Journal of Global Antimicrobial Resistance

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.

Antimicrobial resistance in Pseudomonas aeruginosa has emerged as a major clinical concern. Ciprofloxacin has potent intrinsic activity against P. aeruginosa, but resistance to this antibiotic is increasingly reported in clinical settings. In this study, P. aeruginosa ATCC 27853 strain was exposed to gradually increasing ciprofloxacin concentrations for 50 passages ([~]100 days). The final selected resistant strain (CIP-R) with 256-fold of minimum inhibitory concentration was studied further. Whole-genome sequencing revealed 12 genomic alterations, including known mutations in the quinolone resistance-determining genes gyrA (Thr83Ile), parC (Thr177Asn), parE (Glu459Lys). A duplication mutation in nfxB (Tyr153_Gly154dup) was also observed. In addition to these genes, we observed mutations in pilA, tadB, psdR, NP446_RS32055 (TRAP transporter permease), multiple dppA3 variants, and a prophage-associated hypothetical gene (NP446_RS24255), which have not been reported previously. The gyrA Thr83Ile substitution was conserved in 86.38% of ciprofloxacin-resistant clinical isolates retrieved from the NCBI database. Resistance acquisition was accompanied by slower growth, impaired swimming and swarming motility, diminished surface attachment, reduced biofilm formation. The resistant strain has enhanced {beta}-lactamase activity, and resistance to levofloxacin, cefepime, and meropenem together with sensitivity to piperacillin-tazobactam and aztreonam. This study highlights the gyrA Thr83Ile mutation as a key genomic marker for molecular screening of ciprofloxacin resistance and reveals secondary adaptive trade-offs that can be targeted for clinical diagnostic and therapeutic decision-making. In conclusion, achieving high-level ciprofloxacin resistance in P. aeruginosa involves non-target-site genomic adaptations and physiological trade-offs beyond classical target mutations.

The minimum inhibitory concentration (MIC) assay is the gold standard for evaluating antimicrobial activity1. However, conventional agar-based MIC methods often underestimate the potency of physicochemically complex compounds[1, 2]. Hydrophobic and adhesive molecules, such as lipoglycopeptide antibiotics, exhibit poor diffusion and non-specific binding to agar, leading to artificially elevated MIC values compared to broth-based methods[3]. This issue complicates accurate potency assessment and is particularly an issue when attempting resistance frequency (FOR) studies, which must be conducted on solid media. Here, we developed a modified miniaturised agar MIC assay using 1% agarose, 0.002% Tween 80-supplemented tryptic soy broth (TSB), and a 24-well plate format[4]. These modifications improved compound dispersion, reduced matrix interactions, and lowered compound requirements. The optimised assay was validated with vancomycin, oritavancin, and dalbavancin against Staphylococcus aureus ATCC 43300 (MRSA) and Streptococcus pneumoniae ATCC 700677. This efficient, cost-effective, high-throughput platform overcomes the limitations of traditional agar methods, enhancing reliability in evaluating challenging antimicrobials and supporting next-generation antibiotic development.

Background: The main cause of urinary tract infections (UTIs) are Gram negative bacteria with Escherichia coli as the leading cause and other important pathogens such as Klebsiella pneumoniae, Pseudomonas aeuriginosa and Enterococcus faecalis. Over the years uropathogens have become resistant to commonly used antibiotics, including penicillin's, cephalosporins and fluoroquinolones. Antimicrobial resistance (AMR) in UTIs is mainly caused by the misuse and overuse of antibiotics, recurrent infections, and healthcare-associated factors such as catheterization. Objectives: The aim of this study was to describe the bacteriological profile and antimicrobial susceptibility patterns of uropathogens isolated from positive urine cultures at Chhatrapati Shivaji Subharti Hospital, Meerut, a tertiary care centre in North India and develop an institutional antibiogram to support empirical prescribing and antibiotic stewardship at this institution. Materials & Methods: The study analysed 50 positive urine culture samples and their antimicrobial susceptibility records from July 2025 to December 2025. The isolates were identified, and antimicrobial susceptibility testing was performed using the disc diffusion method and automated Biomerieux Vitek 2 Compact machine. The collected data was analysed using descriptive statistics and Fisher's exact test. Results: Gram-negative bacteria accounted for 80.0% (40/50) of the culture-positive urine isolates. Escherichia coli was the most frequently isolated uropathogen (n=23, 46.0%), followed by Klebsiella pneumoniae (n=12, 24.0%), Candida spp. (n=6, 12.0%), Enterococcus spp. (n=4,8.0%), Pseudomonas aeruginosa (n=3, 6.0%), and Enterobacter cloacae (n=2, 4.0%). Of the total, 74% (37/50) of isolates came from Inpatient samples. E. coli had a 100% resistance to ampicillin and ceftriaxone, 95.7% to ciprofloxacin and cefepime, and 73.9% to meropenem, with fosfomycin (86.4% sensitive) and colistin (69.6% sensitive) as the only effective antimicrobials. K. pneumoniae had 100% resistance to ceftriaxone, amoxicillin-clavulanate, and piperacillintazobactam; carbapenem resistance ranged from 83.3% to 91.7%, and colistin was the only consistently effective treatment (83.3% sensitive). Of all the 35 tested Enterobacteriaceae isolates, Extended-Spectrum Beta-Lactamases (ESBLs) positivity was 100% with Carbapenem-Resistant Enterobacterales (CRE) positivity at 85.0%. All the bacterial isolates met Multi-drug Resistant (MDR) criteria. 31 of 35 (88.6%) tested Enterobacteriaceae isolates showed ESBL and CRE copositivity. The six strains of Candida demonstrated total sensitivity to all the antifungal drugs used. Conclusion: There is a critical burden of AMR at this hospital with 100% ESBL positivity, 85% CRE, and 100% MDR among all bacterial isolates. This study provides the first baseline institutional antibiogram to guide empirical prescribing and antibiotic stewardship at Chhatrapati Subharti Hospital.

Staphylococcus aureus and Streptococcus pyogenes are major causative bacteria responsible for skin and soft-tissue infections (SSTIs) such as impetigo. Increasing resistance to commonly used topical antibiotics necessitates evaluation of newer agents for the treatment of skin infections. Ozenoxacin, a novel non-fluorinated topical quinolone, has shown promise, exhibiting potent activity against a wide range of pathogens, including methicillin-resistant Staphylococcus (MRSA) and Streptococcus pyogenes. The present study compared the in vitro activity of ozenoxacin and comparator agents against clinical isolates of Staphylococcus aureus and Streptococcus pyogenes from multiple sources including skin and soft-tissue, wound, abscess, and blood. Ozenoxacin was assessed for in vitro antimicrobial activity against 109 methicillin-susceptible (MSSA), methicillin-resistant S. aureus (MRSA), and 24 Streptococcus pyogenes isolates by broth microdilution method recommended by the Clinical and Laboratory Standards Institute (CLSI). Ozenoxacin demonstrated potent in-vitro activity against all 109 S. aureus (MIC50/90= 0.125/0.5 {micro}g/ml) and 24 S. pyogenes (MIC50/90= 0.015/0.03 {micro}g/ml) strains. In contrast, higher MICs were observed for fusidic acid and mupirocin among a subset of S. aureus isolates. A comparison of MIC90values demonstrated that ozenoxacin (0.5 {micro}g/ml) was more active against S. aureus isolates than 8 of the 9 comparator agents tested including vancomycin and linezolid (MIC90= 2 & 4 {micro}g/ml) respectively. In vitro studies of ozenoxacin showed potency against staphylococci and streptococci including resistant S. aureus strains. These findings support its role as an effective first-in-class quinolone topical therapeutic option in the management of various SSTIs.

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) remains a potent threat to global public health. Moreover, the alarming surge in the number of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mtb strains will continue to imperil TB control efforts. Thus, the discovery of new TB agents with novel modes of action or resistance-reversing therapeutics is a pressing priority. In this study, we report the generation of spontaneous Mtb mutants exhibiting bedaquiline (BDQ) resistance and the subsequent evaluation of natural product-derived efflux inhibitors (EIs) that restored the antimicrobial efficacy of BDQ against the mutants. BDQ-resistant mutants were successfully isolated, and colonies were observed on agar plates with concentrations up to 100x the minimum inhibitory concentration (MIC). Upon screening against BDQ, the resistant strains exhibited MIC values ranging from 0.098 M to 3.136 M, corresponding to 1-32-fold increases relative to the wild type, with higher resistance observed on 50x- and 100x-selection plates. Genetic analysis identified point mutations and frameshifts in key resistance-related genes, including Rv0678, pepQ, and atpE. Notably, combining BDQ with EIs such as berberine (BER), reserpine (RES), piperine (PIP), and lyoniresinol (LYO) remarkably lowered the MIC in the selected mutant strain. Synergistic effects were observed for BDQ+BER (FICI = 0.188; 16-fold MIC reduction) and BDQ+RES (FICI = 0.37; 8-fold MIC reduction). For BDQ+LYO, the FICI could not be calculated because LYO did not have an MIC at the highest concentration tested; however, this combination produced the strongest effect, restoring susceptibility with a 64-fold MIC reduction and exhibiting bactericidal activity. These results highlight the role of efflux pumps in BDQ resistance and support the use of natural product-derived EIs as potential supplementary therapies against drug-resistant Mtb.

Probiotics produce antimicrobial peptides and small molecules that are secreted into the medium. Antimicrobial activity of cell-free supernatants can be tested using various qualitative and quantitative methods. Many of these techniques employ methods which introduce uncontrolled variables, impacting reproducibility and making comparison of reported results difficult. Here, we present a simple procedure for quantitative estimation of antimicrobial activity of cell-free supernatants which overcomes drawbacks of commonly used methods.

Pseudomonas aeruginosa (P. aeruginosa) is the primary pathogen responsible for morbidity and mortality in patients with cystic fibrosis (CF). Its genomic plasticity and constant selective pressure from antimicrobial treatments have favored the emergence of multidrug-resistant clones. This study conducted a comparative genomic analysis of 41 P. aeruginosa isolated from pediatric patients with CF in Mexico from 2015 to 2024, with the aim of characterizing their evolutionary dynamics, resistome, and virulome. Whole-genome sequencing (MGI, Illumina, and PacBio platforms) was used, with de novo assemblies performed using Unicycler v0.4.8 on the BV-BRC platform. The databases used for the resistome were CARD and NDARO, and for the virulome, VFDB. Phylogenetic reconstruction was based on core-genome alignments generated with Roary v3.13.0, with maximum likelihood reconstruction performed in IQ-TREE v2.1.2. The statistical significance of the segregation of resistance and virulence patterns was evaluated using PERMANOVA analysis. The results revealed a significant clonal prevalence of sequence types (ST) 307 and ST 167. Phylogenomic analysis grouped the isolates into three main clades; Clade 1 stood out for having the highest resistance gene load (mean of 75 genes/genome), establishing itself as the main reservoir of multidrug-resistant profiles. Genotype-phenotype concordance reached 65.5% overall, with high accuracy for aminoglycosides (87.8%) and fluoroquinolones (82.9%). Furthermore, virulome analysis identified 67 distinct patterns that were significantly segregated among the clades (PERMANOVA: R2=0.31, p=0.001). These findings demonstrate that the evolution of P. aeruginosa lineages in the pediatric clinical setting involves parallel and coordinated adaptations in both their resistance potential and their virulence arsenal. This study underscores the need to adopt a multidisciplinary approach to the clinical management of chronic P. aeruginosa infections in pediatric patients. The persistence of extensively drug-resistant (XDR) strains calls for the integration of genomic surveillance and functional diagnostics, as well as the search for therapeutic alternatives for the clinical management of patients with cystic fibrosis.

Background: Rising antibiotic resistance challenges empirical therapies for urinary tract infections (UTIs). This study evaluated the microbial etiology, susceptibility profiles, and multidrug resistance (MDR) patterns of uropathogens among outpatients at the Berekum Holy Family Hospital, Ghana. Methods: This cross-sectional study (February to August 2021) screened 263 symptomatic outpatients. Mid-stream urine samples underwent quantitative culture, biochemical identification, and antimicrobial susceptibility testing via the Kirby-Bauer disc diffusion method following the 2021 CLSI guidelines. Results: Significant bacteriuria prevalence was 22.8% (60/263). UTIs predominated in females (78.3%, 47/60; p = 0.1501) and individuals [≥]45 years (33.3%, 20/60). Gram-negative rods accounted for 90.0% of isolates, primarily Escherichia coli (26.7%), Citrobacter spp. (25.0%), and Enterobacter spp. (21.7%); Staphylococcus aureus (10.0%) was the only Gram-positive pathogen. Extreme phenotypic resistance was observed against piperacillin/tazobactam (98.3%), cefotaxime (93.3%), tetracycline (88.3%), and cefoperazone (85.0%). Conversely, highest therapeutic susceptibilities were retained by amikacin (78.3%), levofloxacin (61.7%), and gentamicin (58.3%). Conclusion: The high prevalence of MDR uropathogens against advanced beta-lactamase inhibitor combinations and cephalosporins necessitates an immediate re-evaluation of regional empirical protocols. Amikacin, levofloxacin, and gentamicin remain viable options prior to culture confirmation. These findings establish a crucial phenotypic baseline to guide localized prescribing policies and regional antimicrobial resistance tracking strategies.

Pseudomonas aeruginosa remains one of the most important clinical pathogens for which new drugs are needed, due to its resistance machinery. Consequently, there is an increasing effort to develop new and effective treatments against this pathogen. We recently showed that tetrasodium ethylenediaminetetraacetic acid (tEDTA) exhibits promising antibacterial and antibiofilm activity against P. aeruginosa in advanced biofilm models. tEDTA is known to chelate divalent cations, with predicted effects on the outer membrane; however, a full understanding of how this kills P. aeruginosa is lacking. Also, it is currently not clear how slowly or rapidly P. aeruginosa will evolve resistance to this treatment. Using membrane disruption assays and RNA-seq, we showed that tEDTA disrupts bacterial membrane potential and permeabilises P. aeruginosa membranes. RNA-seq revealed the significant upregulation of genes involved in the transport of iron, phosphate, potassium, and magnesium ion. The arnABCD operon which is involved in lipid A biosynthesis was also upregulated. Using a 7-day evolutionary ramp approach, we showed that P. aeruginosa could not evolve resistance to tEDTA under strong selection. Lastly, we carried out a cytotoxicity assay with Human Epithelial type 2 (HEp-2) cells and showed that there was reduced cytotoxicity of tEDTA compared to meropenem. This study provides good insight into the mechanism of action of tEDTA and further evidence of its potential as an alternative to antibiotics for P. aeruginosa infections.

Macrolides are key agents for treating infections caused by non-tuberculous mycobacteria (NTM). Nevertheless, chromosomal erm genes conferring inducible macrolide resistance are described in some NTM species, such as Mycobacterium abscessus and M. fortuitum, whereas M. chelonae had long been considered as lacking a functional erm. Recent descriptions from the USA and Japan of a new plasmid-borne erm(55) (erm(55)P) in M. chelonae and other rapidly growing mycobacteria (RGM) have challenged this assumption. We investigated erm(55)P occurrence in clinical RGM referred to the French National Reference Centre for Mycobacteria between 2012 and 2026 by genome screening and erm(55)P specific real-time PCR. Positive isolates underwent long-read whole genome sequencing (GridIon, Oxford Nanopore Technologies). Clarithromycin (CLR) minimum inhibitory concentration (MIC) was determined by broth microdilution (RAPMYCO and FRATMYC, Thermo Fisher) and read up to 14 days. Five clinical isolates showing inducible CLR resistance (MIC range <0.25-64 mg/L on day 3-4 and 128 - >128 mg/L on day 14) were positive for erm(55)P: one M. chelonae, three M. neoaurum, and one M. parafortuitum. erm(55)P-positive M. chelonae genomes from this and previous descriptions did not cluster together in the phylogenetic analysis of 263 genomes. The assembled plasmids showed high similarity to previously reported erm(55)-carrying plasmids, especially within the erm(55)P region. The upstream sequence of erm(55)P showed a secondary structure compatible with a possible translation attenuation mechanism. These findings document the first report of a plasmid-borne erm(55) in Europe in M. chelonae and other RGM and raise concern about the emergence of plasmid macrolide resistance in NTM.

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.

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.

The phenotypic plasticity, slow replication, and complex, hydrophobic cell envelope of Mycobacterium tuberculosis contribute to its successful survival as a pathogen and its drug tolerance. Consequently, the global threat of multidrug-resistant Tuberculosis (MDR-TB), coupled with lengthy and highly toxic treatment regimens, necessitates the development of innovative treatment solutions. Mycobacteriophages are natural viruses of mycobacteria that typically encode two endolysins, which cooperatively facilitate host cell lysis at the end of the lytic life cycle: LysA, a peptidoglycan hydrolase, and LysB, a lipolytic enzyme, targeting the mycolylarabinogalactan-peptidoglycan complex. Their precise and efficient lytic activity, along with their low propensity to induce resistance, make them, particularly LysBs, promising candidates for new treatment solutions. In this study, we report MTB-LysB1, a novel LysB enzyme from an F1 sub-cluster mycobacteriophage isolated from our laboratory collection. While studying its structural features by comparing the modelled structure with representative mycobacteriophage LysB homologues, we found that the /{beta}-hydrolase fold and key motifs are conserved. Also, we identified putative membrane-interaction motifs that may play a role in LysB1s cell permeation. Significantly, we found MTB-LysB1 to be active against both drug-susceptible and multidrug-resistant (MDR) M. tuberculosis strains at nanomolar concentrations, comparable to the well-characterised D29 LysB reference enzyme. Beyond its standalone activity, MTB-LysB1 exhibits an additive effect when combined with the TB drugs rifampicin and moxifloxacin, and co-administration reduces the drugs minimum inhibitory concentrations (MICs), which holds clinical significance. By structurally damaging the mycobacterial cell wall, the enzyme appears to act as a permeability enhancer for the chemotherapeutic drugs, thereby improving antibiotic efficacy. Collectively, our findings position the enzyme not only as a novel antimycobacterial agent but also provide a structural framework for its rational engineering as a promising next-generation adjunct to TB drug regimens. HighlightsO_LIA novel F1 sub-cluster phage-derived LysB is discovered and characterised using integrated computational, biochemical and microbiological methods. C_LIO_LIAlphaFold2 modelling, molecular dynamics simulations and comparative structural analyses revealed an /{beta}-hydrolase fold with conserved catalytic and membrane-interaction features. C_LIO_LIThe enzyme exhibited high esterase activity, thermal stability and potent lytic activity against Mycobacterium tuberculosis. C_LIO_LIAn additive effect with TB drugs rifampicin and moxifloxacin highlights MTB-LysB1s potential as an adjunct therapeutic. C_LI

SynopsisO_ST_ABSBackgroundC_ST_ABSTime kill curve (TKC) assessments are an essential step in the study of an antimicrobials pharmacodynamic characteristics. Surprisingly TKCs have not be formally standardised, therefore there remain concerns that different testing centres/methodologies may produce different results. Six centres participating in Gram-negative-Antibiotics NOW (GNA-NOW) consortium measured a series of TKCs with meropenem against E. coli to establish: Same-day (SD) vs different-day (DD) replication per centre (intra-site), and centre to centre (inter-site) correlations. MethodsMeropenem was tested against three strains of E. coli (ATCC 25922; ESBL producer C1.55; OXA-48 producer C1.62). An inoculum of 1.5x106 CFU was specified with meropenem concentrations of x0, x1 to x16 MIC; and sampling assessment of bacterial density was determined at 0-24h. Experiments were performed in triplicate, aerobically at 37{degrees}C. Centre-specific methodology was collected. Meropenem, media, bacterial strains, were shipped from one central laboratory to participating laboratories. ANOVA and Friedman tests were used to assess SD, DD and between centre replications. ResultsAssessment of the methodologies between centres revealed many differences, including bacterial inoculum, meropenem preparation, volume of TKC vessel, vessel materials, agitation vs static cultures and sampling volumes. Intra-centre SD and DD analysis for all strains were generally associated with P>0.05 suggesting consistency. Inter-centre SD and DD comparisons resulted in P<0.05, indicating variable total bacterial load measurement between centres. ConclusionsTKC methodologies varied between different centres, and while intra-centre comparison of SD and DD were generally consistent, inter-centre comparisons were not. Standardisation of TKC methodologies is required.

The global emergence of multidrug-resistant (MDR) ESKAPE pathogens has significantly reduced the effectiveness of existing antibiotics, highlighting the urgent need for new strategies to restore antimicrobial susceptibility. Here, we report the discovery and mechanism of BMM_1567, a peptide potentiator that enhances aminoglycoside efficacy against MDR pathogens. A genetically defined reporter-based screen identified BMM_1567 as a potent inhibitor of aminoglycoside resistance, potentiating spectinomycin activity against MDR Gram-negative ESKAPE isolates at low micromolar concentrations. Structural modeling and molecular dynamics simulations indicated that BMM_1567 interacts with residues lining the antibiotic-binding groove of aminoglycoside-modifying enzymes (ANT, APH, AAC), with highest affinity for ANT ({Delta}G_bind = -62.25 kcal/mol), suggesting competitive inhibition of substrate binding. Site-directed mutagenesis of key ANT residues identified critical amino acids involved in BMM_1567 binding, confirming their role in mediating spectinomycin potentiation. In murine abscess model using XDR E. coli, BMM_1567 in combination with spectinomycin significantly reduced bacterial burden and pro-inflammatory cytokine levels, comparable to colistin. Collectively, these findings establish BMM_1567 as a promising aminoglycoside potentiator that restores antibiotic activity against MDR pathogens through direct inhibition of resistance enzymes, while exhibiting in vivo efficacy and a remarkably low propensity for resistance development.

SynopsisO_ST_ABSBackgroundC_ST_ABSThe complexity of diagnosing and treating biofilm-associated infections necessitates a comprehensive strategy to mitigate the rising rates of antimicrobial resistance (AMR). Microtiter plate methods are used globally for determination of biofilm eradication concentrations (MBEC) but few have been adapted to observe pharmacodynamic observations. Here, we describe a method which allows for both static and pharmacodynamic assays of biofilm evaluation. MethodsA total of 150 clinical isolates from Southmead Hospital were assessed, representing five bacterial species (N=30 per bacterial species): Pseudomonas aeruginosa, Escherichia coli, Streptococcus pneumoniae, Staphylococcus aureus and Klebsiella pneumoniae. MBECs were determined using a developed method using 96 well plates and glass beads. MBECs of seven different antibiotics were compared to those determined using the established Calgary biofilm device (CBD). Dynamic pharmacodynamic evaluations to produce Biofilm Time Kill curve (BTKC) based on published planktonic time kill curve (TKC) data and ISO recommendations were carried out using the glass bead model for K. pneumoniae and ciprofloxacin, S. aureus and levofloxacin and S. pneumoniae and vancomycin. Quantification of biofilm biomass was assessed at 0, 2, 4, 8 and 24 hours and compared to planktonic culture survival under comparable challenge conditions. ResultsComparing MBEC results for all bacterial strains and antibiotic challenges showed no statistical difference between the glass bead and CBD methods (P <0.05). Biofilm BTKC AUBKC were inferior to planktonic equivalents but demonstrated specific pharmacodynamic patterns of biofilm reduction efficacy. MBEC correlated with biofilm BTKC penetration in line with clinical observations for S. aureus vs vancomycin and S. pneumoniae vs levofloxacin. ConclusionsThe glass bead biofilm models provide robust, reproducible alternatives to the traditional methods of determining MBEC and bridge the gap with biofilm pharmacodynamic evaluations. These methods also provide a low-cost option to current methods as only standard laboratory equipment is required, allowing for the generation of comprehensive data sets. This ensures greater translatability to complex in vitro models and clinical scenarios.

The minimum inhibitory concentration (MIC) is a standard measure for describing the lowest effective dose concentration of an antimicrobial compound in clinical practice; yet, conventional assays often require a substantial amount of antimicrobial compound, limiting their use with scarce, purified agents. Here, we describe a simple and reproducible technique to evaluate the MIC for purified compounds with a limited sample size. The protocol describes the MIC steps against a bacterial strain while minimizing the use of reagents and materials. It is helpful for screening purified natural products as antimicrobial agents and in early-stage drug discovery. The protocol adapts standard microplate-based assays for two-fold dilution of the compound, ensuring their applicability in microbiological studies. The MIC value of the standard antibiotic kanamycin against Staphylococcus aureus, Vibrio fischeri, Klebsiella pneumoniae, and Escherichia coli was determined using our method, and was found to be consistent with the conventional broth microdilution method, validating its reliability. Therefore, this method offers a practical and viable solution for antimicrobial drug discovery, addressing the disparity between limited compound availability and comprehensive microbiological assessment of MIC.

Resistance to the polymyxin antimicrobial colistin in Gram-negative bacteria is associated with a modification of the immunogenic lipid A moiety of the lipopolysaccharide (LPS). Chromosomal and plasmid-borne colistin resistance results in the addition of L-Ara4N and pEtN groups to lipopolysaccharide (LPS), respectively. Here, using THP-1 cells, we studied the impact of different LPS modifications of Klebsiella pneumoniae in stimulating host immune response. K. pneumoniae clinical isolates were screened for colistin resistance using broth microdilution (BMD) and the MALDIxin test. LPS was extracted from colistin-resistant isolates and used to stimulate differentiated THP-1 cells. Luminex cytokine assay measured the immune induction via a panel of proinflammatory cytokines. Out of a collection of 72 clinical K. pneumoniae, eight (11.1%) exhibited phenotypic colistin resistance with a minimum inhibitory concentration (MIC) of 8 to 64 mg/L. In total, five isolates possessed genes associated with polymyxin resistance; three isolates had a mutation in the pmrB gene, and two were mcr-8.1 positive. MALDIxin demonstrated that all eight phenotypic colistin-resistant isolates elaborated peaks at m/z 1,955 and m/z 2,193, indicating an L-Ara4N group of LPS modification. For two mcr-8.1 positive isolates, LPS had a pEtN group. The LPS modification positively correlated with colistin MIC (correlation coefficient, r= 0.6 and R2= 0.4). Compared to the native structure, LPS modification was associated with greater production of IL-1{beta}, IL-6, and CXCL-8 (p<0.001). The pEtN-conjugated LPS triggered a significantly greater production of TNF-, IL-6, and CXCL-8 compared to L-Ara4N (p<0.05). This study reveals that the colistin MIC value can significantly predict lipid A modification in clinical K. pneumoniae, and differences in resistance-mediated lipid A modification result in variation in the immunological response. This study highlights the potential of dynamic host-pathogen interaction in the context of colistin resistance.

Plasmid-encoded mobile colistin resistance (mcr) genes have raised concern due to dissemination potential. While mcr variants are reported across One Health compartments, they remain unreported in grass. This study characterises a novel mcr variant (mcr-13.1), detected in Escherichia coli isolated from the grass phylosphere within an agricultural grassland. The two mcr-positive isolates were clonal copies isolated at timepoints eight weeks apart. They belonged to the serotype O17:H18 and were of the sequence type ST394. The E. coli were phenotypically susceptible to {beta}-lactams, aminoglycosides, quinolones, sulphonamides, phenicols, tetracyclines, diaminopyrimidine and colistin (Minimum Inhibitory Concentration (MIC) = 0.5 {micro}g/mL). The mcr-13.1 gene was encoded on an IncFIB plasmid. This plasmid was transferable by conjugation but the colistin MIC of the E. coli J53 transconjugant did not change (0.5 {micro}g/mL). Further, cloned pUC19::mcr-13.1 did not alter the colistin MIC for E. coli DH5 (0.25 {micro}g/mL). The translated amino acid sequence showed highest homology (82 %) to MCR-10.2 and MCR-10.4. Our findings identify grass as a previously unrecognised reservoir for E. coli carrying mobile mcr genes, reports the identification of the novel mcr-13.1 variant from this niche and demonstrates the importance of genomic screening in identifying mcr genes that would otherwise remain undetected.