Search Results (491)

Aeromonas veronii is a widely distributed opportunistic aquatic pathogen associated with diseases in freshwater fish. Despite the ecological and conservation significance of Diptychus maculatus, a protected cold-water fish inhabiting high-altitude ecosystems, information regarding its associated bacterial communities remains limited. This study aimed to isolate and characterize A. veronii recovered from D. maculatus and provide baseline information on its occurrence and phenotypic characteristics. Eight bacterial isolates were recovered from various tissues, including skin, gills, eye, intestine, dorsal fin, body kidney, gonad, and spleen of randomly sampled fish individuals from Xinjiang, China. Phenotypic and biochemical characterization, together with 16S rRNA sequencing, supported their identification as A. veronii, while gyrB analysis of a representative isolate provided additional species-level confirmation. Antimicrobial susceptibility testing revealed a consistent multidrug-resistance phenotype among all isolates. The isolates were susceptible to enrofloxacin, cefotaxime, ceftriaxone, and florfenicol. Intermediate responses were observed for ciprofloxacin, ofloxacin, doxycycline, oxytetracycline, and trimethoprim–sulfamethoxazole, whereas resistance was detected against norfloxacin, neomycin, penicillin, amoxicillin, tetracycline, and erythromycin. In vitro biofilm assays demonstrated weak to moderate biofilm-forming capacity among isolates. These findings provide baseline data for wildlife microbial surveillance and conservation-oriented monitoring of protected fish populations, supporting future investigations into environmental monitoring, genomic characterization, and host–microbe interactions. Full article

Background: Carbapenem-resistant Klebsiella pneumoniae (CRKP) increasingly combines high-risk clonal expansion, mobile resistance platforms and limited treatment options. We investigated the genomic epidemiology, resistance and virulence architecture, plasmid backbones, and therapeutic vulnerabilities of CRKP circulating in Oman. Methods: Between 2021 and 2024, 135 non-duplicate CRKP isolates were recovered from diverse clinical specimens. New antimicrobial agents were evaluated phenotypically, while 38 representative extensively drug-resistant (XDR)/pan-drug resistant (PDR) isolates underwent whole-genome sequencing (WGS) for multilocus sequence typing (MLST), capsular typing, resistome, virulome, plasmid and mobile genetic elements (MGEs) analysis. In vitro synergy of ceftazidime–avibactam/aztreonam, meropenem/fosfomycin and amikacin/fosfomycin was assessed using gradient diffusion-based FICI. Results: WGS revealed a striking shift towards OXA-232-producing ST-2096, which dominated the sequenced collection and carried KL64 with a conserved multidrug-resistant backbone. NDM-5/ST147 and NDM-1 + KPC-2/ST11 formed distinct high-risk lineages with broader extended-spectrum β-lactamase (ESBL) repertoires, greater plasmid heterogeneity and, in co-producers, the highest MGE burden. Across isolates, resistance was reinforced by widespread blaCTX-M variants, armA, aac(6′)-Ib-cr, fosA, porin alterations and fluoroquinolone-resistance mutations, while core virulence and fitness loci including fimH, mrkA, iutA, fyuA and irp2 were widely retained. Cefiderocol showed the most consistent in vitro activity across carbapenemase groups, and eravacycline remained active, whereas plazomicin and fosfomycin activity was compromised by methyltransferase and fos genes. Ceftazidime–avibactam/aztreonam demonstrated universal synergy, while meropenem/fosfomycin and amikacin/fosfomycin showed limited, carbapenemase-dependent activity. Conclusions: CRKP in Oman is characterised by convergent clonal expansion, plasmid-mediated resistance, retained virulence potential and narrowing therapeutic options. Integrated genomic surveillance with carbapenemase-directed susceptibility and synergy testing is essential to guide precision antimicrobial stewardship in high-risk healthcare settings and inform early infection prevention responses to emerging regional CRKP lineages. Full article

Background/Objectives: Certain strains of Lactobacillus acidophilus are widely used as probiotics. However, their functional potential for female reproductive tract health remains insufficiently characterized. While most studies have focused on individual strains, the distribution of putative probiotic-associated genes across the species remains unclear. This study aimed to evaluate the vaginal probiotic potential of Lb. acidophilus using population genomic analysis and comparative phenotypic characterization. Methods: Pan-genomic analysis was performed on 109 Lb. acidophilus genomes (107 public genomes and 2 vaginal isolates). Putative probiotic-associated gene clusters were identified by functional annotation, categorized into functional modules, and compared among ecological-origin groups. Two vaginal isolates (strains A2 and A3) were characterized in vitro for growth under different pH conditions, cell surface hydrophobicity, lactic acid and hydrogen peroxide production, antimicrobial activity, hemolysis, and antimicrobial susceptibility. Results: The Lb. acidophilus pan-genome was closed, with 1782 of 1902 gene clusters (93.69%) classified as core. Thirty-six putative probiotic-associated gene clusters were identified and grouped into four modules: environmental tolerance, adhesion/colonization, exopolysaccharide/biofilm synthesis, and nutrient metabolism/microbial competition. Thirty-four of the 36 gene clusters were present in all 109 genomes, and no general ecological origin-specific distribution pattern was observed. Three bacteriocin-related gene clusters were conserved across all genomes. A2 and A3 exhibited similar lactic acid production and growth patterns at pH 4–6. Both produced relatively low amounts of hydrogen peroxide compared with the reference strains. A3 showed higher cell surface hydrophobicity and moderate inhibition against Gardnerella vaginalis, while A2 showed no inhibition of this organism. Both isolates were non-hemolytic, and were susceptible to vancomycin and linezolid, resistant to clindamycin, and non-susceptible to daptomycin. No acquired antibiotic resistance genes were detected. Conclusions: Most putative probiotic-associated gene clusters were conserved across the Lb. acidophilus population, whereas A2 and A3 showed strain-dependent phenotypic differences. These findings support combining population genomic analysis with strain-level phenotypic testing when selecting Lb. acidophilus candidates for bacterial vaginal infections. Full article

Global antibiotic consumption continues to rise across pediatric and adult populations, while the genotoxic consequences of host eukaryotic exposure remain less systematically characterized than the parallel problem of antimicrobial resistance. Several lines of evidence, from molecular cytogenetics, redox biology, and systems toxicology, now permit a more mechanistically resolved synthesis of antibiotic-induced genome stress than was previously possible, although a substantial fraction of this evidence is preclinical and warrants cautious clinical extrapolation. This narrative review evaluates the molecular mechanisms, cytogenetic biomarkers, and translational implications of antibiotic-induced genotoxicity, with a primary focus on six clinically prominent classes (fluoroquinolones, nitroimidazoles, aminoglycosides, macrolides, β-lactams, and tetracyclines) and a brief extension to glycopeptides and glycylcyclines. We organize the evidence around three convergent mechanistic axes rather than around individual drugs. Accumulating evidence supports three intersecting off-target axes: (i) eukaryotic topoisomerase II interference, principally documented for fluoroquinolones; (ii) mitochondrial dysfunction, reflecting the evolutionary kinship between the mitoribosome and bacterial ribosomes; and (iii) inflammation-coupled redox stress, often amplified by microbiome perturbation. These pathways converge on a common spectrum of DNA lesions—including double-strand breaks, oxidatively modified bases, replication-fork stalling, and chromosomal mis-segregation) detected by complementary assays (CBMN-Cyt, comet, γH2AX, and oxidative and mitochondrial biomarkers). Pediatric, pregnant, geriatric, and oncology populations may represent biologically distinct susceptibility strata, although direct human evidence for several of these inferences remains limited. Causal inference is constrained by infection as a confounder, frequent use of supratherapeutic in vitro concentrations, reliance on immortalized cell lines that may not recapitulate primary-cell repair capacity, inter-laboratory variability across cytogenetic assays, and a marked scarcity of pediatric and pregnancy biomonitoring data. Most existing positive signals derive from preclinical models; clinically validated long-term outcomes, particularly carcinogenic endpoints, remain inconsistently demonstrated for most antibiotic classes outside metronidazole. Antibiotic-induced genotoxicity appears to be a measurable and mechanistically tractable dimension of drug safety, though its clinical magnitude in real-world exposure scenarios requires further investigation. Integrating multi-omics, microphysiological systems, single-cell genotoxicology, and AI-assisted prediction may improve risk resolution, particularly in vulnerable populations. We argue that antimicrobial stewardship discussions should consider host genome integrity alongside resistance, while remaining mindful that the mechanistic case currently outpaces clinical-endpoint validation. Full article

The rising prevalence of macrolide and fluoroquinolone resistance in human pathogenic mycoplasmas, such as Mycoplasma pneumoniae and Mycoplasma genitalium, threatens global public health. Mutations in 23S rRNA and quinolone resistance-determining regions (QRDR) have compromised the first-line therapies, creating an urgent clinical need for alternatives. Consequently, novel antimicrobial agents (pleuromutilins, novel tetracyclines, topoisomerase inhibitors) have become a top research priority. However, standardized in vitro pharmacokinetic/pharmacodynamic (PK/PD) methodologies for mycoplasmas remain underdeveloped compared to typical bacteria. Key challenges include the lack of a cell wall, slow growth kinetics, and fastidious culture requirements, which invalidate standard colony-counting and susceptibility testing protocols. This review evaluates current in vitro PK/PD models, quantification techniques, and key indices, highlighting the potential of adapting the methodological frameworks established in veterinary mycoplasma research (e.g., Mycoplasma bovis, Mycoplasma hyopneumoniae) to human mycoplasma species. We specifically analyze the utility of propidium monoazide (PMA)-qPCR for viability assessment and hollow-fiber infection models (HFIM) configured for small-cell retention. We conclude that harmonizing these methodologies through a One Health approach is critical for optimizing dosing regimens, reducing resistance, and accelerating the development of novel antimicrobial agents for human use. Full article

Background/Objectives: Third-generation cephalosporins are used to treat many infections, including urinary tract infections. Despite the risk of inducing resistance in SPICE-HaM microorganisms (Serratia, Providencia, indole-positive Proteus, Citrobacter freundii complex, Enterobacter cloacae complex, Klebsiella aerogenes, Hafnia alvei and Morganella morganii), a group of microorganisms with inducible beta-lactamase potentials, guidelines still recommend treating uncomplicated cystitis with third-generation cephalosporins. To improve outpatient pediatric antimicrobial practice, this study aimed to develop a five-year pediatric cumulative antimicrobial susceptibility testing report for SPICE-HaM microorganisms in urine and compare the in vitro sensitivity of cefixime/ceftriaxone with sulfamethoxazole/trimethoprim. Methods: Over 300 pediatric SPICE-HaM urine isolates, processed at regional microbiology laboratories of LifeLabs British Columbia between 2020 and 2024, were analyzed. Results: Compared to cefixime, sulfamethoxazole/trimethoprim demonstrated higher sensitivity against Citrobacter freundii complex (65% versus 95%, p < 0.05, n = 57), Enterobacter cloacae complex (49% versus 92%, p < 0.05, n = 89), and Morganella morganii (68% versus 92%, p < 0.05, n = 76). Compared to ceftriaxone, sulfamethoxazole/trimethoprim failed to show significantly different sensitivities for the SPICE-HaM microorganisms. Conclusions: Sulfamethoxazole/trimethoprim is possibly a more favourable oral agent for SPICE-HaM-associated urinary tract infections in the local pediatric community population compared to cefixime, a third-generation cephalosporin. However, compared to ceftriaxone, sulfamethoxazole/trimethoprim appears to have similar efficacy for SPICE-HaM-associated urinary tract infections. Full article

Eucalyptus bacterial wilt in China, caused predominantly by Ralstonia pseudosolanacearum, severely threatens Eucalyptus plantation management in China and demands plant-derived alternatives to conventional bactericides. This study evaluated the in vitro antibacterial activities and underlying molecular mechanisms of two differentially substituted coumarin derivatives, daphnetin (DAP) and 6-methylcoumarin (MC), against a eucalyptus-derived R. pseudosolanacearum strain. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined using broth microdilution assays. Quantitative phenotypic assays were conducted to evaluate the effects of sub-lethal concentrations on biofilm formation, swimming motility, and extracellular polysaccharide (EPS) accumulation. Furthermore, high-throughput RNA sequencing integrated with GO and KEGG enrichment analyses was employed to characterize the genome-wide transcriptomic responses. Antimicrobial susceptibility testing demonstrated that DAP possessed superior bactericidal efficacy, yielding lower MIC (62.5 μg/mL) and MBC (250 μg/mL) values than MC. Conversely, sub-lethal MC exhibited a more pronounced, early-stage suppression of flagellum-dependent swimming motility and biofilm maturation. Both compounds consistently attenuated EPS production. Transcriptomic analysis revealed distinct yet partially convergent regulatory networks: DAP primarily exerted metabolic strangulation by downregulating genes governing aerobic respiratory chains and peripheral carbon/nitrogen pathways, whereas MC targeted collective behavior and active pathogenesis, systematically downregulating the expression of genes associated with flagellar assembly, quorum sensing, and Type III and VI secretion systems. Notably, both pathways converged downstream to repress the master virulence regulator xpsR and the epsA-P operon. These findings provide valuable insights into the potential molecular pathways affected by DAP and MC, offering a useful reference for future exploration of botanical formulations for ecologically responsible forest disease control. Full article

Nontoxigenic Bacteroides fragilis (NTBF) is defined by the absence of the bft gene and corresponding B. fragilis toxin production; however, nontoxigenic status alone does not establish uniform safety or probiotic function. This review critically evaluates strain-level biological characteristics, safety, mechanisms, metabolites, and disease-model evidence. Selected strains and defined strain-derived preparations, including ZY-312, HCK-B3, NCTC 9343-derived polysaccharide A, and ZY-312-derived zwitterionic capsular polysaccharide preparation TP2, have shown immunomodulatory, barrier-associated, and microbial-community-modulating activities, predominantly in vitro and in animal models. Direct causal evidence is limited to specific strain–preparation–host–model combinations, whereas many changes in cytokines, tight-junction-associated proteins, microbial composition, and organic-acid profiles remain functional or associative. Protective effects have been reported in preclinical models of inflammatory bowel disease, necrotizing enterocolitis, antibiotic-associated diarrhea, Clostridioides difficile infection, and enterotoxigenic B. fragilis (ETBF)-associated tumorigenesis. However, findings are highly dependent on the strain, preparation, dose, administration timing, host, and model. Safety remains incompletely resolved because the absence of B. fragilis toxin (BFT) does not exclude opportunistic or systemic infection, antimicrobial-resistance mobility, bacterial translocation, permeability changes, or adverse effects during long-term administration. Metabolic effects may also be beneficial or adverse depending on the strain, host dietary and genetic background, and experimental context. Human evidence is primarily observational, and robust intervention trials are lacking. Accordingly, NTBF should be regarded as a heterogeneous group of strain-specific live-biotherapeutic candidates requiring rigorous strain-specific manufacturing, potency, dose, antimicrobial-susceptibility, and safety evaluation. Full article

Background/Objectives: Antimicrobial resistance is a critical threat to global public health. Eugenol is a bioactive compound with broad-spectrum antimicrobial activity that has attracted increasing interest as a naturally derived antimicrobial agent with potential complementary applications to conventional antibiotics, but its clinical application is severely limited by its high volatility, low water solubility and thermo-oxidative instability. The main objective of this study was to develop eugenol-loaded microparticles using a ternary biopolymer matrix, to characterise their main physicochemical properties, and to evaluate their in vitro antimicrobial efficacy against clinically relevant bacterial reference strains. Methods: The microparticles were formulated from an emulsion of maltodextrin, gum arabic and soy lecithin, and encapsulated using a spray-drying technique. Product recovery, particle morphology assessed by scanning electron microscopy (SEM), particle size distribution determined by laser diffraction, and encapsulation efficiency quantified by GC-FID were analysed. Subsequently, antimicrobial activity was evaluated by comparing the microparticles with free eugenol using agar well diffusion and broth microdilution assays to determine the minimum inhibitory concentration (MIC) against eight bacterial strains. Results: The spray-drying process achieved a product recovery of 61.88% and an encapsulation efficiency of 52.45%. The resulting microparticles exhibited a smooth, spherical morphology with diameters of less than 20 µm. In microbiological assays, microencapsulation significantly reduced MIC values by 4- to 16-fold compared with free eugenol for susceptible strains. The formulation exhibited potent activity against most of the Gram-positive and Gram-negative pathogens tested, except for Pseudomonas aeruginosa, which remained resistant to both formulations. Conclusions: The encapsulation of eugenol in this optimised biopolymer matrix substantially improved its antimicrobial efficacy against the tested bacterial strains. These findings highlight the potential of spray-dried eugenol microparticles as a promising antimicrobial formulation and provide a basis for their further development for topical applications. Further studies are warranted to evaluate their pharmaceutical performance and antimicrobial mechanisms. Full article

Background/Objectives: Antimicrobial resistance among ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) pathogens has become a major global health threat, significantly reducing the effectiveness of conventional antibiotics. Plant-derived compounds have emerged as promising antibiotic adjuvants capable of restoring antibiotic activity through multiple resistance-modulating mechanisms. This review aims to critically evaluate the current evidence regarding phytochemicals that enhance antibiotic efficacy against drug-resistant ESKAPE pathogens. Methods: Relevant studies investigating plant-derived compounds with antibiotic adjuvant activity against ESKAPE pathogens were identified and critically analyzed. Particular attention was given to mechanisms of action, synergistic interactions with conventional antibiotics, structure–activity relationships, and translational evidence from in vivo studies. Results: Numerous phytochemicals have demonstrated the ability to potentiate antibiotic activity through efflux pump inhibition, biofilm disruption, membrane permeabilization, and quorum sensing interference. For instance, the flavonoid quercetin inhibits the NorA efflux pump in Staphylococcus aureus, restoring ciprofloxacin susceptibility, while the sulfur-containing compound ajoene from garlic disrupts quorum sensing in Pseudomonas aeruginosa, sensitizing biofilms to tobramycin. Although several compounds exhibit promising synergistic effects in vitro, significant barriers remain regarding bioavailability, standardization, pharmacokinetics, and clinical translation. Conclusions: Plant-derived antibiotic adjuvants represent a promising strategy to combat multidrug-resistant ESKAPE pathogens. However, greater emphasis on translational research, standardized methodologies, and clinically relevant experimental models is required to facilitate their development toward therapeutic applications. Full article

Katak, a traditional Bulgarian fermented dairy product distinguished by its unique sensory characteristics and extended shelf life, represents a valuable source of autochthonous microorganisms whose functional and genomic properties remain insufficiently explored. In the present study, strain L3, isolated from katak, was comprehensively characterized by a polyphasic approach integrating classical microbiological methods, molecular identification, and whole-genome sequencing. Functional assessment revealed a broad spectrum of antimicrobial activity against pathogenic bacteria and food-associated fungi, accompanied by pronounced radical-scavenging and antioxidant capacities. The strain also exhibited high transit tolerance in simulated gut passage and a favorable antibiotic susceptibility profile, indicating its potential as a probiotic candidate. Whole-genome sequencing confirmed the taxonomic affiliation of the isolate as Lactiplantibacillus plantarum and enabled the identification of genetic determinants associated with stress response, environmental adaptation, oxidative stress protection, biofilm formation, and antimicrobial activity. The genomic analysis complemented the in vitro findings by identifying genetic determinants consistent with the observed phenotypic traits, supporting the genetic potential of strain L3 for probiotic-associated functions. The integration of phenotypic and genomic evidence allowed a comprehensive evaluation of L. plantarum L3 and demonstrated that its probiotic-related properties are underpinned by a diverse repertoire of functional genes. These findings identify L3 as a promising candidate for further biotechnological/probiotic assessment. Full article

Cherry tomatoes are highly susceptible to Salmonella contamination during pre- and post-harvest handling, leading to foodborne illness outbreaks and significant economic losses. Edible coatings incorporating natural antimicrobials offer a promising alternative to conventional chemical treatments for enhancing food safety while maintaining produce quality. This study developed and evaluated a pectin-based edible coating enriched with zinc nanohydroxide-thymol nanohybrids (ZnNH-T) for controlling Salmonella contamination and extending shelf-life of cherry tomatoes. ZnNH-T nanohybrids were synthesized via precipitation, followed by thymol intercalation, and characterized by SEM. Four coating formulations were prepared: pectin alone (P), pectin-thymol (PT), pectin-ZnNH (PNH), and pectin-ZnNH-T (PNHT). Antibacterial activity of the four coatings was first screened in vitro by disc diffusion against six S. enterica serovars; three serovars (Typhimurium, Enteritidis, and Montevideo) showing a statistically significant, coating-dependent inhibition response were selected for the postharvest assay. Cherry tomatoes were coated and dip-inoculated with three Salmonella serotypes (Typhimurium, Enteritidis, and Montevideo) at approximately 10⁵ CFU/mL and stored at 25 °C for 12 days. Antimicrobial efficacy, antioxidant activity (ABTS assay), and physicochemical quality parameters (weight loss, color, pH, and total soluble solids) were evaluated. Zinc nanohydroxides were successfully synthesized, as observed in SEM morphology. ABTS radical scavenging activity of filmogenic solutions was highest for PT (92.4%) and moderate for PNHT (65.9%), while P and PNH showed minimal activity (20.1% and 17.8%, respectively). PNHT coating achieved an approximately 2-log CFU/g reduction in Salmonella populations compared to uncoated controls over 12 days of storage, demonstrating sustained antimicrobial efficacy. Coated tomatoes exhibited significantly reduced weight loss (8% for PNHT vs. 13% for control), better color retention, lycopene content, maintained firmness, and stable pH and TSS values compared to uncoated controls. The pectin-ZnNH-T coating system represents a novel multifunctional approach for enhancing cherry tomato safety and quality. The use of thymol from the layered hydroxide structure, combined with zinc ion antimicrobial effects, provides sustained pathogen reduction while maintaining desirable physicochemical properties. This natural, biodegradable coating technology has potential for commercial application in fresh produce preservation. Full article

Product Shezi (PS) is a polyherbal African traditional medicine (ATM) formulated from six known South African medicinal plants and is used for treating cutaneous wounds. However, its ethnopharmacological properties have not been scientifically validated. This study aimed to evaluate the antioxidant, anti-inflammatory, and antimicrobial activities of PS in vitro. Aqueous and methanolic extracts were prepared and qualitatively screened for phytochemical constituents. Cytotoxicity in fibroblasts and macrophages was assessed using an ATP-based viability assay. Antioxidant activity was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and a hydrogen peroxide (H₂O₂)-induced oxidative stress model. Anti-inflammatory effects in lipopolysaccharide (LPS)-stimulated macrophages were measured using the Griess reagent system, a human prostaglandin E₂ (PGE₂) ELISA, and a bovine serum albumin (BSA) anti-denaturation assay. Antimicrobial activity was assessed by twofold serial broth microdilution, agar well diffusion, and a crystal violet biofilm assay. Phytochemical screening confirmed the presence of saponins, alkaloids, tannins, glycosides, terpenoids, flavonoids, and steroids. PS exhibited IC₁₀ values of 3 and 10 μg/mL in fibroblasts and macrophages, respectively. PS (1–5 μg/mL) showed 70% DPPH scavenging potential and potent H₂O₂ cytoprotection (p < 0.001). Nitric oxide inhibition was non-significant (p > 0.05) whilst PGE₂ decreased significantly (p < 0.05) compared to LPS-stimulated cells. BSA denaturation was inhibited in a dose-dependent manner (p < 0.05). Staphylococcus aureus and S. epidermidis were the only microorganisms susceptible to PS (MIC 650–5000 μg/mL) with low SI (SI ≈ 0.05–0.06), while others were resistant. PS showed no antibiofilm activity (crystal-violet assay). Overall, PS demonstrated antioxidant and anti-inflammatory activities and selective antibacterial effects against planktonic bacteria in vitro. However, further optimization of extraction methods, detailed mechanistic studies, and in vivo investigations are warranted to substantiate therapeutic relevance. Full article

Objectives: The intent of this study was to report reference in vitro antimicrobial susceptibility testing results for funobactam (formerly XNW4107) in combination with imipenem against recent, worldwide clinical isolates of Gram-negative bacilli. Methods: MICs for imipenem in combination with a fixed concentration of funobactam (8 mg/L), and seven comparator agents, were determined using the reference CLSI M07 broth microdilution method for 4003 clinical isolates of Gram-negative bacilli (2008 Enterobacterales, 999 Acinetobacter baumannii, and 996 Pseudomonas aeruginosa) collected from 211 unique clinical laboratory sites in 54 countries as part of industry-sponsored antimicrobial surveillance studies in 2021 and 2022. MICs were interpreted by 2026 CLSI M100 breakpoints. Most isolates with imipenem-funobactam MICs of ≥4 mg/L (95.4%) underwent whole genome sequencing to identify acquired β-lactamase gene carriage. Results: MIC₉₀ values for imipenem-funobactam were 2 mg/L for all 2008 isolates of Enterobacterales, and 1, 0.5, and 0.5 mg/L, respectively, for metallo-β-lactamase (MBL)-negative Enterobacterales (n = 1969), non-Morganellaceae Enterobacterales (NME) (n = 1752), and MBL-negative NME (n = 1718) isolate subsets. MIC₉₀ values for imipenem-funobactam and imipenem alone were identical or within one doubling dilution for all 14 species of Enterobacterales tested except Klebsiella pneumoniae, Citrobacter freundii, and Enterobacter bugandensis which showed differences of 32-fold (imipenem-funobactam MIC₉₀, 0.5 mg/L; imipenem MIC₉₀, 16 mg/L), 8-fold (0.25 mg/L; 2 mg/L), and 4-fold (0.25 mg/L; 1 mg/L), respectively. Both for all A. baumannii isolates (n = 999) and for MBL-negative isolates (n = 962), the imipenem-funobactam MIC₉₀ value (4 mg/L) was 32-fold lower than for imipenem alone (128 mg/L). Both for all P. aeruginosa (n = 996) isolates and MBL-negative isolates (n = 962), we observed a 4-fold difference in potency between imipenem-funobactam (MIC₉₀, 4 mg/L) and imipenem alone (MIC₉₀, 16 mg/L). Isolates carrying MBL demonstrated the highest MICs for imipenem-funobactam. Conclusions: Imipenem-funobactam demonstrated potent in vitro activity against most carbapenem-resistant isolates of A. baumannii, K. pneumoniae, NME and many isolates of carbapenem-resistant P. aeruginosa. Continued development of imipenem-funobactam is warranted. Full article

Background: Carbapenem-resistant Acinetobacter baumannii is a critical priority pathogen of the Acinetobacter calcoaceticus-Acinetobacter baumannii Complex (Acb Complex) characterized by extensive multidrug resistance, leading to increased reliance on last-line polymyxins and widespread use of cationic disinfectants in healthcare settings. However, shared membrane-targeting mechanisms raise concerns regarding potential cross-resistance between disinfectants, polymyxins, and cationic antimicrobial peptides. Methods: A diverse panel of clinical A. baumannii isolates from Australia (n = 9), Pakistan (n = 15), and Switzerland (n = 3), and standard strains (n = 3), including polymyxin-resistant laboratory and clinical mutant strains (n = 4), was used. Minimum inhibitory concentrations (MICs) of polymyxin B, colistin, three cationic disinfectants (polyquaternium-1; PQ-1), polyhexamethylene biguanide (PHMB), and chlorhexidine (CHX), and four Antimicrobial peptides (AMPS: LL-37, melimine, Mel4, and lactoferricin) were determined using broth microdilution. Correlations between MICs were assessed using Spearman analysis, and differences between polymyxin-resistant and -susceptible isolates were analyzed statistically. Results: Most isolates were susceptible to polymyxins. The MIC data confirmed that one mutant strain, A. baumannii 19606 (R), and three clinical isolates displayed high-level polymyxin B and colistin resistance. PQ-1 exhibited the greatest antibacterial activity among disinfectants, while LL-37 showed the lowest and most consistent MICs among AMPs; lactoferricin was largely inactive. Within this exploratory strain collection, polymyxin-resistant isolates exhibited lower MICs to PQ-1 and PHMB, indicating collateral susceptibility. Correlation analysis revealed significant negative correlations between polymyxin susceptibility and disinfectant MICs (colistin–PQ-1 (r = −0.67 and p = 0.0001), colistin–PHMB (r = −0.44 and p = 0.05), and polymyxin B–PHMB (r = −0.48 and p = 0.005), whereas no consistent correlation was observed between polymyxins and AMPs, including LL-37. A moderate positive correlation was identified between colistin and Mel4 activity (r = 0.45 and p = 0.05). Conclusions: These findings indicate diverse susceptibility patterns of A. baumannii to cationic antimicrobials. Within this exploratory strain collection, polymyxin resistance was not associated with reduced susceptibility to disinfectants or most antimicrobial peptides and was instead associated with lower MICs to certain disinfectants. No evidence of cross-resistance between polymyxins and LL-37 was observed under the conditions tested, suggesting that polymyxin resistance does not necessarily confer reduced in vitro susceptibility to this host defense peptide. Given the small number of polymyxin-resistant isolates, these findings should be considered hypothesis-generating and require confirmation in larger collections of genetically characterized strains. Further mechanistic studies are needed to determine the biological basis and generalizability of these observed susceptibility patterns. Full article