Search Results (784)

In healthy humans, a very low percentage of fungal species are capable of causing severe infections. On the contrary, in individuals with weak or compromised immune system, opportunistic fungal infections result in up to 3.8 million deaths annually. Drug resistance is the major problem for all of the currently available antifungals. Polyethyleneimine (PEI), a cationic polymer, exhibits potent antifungal activity against Aspergillus nidulans, yet the influence of copper ions on its mechanism of activity remains unclear. Here, we investigated how free exogenous Cu²⁺, influences PEI antifungal activity and the membrane-associated events underlying this effect. We demonstrate that (i) exogenous excess of homeostatic Cu²⁺ concentrations protects A. nidulans from PEI toxicity in a concentration-dependent and developmentally regulated manner; (ii) Cu²⁺ is effective only when present during the earliest stages of PEI action, identifying the plasma membrane as the primary site of Cu²⁺ protection; (iii) PEI, like Amphotericin B, induces translocation of ergosterol from the plasma membrane to intracellular compartments while additionally producing a distinct polarized enrichment of ergosterol at the hyphal tip; and (iv) Cu²⁺-mediated protection is independent of eisosome assembly. Together, these findings provide new mechanistic insights into the antifungal activity of PEI and the role of Cu⁺² on PEI-induced cellular damage. Full article

Pseudomonas aeruginosa is a ubiquitous opportunistic pathogen and a leading cause of severe healthcare-associated infections, particularly ventilator-associated pneumonia (VAP) and bloodstream infections (BSIs) in critically ill patients. Its remarkable capacity for both intrinsic and acquired resistance leads to complex phenotypic profiles, culminating in difficult-to-treat resistant P. aeruginosa (DTR-PA). Managing DTR-PA presents a daunting clinical challenge characterised by a narrow therapeutic armamentarium, treatment delays, and high attributable mortality. To bridge the gap between complex molecular microbiology and bedside decision-making, this narrative review employs a pragmatic, clinical vignette-based approach. Through six representative fictional scenarios of pneumonia and BSI, we systematically dissect the underlying mechanisms of resistance and their direct therapeutic implications. The vignettes explore combinations of intrinsic adaptations—such as Pseudomonas-derived cephalosporinase (PDC/AmpC) hyperexpression, OprD porin loss, and efflux pump upregulation—as well as the acquisition of serine- (e.g., GES) and metallo-β-lactamases (e.g., VIM, NDM, IMP). Grounded in the updated 2026 Infectious Diseases Society of America (IDSA) guidelines, we evaluate the optimal deployment of newer β-lactam/β-lactamase inhibitor combinations. We highlight the specific preference for ceftolozane–tazobactam in pneumonia, the roles of ceftazidime–avibactam and imipenem–relebactam, and the critical use of cefiderocol for metallo-β-lactamase producers and highly resistant phenotypes. Furthermore, the review addresses pressing clinical controversies: the superiority of targeted monotherapy over historical, toxic combination regimens; the risks of unconditionally applying “shorter-is-better” duration paradigms to DTR-PA; and the alarming frequency of treatment-emergent cross-resistance among novel agents. We also clarify common clinical misconceptions, such as the limited utility of meropenem–vaborbactam and aztreonam–avibactam against specific pseudomonal mechanisms. Ultimately, effective DTR-PA management precludes class-based empirical assumptions. By providing a phenotype-driven bedside aide-mémoire, this review reinforces that rapid recognition, direct agent-specific antimicrobial susceptibility testing (AST), pharmacokinetic/pharmacodynamic (PK/PD)-optimised dosing, and prompt source control remain the absolute cornerstones of survival for patients afflicted by these formidable infections. Full article

Background: K. pneumoniae is a major opportunistic pathogen recognized by the World Health Organization as a critical-priority antimicrobial-resistant pathogen. This study characterized isolates for antibiotic resistance determinants, virulence-associated genes, mobile genetic elements, and population structure of the isolates, and evaluated the correlation between antimicrobial resistance genotype and phenotype. Methods: Ninety-five isolates were collected from different clinical specimens in August–December 2024 in Farwaniya Hospital, Kuwait. Fifty-six isolates were selected for whole-genome sequencing (WGS) using Oxford Nanopore Technology. Antimicrobial resistance genes, virulence-associated genes, plasmid replicons, insertion sequences, transposons, and sequence types were identified using different bioinformatics tools. Results: The 56 isolates comprised 47 multidrug-resistant and 9 non-multidrug-resistant isolates. β-lactam resistance genes were detected in all isolates, with bla_SHV (96.4%), bla_CTX-M-15 (75.0%), bla_OXA (64.3%), and bla_NDM-5 (30.4%) being the most prevalent. IncFIB(K) was the predominant plasmid replicon, whereas ISSen9, IS26, and IS903 were the most common insertion sequences. Twenty-eight virulence-associated genes were identified, with enterobactin-associated genes, fimbrial adhesion genes, and ompA detected in over 90% of the isolates. MLST identified 32 sequence types, including eight novel sequence types, with ST16 and ST147 predominating. High genotype–phenotype concordance was observed for cephalosporins (87.5%) and penicillins (85.7%). Conclusions: K. pneumoniae isolates exhibited extensive genomic diversity and multidrug resistance associated with multiple resistance determinants, mobile genetic elements, and high-risk lineages. These findings highlight the value of WGS for antimicrobial resistance surveillance and support continued genomic monitoring to support infection prevention and antimicrobial stewardship programs in Kuwait. Full article

Staphylococcus epidermidis is an important opportunistic pathogen and a potential reservoir of antimicrobial resistance determinants, yet comparatively little is known about isolates originating from both humans and companion animals. This study characterized 320 S. epidermidis isolates obtained from humans, cats, and dogs within a One Health framework using phenotypic, molecular, proteomic, and genomic approaches. Antimicrobial susceptibility testing revealed high frequencies of resistance to oxacillin (67.19%), erythromycin (66.56%), tetracycline (55.63%), and clindamycin (53.75%) by disk diffusion. PCR-based analysis identified blaZ as the most prevalent resistance determinant (50.63%), whereas whole-genome sequencing of a selected subset revealed a broader and heterogeneous repertoire of resistance-associated genes. Among 67 sequenced isolates, 26 known sequence types were identified, including several STs occurring in isolates from more than one host species. Core-genome phylogenetic analysis demonstrated substantial genomic diversity without complete segregation according to host species or clinical status. Genotype–phenotype concordance was generally limited and gene dependent, and discrepancies were also observed between PCR- and WGS-based detection for selected resistance determinants. Biofilm formation was significantly influenced by incubation temperature, host species, and clinical status, while growth kinetics showed pronounced strain-specific variability and no consistent relationship with biofilm-forming capacity. MALDI-TOF MS profiling and partial rpoB phylogeny likewise showed considerable overlap among isolates from different host groups. In the Galleria mellonella infection model, mortality was inoculum dependent and varied substantially among strains. Overall, the findings demonstrate marked phenotypic and genomic heterogeneity among S. epidermidis isolated from humans and companion animals and indicate that some clonal backgrounds and resistance determinants occur across host species, highlighting the relevance of this species within a One Health context. Full article

Stenotrophomonas maltophilia is an opportunistic, multidrug-resistant pathogen commonly associated with respiratory and bloodstream infections. Owing to extensive intrinsic and acquired antimicrobial resistance and limited pediatric-specific evidence, contemporary management relies heavily on extrapolation from adult data, underscoring the need to better characterize real-world treatment practices and outcomes in children. This was a retrospective, observational cohort that included hospitalized patients < 18 years of age with a positive S. maltophilia culture who received active antimicrobial therapy, excluding cases determined by the treating provider to represent colonization. Outcomes assessed included in-hospital mortality, adverse drug effects, and clinical success rates using descriptive statistics. Forty pediatric patients (median [IQR] age of 2.7 [0.7–7.9] years) were included. Respiratory infections accounted for 77.5% of cases, and sulfamethoxazole-trimethoprim monotherapy was the most common treatment regimen (70.0%). Five patients (12.5%) experienced in-hospital mortality, three patients (7.5%) experienced adverse effects related to treatment, and all patients exhibited clinical success. Larger, multicenter observational and prospective studies are warranted to strengthen evidence-based therapeutic approaches for pediatric patients with S. maltophilia infections. Full article

Background: Respiratory tract candidiasis, primarily caused by Candida species, is a prevalent opportunistic fungal infection in individuals with HIV/AIDS. A high HIV viral load is considered a significant risk factor for developing respiratory fungal infection. This study aimed to identify the yeast species isolated from sputum samples of HIV-positive and HIV-negative adults, determine their antifungal susceptibility patterns, and investigate associated risk factors. Methods: A hospital-based comparative cross-sectional study was conducted from March to May 2022. Sputum samples were collected from 190 HIV-positive and 190 HIV-negative participants. Candida and other yeast species were isolated and identified, followed by antifungal sensitivity testing. Results: Of the 190 specimens from each group, 77 (40.53%) from HIV patients and 12 (6.31%) from HIV-negative participants tested positive for yeasts. Candida albicans was the most prevalent species, found in 52 (67.53%) HIV-positive patients and 12 (100%) HIV-negative patients. This was followed by Nakaseomyces glabratus (15.58%), Pichia kudriavzevii (9.09%), Candida tropicalis (6.49%), and Candida parapsilosis (1.29%) in HIV-positive patients. Notably, all 12 isolates from HIV-negative participants demonstrated 100% sensitivity to all ten tested antifungal drugs. In contrast, isolates from HIV patients showed significant resistance to fluconazole and ketoconazole (32.5% each). High viral load (p < 0.001), dermatophyte infection (p < 0.001), and antiretroviral (ARV) regimen (p = 0.030) were significantly associated with respiratory tract fungal infections in HIV patients. Conclusions: Based on this exploratory study, respiratory mycosis is frequent in HIV-positive patients in Cameroon, and identified fungi show increased resistance to azoles. While these results must be interpreted with care due to the sample size relative to the high national HIV prevalence, they suggest that public health education is needed to improve awareness. These preliminary findings prompt a review by health authorities concerning the use of fluconazole for prophylaxis in HIV-positive patients in Cameroon. Full article

Candida tropicalis has emerged as one of the most clinically relevant non-albicans Candida species, owing to its increasing global prevalence, high mortality associated with invasive infections, and rising rates of antifungal resistance. Although traditionally considered an opportunistic pathogen, growing evidence indicates that its remarkable adaptive capacity is driven by the coordinated regulation of multiple biological processes that promote host colonization, persistence, and immune evasion. In this review, we summarize current knowledge on the epidemiology, biology, genomic organization, virulence factors, and host–pathogen interactions of C. tropicalis. Particular emphasis is placed on recent advances in comparative genomics and functional studies that have expanded our understanding of the molecular determinants underlying adhesion, biofilm formation, morphogenesis, extracellular hydrolytic enzyme production, thermotolerance, cell wall remodeling, and immune evasion. We also integrate orthology analyses identifying putative C. tropicalis homologs of well-characterized Candida albicans virulence genes, highlighting the evolutionary conservation of key pathogenic mechanisms while emphasizing species-specific adaptations that remain functionally unexplored. Finally, we discuss current knowledge of antifungal resistance and the emerging relationship between genomic plasticity, stress adaptation, and pathogenicity. Together, this review provides an updated and comprehensive overview of the biological mechanisms that contribute to the success of C. tropicalis as an emerging opportunistic pathogen and identifies key areas requiring further investigation to improve diagnosis, treatment, and the development of novel antifungal strategies. Full article

Background/Objectives: Serratia marcescens is an opportunistic pathogen that causes severe hospital-acquired infections, notable for its biofilm formation abilities and development of extensive antibiotic resistance. Here, we aim to evaluate the efficacy of bacteriophages, antibiotics, and antimicrobial peptides (BAP), alone and in combination, against fourteen multidrug-resistant (MDR) S. marcescens isolates sourced from hospitals and other environmental settings. Methods: S. marcescens was grown planktonically or in surface-associated biofilms, and biofilm biomass was measured via changes in absorbance and colony-forming units or live/death staining. Results: Combining bacteriophage with a low-dose cocktail of penicillin–streptomycin, kanamycin, and ciprofloxacin enhanced antimicrobial activity compared with antibiotics alone. Across the isolate panel, responses to BAP treatment varied according to determined antibiotic resistance profiles. The highly resistant AR-0517 isolate was selected for detailed mature biofilm analysis, where the BAP treatment reduced biofilm biomass by 97.8% and recoverable bacteria by 99.99%. Microscopy and viability assays further confirmed extensive biofilm disruption and bacterial killing. Conclusions: These findings demonstrate that simultaneous targeting of multiple bacterial pathways can enhance antimicrobial activity against MDR S. marcescens in vitro and support further evaluation of BAP as a potential strategy for biofilm-associated infections. Full article

Background/Objectives: Pseudomonas aeruginosa is an opportunistic Gram-negative bacterium and a major cause of healthcare-associated infections worldwide, exhibiting intrinsic antimicrobial resistance and readily acquiring novel resistance mechanisms. Divalent cations such as Mg²⁺ and Ca²⁺ in the culture environment can influence bacterial antibiotic susceptibility. This study evaluated the impact of varying concentrations of Mg²⁺ and Ca²⁺ on the antibiotic susceptibility of P. aeruginosa to tobramycin and ciprofloxacin under both planktonic and biofilm growth modes. Methods: The study determined the minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and minimum biofilm eradication concentration (MBEC) to compare alterations in antibiotic susceptibility across different ion conditions and bacterial growth patterns. Results: Our findings suggest that elevated concentrations of Mg²⁺ and Ca²⁺ significantly modulate bacterial antibiotic susceptibility. Conclusions: The results of our study has implications for limitations in standardised antibiotic susceptibility tests and to therapeutic strategies in cation-rich environments such as cystic fibrosis airways. Full article

Background and Clinical Significance: Sodium–glucose cotransporter-2 (SGLT2) inhibitors cause persistent glucosuria, which has been hypothesized to facilitate urinary tract infection (UTI) when urinary stasis or anatomic variants coexist; causality, however, remains unproven and almost certainly multifactorial. Case Presentation: A 72-year-old man treated with dapagliflozin 10 mg/day for 4 months presented with 3 days of dysuria and nocturia, without fever or systemic signs. One month before SGLT2 inhibitor initiation, urological work-up had been unremarkable: prostate ~50 cm³, post-void residual (PVR) 0 mL, and a negative midstream culture. At presentation we obtained a midstream clean-catch specimen before antibiotics. Dipstick showed glucose 2+ (~100 mg/dL, as expected with SGLT2 inhibition), leukocyte esterase 3+ and nitrites negative; microscopy revealed 45 leukocytes/high-power field with pronounced bacteriuria. Quantitative culture grew Morganella morganii at 1 × 10⁵ CFU/mL in pure culture. Antimicrobial susceptibility (VITEK^® 2 Compact, EUCAST v14.0, 2024) demonstrated resistance to ampicillin, amoxicillin–clavulanate, ampicillin–sulbactam, ceftriaxone, ceftazidime, gentamicin and trimethoprim–sulfamethoxazole, with susceptibility (S) retained only to piperacillin–tazobactam, levofloxacin/norfloxacin, cefepime and carbapenems (ertapenem, meropenem). Imaging revealed a right duplicated ureter with distal fusion (single bladder insertion, no dilatation or obstruction) and benign prostatic hyperplasia with PVR ~100 mL; renal function was preserved, two blood culture sets (pre-antibiotic) were negative, and repeat urine culture on day 7 was sterile. Management/outcome: The episode was classified as a localized (cystitis-range) UTI per European Association of Urology (EAU) criteria (no fever, flank pain or bacteremia). Meropenem 1 g intravenously every 8 h (3 g/day) was given for 10 days after urology/infectious-disease review. Dapagliflozin was held at presentation and not restarted during the 3-month follow-up period; reintroduction was planned only after full urological reassessment with cardiology input. Transurethral resection of the prostate (TUR-P) was performed 18 days after completing antibiotics (28 days after presentation) for bladder outlet obstruction refractory to tamsulosin 0.4 mg daily, with complete resolution of symptoms, normalization of inflammatory markers and PVR 0 mL. No recurrence occurred during 3 months of follow-up after TUR-P. Conclusions: This single case illustrates a temporal association—not proven causation—between SGLT2-related glucosuria, incomplete emptying and a non-obstructive duplicated ureter that likely created a permissive milieu for opportunistic Morganella UTI. The narrative is hypothesis-generating; urinary stasis was the dominant modifiable factor. Culture-guided therapy, individualized decisions on SGLT2 continuation, and definitive correction of outlet obstruction are the practical takeaways. Full article

Klebsiella pneumoniae (KP) is an important opportunistic pathogen that can persist in the gastrointestinal tract and serve as a reservoir for subsequent infection. The increasing prevalence of multidrug-resistant KP highlights the need for non-antibiotic strategies to limit intestinal KP burden and associated host injury. Lactiplantibacillus plantarum GUANKE (L. plantarum GUANKE) is a candidate probiotic strain with reported effects on mucosal barrier protection and inflammatory regulation, but its role in intestinal KP challenge remains unclear. In this study, the effects of L. plantarum GUANKE and its metabolite phenyllactic acid (PLA) on KP growth, intestinal KP burden, and associated inflammatory injury were investigated using antibacterial assays in vitro, metabolomic analyses, an antibiotic-pretreated mouse model of intestinal KP challenge, and an influenza A virus (IAV)/KP intestinal co-exposure model. L. plantarum GUANKE and its culture-derived products inhibited KP growth in vitro. Metabolomic analysis identified PLA as a metabolite enriched in L. plantarum GUANKE fermentation supernatants, and exogenous PLA directly inhibited KP growth in a dose-dependent manner. In an antibiotic-pretreated mouse model of intestinal KP challenge, oral administration of L. plantarum GUANKE reduced intestinal KP burden and was associated with changes in gut microbiota composition, increased cecal PLA abundance, improved intestinal barrier-related parameters, and reduced inflammatory responses, while exogenous PLA partially reproduced these effects. IAV infection increased susceptibility to intestinal KP expansion, and oral L. plantarum GUANKE reduced KP burden in the IAV/KP intestinal co-exposure model. In mice challenged with multidrug-resistant KP strain NK04152, L. plantarum GUANKE and PLA reduce intestinal KP burden and associated tissue injury in mice, supporting their potential as candidate microbiota and metabolite strategies against intestinal KP challenge. Full article

Antimicrobial resistance (AMR) is one of the main public health problems that also affects environmental ecosystems. Sinkholes are understudied groundwater ecosystems that may act as reservoirs and dissemination routes for AMR. This study evaluated the composition, distribution, and antimicrobial resistance profiles of culturable ampicillin-resistant Gram-negative bacteria recovered from sinkholes of the Yucatán Peninsula, Mexico. Water samples were collected from 27 sinkholes during dry and rainy seasons. The isolates were identified by MALDI-TOF MS and evaluated by broth microdilution. Representative E. coli isolates were analyzed by whole-genome sequencing. A total of 193 ampicillin-resistant Gram-negative isolates were recovered. The most frequently recovered genera were Enterobacter, Klebsiella, and Escherichia, which were detected across all hydrogeological zones. Resistance to cefotaxime, levofloxacin, gentamicin, and tetracycline was detected among several bacterial genera. Opportunistic bacterial species associated with healthcare-associated infections, including K. pneumoniae, A. baumannii, and P. aeruginosa, were also identified. Genomic analysis of 19 E. coli isolates revealed resistance determinants associated with multiple antimicrobial classes and a diverse population structure dominated by phylogroup B1. These findings show that the Ring of Cenotes aquifer harbors diverse populations of culturable ampicillin-resistant Gram-negative bacteria and emphasize the importance of groundwater ecosystems as environmental reservoirs of AMR. Full article

Yeast infections are becoming an increasing public health concern, mainly due to the spread of opportunistic species and the emergence of strains resistant to commonly used antifungal drugs. Marine resources are a promising source of bioactive compounds, including polysaccharides and other biopolymers with potential antifungal applications. In this study, a sulphated polysaccharide-rich extract was obtained from the red alga Jania pedunculata var. adhaerens and chemically characterized. Its antifungal activity was compared with that of a commercial chitosan formulation against clinically relevant yeasts, including species of Candida, Cryptococcus, Clavispora, Naganishia and Trichosporon. Growth kinetics were monitored in liquid medium over 24 h, and antifungal activity was evaluated through growth rate analysis, growth inhibition at 20 h and susceptibility clustering. The sulphated polysaccharide-rich extract showed moderate but consistent growth inhibition, with the strongest effects observed at 5 mg mL⁻¹. Maximum growth inhibition reached 60.9% in Cryptococcus deuterogattii and 59.8% in Candida albicans, although no complete inhibition was observed within the tested concentration range. Chitosan showed a stronger antifungal effect, with minimal inhibitory concentration (MIC) values between 10 and 20 µg mL⁻¹ in several species and maximum inhibition values above 80% in the most susceptible yeasts. However, C. albicans showed marked resistance to chitosan, with inhibition below 12%. K-means clustering confirmed distinct susceptibility profiles between treatments, supporting a species-dependent response. Overall, these results highlight marine-derived biopolymers as promising antifungal candidates and show that chitosan and algal sulphated polysaccharides produce distinct, species-dependent antifungal profiles. Full article

Stenotrophomonas maltophilia is increasingly recognized as a difficult-to-treat healthcare-associated opportunistic pathogen, particularly in critically ill and immunocompromised patients, in whom it causes severe respiratory, bloodstream, and device-associated infections. Its intrinsic resistance to multiple antimicrobial classes, capacity to acquire additional resistance determinants, and ability to establish persistent biofilms substantially limit therapeutic options. This review integrates current knowledge of the structural basis, regulatory circuitry, and ecological interactions governing S. maltophilia biofilm development and examines how these processes converge with antimicrobial resistance. Biofilm formation is driven by coordinated adhesion and motility, extracellular matrix production, quorum sensing, cyclic di-GMP signaling, two-component regulatory systems, and adaptive responses to iron limitation and oxidative stress. Multidrug efflux systems contribute not only to antibiotic extrusion but also to membrane homeostasis, motility, stress adaptation, and biofilm-associated phenotypes, thereby providing a functional link between antimicrobial resistance and bacterial persistence. In polymicrobial communities, interspecies signaling and competitive or cooperative interactions further reshape biofilm architecture and antimicrobial tolerance. Collectively, current evidence indicates that S. maltophilia biofilm formation arises from interconnected regulatory networks rather than isolated molecular determinants. Targeting matrix assembly, signaling pathways, stress adaptation, or resistance-associated physiology may therefore complement conventional antimicrobial therapy. Future studies should prioritize clinically representative isolates, physiologically relevant multispecies models, and in vivo validation to translate mechanistic insights into effective anti-biofilm interventions. 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