Journal of Antimicrobial Chemotherapy

Background: Most patients with melioidosis receive prolonged intravenous ceftazidime during the intensive phase of their antibiotic therapy. Contemporary guidelines use weight and renal function to guide dosing, but therapeutic drug monitoring (TDM) might enable further individualisation of therapy. Objective: To examine the potential utility of ceftazidime TDM in the management of melioidosis. Methods: We reviewed consecutive serum free ceftazidime concentrations in patients with culture-confirmed melioidosis at an Australian referral hospital. We documented the minimum inhibitory concentration (MIC) for ceftazidime Burkholderia pseudomallei isolates of the patients. We then recorded the ceftazidime dosing regimen for each patient, their serum free ceftazidime concentration and if any adverse drug reactions occurred during their treatment. Results: Trough concentrations were measured in 31 patients receiving intermittent ceftazidime dosing, while random concentrations were measured in 91 patients receiving a continuous infusion. The median (range) trough concentration:MIC ratio was 37.7 (2.7-156.6) in those receiving intermittent dosing and 47.5 (8.1-181.5) in those receiving a continuous infusion. Serum ceftazidime concentrations correlated with neurotoxicity, which was documented in 5/31 (16%) receiving intermittent dosing and in 4/91 (4%) receiving a continuous infusion. Serum ceftazidime concentrations were also higher in individuals who died from their infection than in those who survived. There was no association between ceftazidime concentrations and subsequent disease recurrence. Conclusion: Current dosing recommendations for the treatment of melioidosis achieve serum ceftazidime concentrations that greatly exceed the MIC of B. pseudomallei in this region of Australia. TDM-guided reductions in the ceftazidime dose and/or dosing frequency may mitigate the risk of ceftazidime toxicity.

Reduced cephalosporin resistance in Enterococcus faecium has traditionally been reported in laboratory mutants and, more recently, in a single clinical ampicillin-susceptible (AmpS) isolate. Herein, we investigated whether this phenotype is widespread by analysing 95 clinical enterococcal isolates (78 AmpS and 17 ampicillin resistant [AmpR]) collected from three hospitals in Spain and Portugal (2009-2025). Low ceftriaxone MICs ([≤]4 mg/L) were detected in 19/51 (37.3%) AmpS E. faecium and 7/27 (25.9%) E. lactis but in none of the AmpR isolates. Low ceftriaxone MICs were associated with older patient age in both species and with prior ampicillin therapy in E. faecium, but not with other clinical or epidemiological variables. Ceftaroline MICs were consistently low among AmpS isolates, while ceftriaxone and cefotaxime showed greater variability. Low-MIC isolates were distributed across multiple clonal lineages and hospitals and did not share a distinctive resistance or virulence gene profile. PBP5 phylogeny and variation at the psr-pbp5 region separated AmpS from AmpR E. faecium but did not explain variability in ceftriaxone MICs. Five AmpS isolates with reduced ceftriaxone MICs carried chromosomal deletions that included the psr-pbp5 region and genes with diverse cellular functions. Variation in other candidate resistance genes (pbpA, ponA, pbpF, croRS, stpA/stk and murAA) did not consistently explain the MIC differences. These results reveal unexpected heterogeneity in intrinsic cephalosporin resistance in clinical E. faecium and E. lactis and suggest that additional genetic or regulatory mechanisms underlie reduced susceptibility.

Background Urine tenofovir (uTFV) and dried blood spot (DBS) tenofovir diphosphate (TFV-DP) concentrations respectively estimate short- and medium-term adherence to tenofovir disoproxil fumarate (TDF)-based antiretroviral therapy (ART). We evaluated the accuracy of a point-of-care uTFV assay, and associations between uTFV/TFV-DP, and viral load (VL) and retention outcomes within a South African community ART programme. Methods We measured uTFV and DBS TFV-DP concentrations using liquid chromatography-tandem mass spectrometry (LC-MS/MS). We calculated sensitivity and specificity of the point-of-care uTFV assay at the manufacturer-recommended threshold of [&ge;]1,500 ng/mL compared to LC-MS/MS. We assessed associations of the point-of-care uTFV assay, and DBS TFV-DP concentrations with concurrent viraemia, and with retention-in-care by 16 weeks post-enrolment. Results Of 196 adults median age was 44 years, 127 (64.8%) were female, and 191 (97.4%) were receiving TDF. 185 (94.4%) had detectable point-of-care uTFV, which had high sensitivity (99.5%, 95% CI 96.5-100%) and moderate specificity (76.9%, 95% CI 46.0-93.8%) for detecting uTFV [&ge;]1,500 ng/mL. Two participants had concurrent viraemia [&ge;]1,000 copies/mL; of these 50.0% (95% CI 9.4-90.5) had undetectable point-of-care uTFV, and 100% (95% CI 19.7-100) had low TFV-DP <483 fmol/punch. Among participants without viraemia 97.4% (95% CI 93.6-99.0) had detectable uTFV, and 98.1% (95.3-99.6) had high TFV-DP [&ge;]483 fmol/punch. Point-of-care uTFV and DBS TFV-DP were not associated with retention-in-care. Conclusions The point-of-care uTFV assay demonstrated high sensitivity and moderate specificity to detect uTFV. Over 95% of people without viraemia had detectable point-of-care uTFV or high DBS TFV-DP levels respectively, but these were not associated with 16-week retention-in-care.

IntroductionIn sub-Saharan Africa, and more specifically in Cameroon, antimicrobial resistance (AMR) represents a major public health threat. This is underlined by the increasing appearance of multidrug-resistant bacteria. Extended-spectrum {beta}-lactamase producing Escherichia coli (ESBL-Ec), a critical priority bacterium, is increasingly implicated in life-threatening infections in hospital and community settings in Cameroon. Data on the genetic composition of ciprofloxacin-resistant Escherichia coli are limited in Cameroon. This study aimed to investigate the prevalence, genetic diversity, resistance mechanisms in multidrug-resistant Escherichia coli organisms isolated from clinical samples in two hospitals in Yaounde, Cameroon. MethodA cross-sectional study was conducted from February to June 2025 in two healthcare facilities in Yaounde, Cameroon. All clinical samples from in- and out-patients were analysed. After culturing, identification was performed using API20E as per the manufacturers instructions and ESBL production was screened in CHROMagarTM ESBL. Antimicrobial susceptibility testing was performed using the Kirby-Bauer disc diffusion method. Polymerase chain reaction (PCR) was used to detect ESBL and plasmid mediated quinolone resistance (PMQR)genes, as well as mutations in quinolone resistance-determining region (QRDR) (gyrA/parC) Horizontal. plasmid transfer was also investigated. Finally, phylogroup analysis was assessed. ResultThe prevalence of MDR E. coli was 50.7% (n=33/65), all of which (100%) were ESBL producers and 91% were ciprofloxacin-resistant. Highest resistance rates were observed for cefotaxime (100%), ceftriaxone (100%), and ciprofloxacin (91%). The most frequent ESBL genes were blaTEM (36.3%; n=12/33). Among PMQR genes, qnrB was detected in 16.6% (n=5/30) of isolates. Only the ESBL genes were carried by plasmids; the most prevalent plasmid-borne gene was blaTEM (40%), followed by blaCTX-M (26.7%). Mutations within the topoisomerase QRDR (parC gene) were identified in 36.6% (n=11/30) of ciprofloxacin-resistant strains. Phylogroup analysis revealed a predominance of phylogroup A, followed by group B. ConclusionThis study reveals a high prevalence of multidrug-resistance, ESBL (blaTEM dominant) and fluoroquinolone resistance in E. coli in Yaounde, with plasmid dissemination of ESBL genes and chromosomal stabilization of PMQR determinants. The predominance of commensal phylogroups in clinical samples underlines the role of the community reservoir. It is urgent to reinforce " real-time One Health" genomic surveillance in Cameroon.

Pharmacodynamic curves describe how changes in drug concentration affect pathogen growth. They are essential for designing treatments that promote pathogen eradication and minimize the evolution of antibiotic resistance. The classical function for modelling pharmacodynamics is a phenomenological, S-shaped curve with stable growth and death rates separated by a single drop. In this study, we characterized the pharmacodynamic curve of the {beta}-lactam antibiotic cefotaxime (CTX) acting against Escherichia coli. We found that the relationship between CTX concentration and net growth rate diverged from classical model predictions, instead yielding a two-step curve defined by distinct phases of growth, population maintenance, and killing. We hypothesized that the intermediate phase arose from antibiotic tolerance conferred by bacterial filaments. Microscopic assessment of treated cells indeed showed a difference in degree of filamentation with concentration. We further sought to explain this with a semi-mechanistic pharmacodynamic function, modelling the binding of CTX to its cellular targets, penicillin binding proteins (PBP) 1 and 3. By incorporating the preferential concentration-dependent binding of CTX to PBP3 and then PBP1, yielding filaments or lysed cells respectively, we replicated the two-step curve in silico. We also assessed the pharmacodynamics of CTX against mutants conferring resistance; these displayed further altered curves, in line with their fitness costs. Altogether, our results show that CTX has a two-step pharmacodynamic curve against E. coli arising from multiple targets separated in their affinity for the antibiotic. We present a model offering a mechanistically grounded framework for capturing such dynamics. These pharmacodynamic curves deserve careful consideration when defining optimal dosing.

The emergence of antibiotic tolerance in Staphylococcus aureus reduces antibiotic efficacy by allowing bacterial survival despite prolonged antibiotic exposure, the molecular basis of which remains poorly understood. Moreover, the phenotypic indistinguishability of tolerant isolates in antimicrobial susceptibility testing impedes effective diagnosis and therapy. Increased concentration of the second-messenger, cyclic-di-AMP (CDA), has recently been implicated in tolerance to {beta}-lactams as well as other cell-wall-reactive antibiotics. Using the ScanLag assay, Tolerance-Disk test, and traditional methodologies and employing isogenic mutagenized strains, we demonstrate that loss of GdpP function, a phosphodiesterase that hydrolyzes CDA, confers tolerance specifically to {beta}-lactam antibiotics independent of their class. The extent of {beta}-lactam tolerance correlated directly with the intracellular CDA concentration and inversely with the inhibition of bacterial cell-wall synthesis. {Delta}gdpP mutants caused higher mortality than wild-type strains in the Galleria mellonella infection model upon {beta}-lactam treatment, suggesting GdpP-mediated tolerance could lead to {beta}-lactam treatment failure. Large-scale within-host evolution analysis demonstrated that MRSA and MSSA strains isolated from patients acquire GdpP loss-of-function mutations during invasive infections but not during nasal carriage. Overall, this study highlights the clinical relevance of gdpP mutations, frequently selected in persistent S. aureus infections, as key mediators that could promote treatment failure due to {beta}-lactam tolerance.

ObjectiveCarbapenem-resistant Klebsiella pneumoniae harboring blaNDM poses a serious threat to public health; however, blaNDM-15 remains poorly characterized outside the dominant epidemic lineages. MethodsWe characterized K. pneumoniae strain ETFK6090, isolated from a perianal surveillance swab of an 11-month-old immunocompromised child in a paediatric intensive care unit. Investigations included antimicrobial susceptibility testing, broth conjugation, S1 nuclease PFGE with Southern blotting, complete genome sequencing, and comparative genomic analysis against 465 curated blaNDM-positive K. pneumoniae genomes from 37 countries. ResultsETFK6090 belonged to ST580 and exhibited resistance to carbapenems, ceftazidime-avibactam, broad-spectrum cephalosporins, fluoroquinolones, gentamicin, chloramphenicol and trimethoprim-sulfamethoxazole; amikacin and fosfomycin retained low MICs. The complete genome comprised one chromosome and five plasmids, blaNDM-15 was localized on a 46,161-bp IncX3 plasmid, confirmed by Southern blotting. Conjugation into Escherichia coli EC600 transferred carbapenem and cephalosporin resistance, confirming in vitro mobility. The blaNDM-15 genetic environment retained a conserved blaNDM module, with IS-mediated rearrangements at the downstream boundary. In the global comparison, blaNDM-1 and blaNDM-5 predominated, the ST580-blaNDM-15 combination was exceedingly rare, and ETFK6090 constituted a distinct branch apart from major epidemic lineages. ConclusionsA transferable IncX3-blaNDM-15 plasmid can emerge in an uncommon ST580 background, underscoring the necessity to extend genomic surveillance of carbapenem-resistant K. pneumoniae beyond dominant epidemic clones, particularly in high-risk paediatric and intensive-care settings.

Human-targeted non-antibiotic drugs are increasingly recognized for their intrinsic antibacterial activity, yet Gram-negative pathogens such as Acinetobacter baumannii exhibit substantial tolerance to these compounds. This tolerance is largely attributed to restricted outer membrane permeability and the activity of multidrug efflux systems. While Resistance Nodulation Division (RND) transporters have been extensively studied, the contribution of individual Major Facilitator Superfamily (MFS) transporters to non-antibiotic drug tolerance remains poorly understood. Here, we investigated H0N29_04330, designated Drug Resistance Transporter A (DrtA), a Bcr/CflA subfamily MFS transporter, to define its substrate specificity and contribution to antibiotic and non-antibiotic drug tolerance. DrtA was highly conserved across the A. calcoaceticus-baumannii complex and exhibited broad substrate specificity when heterologously expressed in an efflux-deficient Escherichia coli background, conferring resistance to benzalkonium, ethidium bromide, phenicols, and the antineoplastic agent mitomycin C. Intriguingly, drtA expression increased E. coli susceptibility to the antifolate compounds methotrexate and aminopterin, suggesting that DrtA may recognize folate-related metabolites rather than function as a dedicated antifolate transporter. In contrast, loss of drtA in its native A. baumannii host primarily impaired tolerance to mitomycin C, highlighting a context-dependent physiological role influenced by the extensive functional redundancy among A. baumannii efflux systems. Site-directed mutagenesis further identified M18 and the membrane-embedded protonatable residue D26 as critical determinants of DrtA transport activity and substrate recognition. Together with previous characterization of CraA, our findings demonstrate that Bcr/CflA subfamily MFS transporters contribute to protection against structurally diverse human-targeted compounds and expand the functional landscape of efflux-mediated intrinsic tolerance beyond conventional antibiotic resistance.

Background: Global HIV programmes are transitioning virally suppressed children and adolescents with HIV (CAWH) from prior regimens to dolutegravir-based antiretroviral therapy (ART). However, the supporting evidence largely stems from randomised trials in viraemic CAWH. The effect of transition for virally suppressed CAWH is unknown. Methods: We used observational, de-identified data from 724 clinics in KwaZulu-Natal, South Africa. We sequentially emulated three distinct target trials to estimate the effect of transitioning to dolutegravir-based ART in three paediatric populations: i) ages 8-17 years taking efavirenz-based ART, ii) 8-17 years taking ritonavir-boosted lopinavir (LPV/r)-based ART, and iii) 0-7 years taking LPV/r-based ART, all with a last viral load <1,000 copies/mL. The risk difference (RD) of death or viraemia >1,000 copies/mL through 12 and 24 months was estimated using an inverse probability weighting approach. Findings: From January 2020 to August 2024, 37,145 CAWH contributed 454,081 person-trials. In CAWH initially taking efavirenz, the standardised 12-month risk of death or viraemia was 11.9% with continued efavirenz and 6.7% with transition to dolutegravir (RD -5.2 [95% CI -5.8 to -4.6]). In older CAWH initially taking LPV/r, these risks were 17.8% and 9.5%, respectively (RD -8.3 [-10.0 to -6.8]). In younger children, the respective risks were 15.8% and 6.7% (RD -9.0% [-12.7 to -5.4]). Where available, 24-month endpoints showed slightly greater RDs. Interpretation: This large-scale, causal analysis highlights improvements in viral suppression and strongly supports ongoing transition to dolutegravir-based ART for virally suppressed CAWH. Funding: Gates Foundation, National Institute for Health and Care Research, Swiss National Science Foundation

Background Rising antimicrobial resistance (AMR) in the African region contributes to high morbidity and mortality. Continuous national AMR surveillance is critical in understanding the spread of AMR and informing policies on containment. We present results of national AMR surveillance in Kenya Methods Passive surveillance was prospectively conducted in 20 sites in Kenya between 2021 and 2025. Sites included national and sub-national level tertiary public and private hospital laboratories. Non-duplicate isolates of WHO priority Gram-negative and Gram-positive pathogens were included in this analysis. Bacterial isolates were identified using either conventional identification methods, Analytical Profile Index or automated systems while antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method or automated systems and interpreted using the Clinical and Laboratory Standards Institute guidelines. The primary outcomes were the proportions of various priority bacteria isolated and the proportions resistant to commonly used antibiotics. Results Between 2021 and 2025, there were 15,124 priority pathogens isolated with 7,592 (50.2%) from urine, 5,430 (35.9%) from blood (35.9%), and 1,784 (11.8%) from respiratory specimens. Escherichia coli and Klebsiella pneumoniae accounted for 76.3% of the priority pathogens. Resistance to 3rd generation cephalosporins was 63.2% for Escherichia coli and 79.1% for Klebsiella pneumoniae for the period 2021 to 2025 while carbapenem-resistance was 30.4% for Klebsiella pneumoniae and 7.2% for Escherichia coli. Resistance to carbapenems by Klebsiella pneumoniae increased from 17.9% in 2021 to 35.9% in 2025 while Methicillin resistance in Staphylococcus aureus increased from 36.5% in 2021 to 56.4% in 2025. Conclusion Resistance to critical antibiotics is a significant problem in Kenya, with alarming rates of Methicillin Resistant Staphylococcus aureus and carbapenem resistant Klebsiella pneumoniae. Ugent and sustained infection prevention and control measures and appropriate antimicrobial stewardship activities should be instituted across all health facilities in the country. There is need for improved access to antibiotics with activity against these resistant pathogens.

Background Carbapenem-resistant bacteria are a major global public health threat, classified as critical priority pathogens by the WHO. In Indonesia, despite a national antimicrobial resistance control programme established by the Ministry of Health in 2015, resistance rates continue to rise, including increasing carbapenem resistance among clinically important bacteria. Strengthening approaches to directly interrupt transmission is essential, yet transmission pathways remain poorly understood with limited research and policy guidance within the Indonesian context. Methods and analysis The INTERCEPT study is a UK-Indonesia multidisciplinary collaboration aiming to identify transmission routes of carbapenem-resistant bacteria across healthcare and community settings, and the mechanisms of resistance gene transfer between bacteria and mobile genetic elementss. We will conduct genomic surveillance of hospital inpatients, healthcare workers, hospital environments, and surrounding communities, including wastewater systems, combined with genomic analyses and mathematical transmission modelling. A cohort of patients with bloodstream infections will be recruited to evaluate resistant bacteria, treatment practices, and clinical outcomes. Qualitative research will explore behavioural and system-level factors influencing transmission and intervention implementation. Findings will inform stakeholder workshops to co-design context-specific interventions, with pilot intervention over 9 months with pre- and post-intervention assessment to guide scalable strategies to reduce AMR transmission. Discussion The INTERCEPT study addresses carbapenem resistance in Indonesia using an integrated approach combining microbiological surveillance, genomics, modelling, and qualitative methods. Strengths include cross-sectoral analysis (patients, workers, environment) and participatory intervention design. Limitations include geographic scope restricted to Central Java, Indonesia.

Klebsiella aerogenes, a member of the Enterobacteriaceae, is a causative agent of healthcare-associated infections, and outbreaks caused by drug-resistant K. aerogenes have been reported worldwide. The range of antimicrobial agents available for treating infections caused by carbapenem-resistant K. aerogenes is limited. While in vivo animal experiments using clinical K. aerogenes isolates to evaluate antimicrobial therapy could facilitate selection of the most effective treatment, conducting infection experiments involving large numbers of mammals such as mice is challenging due to ethical concerns related to animal welfare. Silkworms are invertebrates increasingly used as experimental models for infectious disease research to evaluate antimicrobial efficacy. In this study, we aimed to establish a silkworm infection model using a clinical K. aerogenes isolate to evaluate its utility for determining effective antimicrobial doses. K. aerogenes strains were isolated from a patient at a Japanese hospital, and a silkworm infection model was established using the clinical isolate. The non-metallo-beta-lactamase-producing strain K. aerogenes TUM25562, isolated from a patient with a complicated urinary tract infection, was susceptible to meropenem (MEPM) and gentamicin (GM) in vitro. During treatment, additional isolates with increased resistance to MEPM and subsequently to both MEPM and GM emerged. K. aerogenes TUM25562 caused dose-dependent mortality in silkworms. Treatment with clinically equivalent weight-based doses of MEPM or GM did not cure the infected silkworms. The median effective (ED50) doses of MEPM and GM were therefore investigated using the silkworm infection model. Administration of higher doses corresponding to four times the ED50 significantly prolonged the survival of infected silkworms. These results suggest that a silkworm infection model using clinical K. aerogenes isolates may provide a practical approach for evaluating antimicrobial efficacy and determining effective antimicrobial doses.

Quinolone antibiotics such as ciprofloxacin inhibit DNA gyrase, leading to DNA double-strand breaks that result in rapid bacterial killing and induction of the mutagenic SOS DNA repair response. By contrast, the ciprofloxacin analogue IMP-1700 inhibits ciprofloxacin-induced SOS, suggesting a novel mechanism of action. Here, we provide evidence that IMP-1700 targets the quinolone binding domain of DNA gyrase but triggers a significantly higher frequency of division septa in S. aureus compared with other DNA gyrase targeting antibiotics, including ciprofloxacin. In keeping with this finding, the lipopeptide antibiotic daptomycin, which targets the division septum, bound more strongly to IMP-1700-treated cells relative to S. aureus exposed to other DNA gyrase inhibitors, leading to increased bacterial killing. This finding extended to a panel of paired daptomycin susceptible and resistant clinical isolates. We conclude that the ciprofloxacin analogue IMP-1700 has distinct effects on the cell envelope of S. aureus, despite appearing to share the same target as the parent drug, which result in the resensitisation of daptomycin resistant bacteria to the lipopeptide antibiotic.

Background Using a population-based cohort from the Calgary Health Zone (CHZ), Canada, we integrated longitudinal antimicrobial susceptibility and prescribing data with the whole genome sequences of five major pathogens. We aimed to assess how antimicrobial resistance (AMR) responds to prescribing changes and determine which bacterial strains shape these dynamics. Methods We analysed antibiotic prescribing rates, clinical and genomic data from 7,271 Staphylococcus aureus, 1,609 Enterococcus faecalis, 801 Enterococcus faecium, 11,363 Escherichia coli, and 2,319 Klebsiella pneumoniae isolates, associated with bacteraemia episodes in the CHZ between 2006-2022. Genomic clusters (referred to as strains) were identified using StrainGST and assigned to known sequence types (STs) or clonal complexes (CCs). Strain-level incidence, stratified by community-onset (isolates collected [&le;]48h after admission) and hospital-onset (>48h after admission), AMR phenotypes, and prescribing rates were modelled using negative-binomial and binomial regression. Temporal trends were quantified using average annual percentage change (AAPC). Findings Between 2010-2022, fluoroquinolone prescribing declined in both community (AAPC=-6.8% [95% CI -8.1, -5.4]; p<0.0001) and hospital settings (AAPC=-5.1% [-6.5, -3.7]; p<0.0001). This was accompanied by a significant reduction in fluoroquinolone resistance among Gram-positive species. Specifically, S aureus bacteraemia resistant to clinically important antibiotics, cloxacillin, ciprofloxacin, erythromycin, and clindamycin, declined from 2006 to 2022, mostly in hospital-onset cases (AAPC=-16.0%, [-19.3%, -12.7%], p<0.0001). In E coli, ceftriaxone and ciprofloxacin resistance were clustered in ST131 and the emerging ST1193; the latter increased steadily, particularly in community-onset cases (AAPC=17.7%, [0.0%, 30.0%], p<0.0001). CTX-M-27-producing E coli ST131 strains increased (AAPC=23.8%, [17.4%, 30.5%], p<0.0001) between 20082022, while CTX-M-14-producing E coli ST131 declined (AAPC=-15.9%, [-21.3%, -10.2%], p<0.0001) between 2013-2022. These trends were paralleled by an increase in community cephalosporin prescribing (AAPC=7.3%, [4.2%, 10.5%], p<0.0001) between 2010-2022. For K pneumoniae, hypervirulent ST23 was most common (N=88) with an increasing trend in incidence (AAPC=3.0%, [-2.8%, 9.2%]) between 2006-2019. Conclusions The contrasting resistance trends between Gram-positive and Gram-negative species underscore the complexity of AMR control efforts. Effective strategies will require stewardship efforts targeting multiple drug classes, genomic surveillance for emerging resistant strains, and interventions extending beyond hospital settings.

Objectives: To investigate whether ethambutol resistance in Mycobacterium avium complex is associated with the emergence of macrolide resistance. Methods: Patients who developed macrolide resistance during guideline-based treatment were included, and longitudinal analyses of minimum inhibitory concentrations and mutations in embB or the upstream region of embA were performed. Clinical, microbiological, and radiological characteristics were compared according to the mutation status of embB or embA upstream region, prior to the emergence of macrolide resistance. We further evaluated the impact of embB mutation on the development of macrolide resistance using in vitro time-kill assays. Results: Sixteen patients developed macrolide resistance during guideline-based treatment. None of these patients had an ethambutol minimum inhibitory concentration >=16 ug/mL or embB or embA upstream mutations at treatment initiation; however, 8/16 patients (50.0%) had an ethambutol minimum inhibitory concentration >=16 ug/mL at the time of macrolide resistance detection, and 7/16 (43.8%) had developed embB or embA upstream mutations prior to the emergence of macrolide resistance. Cavitary lesions were present in 1/7 (14.3%) patients with embB or embA upstream mutations. In strains with embB mutations, the minimum inhibitory concentration of ethambutol increased by 1-2 dilutions relative to that of pretreatment isolates, with a corresponding increase in the concentration required to suppress macrolide resistance. Conclusions: Ethambutol resistance may contribute to the development of macrolide resistance in patients with M. avium complex pulmonary disease, particularly in those without cavitary lesions.

BackgroundOutbreaks of fluconazole-resistant Candida parapsilosis have recently emerged worldwide. In Spain, this phenomenon has been reported since 2020, mainly involving isolates from different clones harbouring the Y132F mutation at Erg11. MethodsWe analysed the expansion of fluconazole resistant C. parapsilosis strains within the national antifungal resistance surveillance program. Genetic clustering and relationships were assessed using microsatellite typing and whole genome sequencing. FindingsWe identified the expansion of three distinct clones carrying the Y132F mutation. Additionally, there was an increase in strains harbouring the G458S mutation, most of which belonged to a clonal complex, although other less prevalent clones were also detected. G458S isolates showed higher resistance to azoles than Y132F strains, particularly to voriconazole and isavuconazole. This increased resistance was associated with mutations in the Tac1 transcriptional regulator and duplication of a chromosomal region containing Tac1 and Erg11. One G458S isolate without mutation at Tac1 exhibited lower MIC values. Furthermore, two isolates carried the K143R mutation, and a distinct group of resistant strains without detectable ERG11 mutations was also identified. Resistant cases were detected across 31 hospitals in 12 autonomous regions. InterpretationOur findings indicate a concerning nationwide expansion of antifungal-resistant C. parapsilosis in Spain, involving multiple resistance mechanisms and clonal lineages, with implications for antifungal treatment and infection control strategies.

Antimicrobial resistance generates a vast, rapidly growing literature, yet no resource offers a comprehensive, evidence-linked repository of AMR findings at scale. We present ResLit, an automated pipeline and public database that mines the AMR literature for resistance genes, mutations, organisms, and mechanisms. From 2 million candidate PubMed records, BioMistral-7B screened abstracts to 356,000 relevant papers; multi-tier retrieval yielded 117,000 full texts, from which Qwen3-30B performed two-step extraction. ResLit contains 3,120 genes and 13,593 mutations, cross-linked to CARD, ResFinder, and NCBI Reference Gene Catalog across four evidence tiers. It further supports community-driven curation of automated outputs and reference databases. Freely available at www.reslit.info.

BackgroundThe epidemiology of Klebsiella pneumoniae carbapenemase (KPC)-producing Pseudomonas aeruginosa is rapidly evolving in China. While blaKPC-2 remains the predominant KPC variant in P. aeruginosa, blaKPC-3 has rarely been documented in this pathogen. This study investigated the molecular epidemiology, resistance and virulence characteristics, and plasmid features of blaKPC-3-producing CRPA isolates collected from a tertiary hospital in eastern China. MethodsA total of 65 non-duplicate CRPA isolates collected in 2023 were subjected to whole-genome sequencing. Antimicrobial susceptibility testing, phylogenetic analysis, plasmid characterization, conjugation experiments, and virulence assays were performed. ResultsAmong the 65 CRPA isolates, 37 (56.9%) carried blaKPC-3. These blaKPC-3-positive isolates belonged to four sequence types (STs), including ST1076 (62.2%), ST463 (21.6%), ST646 (10.8%), and ST3393 (5.4%). To our knowledge, this is the first report of blaKPC-3 in P. aeruginosa ST463, ST646 and ST3393. All isolates exhibited extensive drug resistance, and 51.8% were resistant to ceftazidime-avibactam. Phylogenetic analysis indicated that blaKPC-3 dissemination was driven by both clonal expansion and horizontal transmission. Comparative genomic analysis identified three kinds of blaKPC-3 -carrying plasmid. A transferable IncP-2 megaplasmid was widely distributed among ST1076, ST646, and ST3393 isolates, whereas non-transferable IncP-10 plasmids were primarily restricted to ST463. The genetic environments and plasmid backbones of blaKPC-3 were highly conserved and closely related to those of blaKPC-2 and its variants, suggesting evolution from pre-existing blaKPC-2-associated plasmids. Virulence analysis demonstrated marked heterogeneity across lineages. ST463 isolates co-harbored exoU and exoS, exhibited enhanced biofilm formation and pyocyanin production, and caused significantly higher mortality in the G. mellonella infection model, indicating a hypervirulent phenotype. ConclusionsThe blaKPC-3 is becoming an increasingly important determinant of carbapenem resistance in P. aeruginosa in China. The IncP-2 megaplasmid and IncP-10 plasmid derived blaKPC-3 spread across multiple lineages. Continuous genomic surveillance and enhanced infection control measures are urgently needed to prevent its further prevalence in clinical settings.

BackgroundDespite the importance of oropharyngeal gonorrhoea in transmission, suboptimal antimicrobial responses and propensity for horizontal transfer of antimicrobial resistance at this site, it remains understudied. An oropharyngeal N. gonorrhoeae controlled human infection model (CHIM) represents a promising tool to study infection and undertake translational research. MethodsA panel of five contemporary N. gonorrhoeae isolates were subject to detailed characterisation to assess antimicrobial susceptibility, in vitro infectivity, cytotoxicity and serum sensitivity to inform challenge agent selection. A method for challenge agent manufacture, including release testing, was developed and validated. FindingsAll candidate isolates were able to infect the surface of pharyngeal and cervical cells in vitro. One isolate displayed an invasive phenotype, induced higher inflammatory cytokine production and displayed elevated serum resistance and was excluded. The remaining four isolates were minimally inflammatory, did not induce cytotoxicity and were susceptible to serum killing. Three of the four isolates grew in a defined liquid medium. Together these results led to the selection of a contemporary N. gonorrhoeae isolate suitable for use in CHIM. A challenge agent manufacture workflow was established and shown to reliably and reproducibly generate doses suitable for direct inoculation in an oropharyngeal CHIM. ConclusionPhenotypic characterization of candidate N. gonorrhoeae challenge agents led to the successful identification of a contemporary isolate suitable for implementation in a novel oropharyngeal gonorrhoea CHIM. We demonstrate the feasibility of a challenge inoculum manufacturing process that aligns with international best practice guidelines.

Introduction Miltefosine is the only approved oral antileishmanial agent, but its use in women of childbearing potential (WOCBP) is restricted due to preclinical teratogenicity. Current labeling recommends contraception during treatment and for at least five months thereafter, based solely on its long terminal elimination half-life. This study re-evaluated the required contraceptive duration using an exposure margin-based approach. Methods Virtual populations were generated from anthropometric data of 382 Indian, 4,462 Eastern African, and 4,019 Brazilian WOCBP with leishmaniasis. Published population pharmacokinetic models were used to simulate miltefosine exposure following 14-42-day regimens for visceral leishmaniasis (VL), post-kala-azar dermal leishmaniasis (PKDL), and cutaneous leishmaniasis (CL). A developmental safety exposure threshold was derived from the rat no-observed-adverse-effect level (0.6 mg/kg/day for 10 days) and adjusted using a 10-fold safety margin. Contraceptive durations resulting in median residual post-contraception exposure (AUCEOC-{infty}) below this threshold were considered supportive of contraceptive discontinuation. Results The developmental safety exposure threshold was estimated at 2.5 mg{middle dot}day/L. Despite pharmacokinetic differences across geographical regions and disease manifestations, required minimum contraceptive durations were consistent: three months from treatment initiation for the 14-day regimen, four months for 21- and 28-day regimens, and five months for the 42-day regimen. For the 14-day regimen, a single dose of a long-acting injectable contraceptive administered at treatment initiation would provide sufficient coverage. Conclusion An exposure margin-based approach supports shorter contraceptive durations than current recommendations. For the 14-day VL regimen, three months of contraception may provide a practical alternative to current labeling.