Antimicrobial Agents and Chemotherapy最新文献

Vancomycin remains a key treatment for infections caused by β-lactam-resistant gram-positive cocci. While there is unanimity that only drug not bound to plasma proteins is pharmacologically active, a wide range of values and interdependencies for the unbound fraction (f_u) of vancomycin have been reported in the past. In the present study, we evaluated 706 plasma samples from 228 adult in-patients who were sent for therapeutic drug monitoring. Total and free concentrations of vancomycin were analyzed by a validated method using ultrafiltration and HPLC-UV. Covariate effects on f_u were assessed by a linear mixed-effects model. The mean unbound fraction was 72.2 ± 5.5% (coefficient of variation 7.7%, range 53-93%), the intra-individual and inter-individual variability were low (median coefficient of variation 5.7% and 6.4%, respectively). The unbound fraction was independent of total vancomycin, plasma albumin or total protein concentrations, or other biochemical or demographic variables, and did not differ between patients treated inside or outside of intensive care (P=0.465). Linear mixed-effects modeling confirmed low overall variability (coefficient of variation 7.0%), decomposed into 2.2% inter-individual, 3.8% inter-occasion, and 5.5% residual variability. Method comparison showed an excellent agreement between high-performance liquid chromatography with ultraviolet detection (HPLC-UV) and the immunoassay used for routine drug monitoring (bias +0.2%). Free concentrations of vancomycin can be reliably predicted from total concentrations. An unbound fraction of approximately 70% provides a robust and clinically useful estimate. Remaining variability appears to be primarily methodological, and not of clinical relevance.

Azithromycin is widely used to treat Chlamydia trachomatis infections, yet the extent of resistance to the drug across the species has not been addressed. We surveyed mutations and substitutions linked to putative azithromycin resistance across 1,349 high-quality C. trachomatis genomes. Mutations in the rplV gene encoding three non-synonymous substitutions, compared with the canonical C. trachomatis reference strain D//TW-3/Cx sequence, were found to be common but largely conserved within phylogenetic lineages causing prevalent urogenital and anorectal infections and lymphogranuloma venereum. However, no mutations were identified in the ocular lineage. Time-scaled phylogenetic analysis suggested that these mutations predate the clinical introduction of azithromycin. In contrast, no consistent resistance-associated patterns were observed in 23S rRNA or rplD genes. This large-scale genomic surveillance provides critical insights into the evolutionary trends of putative azithromycin resistance in C. trachomatis and underscores the importance of integrating genomic monitoring with phenotypic susceptibility testing to accurately assess and manage antimicrobial resistance.

Current recommendations for daptomycin dosing are based on body weight. However, it can be hypothesized that dosing based on renal function may improve the attainment of recommended pharmacokinetic (PK)/pharmacodynamic (PD) targets. The aim of this study was to develop a population pharmacokinetic model of daptomycin and propose an individualized dosing strategy to optimize target attainment. Therapeutic drug monitoring data from adult patients treated with daptomycin at a single center between 2022 and 2025 were analyzed using a nonlinear mixed-effects modeling. Monte Carlo simulations were then employed to identify the optimal dosing strategy that maximizes the probability of attaining the PK/PD target. A total of 143 daptomycin serum concentrations from 31 patients were included in the analysis. Estimated glomerular filtration rate (eGFR) was identified as the most predictive covariate for daptomycin pharmacokinetics. In a patient with an eGFR of 90 mL/min, the estimated volume of distribution and clearance of daptomycin were 11.47 L and 0.69 L/h, respectively. An eGFR-guided dosing nomogram was proposed, and simulation results demonstrated that this approach outperformed conventional weight-based dosing in achieving the PK/PD target. These findings support the use of an initial loading dose and individualized maintenance dosing based on eGFR to improve the efficacy and safety of daptomycin therapy.

Staphylococcus argenteus, a member of the S. aureus complex, is increasingly recognized as a globally distributed pathogen with significant clinical relevance. Among its lineages, sequence type (ST) 2250 has emerged as the most prevalent and geographically widespread, yet its evolutionary history and genomic adaptations remain incompletely understood. In this study, we conducted a comprehensive genomic analysis of 277 ST2250 genomes from 26 countries between 2008 and 2025, integrating 14 newly sequenced isolates from China. Phylogenetic reconstruction resolved a basal clade I around 1989 and sister clades II and III that diversified later, in approximately 1996 and 1997, with frequent cross-regional, intercontinental, and cross-host transmission events. A methicillin-resistant S. argenteus subclade within clade II likely arose from a single SCCmec IVc acquisition, accompanied by a blaZ-carrying plasmid. Clade III genomes carried a related multidrug-resistant (MDR) plasmid encoding blaZ, tet(L), and aph(3')-III; Bayesian phylogenetic inference indicated that this plasmid was introduced into the ancestor of the clade III MDR subclade around 2001, potentially promoting its subsequent expansion. Both clades also exhibited enriched virulence profiles, particularly the secretion system gene esaG7. Despite the widespread presence of active defense systems that might limit the acquisition of mobile genetic elements, the ST2250 pan-genome remains open, with evidence of active gene flux and convergent selection targeting resistance, virulence, and metabolic pathways. These findings elucidate the global spread, ecological plasticity, and adaptive evolution of ST2250, providing critical genomic insights into the emergence and persistence of this lineage.

An exposure-efficacy analysis of the phase 3 RESTORE-IMI 2 study (NCT02493764) evaluated the relationship between plasma exposure of imipenem and relebactam and key efficacy endpoints (primary: 28-day all-cause mortality [ACM]; secondary: clinical response at early follow-up [EFU; 7-14 days after the end of treatment]) in adult participants with hospital-acquired bacterial pneumonia (HABP) or ventilator-associated bacterial pneumonia (VABP) who received imipenem/cilastatin/relebactam 500/500/250 mg (IMI/REL). Participants from the IMI/REL treatment group in the microbiological-modified intent-to-treat population who had pharmacokinetic (PK) data and relevant baseline pathogen susceptibility data available were included (N = 211). Previously developed population PK models were used to derive steady-state imipenem and relebactam exposures. Exposures were analyzed against the primary and secondary endpoints overall and by the most common key pathogens identified during RESTORE-IMI 2 (Pseudomonas aeruginosa, Klebsiella pneumoniae, Acinetobacter calcoaceticus-baumannii complex, and Escherichia coli). Most participants (82.0%; n = 168/205) achieved the imipenem exposure target, and 83.9% (n = 177/211) achieved the relebactam exposure target. ACM was 16.1% overall; 11% among participants who met the imipenem exposure target, and 18% among those who met the relebactam exposure target. At EFU, 62.1% of participants experienced a favorable clinical response. Efficacy was similar across the overall exposure range and by key pathogens. There were no apparent trends in ACM rates by imipenem or relebactam exposure distributions overall or by individual key pathogens, suggesting an exposure-efficacy plateau. These results further support the recommended and currently approved IMI/REL 500/500/250 mg dosing regimen for patients with HABP/VABP.

Achromobacter xylosoxidans harbors robust intrinsic and acquired resistance mechanisms and is responsible for severe nosocomial infections in high-risk individuals. Here, we investigated the effectiveness of β-lactam antibiotic combinations against three sequentially collected A. xylosoxidans isolates from a pediatric patient with chronic myeloid leukemia, which were previously genotyped and sequenced to assess and characterize the evolution of resistance. The time course killing activity from in vitro static concentration time-kill (SCTK) assays and genomics of these longitudinally collected isolates guided the development of an in silico mechanistic pharmacokinetic/pharmacodynamic (PK/PD) model. As previously described, the sequentially collected A. xylosoxidans isolates developed resistance to meropenem and ceftazidime/avibactam during treatment, along with reduced susceptibility to cefiderocol, driven by the acquisition of β-lactamase genes, point mutations, and increased β-lactamase expression. Building on these findings, SCTK assays showed that the combination of ceftazidime/avibactam and cefiderocol achieved ≥2-log reductions in bacterial colony-forming units. The PK/PD model included two bacterial subpopulations, one resistant to ceftazidime but susceptible to cefiderocol and another resistant to both. Avibactam's mechanistic synergy restored ceftazidime activity. However, the acquisition of resistance genes and mutations led to a 14-fold and 1.5-fold reduction in susceptibility to ceftazidime/avibactam and cefiderocol, respectively. Simulations with the developed model at clinical exposures revealed that this combination had bactericidal activity, and the infusion duration was a critical driver of efficacy. These findings underscore the therapeutic promise of combining ceftazidime/avibactam with cefiderocol for managing complex A. xylosoxidans bacteremia and highlight the potential of integrated mechanism-based modeling to guide treatment strategies in resistant infections.

Brucellosis, caused by Brucella spp., is a globally zoonotic disease that results in substantial economic losses and public health concerns. Although antibiotic-resistant Brucella strains have been reported worldwide, the current status and underlying mechanisms of resistance among Chinese isolates remain poorly characterized. In this study, we analyzed 636 clinical human isolates of B. melitensis from China using genomic sequencing, transcriptomic sequencing, and neural network prediction to identify key determinants and mechanisms of antibiotic resistance. Functional validations were performed using gene editing and protein-protein interaction assays. We found a gradual increase in resistance to trimethoprim-sulfamethoxazole (SXT) among Chinese isolates in recent years, despite the absence of known antibiotic resistance genes. Comparative genomic analyses between high- and low-minimum inhibitory concentration (MIC) isolates revealed specific single nucleotide polymorphisms (SNPs) that were present only in high-MIC isolates. Transcriptomic analysis demonstrated that high-MIC and low-MIC isolates activated distinct metabolic pathways in response to SXT exposure. Notably, genes influenced by specific SNPs exhibited opposing expression patterns after SXT treatment. Gene-editing experiments revealed that deletion of the glycoside hydrolase family 25 (GH25) gene, which was identified through SNP analysis, was associated with SXT resistance and notably altered Brucella energy metabolism, although it did not impact virulence in host cells. Further, we identified a direct interaction between GH25 and XylF. Collectively, our study reveals a novel genetic mechanism driving SXT resistance in B. melitensis. These findings highlight the critical need for vigilant surveillance of antibiotic resistance to mitigate public health risks associated with the potential widespread emergence of antibiotic resistance.

Chagas disease, caused by Trypanosoma cruzi, remains a leading cause of heart failure in Latin America, with current treatments limited to acute-phase efficacy, significant toxicity, and emerging resistance. Inosine monophosphate dehydrogenase (IMPDH) is an essential enzyme in guanine nucleotide salvage pathway and represents a promising alternative target. Here, we combined computational screening, biochemical and cell-based phenotypic assays that support T. cruzi IMPDH (TcIMPDH) as a druggable target and identify repurposing opportunities among clinical-stage inhibitors. Using Tanimoto similarity scoring against the library of 222 Chagas Box compounds, we identified TCMDC-143376 as uniquely similar to the clinical IMPDH inhibitors merimepodib and AVN-944. Phylogenetic analysis and multiple sequence alignment confirmed conservation of both catalytic and allosteric residues-drawn from T. foetus and T. brucei structures-within TcIMPDH. Recombinant TcIMPDH kinetics revealed Michaelis constants of 155 µM for IMP and 292 µM for NAD⁺. Biochemical IC₅₀ assays showed submicromolar inhibition by AVN-944 (0.20 µM), (S)-Merimepodib (0.21 µM), and (R)-Merimepodib (0.37 µM). In H9c2 cardiomyoblasts infected with intracellular amastigotes, AVN-944 achieved the lowest EC₅₀ (0.4 µM), outperforming benznidazole (EC₅₀ = 3.0 µM) and other inhibitors. Our findings support TcIMPDH as a promising alternative drug target for Chagas disease and position AVN-944 as a compelling candidate to evaluate this therapeutic strategy in animal models.

Roseomonas mucosa is an opportunistic bacterium found in clinical and environmental samples that primarily affects immunocompromised patients. Treatment is challenging owing to the lack of standardized susceptibility testing methods, breakpoints, and variable antimicrobial resistance profiles published. This study evaluated different antimicrobial susceptibility testing approaches and searched for new insights into resistance mechanisms, especially against third-generation cephalosporins. Antimicrobial susceptibility profiles of a panel of 17 R. mucosa strains were analyzed using disk diffusion method (DDM), broth microdilution (BMD) method, and MIC gradient strips. Discrepancies between susceptibility methods were further explored using beta-lactamase inhibitors, whole-genome sequencing, and transcriptomic analyses. Antimicrobial susceptibility testing revealed high susceptibility to aminoglycosides, fluoroquinolones, and carbapenems, while resistance to many beta-lactams was detected. Significant discrepancies were observed between the DDM and BMD methods, particularly with respect to the use of third- and fourth-generation cephalosporins and aztreonam. Genomic analysis identified two putative class-A and one class-C beta-lactamases within all strains. Transcription of one class A beta-lactamase, controlled by an lysR regulator, was significantly induced by cephalosporins and explained the phenotype observed. This study provides the antimicrobial susceptibility profiles against a large panel of antibiotics from 17 R. mucosa strains. It also explained the deep discrepancies between phenotypic approaches regarding cephalosporins.

Pan-drug-resistant Acinetobacter baumannii (PDR-AB) causes severe infections and constitutes a threat in several geographic regions. Little is known about the differential effectiveness of last-resort regimens, frequently used in this setting. We compared the effectiveness of two literature-proposed regimens against PDR-AB infections consisting of colistin, ampicillin-sulbactam, and either meropenem (regimen A) or tigecycline (regimen B). This is a retrospective analysis of prospectively collected data from 12 centers on adult patients with hospital-acquired pneumonia (HAP) or bloodstream infection (BSI), who had received definitive treatment with either regimen A or regimen B. The primary outcome was clinical failure, defined as any of the following occurring by day 14 from infection onset: death, initiation of salvage treatment, treatment withdrawal due to toxicity, persistent bacteremia for BSI patients and failure to improve oxygenation for HAP patients before and after propensity matching. Eighty-three patients were included in the primary analysis; 60 had received regimen A and 23 regimen B. Regimen B was significantly associated with clinical failure before and after propensity matching (odds ratios [OR]: 3.11; 95% confidence interval [CI]: 1.10-8.84 vs OR: 3.83; 95% CI: 1.26-11.63), respectively. Salvage therapy and treatment discontinuation due to toxicity were more frequent in patients treated with regimen B. In multivariable analysis, regimen B was independently associated with 28-day mortality before (hazard ratio [HR]: 2.53; 95% CI: 1.08-5.94) but not after propensity matching (HR: 2.64; 95% CI: [0.99-7.02]). Treatment with colistin, ampicillin-sulbactam, and meropenem against severe PDR-AB infections was associated with favorable outcomes compared to colistin, ampicillin-sulbactam, and tigecycline.