Antibiotic tolerance is the ability of bacteria to survive normally lethal doses of antibiotics for extended time periods. Clinically significant Enterobacterales, for example, can exhibit high tolerance to the last-resort antibiotic meropenem. Meropenem tolerance is associated with formation of cell wall-deficient spheroplasts that readily recover to rod shape and normal growth upon removal of the antibiotic. Both the true prevalence of tolerance, and genetic mechanisms underlying it, remain poorly understood. Here, we find that meropenem tolerance is widespread among clinical Enterobacterales. Using forward genetics, we uncover tolerance factors in a hypertolerant isolate of the ESKAPE pathogen Klebsiella pneumoniae. We find that multiple mechanisms contribute to tolerance, and that cell envelope stress responses (PhoPQ, CpxPRA, Rcs phosphorelay and OmpR/EnvZ) collectively promote spheroplast stability and recovery, while the lytic transglycosylase MltB counteracts it. Our data indicate that tolerance is widespread among clinical isolates, and that outer membrane maintenance is a key factor promoting survival of tolerant K. pneumoniae.

Background: Rates of Candida auris are rising across the US, particularly in New York. Due to C. auris’ affinity for environmental contamination and prolonged skin colonization, rapid implementation of comprehensive infection prevention & control (IP&C) measures is essential. Given the complexity and multidisciplinary involvement required for these efforts, we developed the C.A.R.E (Candida Auris Response & Engagement) framework in response to an inpatient outbreak to guide multidisciplinary efforts and provide a model for other facilities facing similar challenges with C. auris or other pathogens with extensive contact transmission. Methods: A C. auris cluster was identified in an 862-bed New York City academic medical center between July and October 2025. 23 cases were found involving a medical stepdown unit and adjacent intensive care unit. Baseline IP&C C. auris efforts include isolation precautions (gown and gloves), twice-daily room cleaning/disinfection, dedicated equipment, ATP testing of high touch surfaces (HTS) post terminal room cleaning, observations of personal protective equipment (PPE) use and hand hygiene, and screening of exposed roommates. After an August point prevalence surveillance (PPS) identified additional cases, we expanded interventions across various categories. The C.A.R.E. framework (Fig. 1) summarizes baseline and expanded efforts during this cluster. Figure 1. The C.A.R.E. (Candida Auris Response & Engagement) Framework to approaching a rise in C. auris cases. Results: Of 23 cases, 83% (19/23) were detected through surveillance. Clinical cases included bloodstream (3/4) and respiratory (1/4) sources. Shared rooms, either roommates or subsequent room occupants, were associated with 52% (12/23) of cases. Following implementation of the C.A.R.E. framework, further transmission ceased, confirmed by two negative rounds of PPS on each unit (Fig. 2). Figure 2. A timeline of C.auris cases identified on 2 units with corresponding IP&C effort implementation. To address identified gaps, a C. auris task force was created to improve IP&C processes. Key actions included clarifying equipment cleaning responsibility in collaboration with Environmental Services and Nursing, reevaluating the C. auris isolation category, and expanding screening for high-risk patients. Further, we incorporated fluorescent marker audits alongside ATP testing into routine practices to monitor environmental and equipment cleaning. While not all measures in the C.A.R.E. framework may be needed for every outbreak, facilities can adapt and scale interventions based on feasibility and outbreak severity. Conclusions: Effective prevention of C. auris transmission requires coordinated and multidisciplinary efforts. Establishing a structured response after early case detection can help close gaps in infection prevention that contribute to spread.

Abstract Background Acinetobacter baumannii-calcoaceticus complex (ABC) isolates are responsible for severe infections, such as bacteremia, healthcare-associated pneumonia, and skin and soft tissue infections. Sulbactam-durlobactam is a FDA-approved targeted β-lactam-β-lactamase inhibitor combination antibiotic developed to treat infections caused by ABC. This study aims to evaluate the in vitro activity of sulbactam-durlobactam and clinically utilized antibiotics against ABC strains with a predominance of carbapenem resistance.Table 1.Susceptibility test results of sulbactam-durlobactam and comparator agents against Acinetobacter baumannii-calcoaceticus complex isolates Methods 164 ABC isolates in addition to de-identified data including patient location at the time of culture and culture source were submitted by 11 geographically dispersed U.S medical centers in 2023 and 2024. Susceptibility tests for sulbactam-durlobactam (durlobactam fixed concentration of 4 mg/L), and comparator agents were conducted by manual broth microdilution and interpreted according to CLSI M100Ed34 standards. Carbapenem-resistant ABC (CRAB) was defined by phenotypic resistance to meropenem (MIC ≥8 mg/L). Results ABC isolates were primarily cultured from respiratory sources (57%), followed by blood (19%) and urine (11%). Of the 164 isolates, majority were isolated from non-ICU patients (n=102; 62%) versus ICU (n=62; 38%). The MIC50 and MIC90 values of the sulbactam component of ampicillin-sulbactam for all isolates was 8 and 32 mg/L, respectively resulting in a susceptibility rate of 40.8%. The addition of durlobactam to sulbactam decreased the MIC50 and MIC90 by 2-doubling dilutions to 1 and 4 mg/L and increased the susceptibility rate to 94.5%. The MIC50/90 and susceptibility rates for all other antimicrobial agents are shown in Table 1. Notably, a majority of isolates were CRAB (n=122; 74.4%) and among these isolates, sulbactam-durlobactam MIC50, MIC90, and %S was 2, 4 mg/L, and 92.6%, respectively. Conclusion Sulbactam-durlobactam demonstrated potent in vitro activity against a contemporary challenge set of clinical ABC isolates, including carbapenem-resistant isolates among hospitalized patients in the United States. This study highlights the important role of sulbactam-durlobactam, relative to other clinically utilized agents for the treatment of infections caused by ABC isolates. Disclosures Amanda Harrington, PhD, Beckman Coulter: Advisor/Consultant|bioMeriuex: Advisor/Consultant|bioMeriuex: Grant/Research Support|Bio-Rad: Advisor/Consultant|Day Zero: Advisor/Consultant|Selux Diagnostics: Grant/Research Support Wesley D. Kufel, Pharm.D., BCPS, BCIDP, Merck & Co.: Grant/Research Support|Shionogi, Inc: Grant/Research Support Lars Westblade, PhD, Accelerate Diagnostics, Inc: Grant/Research Support|bioMerieux, Inc: Grant/Research Support|Element Materials Technology: Grant/Research Support|Hardy Diagnostics: Grant/Research Support|Roche Molecular Systems, Inc.: Advisor/Consultant|Roche Molecular Systems, Inc.: Grant/Research Support|Selux Diagnostics, Inc.: Grant/Research Support|Shionogi, Inc: Advisor/Consultant|Talis Biomedical: Advisor/Consultant David P. Nicolau, PharmD, CARB-X: Grant/Research Support|Innoviva: Grant/Research Support|Innoviva: Honoraria|Merck: Advisor/Consultant|Merck: Grant/Research Support|Merck: Honoraria|Pfizer: Advisor/Consultant|Pfizer: Grant/Research Support|Pfizer: Honoraria|Shionogi: Advisor/Consultant|Shionogi: Grant/Research Support|Shionogi: Honoraria|Venatorx: Grant/Research Support Tomefa E. Asempa, PharmD, FDA/CDER: Grant/Research Support|Paratek: Grant/Research Support|Shionogi: Grant/Research Support|Spero: Grant/Research Support|VenatoRx: Grant/Research Support

Abstract Background Obtaining a urine culture (UCx) in the absence of urinary symptoms and inflammation has been shown to result in misdiagnosis and over treatment of urinary tract infections (UTIs) and catheter-associated UTIs in adults. Reflex UCx is a diagnostic stewardship strategy to reduce unnecessary UCx by performing UCx only if a urinalysis (UA) meets criteria for infection. Although the AAP has recommendations for reflex UCx in pediatrics, there are little data to support this approach. We aimed to assess the potential impact of reflex UCx on reducing unnecessary UCx in children. Age, specimen type, and hospital location in children with positive and negative UCx. Methods We performed a retrospective review of children age 2 to 18 years at our network of 8 hospitals from the emergency department or inpatient settings from 11/1/2020 to 7/20/2023. We included children with a matched microscopic UA (mUA) and UCx on the same calendar day. Positive UCx was defined as ≥ 50,000 CFU/ml for catheterized specimens and ≥ 100,000 CFU/ml for clean catch or unspecified specimens. Pyuria was defined as ≥ 10 WBC/HPF. Manual chart review was performed for positive UCx when < 10 WBC/HPF to determine cases consistent with clinical UTI. Sensitivity, specificity, positive predictive value, and negative predictive value with 95% confidence intervals were calculated. Sensitivity, Specificity, Positive Predictive Value (PPV) and Negative Predictive Value (NPV) of Pyuria Compared to Positive Urine Culture and Clinical UTI. Results During the baseline period, 10,235 patients had a mUA and UCx, of which 893 (8.7%) UCx were positive. Median age, specimen types and hospital location are listed in Table 1. Of the positive UCx, 162 (18%) were associated with < 10 WBC/HPF. Of these cases, 44 (27%) had conditions that would have excluded them from reflex UCx per our hospital guideline: 36 (22%) had urologic abnormalities, 5 (3.1%) were pregnant, 3 (1.9%) were renal transplant recipients, and 0 (0%) had neutropenia. Of the remaining 118 positive cultures with < 10 WBC/HPF, 93 (79%) were not consistent with clinical UTI. Table 2 shows the sensitivity and negative predictive value (NPV) of pyuria for a positive UCx and clinical UTI. Conclusion In our study, we demonstrated the safety of a reflex UCx approach in a large pediatric population. Reflex UCx had low risk for missing clinical UTIs and would have reduced the number of unnecessary UCx during the pre-implementation period as 7349 (72%) would not have been performed. Reflex UCx should become standard of care in pediatrics. Disclosures Lars Westblade, PhD, Accelerate Diagnostics, Inc: Grant/Research Support|bioMerieux, Inc: Grant/Research Support|Element Materials Technology: Grant/Research Support|Hardy Diagnostics: Grant/Research Support|Roche Molecular Systems, Inc.: Advisor/Consultant|Roche Molecular Systems, Inc.: Grant/Research Support|Selux Diagnostics, Inc.: Grant/Research Support|Shionogi, Inc: Advisor/Consultant|Talis Biomedical: Advisor/Consultant

Ceftibuten is being developed in combination with the oral prodrug of avibactam. Outpatient isolates (n = 500) from 11 US states underwent susceptibility testing with manual broth microdilution. Ceftibuten had susceptibility rates of 64% (CLSI) and 23% (EUCAST). Ceftibuten-avibactam achieved 96.4% inhibition at MIC ≤ 1 µg/mL. Susceptibility rates were as follows: cefpodoxime (2.6%), ceftriaxone (1%), ceftazidime-avibactam (99.6%), tebipenem (89%), ertapenem (94.4%), levofloxacin (26.6%), trimethoprim-sulfamethoxazole (40.2%), and fosfomycin (96.8%). Ceftibuten-avibactam demonstrates potent in vitro activity against cephalosporin non-susceptible isolates.

Currently available rapid blood culture diagnostics detect few gram-negative resistance determinants, limiting their clinical utility. We prospectively evaluated the prototype BIOFIRE FILMARRAY Antimicrobial Resistance (AMR) Panel, a rapid multiplex PCR test that detects 31 AMR genes, on residual positive blood culture broths from patients with gram-negative bacteremia due to five target organisms at a New York City hospital. Predicted antimicrobial resistance based on the AMR Panel was compared to results from broth microdilution testing of bloodstream isolates recovered in culture. A simulated stewardship study assessed opportunities for the optimization of therapy if the AMR Panel results had been available for patient care in real time. We enrolled 148 patients with gram-negative bacteremia (Escherichia coli, n = 75; Klebsiella pneumoniae, n = 44; Pseudomonas aeruginosa, n = 17; Enterobacter cloacae complex, n = 9; and Acinetobacter baumannii, n = 3). The sensitivity of the AMR Panel for predicting antimicrobial resistance was ≥90% for 10/14 antimicrobial agents in E. coli and for 10/16 agents in K. pneumoniae. Specificity was ≥90% for 15/17 agents in E. coli and for all 16 agents in K. pneumoniae. Performance for other organisms was poor. For E. coli or K. pneumoniae bacteremia, use of the AMR Panel could have led to earlier escalation or de-escalation of β-lactam therapy in a majority of patients compared to what actually occurred. This study demonstrates that a rapid multiplex PCR test with a large menu of AMR genes can be applied to positive blood culture broths to rapidly predict resistance to frontline antimicrobial agents in patients with E. coli or K. pneumoniae bacteremia.IMPORTANCEPatients with gram-negative bacteremia require urgent treatment with antimicrobial agents that are effective against their infecting pathogen. However, conventional laboratory work-up of blood cultures takes days to yield results, and during this time, patients may receive ineffective therapies. We evaluated the prototype BIOFIRE FILMARRAY AMR Panel, an assay that detects 31 genes in gram-negative bacteria that confer resistance to β-lactams, fluoroquinolones, and aminoglycosides in approximately 1 hour, directly from positive blood culture broths, and compared these results to antimicrobial susceptibility testing of isolates recovered in culture. We found that the AMR Panel accurately predicted resistance in Escherichia coli and Klebsiella pneumoniae to most antimicrobials. Moreover, if results from this assay had been used for patient care, there would have been opportunities to optimize antimicrobial prescribing more quickly than using conventional methods. These data demonstrate how novel molecular assays could optimize care for patients with E. coli and K. pneumoniae bacteremia.

Abstract Background Hematopoietic cell transplant (HCT) recipients and patients with acute leukemia are at high risk of Gram-negative bacteremia during neutropenia. Fluoroquinolone (FQ) prophylaxis is used to prevent bacterial infections during neutropenia, but the impact of colonization with FQ-resistant Enterobacterales (FQRE) on its effectiveness is unclear. Methods Adult patients undergoing HCT or receiving induction chemotherapy for acute leukemia were enrolled at 10 U.S. centers from 2021 to 2023. Patients received FQ prophylaxis during neutropenia. Perianal swabs were collected within 4 days of initiating chemotherapy or during the week before HCT, and underwent selective broth enrichment culture for FQRE. Isolates underwent antimicrobial susceptibility testing by disk diffusion. Risk factors for FQRE colonization were identified and infections prior to neutrophil recovery were compared between FQRE-colonized and non-colonized patients. Results Among 784 patients (376 allogeneic HCT recipients, 291 autologous HCT recipients, and 117 receiving chemotherapy for acute leukemia), 81 (10.3%) were colonized with FQRE. Risk factors for FQRE colonization were non-White race, prior HCT, receipt of a β-lactam or any antibacterial agent within last 3 months, and having prior detection of FQRE or a 3rd-generation cephalosporin-resistant Enterobacterales (Table 1). Of the 87 colonizing FQRE isolates (Escherichia coli: n=71; Klebsiella pneumoniae: n=12), 33% were susceptible to trimethoprim-sulfamethoxazole, 53% to amoxicillin-clavulanate, and 66% to cefpodoxime (Figure 1). FQRE-colonized patients had increased risk of bloodstream infections (BSIs) due to any Gram-negative bacteria (28.4% vs. 3.6%; p< 0.001) and FQRE (23.5% vs. 1.6%; p< 0.001) compared to non-colonized patients (Figure 2). They also had an increased risk of infections other than BSIs (12.3% vs. 4.0%; p=0.003) and intensive care unit admissions (12.3% vs. 4.2%; p=0.005) prior to neutrophil recovery, but similar 90-day mortality (4.9% vs. 4.0%, p=0.6). Conclusion Screening for FQRE colonization identifies patients at high risk of Gram-negative bacteremia following FQ prophylaxis. Alternate infection prevention strategies are needed in FQRE-colonized patients. Disclosures Catherine Liu, MD, Pfizer: Grant/Research Support Sarah B. Doernberg, MD, MAS, Basilea Pharmaceutica: Grant/Research Support|F2G Limited: Grant/Research Support|Genentech: Advisor/Consultant|Gilead Biosciences: Grant/Research Support|Janssen/J+J: Advisor/Consultant|Pfizer, Inc: Grant/Research Support|Regeneron, Inc: Grant/Research Support|Shinogi: Grant/Research Support Scott D. Rowley, MD, COTA: Stocks/Bonds (Private Company)|Genetic Testing Cooperative: Stocks/Bonds (Private Company)|SirPant Immunotherapeutics: Advisor/Consultant Ryan K. Shields, PharmD, MS, Allergan: Advisor/Consultant|Cidara: Advisor/Consultant|Entasis: Advisor/Consultant|GSK: Advisor/Consultant|Melinta: Advisor/Consultant|Melinta: Grant/Research Support|Menarini: Advisor/Consultant|Merck: Advisor/Consultant|Merck: Grant/Research Support|Pfizer: Advisor/Consultant|Roche: Grant/Research Support|Shionogi: Advisor/Consultant|Shionogi: Grant/Research Support|Utility: Advisor/Consultant|Venatorx: Advisor/Consultant|Venatorx: Grant/Research Support David van Duin, MD, PhD, Merck: Advisor/Consultant|Merck: Grant/Research Support|Pfizer: Advisor/Consultant|Qpex: Advisor/Consultant|Roche: Advisor/Consultant|Shionogi: Advisor/Consultant|Shionogi: Grant/Research Support Samantha E. Jacobs, MD, MS, Ansun Biopharma: Advisor/Consultant|Eurofins, Viracor, LLC.: Grant/Research Support Thomas J. Walsh, MD, PhD (Hon), FIDSA, FAAM, FECMM, Abbott Laboratories: Advisor/Consultant|Basilea: Advisor/Consultant|Basilea: Grant/Research Support|Cape Cod Associates: Advisor/Consultant|F2G: Advisor/Consultant|F2G: Grant/Research Support|Omeros: Advisor/Consultant|Omeros: Grant/Research Support|Partner Therapeutics: Advisor/Consultant|Scynexis: Advisor/Consultant|Scynexis: Grant/Research Support|Statera: Advisor/Consultant|T2 Biosystems: Advisor/Consultant|T2 Biosystems: Grant/Research Support Henry Chambers, MD, Merck: Stocks/Bonds (Private Company)|Moderna: Stocks/Bonds (Private Company) Vance G. Fowler, MD, MHS, Affinergy: Advisor/Consultant|ArcBio: Stocks/Bonds (Private Company)|Armata: Advisor/Consultant|Astra Zeneca: Advisor/Consultant|Astra Zeneca: Grant/Research Support|Basilea: Advisor/Consultant|Basilea: Grant/Research Support|ContraFect: Advisor/Consultant|ContraFect: Grant/Research Support|Debiopharm: Advisor/Consultant|Destiny: Advisor/Consultant|EDE: Grant/Research Support|Genentech: Advisor/Consultant|Genentech: Grant/Research Support|GSK: Advisor/Consultant|Janssen: Advisor/Consultant|Karius: Grant/Research Support|MedImmune: Grant/Research Support|Merck: Grant/Research Support|sepsis diagnostics: Patent pending|UptoDate: Royalties|Valanbuio: Stocks/Bonds (Private Company)|Valanbuio: Stocks/Bonds (Private Company) Lars Westblade, PhD, Accelerate Diagnostics, Inc: Grant/Research Support|bioMerieux, Inc: Grant/Research Support|Element Materials Technology: Grant/Research Support|Hardy Diagnostics: Grant/Research Support|Roche Molecular Systems, Inc.: Advisor/Consultant|Roche Molecular Systems, Inc.: Grant/Research Support|Selux Diagnostics, Inc.: Grant/Research Support|Shionogi, Inc: Advisor/Consultant|Talis Biomedical: Advisor/Consultant Michael J. Satlin, MD, AbbVie: DSMB participant|bioMerieux: Grant/Research Support|Merck: Grant/Research Support|Selux Diagnostics: Grant/Research Support|SNIPRBiome: Grant/Research Support

The cefazolin inoculum effect (CzIE), defined here as a cefazolin MIC at high inoculum (107 colony-forming units/mL) ≥16 mg/L in MSSA, has been associated with less favourable clinical outcomes. However, detection of this phenotype is challenging in the clinical microbiology laboratory. We previously described modification of a rapid nitrocefin test using ampicillin disks rather than ampicillin powder for induction of the Staphylococcus aureus β-lactamase (BlaZ). Evaluate the performance of the modified rapid nitrocefin test in a blinded fashion using MSSA isolates recovered from patients with bacteraemia. We evaluated 200 MSSA isolates recovered from Latin American (LA) and North American (NA) hospitals (67 and 133 from NA and LA, respectively). The CzIE was determined using the modified rapid nitrocefin test with ampicillin disks and compared with MIC determination at high inoculum (gold standard). All isolates were subjected to whole-genome sequencing on an Illumina Hi-Seq platform. Performance metrics were calculated for the complete dataset and according to specific BlaZ types. The prevalence of the CzIE was 53% (105/200). Compared with the gold standard, the modified nitrocefin rapid test had a sensitivity of 96% and a specificity of 91.6%, with an overall accuracy of 94%. There were no false-positive results among blaZ-negative MSSA strains. The modified nitrocefin rapid test exhibited a robust performance to detect the CzIE in isolates from the Americas. This methodology is inexpensive and can be implemented in clinical microbiology laboratories around the world, including those with limited resources.

We report two cases of recurrent malaria in U.S. travelers returning from Africa (Ghana and Central African Republic) despite a full course of artemether-lumefantrine (AL). Both patients presented to New York City hospitals, received AL treatment, and clinically improved. Within 2 weeks, they presented with recurrent Plasmodium falciparum malaria. Parasite isolates were sequenced, and P. falciparum kelch 13 propeller domain mutations that are validated or candidate markers of artemisinin partial resistance were not identified. Parasites had mutations within the P. falciparum multidrug resistance protein 1 gene. It is crucial to remain vigilant for recurrent malaria in travelers, even from African regions where partial resistance to artemisinin-based combination therapy has only rarely been reported.

Abstract Background CTB is a currently available oral third-generation cephalosporin that is being developed in combination with the oral prodrug of AVI. In this study, we evaluated the in vitro activity of CTB-AVI against clinical ESBL-like Enterobacterales that were collected from outpatient settings. Methods 156 ESBL-like Enterobacterales isolates were received from 10 US medical centers that processed cultures from affiliated outpatient centers in 2022. Susceptibility tests for CTB-AVI and standard-of-care antibiotics were performed by CLSI broth microdilution method. Isolates were designated ESBL-like based on cefpodoxime MIC ≥2 mg/L for Proteus mirabilis and ceftriaxone MIC ≥2 mg/L for all other Enterobacterales. Fosfomycin disk diffusion was performed on E. coli isolates only and interpreted according to CLSI M100Ed32 guidance. CTB-susceptible breakpoints currently published by CLSI (≤8 mg/L) and EUCAST (≤1 mg/L) were applied to CTB-AVI for comparison. Results Isolates were primarily E. coli (60%) and Klebsiella pneumoniae (16%) and were recovered from patients seen in nursing home/long-term care (38%), urology (21%), and ambulatory care (19%) clinics. Based on CLSI and EUCAST breakpoints, CTB had susceptibility rates of 66% and 32%, respectively. The addition of AVI (fixed concentration of 4 mg/L) to CTB resulted in in vitro potentiation, resulting in 99% (CLSI) and 97% (EUCAST) susceptibility. Susceptibility rates of all isolates against comparator antimicrobials were as follows: cefpodoxime (7%), ceftriaxone (2%), ceftazidime/avibactam (CAZ-AVI) (99.4%), tebipenem (86% at preliminary susceptible breakpoint ≤0.125 mg/L), ertapenem (92.3%), levofloxacin (29%), sulfamethoxazole/trimethoprim (SMX-TMP) (47.4%), and fosfomycin (96%). CTB-AVI had 4-fold lower MIC50/90 values relative to CAZ-AVI (MIC50/90; 0.031/0.25 versus 0.25/1 mg/L). Overall, 100% of levofloxacin and SMX-TMP co-resistant isolates (n=43) were inhibited at CTB-AVI MIC breakpoint concentrations of 8 and 1 mg/L. Conclusion These data demonstrate potent in vitro activity of CTB-AVI against ESBL-like Enterobacterales isolated from patients in US nursing homes and outpatient clinics warranting further studies this oral treatment option. Disclosures April M. Bobenchik, PhD, Becton Dickinson: Grant/Research Support|BioMerieux: Advisor/Consultant|BioMerieux: Grant/Research Support|BioMerieux: Honoraria|Q-Linea: Grant/Research Support|QuidelOrtho: Grant/Research Support|TechLab: Grant/Research Support Lars Westblade, PhD, Accelerate Diagnostics, Inc: Grant/Research Support|bioMerieux, Inc: Grant/Research Support|Element Materials Technology: Grant/Research Support|Hardy Diagnostics: Grant/Research Support|Roche Molecular Systems, Inc.: Advisor/Consultant|Roche Molecular Systems, Inc.: Grant/Research Support|Selux Diagnostics, Inc.: Grant/Research Support|Shionogi, Inc: Advisor/Consultant|Talis Biomedical: Advisor/Consultant Erik Munson, PhD, Hologic, Incorporated: Advisor/Consultant|Hologic, Incorporated: Honoraria David P. Nicolau, PharmD, CARB-X: Grant/Research Support|Innoviva: Grant/Research Support|Innoviva: Honoraria|Merck: Advisor/Consultant|Merck: Grant/Research Support|Merck: Honoraria|Pfizer: Advisor/Consultant|Pfizer: Grant/Research Support|Pfizer: Honoraria|Shionogi: Advisor/Consultant|Shionogi: Grant/Research Support|Shionogi: Honoraria|Venatorx: Grant/Research Support Tomefa E. Asempa, PharmD, FDA/CDER: Grant/Research Support|Paratek: Grant/Research Support|Shionogi: Grant/Research Support|Spero: Grant/Research Support|VenatoRx: Grant/Research Support

Infections caused by carbapenem-resistant Acinetobacter baumannii-calcoaceticus complex (ABC) are associated with high mortality rates and limited treatment options. This study aims to evaluate the in vitro activity of clinically utilized antimicrobials against a contemporary collection of ABC isolates with a predominant carbapenem-resistant phenotype. Geographically dispersed US medical centers (n = 22) provided non-duplicate respiratory and bloodstream ABC isolates for surveillance testing. Antimicrobial susceptibility testing was conducted by broth microdilution and interpreted according to Clinical & Laboratory Standards Institute (CLSI) and Food and Drug Administration (FDA) breakpoints. ABC isolates (n = 523) from respiratory tract (74.4%) and blood (25.6%) sources were recovered from patients (2023-2024). Forty percent were obtained from intensive care unit patients. Carbapenem non-susceptibility was observed in 76.9% of isolates and was more common among respiratory tract cultures. The addition of durlobactam to sulbactam decreased the MIC90 by three-doubling dilutions from 32 to 4 µg/mL, increasing the susceptibility rate to 96.9% from 33.8%. Genome sequencing of sulbactam-durlobactam non-susceptible isolates (16/523; n = 3.1%) revealed MBL and non-enzymatic resistance mechanisms. Cefiderocol inhibited 93.5% and 76.1% of isolates at CLSI and FDA susceptible breakpoints, respectively. Minocycline susceptibility was <50%, while tigecycline and eravacycline MIC50/90 were 1/2 and 0.5/1 µg/mL, respectively. Sulbactam-durlobactam displayed high activity against sulbactam (95.4%), carbapenem (96.3%), and cefiderocol (95.2%) non-susceptible isolates. Susceptibility rates of clinically utilized antimicrobials against a US collection of ABC isolates ranged from 23% to 97%, with meropenem displaying the lowest rate and sulbactam-durlobactam demonstrating the highest overall rate. Sulbactam-durlobactam activity was preserved against sulbactam, carbapenem, and cefiderocol non-susceptible isolates among respiratory tract and bloodstream isolates.

BACKGROUND:Infections are the second leading cause of death in patients with cancer and are often caused by resistant bacteria. However, the frequency of antimicrobial resistance (AMR) in outpatients with cancer is not well understood. We aimed to compare the frequency of AMR bacterial pathogens in outpatients with and without cancer. METHODS:This retrospective cohort study evaluated antimicrobial susceptibility of bacteria isolated from adults (aged ≥18 years) with and without cancer seeking care in 198 outpatient health-care settings in the USA. Data were collected using the BD Insights Research Database. Patients who were not prescribed cancer medications or not admitted to an inpatient cancer unit in the predefined period were categorised as patients without cancer. Patients were included in the cancer cohort if they received medication solely or sometimes indicated for cancer. Data on gender and race or ethnicity were not collected. Non-duplicate and non-contaminant pathogens collected from various samples (ie, blood, intra-abdominal, respiratory, urine, skin or wound, and other) in outpatients were used to assess the coprimary outcomes: overall and source-specific proportions of non-susceptible pathogen isolates with corresponding AMR odds ratios (ORs); and rates of AMR pathogens per 1000 isolates with corresponding AMR incidence rate ratio (IRR) in patients with and without cancer. FINDINGS:Data were collected between April 1, 2018, and Dec 31, 2022. 53 006 (3·2%) of 1 655 594 pathogens identified were from 27 421 patients with cancer and 1 602 588 (96·8%) were from 928 128 patients without cancer. For Pseudomonas aeruginosa, carbapenem non-susceptibility was higher in pathogen isolates from patients with cancer (816 [14·4%] of 5683) than patients without cancer (10 709 [11·3%] 94 419; OR 1·22 [95% CI 1·13-1·32]). For Enterobacterales, fluoroquinolone non-susceptibility was higher in pathogen isolates from patients with cancer (8662 [28·0%] of 30 867) than patients without cancer (238 479 [21·8%] of 1 095 996; OR 1·44 [1·40-1·47]), as was carbapenem non-susceptibility (472 [1·5%] of 30 867 vs 9165 [0·8%] of 1 095 996; OR 1·89 [1·72-2·07]), multidrug-resistant pathogens (2672 [8·7%] of 30 867 vs 48 962 [4·5%] of 1 095 996; OR 2·03 [1·95-2·11]), and extended-spectrum β-lactamase producers (4343 [16·5%] of 26 327 vs 93 977 [9·4%] of 996 853; OR 1·96 [1·90-2·03]). For Staphylococcus aureus, meticillin resistance was higher in pathogen isolates from patients with cancer (4747 [53·0%] of 8959) than patients without cancer (129 291 [48·3%] of 267 520; OR 1·20 [1·15-1·25]). For Enterococcus spp, vancomycin resistance was higher in pathogen isolates from patients with cancer (1329 [18·6%] of 7145) than patients without cancer (12 333 [9·1%] of 135 772]; ORR 2·20 [2·06-2·34). The rates and corresponding IRRs of AMR pathogens per 1000 isolates was also higher in patients with cancer compared with patients without cancer, particularly for carbapenem non-susceptible P aeruginosa (IRR 2·06 [1·91-2·21]) and vancomycin-resistant enterococci (IRR 3·06 [2·89-3·24]). For all comparisons, p<0·0001. INTERPRETATION:AMR proportions and IRRs for most key pathogens were up to three-times higher in isolates from outpatients with cancer than those without cancer, highlighting the need for enhanced surveillance, infection prevention, and timely diagnostic stewardship to improve antibiotic prescribing in this population. FUNDING:AMR Action Fund.

Background and objectives:The β-lactam/β-lactamase inhibitor combinations ampicillin-sulbactam (SAM) and amoxicillin-clavulanate (AMC) are frequently used to treat Enterobacterales infections and are often assumed to be interchangeable, leading some clinical microbiology laboratories to report antimicrobial susceptibility testing (AST) results for only one of these agents. Given differences in β-lactamase inhibition between sulbactam and clavulanate, we hypothesized that the in vitro activities of SAM and AMC may differ. Methods:To understand the prevalence of discordant SAM and AMC susceptibility results in Enterobacterales species, we analysed AST results obtained by broth microdilution (MicroScan WalkAway, Beckman Coulter) for Enterobacterales isolates recovered from clinical specimens between 2018 and 2022 at an academic medical centre in New York City. Results:Percentages of isolates susceptible to SAM were lower than percentages susceptible to AMC for Escherichia coli (58.1% versus 85.4% of 23,746 isolates, P < 0.0001), Klebsiella pneumoniae group (76.7% versus 88.7% of 6,630, P < 0.0001), Proteus mirabilis (88.0% versus 95.4% of 3,185, P < 0.0001) and Klebsiella oxytoca (69.6% versus 90.7% of 890, P < 0.0001). Isolates of E. coli, K. pneumoniae group and P. mirabilis with susceptibility profiles consistent with ESBL production (ceftriaxone resistant and cefoxitin susceptible) were more likely to be susceptible to AMC but not susceptible to SAM than isolates without this susceptibility phenotype (E. coli, 38% versus 27%, P < 0.0001; K. pneumoniae group: 40% versus 10%, P < 0.0001; P. mirabilis: 24% versus 6%, P < 0.0001). Conclusions:The high prevalence of SAM-not susceptible, AMC-susceptible isolates supports reporting AST results for both SAM and AMC to maximize options for antimicrobial therapy and to support antimicrobial stewardship.

BACKGROUND:Obtaining urine cultures (UCx) in the absence of symptoms and inflammation can result in misdiagnosis of urinary tract infections (UTIs) and inappropriate use of antibiotics. Reflex UCx is a diagnostic stewardship strategy in which a UCx is performed only if a urinalysis (UA) meets UTI criteria. We retrospectively applied a reflex UCx algorithm to assess its performance and safety in children. METHOD:From November 1, 2020, to July 23, 2023, we studied children aged >24 months to <18 years with paired UA and UCx, ie, a UTI evaluation, in emergency departments or inpatient units at our 8-hospital network. We assessed the diagnostic performance of pyuria of ≥10 white blood cells (WBC)/high power field (hpf) using a positive UCx as the reference standard; assessed reflex UCx exclusion criteria; and reviewed medical records of children with <10 WBC/hpf and positive UCx for signs and symptoms consistent with clinical UTI. RESULTS:Of 79 960 UA and UCx, 10 226 UTI evaluations were eligible for inclusion. Of the 8.7% (890/10 226) positive UCx, 81.5% (725/890) had UA with ≥10 WBC/hpf, and 18.5% (165/890) had UA with <10 WBC/hpf. The sensitivity of ≥10 WBC/hpf was 81% and the negative predictive value (NPV) was 98%. Of 165 UTI evaluations with positive UCx and <10 WBC/hpf, 26% (43/165) met reflex UCx exclusion criteria, 58 (35%) met neither exclusion criteria nor clinical UTI definition, and 39% (64/165) not meeting exclusion criteria fulfilled the clinical UTI definition, representing 0.6% (64/10 226) of all UTI evaluations. CONCLUSIONS:Retrospective application of a reflex UCx algorithm demonstrated high NPV and sensitivity, suggesting the algorithm had low risk for missing clinical UTIs and could have avoided unnecessary UCx.

Staphylococcus saprophyticus, a common uropathogen, is usually susceptible to urine-concentrating antimicrobials, so routine AST is not recommended by CLSI. Our study evaluated the antimicrobial resistance profiles of 277 S. saprophyticus isolates from North America and a globally diverse cohort. Notably, 24% (67/277) of our isolates come from non-urinary sources. AST was performed against 12 antimicrobials using standard disk diffusion, PCR for mecA and mecC, PBP2a production assays, and cefinase. 5% (13/277) of isolates were mecA positive and cefinase positive, 63% (176/277) were mecA negative but cefinase positive, 4% (11/277) were mecA positive but cefinase negative, and 28% (77/277) were mecA and cefinase negative. All (277/277) isolates were susceptible to delafloxacin, ciprofloxacin, rifampin, linezolid, and nitrofurantoin and 95% (262/277) were susceptible to trimethoprim-sulfamethoxazole. Our results showed that regardless of using CLSI or EUCAST breakpoints oxacillin had low categorical agreement for mecA presence, making it unsuitable for surrogate testing, while cefoxitin disk diffusion had high very major error rate. If possible, PBP2a or mecA testing is recommended for guiding therapy for non-urinary infections. Our work supports CLSI guidelines on routine susceptibility to urinary tract antibiotics.

Background: Infections are a leading cause of death in patients with cancer, but the proportion and rate of antimicrobial resistance (AMR) in hospitalized patients with cancer are not well understood. Methods: This retrospective, cross-sectional evaluation of AMR assessed hospitalized adult patients in 168 United States (US) healthcare facilities between April 2018 and December 2022. Nonduplicate, noncontaminant Gram-negative and Gram-positive bacteria recovered from various samples (blood, respiratory, urine, etc.) were used to assess the rate of AMR pathogens per 1000 admissions and the proportion of AMR among bacterial isolates in patients with and without cancer. Findings: Among 4,612,620 admissions, 6.4% (297,500) were of patients with cancer and 93.6% (4,315,120) were of patients without cancer. AMR pathogen rates were higher in cancer patients than patients without cancer for most pathogen groups, including vancomycin-resistant enterococci with incidence rate ratio (IRR), 1.95 (95% confidence interval [CI], 1.84, 2.07), extended-spectrum beta-lactamase (ESBL) producers (IRR, 1.48 [95% CI, 1.43, 1.53]), carbapenem-nonsusceptible Enterobacterales (IRR, 1.46 [95% CI, 1.32, 1.61]), and multidrug-resistant Pseudomonas aeruginosa (IRR, 1.31 [95% CI, 1.18, 1.45]). The percentage of nonsusceptible isolates in most pathogen groups was lower in patients with versus without cancer except for ESBL producers among Enterobacterales (odds ratio (OR), 1.11 [95% CI, 1.07, 1.15]) and vancomycin resistance among enterococci (OR, 1.22 [95% CI, 1.14, 1.30]), which were higher in cancer patients. Conclusion: AMR rates for certain key pathogens were 1.5-2 times greater in hospitalized cancer patients compared to hospitalized noncancer patients. The increased AMR rate in cancer patients highlights the need for enhanced infection prevention and diagnostic stewardship efforts.

Importance:Trichophyton indotineae is an emerging dermatophyte causing outbreaks of extensive tinea infections often unresponsive to terbinafine. This species has been detected worldwide and in multiple US states, yet detailed US data on infections with T indotineae are sparse and could improve treatment practices and medical understanding of transmission. Objective:To correlate clinical features of T indotineae infections with in vitro antifungal susceptibility testing results, squalene epoxidase gene sequence variations, and isolate relatedness using whole-genome sequencing. Design, Setting, and Participants:This retrospective cohort study of patients with T indotineae infections in New York City spanned May 2022 to May 2023. Patients with confirmed T indotineae infections were recruited from 6 New York City medical centers. Main Outcome and Measure:Improvement or resolution at the last follow-up assessment. Results:Among 11 patients with T indotineae (6 male and 5 female patients; median [range] age, 39 [10-65] years), 2 were pregnant; 1 had lymphoma; and the remainder were immunocompetent. Nine patients reported previous travel to Bangladesh. All had widespread lesions with variable scale and inflammation, topical antifungal monotherapy failure, and diagnostic delays (range, 3-42 months). Terbinafine treatment failed in 7 patients at standard doses (250 mg daily) for prolonged duration; these patients also had isolates with amino acid substitutions at positions 393 (L393S) or 397 (F397L) in squalene epoxidase that correlated with elevated terbinafine minimum inhibitory concentrations of 0.5 μg/mL or higher. Patients who were treated with fluconazole and griseofulvin improved in 2 of 4 and 2 of 5 instances, respectively, without correlation between outcomes and antifungal minimum inhibitory concentrations. Furthermore, 5 of 7 patients treated with itraconazole cleared or had improvement at the last follow-up, and 2 of 7 were lost to follow-up or stopped treatment. Based on whole-genome sequencing analysis, US isolates formed a cluster distinct from Indian isolates. Conclusion and Relevance:The results of this case series suggest that disease severity, diagnostic delays, and lack of response to typically used doses and durations of antifungals for tinea were common in this primarily immunocompetent patient cohort with T indotineae, consistent with published data. Itraconazole was generally effective, and the acquisition of infection was likely in Bangladesh.

A quaternary ammonium and alcohol-based disinfectant with reported continuous activity demonstrated reduced microbial buildup on surfaces over time compared to routine disinfectants without continuous activity in in vitro and hospital studies. We compared these disinfectants in ambulatory settings and found no difference in bioburden on high-touch surfaces over time.

Background: Neonatal intensive care units (NICU) outbreaks caused by methicillin-susceptible Staphylococcus aureus (MSSA) are less commonly reported than outbreaks caused by methicillin-resistant S. aureus. We report an unusual outbreak of MSSA skin and soft tissue infections (SSTIs) in a level IV NICU investigated by whole genome sequencing (WGS) and molecular typing. Methods: An investigation was initiated in a 56-single-bed NICU after four patients developed MSSA SSTIs in Week 1. Case-patients had positive MSSA cultures identified by clinical cultures or surveillance sampling (bilateral nares, axillae, umbilicus, and groin), and antibiotic susceptibility testing was performed. WGS and assessment of isolate relatedness through mutation event analysis and multi-locus sequence typing (MLST) was performed by the NYS DOH. Demographic and isolate characteristics were compared using Wilcoxon rank sum test, Fisher’s exact test and Pearson’s Chi-squared test, as appropriate. Results: From Week 2 to Week 32, 9 rounds of surveillance for MSSA colonization were conducted. In all, 30 case-patients had MSSA colonization and 16 infants developed infections including impetigo (n=7), pustules (n=5), staphylococcal scalded skin syndrome (SSSS, n=2), abscess (n=1), and bacteremia (n=1). All SSTI cases presented on infants’ faces, all of whom were on non-invasive respiratory support. MLST identified 4 distinct types including MLST 121 (n=12), MLST 398 (n=10), MLST 30 (n=6), and MLST 15 (n=6). Eight isolates were unrelated to other isolates. MLST 398 and MLST 30 included isolates not closely related (>9 mutation events). The 12 MLST 121 isolates were closely related (≤9 mutational events between all isolates), harbored the mupA gene, and were mupirocin-resistant (MIC>1024 ug/ml). Clinical infection and mupirocin resistance were associated with MLST 121 (Table 1). Multiple infection control measures were implemented, including increased availability of alcohol-based hand sanitizers, introducing bare-below-the-elbows practice for staff, contact precautions for case-patients, decolonization with mupirocin and chlorhexidine baths, environmental cleaning/disinfection, and removing excess equipment and supplies. No new cases of mupirocin-resistant or MLST 121 SSTIs occurred after Week 25. Conclusion: We report a MSSA outbreak associated with multiple MLST types and a predominant mupirocin-resistant strain. This report highlights the ability of molecular typing to characterize strains causing infections versus colonization and the potential loss of mupirocin as a control measure when outbreaks are caused by mupirocin-resistant strains. WGS analysis allows for increased discrimination of mutation events allowing for improved resolution of case relatedness compared to other typing methods. Successful control of this outbreak was achieved with a multitude of infection prevention and control.