Antimicrobial Agents and Chemotherapy最新文献

Ceftazidime-avibactam (CAZ-AVI), a novel antibiotic, is effective in treating infections caused by carbapenem-resistant Gram-negative bacteria. However, in patients receiving continuous renal replacement therapy (CRRT), both the pharmacokinetics (PK) and pharmacodynamics (PD) of the drugs can be significantly altered. Currently, there remains a lack of clear guidelines regarding optimal dosing regimens for CAZ-AVI during CRRT. Prospectively, this study evaluated the PK/PD of CAZ-AVI in 21 critically ill patients receiving CRRT. We collected blood samples at 5-7 sampling points within one administration cycle and then determined the total plasma drug concentrations. Phoenix was used to calculate the PK parameters. The clearance at steady state (CL_SS) of patients receiving CRRT was significantly reduced, and drug exposure was also significantly increased compared to healthy subjects. Notably, four patients demonstrated the free minimum plasma concentrations (fC_min) of CAZ exceeding eight times the MIC, and 90.48% (19 cases) of the patients exhibited CAZ plasma concentrations exceeding the neurotoxicity threshold of 104 mg/L. PK/PD analysis indicated that the standard dosing regimen of 2.5 g every 8 hours of CAZ-AVI may pose a risk of excessive drug exposure. In addition, CRRT was the primary elimination pathway for CAZ-AVI in critically ill patients with acute kidney injury receiving CRRT. Significant differences in extracorporeal clearance were observed between continuous veno-venous hemodialysis (CVVHD) and continuous veno-venous hemofiltration (CVVH) for both CAZ and AVI; CVVH demonstrated higher clearance for CAZ and AVI compared to CVVHD. To prevent potential toxic reactions, it is urgent to establish a safer and more rational dosing regimen for patients receiving CRRT.

Increased resistance to β-lactams/β-lactamase inhibitors by mutations in β-lactamase genes, porins, and efflux pumps complicates the management of carbapenem-resistant Klebsiella pneumoniae (CRKP). Polymyxin B (PMB)-based combination therapy is the best alternative treatment for middle and low-income countries that cannot access the latest medicines. It is crucial to know both phenotypic and genotypic characteristics of a pathogen to understand the killing effect of each drug and its combinations. Hence, our objective was to incorporate mechanistic insights gained from resistance mechanisms of each isolate to develop a mechanism-based pharmacokinetic/pharmacodynamic model. Six clinical CRKP isolates with diverse genotypic resistance expressing bla_KPC, bla_NDM, porin, and mgrB mutations were used for static concentration time kill (SCTK) assays to evaluate the rate and extent of killing by monotherapy, double and triple combinations using PMB (0.5-64 mg/L), meropenem (10-120 mg/L), and fosfomycin (75-500 mg/L). Isolate BRKP28 expressed non-functional MgrB (a regulatory protein) and high-level phenotypic resistance (PMB MIC: >128 mg/L). In line with the observed resistance, the model estimated that BRKP28 had a reduced maximum killing rate constant for PMB (3.61 h⁻¹) relative to other isolates. The mechanistic synergy of PMB, due to outer membrane disruption, was incorporated into three isolates with porin mutations. PMB demonstrated 83%-88% mechanistic synergy with meropenem and 81%-98% with fosfomycin. The model further estimated that a very low concentration of PMB (0.49-0.64 mg/L) was sufficient to achieve 50% of the maximum synergy. Simulations using population pharmacokinetic models showed that combination therapy of PMB (1 mg/kg q12h) and fosfomycin (8 g q8h) achieved >73% reduction in area under the bacterial load-versus-time curve across four isolates. The triple combination therapy achieved a 67.7% reduction in non-carbapenamase producing isolate. These findings demonstrates that a low PMB dosing regimen (1 mg/kg q12h) can produce synergistic effects in combination therapy and may be effective in managing infections caused by CRKP, including PMB resistant isolates.

Antimicrobial resistance driven by multidrug-resistant (MDR) Gram-negative pathogens poses a major global threat, contributing to substantial morbidity and mortality. Novel β-lactam/β-lactamase inhibitor combinations, particularly meropenem-vaborbactam (M/V) and ceftazidime-avibactam (C/A), have expanded therapeutic options; however, their comparative efficacy and safety remain uncertain. This meta-analysis compared M/V and C/A in adult patients with MDR Gram-negative infections. MEDLINE, Embase, and Cochrane Central were searched for studies evaluating M/V versus C/A in hospitalized adults. Outcomes included all-cause mortality, clinical cure, and microbiological recurrence; safety was assessed qualitatively. Data were synthesized using Review Manager, with trial sequential analysis (TSA) applied to minimize random error. Five retrospective cohort studies (three full articles and two conference abstracts) comprising 3,280 patients were included, of whom 577 received M/V and 2,703 received C/A. Populations predominantly consisted of older adults aged 57-70 years, with respiratory tract infections being most common. Pooled analyses demonstrated no statistically significant differences between M/V compared to C/A in all-cause mortality (Odds ratio [OR] 0.87; 95% CI 0.69-1.11; P = 0.26; I² = 16%), clinical cure (OR 1.41; 95% CI 0.66-3.03; P = 0.37; I² = 55%), and microbiological recurrence (OR 0.67; 95% CI 0.32-1.40; P = 0.29; I² = 0%). Qualitative synthesis indicated comparable tolerability. TSA for mortality demonstrated insufficient evidence for definitive conclusions. M/V showed no statistically significant difference over C/A; therefore, selection should be guided judiciously based on clinical context. Further studies are needed to define the optimal role of each agent within antimicrobial stewardship frameworks.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a highly conserved bacterial enzyme essential for glycolysis, yet it also plays important non-metabolic, "moonlighting" roles, including host immunomodulation. Here, we describe the generation and characterization of a monoclonal antibody (mAb01) that targets extracellular GAPDH from Streptococcus agalactiae (GBS) and Streptococcus pneumoniae. Using bio-layer interferometry (BLI) and surface plasmon resonance (SPR), we demonstrate that mAb01 binds with high affinity, exhibiting dissociation constants in the low nanomolar range for both antigens. Functionally, mAb01 significantly improves survival in a neonatal murine model of sepsis caused by either GBS or S. pneumoniae, two relevant neonatal pathogens. The addition of mAb01 to ex vivo cultures of human peripheral blood infected with GBS or S. pneumoniae induced a significant decrease in bacterial replication, further supporting its protective potential. These results provide the first demonstration of a high-affinity anti-GAPDH monoclonal antibody that is effective in both in vivo and ex vivo models of streptococcal infection.

Enterococcal bacteremia is a common healthcare-associated infection, associated with significant morbidity and mortality, with the emergence of vancomycin-resistant enterococci further complicating treatment and clinical outcomes. Despite this, long-term estimates of population-based incidence and antimicrobial resistance trends are limited. We aim to describe the burden of enterococcal bacteremia in Victoria, Australia (population 7.0 million), over a 35-year period. We conducted a retrospective analysis of laboratory-confirmed enterococcal bacteremia episodes voluntarily reported to the Victorian Hospital Pathogen Surveillance Scheme database from 1988 to 2022. Population-based incidence was estimated using inverse probability weighting to adjust for inconsistent hospital participation. Incidence per 10,000 hospital admissions was determined for the period 2011-2022. Antimicrobial resistance was calculated as the annual proportion of resistant isolates among all tested isolates. Overall, 11,157 enterococcal bacteremia episodes were identified, mainly Enterococcus faecalis (n = 6,915, 61.9%) and Enterococcus faecium (n = 3,558, 31.9%). Incidence increased from <3 episodes/100,000 population in 1988 to >10 by 2022. Incidence per 10,000 hospital admissions within Victoria has also increased from 2.8 in 2011 to 4 in 2022. Although E. faecalis remained mostly susceptible to tested antibiotics, E. faecium showed persistently high levels of vancomycin resistance, ranging from 50.7% (n = 69/136) to 66.5% (n = 139/209) over the past decade. Increasing incidence and high rates of vancomycin resistance among E. faecium highlight the ongoing clinical and public health challenge posed by enterococcal bacteremia. Applying statistical modeling to account for variability in hospital participation improves the certainty of incidence measures and strengthens the evidence for true increase in disease burden.

Francisella tularensis is a gram-negative, intracellular bacterium that causes the disease tularemia. Tularemia is prevalent in North America, Europe, and Asia and is typically treated with injected and orally administered antibiotics, including streptomycin, gentamicin, doxycycline, and ciprofloxacin, administered for 10 to 21 days. New therapeutic options are required to reduce the potential of a relapse of disease. Inhaled liposomal-encapsulated ciprofloxacin has demonstrated protection in a murine model of tularemia. The efficacy was further assessed in a nonhuman primate model of tularemia. Mixed-sex common marmosets were challenged with F. tularensis by the inhalational route, and the efficacy of ciprofloxacin delivered by either the inhalational (Apulmiq liposomal formulation) or oral route was compared. Antibiotics were initiated either at 24 h post-challenge (post-exposure prophylaxis) or at the onset of fever (treatment) and continued for 7 days. All control (untreated) animals succumbed to infection by 8 days post-challenge. All animals that received antibiotics, by either route, survived the duration of the study, with bacterial clearance in all but one animal that received inhalational ciprofloxacin. Antibiotic treatment also reduced the physiological and immunological responses observed when compared to animals that received no antibiotics. Histological changes in the lungs were less frequent, although mild, resolving lesions were present in animals treated with ciprofloxacin delivered at the onset of fever by either route.

The persistence of multidrug-resistant Acinetobacter baumannii remains a clinical challenge. Cefepime/enmetazobactam is a novel combination with demonstrated activity against extended-spectrum β-lactamase-producing Enterobacterales, but its activity against Acinetobacter has not yet been thoroughly explored. We aimed to assess its activity against Acinetobacter spp., including multidrug-resistant strains producing carbapenem-hydrolyzing class D β-lactamases (CHDLs). We analyzed 208 clinical isolates of Acinetobacter spp., including 67 carbapenem-resistant Acinetobacter baumannii (CRAB). Antibiotic susceptibility testing was conducted with cefepime, sulbactam, and imipenem, alone and in combination with enmetazobactam; the latter was also tested individually. Additionally, MICs of enmetazobactam/durlobactam and sulbactam/durlobactam were determined for CRAB and CHDL-producing A. baumannii ATCC 17978 transformants. PBP binding assays (IC₅₀), molecular docking, simulation studies with the enmetazobactam/OXA-23 adduct, hydrolysis kinetics (k_cat, K_m), and OXA-23 inhibition assays (IC₅₀, k_off, t_₁/₂) were performed to elucidate the mechanism of enmetazobactam and detect reduced susceptibility. Enmetazobactam showed high intrinsic activity against Acinetobacter spp., displaying reduced MICs against carbapenem-susceptible isolates. MIC_50/90 of the enmetazobactam/durlobactam combination was 2/2 mg/L for CHDL-producing A. baumannii. Enmetazobactam exhibited bactericidal activity comparable to sulbactam. Binding assays revealed that the antimicrobial activity is driven by selective affinity for PBP2 (IC₅₀ 3.6 mg/L) and PBP3 (IC₅₀ 4.2 mg/L). OXA-23 readily inactivated enmetazobactam, confirming the major role of CHDLs in resistance to enmetazobactam, via substrate-assisted de-acylation. This study evidences the potent antimicrobial activity of enmetazobactam against A. baumannii via inhibition of PBP2 and PBP3. Its combination with new OXA-type inhibitors (e.g., durlobactam) represents a potential therapeutic alternative for multidrug-resistant A. baumannii.

Ertapenem combination therapy has been shown to expedite the time to blood culture sterilization among patients with MSSA bacteremia. The purpose of this study was to define what proportion of patients sterilizes blood cultures within 72 h of ertapenem combination treatment initiation. This was a retrospective, multicenter study of patients who received ertapenem combination therapy for MSSA bacteremia. Patients were considered to have rapid blood culture sterilization if blood cultures were negative within 72 h of ertapenem initiation and delayed blood culture sterilization if blood cultures remained positive after 72 h of ertapenem initiation. Of the 304 patients with MSSA bacteremia who received ertapenem for combination treatment, 197 met the inclusion criteria. The median (IQR) time to ertapenem initiation from the time of blood culture obtainment was 4 (3-5) days, and 47% (93/197) had definitive endocarditis. Overall, 85% (167/197) had rapid blood culture sterilization. Patients who had delayed blood culture sterilization had a trend toward a higher Pitt Bacteremia Score at the time of blood culture obtainment (2 [0-4] vs 1 [0-2], P = 0.091) and were more likely to have an oxacillin minimum inhibitory concentration of ≥0.5 µg/mL (67% vs 43%, P = 0.015) compared to those with rapid blood culture sterilization. In this large study of patients who received ertapenem combination therapy for MSSA bacteremia, 85% of patients sterilized their blood cultures within 72 h of treatment. These results suggest that a standard 3-day ertapenem course could be a reasonable stewardship strategy for patients initiated on combination therapy for MSSA bacteremia.

The combined use of phages and antibiotics offers an alternative avenue against multidrug-resistant bacteria. We have previously described the synergistic antibacterial effect of the phage pB23 and meropenem combination against carbapenem-resistant Acinetobacter baumannii (CRAB). The study uncovers the underlying molecular mechanism of phage resistance in CRAB mediated by a novel stop-gain mutation in the gene gtr9. Through phenotypic characterization of pleiotropy, including reduction of capsular polysaccharide production and biofilm formation caused by the mutation in gtr9, we revealed an evolutionary trade-off mechanism whereby phage-resistant CRAB exhibits reduced carbapenem resistance. The zebrafish infection model demonstrated that these phage-resistant mutants were attenuated in virulence in vivo. Throughout continuous passage experiments in vitro, gtr9 mutants displayed the stability of decreased growth rate, phage resistance, and virulence reduction. The combination therapy between phage pB23 and meropenem in different matrices exhibited consistent synergistic antibacterial activity in vitro, demonstrating its potential therapeutic in vivo. Collectively, our study reveals a trade-off mechanism underlying phage-antibiotic synergy, thereby providing a novel insight into bacterial resistance evolution and demonstrating the therapeutic potential of this approach against CRAB infections.

The development of new regimens to treat tuberculosis (TB), the disease caused by Mycobacterium tuberculosis, is critical to improving patient outcomes and decreasing global infectious disease mortality. Early evaluation of candidate regimens in non-clinical models of TB, such as the relapsing mouse model (RMM), remains an important step in prioritizing the most efficacious regimens for further clinical evaluation. Although RMM studies may be informative, they are also animal-, labor-, and time-intensive to complete and represent a significant investment in time and resources during non-clinical development. Given the strong pipeline of regimens in development, identification of "leaner" RMM studies may have a significant impact on resource utilization, and hence we compared alternative study designs to identify study attributes that can be modified to improve resource use, particularly animal use. By simulating relapse outcomes from "virtual" studies (i.e., groups of mice treated for selected durations with control and hypothetical anti-TB regimens) followed by model-based analysis of the simulated data, we were able to compare the "true" (input) values with model estimates of time to 95% cure probability (T₉₅) and assess bias and precision of competing designs. Using this approach, we demonstrated that 28% fewer mice could be used in RMM studies while maintaining low bias and a precision for T₉₅ estimation within ±1-2 weeks for most regimens. Therefore, it is expected that RMM studies based upon the alternative designs evaluated herein may be employed to promote improved animal stewardship while generating informative data for decision-making.