Antimicrobial Agents and Chemotherapy最新文献

Members of the Stenotrophomonas maltophilia complex are intrinsically multidrug-resistant pathogens that disproportionately affect critically ill patients. Aztreonam-avibactam (ATM-AVI), FDA approved in 2025, combines aztreonam (ATM; stable to L1 β-lactamase) with avibactam (AVI; an L2 β-lactamase inhibitor). Aztreonam plus ceftazidime-avibactam (ATM-CZA) has been used as a surrogate for ATM-AVI, but direct comparisons between the two regimens are lacking. Twenty-three clinical S. maltophilia complex isolates underwent broth microdilution (BMD) testing for ATM, ceftazidime, ATM-AVI, and ATM-CZA, with gradient diffusion performed in parallel for ATM-AVI and ATM-CZA. Static 24-h time-kill assays at humanized steady-state Cmax concentrations evaluated bactericidal activity (≥3-log₁₀ reduction). Semi-mechanistic pharmacodynamic modeling characterized growth kill dynamics by resistance determinants (blaL1, blaL2, smeABC). ATM-CZA and ATM-AVI MIC_50/90 values for BMD were 1/2 and 2/4 mg/L, respectively. Both regimens were bactericidal against most isolates, with a mean paired difference of 0.09 log₁₀ colony-forming units (CFU)/mL (P = 0.83). Isolate-level variation was evident: ATM-AVI sustained killing, whereas ATM-CZA permitted regrowth for MD17639, -4.86 vs 0.13 log₁₀ CFU/mL, P = 0.019; MD17061, -2.61 vs 0.64 log₁₀ CFU/mL, P < 0.001). Conversely, ATM-CZA achieved greater reductions in MD17662 (-3.84 vs -1.95; P = 0.026), MD17047 (-4.27 vs -2.64; P = 0.021), and UK4 (-3.47 vs -1.58; P = 0.017). Modeling predicted ATM-AVI benefit in blaL2 and ATM-CZA benefit against blaL1 or smeABC dominant isolates, and diminished activity of both when mechanisms coexisted. ATM-AVI and ATM-CZA show comparable in vitro activity against S. maltophilia complex. Isolate-level heterogeneity warrants further study of genotype-phenotype relationships.

The rapid increase in antimicrobial resistance underscores the urgent need for new antibacterial agents. One promising strategy involves designing novel compounds through targeted chemical modifications of existing antibiotics. Azithromycin (AZI), a widely used macrolide, has served as a versatile scaffold for developing numerous antibacterial candidates. However, the mechanistic consequences of such modifications remain largely unexplored. Here, we characterize the activity and mechanism of action of three AZI-benzoxaborole (AZI-BB) conjugates. We show that these compounds inhibit bacterial translation in vitro and remain active against a model Escherichia coli strain carrying an inducible ermCL-ermC operon, which confers resistance to macrolide antibiotics. Unlike erythromycin, these derivatives, along with AZI itself, exhibit minimal induction of ErmC expression. Structural analysis reveals that the benzoxaborole moiety of AZI-BB2 forms additional interactions with nucleotides C2441 and C2586 of 23S rRNA, likely contributing to premature ribosome stalling at the ermCL regulatory sequence and thereby preventing ErmC expression. Furthermore, high-throughput toeprinting analysis combined with deep sequencing (Toe-seq) demonstrates that AZI-BB2 exhibits reduced sequence specificity for canonical macrolide-sensitive stalling motifs. Altogether, these findings demonstrate that targeted chemical modification of AZI can reshape its context-specific interaction with the ribosome and attenuate the induction of macrolide resistance mechanisms.

Piperacillin-tazobactam (TZP) resistance in Klebsiella pneumoniae involves diverse mechanisms with unclear prevalence and phenotypic impact. To elucidate these mechanisms, we analyzed K. pneumoniae clinical isolates resistant to TZP but susceptible to cefotaxime and cefepime. Among 53 isolates, 14 were further studied by MIC testing for TZP, amoxicillin-clavulanic acid (AMC), and ceftazidime (CAZ). Short-read sequencing was performed for all 14 isolates and long-read sequencing for two. Core-genome MLST showed that all were unrelated. Two had a bla_OXA-1 gene, one also carrying an ompK35 porin gene mutation; two others had the same mutation in the promoter of the chromosomal copy of bla_SHV usually associated with overexpression. In the remaining 10, resistance correlated with plasmid-borne bla_SHV-1 copies. Nine isolates carried bla_SHV-1v1 in the same IS26 pseudocompound transposon (PTn), corresponding to PTnSHV-L and located on a conserved IncFIB(K)_1_Kpn3 plasmid in eight. The tenth isolate carried PTnSHV-L with a distinct bla_SHV-1 variant on both an IncHI1B_1_pNDM-MAR plasmid and a high-copy-number Col-type plasmid. Read depth analysis confirmed that bla_SHV copy number correlated with TZP, AMC, and CAZ MICs. Large-scale database screening identified related IncFIB(K)_1_Kpn3 plasmids, strongly associated with K. pneumoniae and frequently carrying a PTnSHV-L marker. Analysis of a K. pneumoniae genome data set confirmed the frequent co-occurrence of this plasmid and the PTnSHV-L marker in strains with multiple bla_SHV copies. These findings suggest the emergence of an epidemic plasmid adapted to K. pneumoniae and driving TZP resistance through bla_SHV-1 amplification, underscoring the need for genomic surveillance to detect amplification-based resistance overlooked by standard phenotypic or PCR assays.

A novel acquired aminoglycoside resistance gene, aph(3')-IVb, was identified via whole-genome sequencing of a multidrug-resistant Riemerella anatipestifer isolate from a duck. The gene encodes a 262-amino-acid phosphotransferase, APH(3')-IVb, sharing only 39.9% amino acid identity with its closest known homolog, APH(3')-IVa. Heterologous expression of aph(3')-IVb in Escherichia coli and a susceptible R. anatipestifer strain conferred resistance to neomycin, paromomycin, and ribostamycin, a phenotype validated by gene deletion and complementation experiments. Kinetic analysis of the purified APH(3')-IVb enzyme confirmed phosphotransferase activity against these three aminoglycosides, with catalytic efficiencies (k_cat/K_m) ranging from 10⁴ to 10⁵ M⁻¹·s⁻¹. Furthermore, site-directed mutagenesis identified key residues critical for enzymatic function. While the prevalence of aph(3')-IVb in R. anatipestifer isolates was low (1.6%), analysis of public databases identified 93 aph(3')-IVb-positive sequences, of which 36.6% originated from human pathogens. Genetic environment analysis revealed that aph(3')-IVb resides within a genomic resistance island flanked by mobile genetic elements, suggesting its horizontal acquisition. The emergence of this novel enzyme, coupled with its association with mobile elements and distribution among human pathogens, underscores a potential pathway for resistance dissemination across veterinary and clinical environments, posing a significant public health concern.

Staphylococcus capitis NRCS-A is a major cause of neonatal sepsis worldwide and exhibits resistance to multiple antibiotics. We assessed the prevalence and mechanisms of daptomycin resistance (DAP-R) in bloodstream isolates from a German neonatal intensive care unit. Ten of 11 NRCS-A isolates (91%) were resistant to daptomycin, and 18% displayed decreased susceptibility to vancomycin. Genomic analysis revealed diverse polymorphisms in genes associated with DAP-R in Staphylococcus aureus, but no single amino acid variant explained resistance. Phospholipid composition remained unchanged, whereas isolates displayed increased cell surface charge and cell wall thickening. Consistently, BODIPY-labeled daptomycin binding was reduced and more diffusely distributed in DAP-R NRCS-A with weaker septal enrichment. In serial passaging experiments, S. capitis acquired DAP-R more rapidly and robustly than S. aureus or S. epidermidis under subinhibitory concentrations of either daptomycin or vancomycin. Resequencing after in vitro DAP-R evolution in S. capitis identified newly acquired mutations in cell envelope-associated genes, including walK and mprF. These results indicate that S. capitis NRCS-A rapidly evolves resistance via polygenic, cell-envelope-driven mechanisms distinct from those in S. aureus. The high prevalence and adaptive capacity of DAP-R in neonatal isolates raise concern for therapeutic failure in neonatal intensive care.

Candida albicans, a World Health Organization critical-priority fungal pathogen, represents the predominant cause of candidemia. Therapeutic failure is sometimes driven by antifungal tolerance, a phenotype distinct from resistance, whose underlying mechanisms remain incompletely defined. Here, we identify the peroxisomal protein Pex8 as a key regulator of tolerance to both azoles and amphotericin B. Although neither deletion nor overexpression of PEX8 altered minimum inhibitory concentrations, both modifications significantly reduced drug tolerance, as demonstrated by reduced fractional growth (FoG₂₀) and impaired survival under drug pressure. RNA-seq analysis showed that PEX8 overexpression leads to downregulation of ergosterol biosynthesis genes and remodeling of stress-response pathways, suggesting a possible transcriptional basis for the loss of azole tolerance. Complementary lipidomic profiling demonstrated that PEX8 genetic manipulations induce extensive membrane lipid remodeling, characterized by specific alterations in ceramide and lysophospholipid subclasses, thereby revealing an ergosterol-independent mechanism underlying amphotericin B tolerance attenuation. Phenotypically, PEX8 overexpression attenuated serum-induced hyphal morphogenesis and reduced virulence in a Galleria mellonella infection model, consistent with downregulation of hyphal-associated and virulence-related genes. Our findings establish Pex8 as a central coordinator of oxidative stress adaptation, membrane homeostasis, filamentation, and pathogenicity, revealing a promising target for combating antifungal tolerance.

Suraxavir marboxil (GP681, abbreviated as suraxavir) is a novel, orally active small-molecule polymerase acidic (PA) inhibitor for the treatment of influenza. Its active metabolite, GP1707D07, specifically inhibits PA endonuclease activity. Suraxavir has been approved for use in adolescents (≥12 years) and adults with uncomplicated influenza A and B. This non-randomized, open-label, parallel-group phase I clinical trial evaluated the effects of hepatic impairment on the pharmacokinetics (PK) and safety of suraxavir. Subjects with mild or moderate hepatic impairment and matched healthy controls (n = 8 per group) received a single oral dose of 40 mg suraxavir. PK parameters, including maximum plasma concentration (C_max), area under the plasma concentration-time curve from time 0 to last time point of measurable concentration (AUC_0-t), and area under the plasma concentration-time curve from time 0 to infinity (AUC_0-∞), were compared. Compared with subjects with normal hepatic function, the least-squares geometric mean ratios (90% CI) of GP1707D07 in subjects with mild hepatic impairment were 101.50% (72.63%-141.83%) for C_max, 86.98% (69.80%-108.38%) for AUC_0-t, and 87.06% (70.57%-107.40%) for AUC_0-∞. In subjects with moderate impairment, the corresponding ratios were 203.63% (147.50%-281.13%) for C_max, 155.23% (129.11%-186.64%) for AUC_0-t, and 157.26% (131.39%-188.22%) for AUC_0-∞. Mild impairment had minimal effect on GP1707D07 exposure, while moderate impairment increased C_max and AUC by ~1-fold and 0.5-fold, respectively, without resulting in clinically significant changes. A single 40-mg dose of suraxavir was safe and well tolerated in subjects with mild or moderate hepatic impairment. No dose adjustment is required for these populations.CLINICAL TRIALSThis study is registered with ClinicalTrials.gov as NCT05814926.

Thirty-day mortality was similar in a propensity-score-weighted cohort of 73 patients with KPC-producing Enterobacterales infections treated with ceftazidime-avibactam or meropenem-vaborbactam. Emergence of resistance was higher in the ceftazidime-avibactam group (12% vs 0%); putative resistance mechanisms included porin mutations (Klebsiella pneumoniae) and R2 loop structural changes in AmpC (Enterobacter cloacae complex).

The male genital tract (MGT) plays a critical role in HIV transmission and persistence, serving as a viral reservoir and potential site of HIV compartmentalization. While antiretroviral therapy effectively suppresses systemic viral replication, drug penetration into the MGT tissues and semen varies considerably between and within drug classes, potentially leading to subtherapeutic concentrations in the MGT. The organs comprising the MGT have anatomical barriers and express several drug-metabolizing enzymes, resulting in immune privilege, active drug efflux, and site-specific metabolism. These factors may collectively limit antiretroviral efficacy in this compartment. This review discusses the evidence of HIV persistence in MGT organs and provides insight into the anatomical, physiological, and pharmacological considerations to target this viral reservoir. Additionally, we synthesize current knowledge on contemporary antiretroviral pharmacokinetics within the MGT, highlighting differences in drug penetration between and within classes. We identify associations between drug properties (e.g., lipophilicity and protein binding) and distribution into the MGT. Finally, we forecast emerging therapeutic approaches that introduce new pharmacological opportunities and challenges, as well as advanced computational techniques to help us better understand the downstream effects of antiretroviral pharmacology at the site of action. Understanding the interplay between antiretroviral penetration, local inflammation, and viral dynamics is essential for optimizing HIV treatment and prevention strategies. Together, these insights set the stage for targeted studies to guide precision dosing based on local therapeutic exposure thresholds. Addressing remaining knowledge gaps in MGT pharmacology will be essential to overcome anatomical and physiological barriers and achieve sustained viral suppression in the MGT.

COVID-19's main protease (Mpro) unique structure and function, which are conserved among coronaviruses, make it an attractive target for viral inhibition. Limnetrelvir is a novel Mpro inhibitor intended for once-daily administration. The pharmacokinetics, safety, and tolerability results of two phase 1 studies of limnetrelvir are reported herein. These studies consisted of a first-in-human, single-, and multiple-ascending dose study in healthy non-Japanese participants and a single- and multiple-dose study in healthy Japanese participants. Across both studies, a total of 104 participants received limnetrelvir single doses ranging from 200 to 800 mg and multiple doses from 200 to 800 mg QD for 10 days. The harmonic mean half-life of limnetrelvir ranged from 6 to 21 h following a single dose. No clinically significant differences in exposures were observed between Japanese and non-Japanese participants. Limnetrelvir was generally well tolerated in both studies in healthy participants with up to 10 days of dosing, with only mild or moderate adverse events observed.CLINICAL TRIALSThis study is registered with ClinicalTrials.gov as NCT05691699 and NCT06009237.