Mycobacterium tuberculosis (Mtb) evades host defenses by inhibiting phagosome acidification in part through the secreted phosphatase PtpA, binding to the vacuolar ATPase (v-ATPase), and disrupting downstream cellular events. We investigated the antimicrobial effects of three v-ATPase inhibitors, Bafilomycin A1 (BafA1), Bafilomycin D, and Cladoniamide B (ClaB), on the growth of Mtb, M. abscessus (Mabs), and M. bovis BCG in THP-1 and murine infection models. We found potent inhibition of intracellular growth with MIC50 in the nanomolar range, with compounds showing a bacteriostatic inhibition of Mtb growth in THP-1 macrophages. Axenic bacteria were not affected by 2 µM compound in broth, although lysate from macrophages incubated with ClaB resulted in a 50% reduction in bacterial growth in broth, which was further enhanced by the addition of zinc. We further discovered that BafA1 amplifies the cytotoxic effects of Mtb infection and limits Mtb's ability to delay apoptosis in host cells. BafA1 antimicrobial activity was abolished in Mtb PtpA knockout mutant, and BafA1 binding to PtpA was shown via an in vitro thermal shift assay. Our findings reveal a complex interplay between v-ATPase inhibition, host cell responses, and bacterial survival, challenging traditional views on phagosome acidification in pathogenesis and suggesting novel avenues for host-directed therapies against intracellular mycobacterial infections.

Imipenem-relebactam demonstrates in vitro activity against multidrug-resistant (MDR) Pseudomonas aeruginosa, but real-world effectiveness data are limited. MIRAGE was a multicenter, retrospective, observational study of imipenem-relebactam for MDR P. aeruginosa pneumonia and bacteremia. Patients were included if they received imipenem-relebactam for >48 h within 7 days of index P. aeruginosa culture. The primary outcome was clinical success at day 30, defined as survival, resolution of signs and symptoms of infection, completion of intended treatment course, and absence of recurrent infection. Secondary outcomes included 30- and 90-day mortality, infection recurrence, and development of non-susceptibility. Sixty-three patients were included. Median (IQR) age was 61 (51-70) years, and the median Charlson Comorbidity Index was 5 (3-6). Forty-six percent of patients had an immunocompromising condition, 79% were in the intensive care unit, 76% were receiving mechanical ventilation, and 48% required vasopressors. Median SOFA score was 7 (5-12). Forty percent of index isolates that were tested displayed non-susceptibility to both ceftolozane-tazobactam and ceftazidime-avibactam. Fifty-six percent of patients achieved clinical success at day 30. All-cause 30- and 90-day mortality rates were 18% and 29%, respectively. Recurrent infections were documented in 37% of patients within 90 days, and resistance developed in 39% (16/41) of evaluable patients. Clinical outcomes following imipenem-relebactam for treatment of MDR P. aeruginosa were comparable to those reported in real-world studies for other novel β-lactam agents. Our data suggests that imipenem-relebactam has a role in the treatment of patients infected with MDR P. aeruginosa.

Carbapenemase-producing Enterobacter cloacae complex (CPEC) represents an emerging threat in healthcare settings; however, its spread across local and regional hospitals remains elusive. Between 2014 and 2022, 211 non-duplicate E. cloacae complex isolates (ECC) with reduced carbapenem susceptibility based on automated susceptibility testing were collected from 58 hospitals in 14 prefectures across Japan. PCR detected the blaIMP-1 group in 92.9% of isolates. Among these, 80 representative CPEC isolates underwent whole-genome sequencing. Two dominant high-risk clonal groups, ST78 and ST133 (including single-locus variants), accounted for 62.5% of sequenced isolates. Notably, ST133-rarely reported in Japan-was the second most common type and detected widely, suggesting gradual and inconspicuous dissemination. ST78 exhibited substantial genomic diversity, frequent co-carriage of extended-spectrum beta-lactamase genes, and multiple plasmid replicons, while ST133 formed a more uniform lineage with limited resistance determinants. Most isolates remained highly susceptible to amikacin and cefiderocol. Core-genome multi-locus sequence typing suggested possible intra-facility persistence and inter-facility transmission of closely related strains (≤10 allele differences) in some hospitals over time. Among the 46 facilities with blaIMP-1 group-positive isolates, 73.9% (34/46) were small hospitals (<200 beds). The proportion among screened ECC isolates was similarly high in small and large hospitals (90.5% vs 94.8%), with no significant difference, suggesting the need to extend molecular surveillance even in resource-limited settings. These findings highlight the utility of molecular confirmation and targeted genomic analysis, particularly in regions or settings where high-risk CPEC clones may circulate undetected, to support timely detection and containment efforts.

In our institution, therapeutic drug monitoring of daptomycin is performed routinely and cases of high trough concentrations have been observed in patients without known risk factors. The aim of this study was to identify risk factors of daptomycin overexposure. We performed a case-control study of daptomycin overexposure in patients who received daptomycin between 2013 and 2021. Cases and controls were defined as patients with trough concentration (Cmin) ≥60 mg/L and Cmin <60 mg/L, respectively. Univariate and multivariate analyses were performed with logistic regression models. Retained variables were further analyzed by subgroup analysis and comparison of the pharmacokinetic parameters of daptomycin. We analyzed data from 78 and 26 patients in the control and case groups, respectively. The male-to-female ratio was 1.5. The median (interquartile range) of age, body weight, and creatinine clearance was 66.5 (55-77) years, 77 (65-96) kg, and 98.5 (53-124) mL/min, respectively. Increasing body mass index (BMI) and co-administration of irbesartan were identified as risk factors of daptomycin overexposure with odds ratio (OR) (95% confidence interval [CI]) of 2.9 [1.4-6.2], and 6.1 [1.1-40.8], respectively, whereas increasing creatinine clearance was associated with decreasing risk, with OR of 0.16 [0.05-0.35]. The influence of BMI was attributed to the non-linear relationship between body weight and daptomycin PK parameters and the use of weight-based dosing in patients with high BMI. In addition to renal impairment, high BMI and irbesartan co-administration may be associated with an augmented risk of daptomycin overexposure. Dosing based on actual body weight should be avoided in obese patients.

Invasive pulmonary aspergillosis (IPA), mainly caused by A. fumigatus, remains a life-threatening fungal infection, with rising reports of infections caused by resistant species such as Aspergillus lentulus and Aspergillus calidoustus. EL219 (formerly known as SF001) is a novel, next-generation polyene with enhanced ergosterol selectivity and reduced nephrotoxicity. We evaluated the efficacy of EL219 compared to liposomal amphotericin B (LAMB) in vitro using the Clinical Laboratory and Standards Institute M38 methodology and in immunosuppressed murine models of IPA caused by A. fumigatus, A. lentulus, and A. calidoustus. Immunosuppressed ICR mice were infected via inhalation (A. fumigatus) or via intratracheal instillation (A. lentulus and A. calidoustus), then treated intravenously once daily with placebo, EL219 (0.3, 1.5, 7.5, and 30 mg/kg), or LAMB (5 mg/kg) starting 16 h post-infection. Treatment lasted 4 days (A. fumigatus and A. lentulus) or 7 days (A. calidoustus). Survival through Day 21 and lung fungal burden at Day 4 were assessed. EL219 showed enhanced in vitro activity against A. lentulus and A. calidoustus compared to LAMB. EL219 significantly improved survival in a dose-dependent manner, with 30 mg/kg outperforming LAMB. EL219 also resulted in >5-log fungal burden reductions in A. fumigatus-infected lungs. EL219 demonstrated broad-spectrum efficacy, improved survival, and reduced lung fungal burden, supporting its potential as a novel therapy for IPA.

Piperacillin-tazobactam is widely used off-label in neonates for the empirical treatment of severe infections, resulting in diverse dosing regimens across clinical settings. This variability, combined with high interindividual differences in renal maturation that impact drug disposition, complicates standardized dosing and emphasizes the need for individualized, evidence-based strategies. This study aimed to develop and evaluate a population pharmacokinetic model of piperacillin in neonates to support optimized initial dosing recommendations. Neonatal patients (postnatal age ≤28 days) admitted to an intensive care unit who received piperacillin-tazobactam (8:1 ratio) at Neofax-recommended doses were included. Plasma concentrations were measured using an ultra-high-performance liquid chromatography with tandem mass spectrometry method. Population pharmacokinetic analysis for piperacillin was performed using nonlinear mixed-effects modeling. A total of 65 blood samples were collected from 25 neonates, both preterm (56%) and full-term. Piperacillin pharmacokinetics was best described by a one-compartment model incorporating body weight-based allometric scaling, postmenstrual age, and serum creatinine as covariates influencing clearance. For a typical neonate in the study (1.76 kg), the estimated clearance was 0.748 L/h (coefficient of variation, 38.3%), and the volume of distribution was 0.866 L (37.7%). Simulations indicated adequate probability of target attainment with current recommendations, but a high proportion of preterm neonates (>75%) were at risk of overexposure (trough piperacillin plasma concentration >50 mg/L). Additional simulations supported individualized initial regimens based on renal maturation and suggested that extended infusions (1-4 h) may improve target attainment for stricter targets and less-susceptible pathogens. This study provides a validated pharmacokinetic model for piperacillin in neonates with severe infections, offering a framework to optimize empiric dosing based on renal function and developmental stage.

HRS-8427, a novel siderophore cephalosporin antibiotic, is under development for treating Gram-negative infections. This study evaluated the intrapulmonary penetration and pharmacokinetic (PK) profile of HRS-8427 injection following single and multiple dose administrations in healthy Chinese subjects. A single-center, randomized, open-label Phase 1 trial enrolled 38 subjects, with 35 completing the study. In the single-dose group, subjects received a 1,500 mg intravenous infusion of HRS-8427 over 2 h. In the multiple-dose group, subjects were administered 2,000 mg of HRS-8427 intravenously every 8 h for four consecutive doses, each infused over 2 h. Bronchoalveolar lavage (BAL) was conducted to collect epithelial lining fluid (ELF) and alveolar macrophage (AM) specimens. PK analysis demonstrated a maximum plasma concentration (Cmax) of 176 µg/mL and an area under the time-concentration curve from time zero to time infinity (AUC0-∞) of 942 h·μg/mL following the single 1,500 mg dose. After multiple 2,000 mg dosing, the Cmax increased to 262 µg/mlL with a corresponding AUC0-∞ of 1,640 h·μg/mL. The ELF-to-plasma concentration ratio (CELF/Cplasma) exhibited a time-dependent increase, reaching 12.2% at 8 h post-final dose. Intracellular accumulation in AM remained minimal (<1%). Multiple-dose administration resulted in higher ELF exposure than single dosing. Safety assessments indicated an overall favorable tolerability profile, with most adverse events being mild in severity. Based on PK and microbiological data, a 2,000 mg regimen achieved concentrations exceeding the MIC₉₀ values of major Gram-negative pathogens, supporting further clinical development of HRS-8427 for respiratory and other Gram-negative bacterial infections.CLINICAL TRIALSThis study is registered with Chinese Clinical Trial Registry Platform as ChiCTR2300072350.

The widespread emergence of multidrug-resistant (MDR) Gram-negative bacteria prompted the reintroduction of polymyxins in the clinic despite their adverse effects. Ongoing research is primarily focused on the development of non-nephrotoxic and -neurotoxic polymyxins as not only standalone agents but also as potentiators that enhance the activity of a partner antibiotic. Safer derivatives of polymyxin B3, a minor component of polymyxin B, were synthesized and utilized as a potentiator of multiple antibiotics. Compound 1, consisting of Dap residues, was nontoxic to kidney cells and is a promising outer membrane permeabilizer that synergized with six different classes of antibiotics against MDR Gram-negative bacteria. Compound 1 extended the activity spectrum of rifampicin, zoliflodacin, and pristinamycin by lowering the minimum inhibitory concentrations of these antibiotics below their interpretative susceptibility breakpoints in MDR Pseudomonas aeruginosa, Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, and Enterobacter cloacae. Notably, the novel combination of zoliflodacin, a first-in-class antibiotic in phase III trials for gonorrhea, and compound 1 exhibited potent bactericidal activity in MDR P. aeruginosa and A. baumannii.

Mycobacterium abscessus (MAB), a rapidly growing non-tuberculous mycobacterium, is becoming increasingly recognized as a significant pathogen affecting humans. These bacteria particularly impact individuals with cystic fibrosis (CF), non-CF bronchiectasis, and compromised immune systems. Treating pulmonary infections with MAB is challenging due to the bacteria's inherent and acquired resistance to many antibiotics, including most anti-tuberculosis antibiotics. Antibiotic therapy of MAB infection is lengthy, involves multiple oral and parenteral administered drugs, induces significant toxicity, and, on many occasions, fails to cure. Consequently, developing more effective antibiotics has become a high priority. Preclinical studies to evaluate antibiotic efficacy against MAB are challenging because they fail to establish a progressive and sustained pulmonary infection in commonly used animal models. To address this issue, the course of MAB pulmonary infection was evaluated in 15 immunocompetent or deficient mouse strains. We report bacterial burden and histopathology and classify the models according to their ability to clear or sustain progressive infection beyond 28 days. We also examined the potential of these models for drug screening. Our findings provide a foundation for selecting suitable mouse models of pulmonary MAB infection for drug discovery.