduce the time to both pathogen identification and antibiotic optimization in monomicrobial bloodstream infections. Faster diagnostic turnaround supports more timely and targeted therapy, with important implications for antimicrobial stewardship and patient outcomes.

OBJECTIVE:To develop, externally validate, and test a series of computer algorithms to accurately predict antibiotic susceptibility test (AST) results at the time of clinical diagnosis, up to 3 days before standard urine culture results become available, with the goal of improving antibiotic stewardship and patient outcomes. PATIENTS AND METHODS:Machine learning algorithms were developed and trained to predict susceptibility or resistance using over 4.7 million discrete AST classifications from urine cultures in a cohort of adult patients from outpatient and inpatient settings from 2012 to 2022. The algorithms were validated on a cohort from a geographically-distant hospital system, ~1931 km (~1200 miles) from the training cohort facilities, from the same time period. Finally, algorithms were clinically validated in a contemporary cohort and compared to the empiric therapy prescribed by clinicians. Appropriateness of the antibiotics selected by clinicians and the algorithm during the clinical validation was compared. RESULTS:Algorithms were accurate during clinical validation (area under the receiver operating characteristic curve [AUC] 0.71-0.94) for all 11 tested antibiotics. The algorithms' accuracy improved as the organism was identified (AUC 0.79-0.97). In external validation in a geographically-distant cohort, the algorithms remained accurate even without additional training on this group (AUC 0.69-0.87). When the algorithms were trained on the antibiogram from the geographically-distant hospital, the accuracy improved (AUC 0.70-0.93). When algorithms' performances were tested against clinicians in a contemporary cohort for the empiric prescription of oral antibiotics, the drug agent suggested by the algorithms more frequently resulted in adequate empiric coverage. CONCLUSIONS:Machine learning algorithms trained on a large dataset are accurate in prediction of urine culture susceptibility vs resistance up to 3 days prior to urine AST availability. Clinical implementation of such an algorithm could improve both clinical care and antimicrobial stewardship.

We characterized the molecular determinants of meropenem-vaborbactam (MV) non-susceptibility among non-metallo-beta-lactamase-producing KPC-Klebsiella pneumoniae (KPC-KP). Whole-genome sequencing was performed to identify mutations associated with MV non-susceptibility. Isolates with elevated MV MICs were found to have mutations encoding truncated or altered OmpK36 porins and increased blaKPC copy numbers. KPC-KP isolates with decreased susceptibility to MV were detected among a collection of isolates predating the availability of MV.

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), MIC90 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, MIC90 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.

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.