International Journal of Antimicrobial Agents

ObjectivesTo develop a population pharmacokinetic (PPK) model of polymyxin B (PMB) for intravenous (IV) and combined intravenous plus inhaled (IV+IH) administration in critically ill patients, and evaluate the association between the 24-h steady-state area under concentration-time curve to minimum inhibitory concentration ratio (AUCss,24h/MIC) and clinical outcomes. MethodsThis prospective cohort was conducted in the ICU of the Third Xiangya Hospital, Central South University (ethics R19048; ChiCTR1900028602). Adults with multidrug-resistant Gram-negative bacterial infections receiving PMB [≥]48 h were enrolled and assigned to IV or IV+IH groups. Serial plasma samples were analyzed by validated LC-MS/MS. The PPK model was developed with NONMEM(R). Clinical efficacy at end of treatment was blindly assessed. ResultsForty-three patients were enrolled (IV, n=22; IV+IH, n=21), with an overall clinical success rate of 66.7%. A two-compartment PPK model best described the data, with typical values of clearance (2.6 L/h), central volume (13.6 L), and peripheral volume (17.6 L). Clearance was influenced by creatinine clearance and total bile acids. In the overall cohort, neither AUCss,24h nor AUCss,24h/MIC differed significantly between clinical success and failure (p=0.591 and 0.143). In the IV group, AUCss,24h/MIC was significantly higher in responders (p=0.005) with an ROC-derived efficacy threshold of 94.37; AUCss,24h showed a non-significant trend (p=0.076). No exposure- response relationship was observed in the IV+IH group (p=0.398 and 0.495). ConclusionsPlasma AUCss,24h/MIC appears to be associated with clinical efficacy during IV monotherapy but not in IV+IH regimens, likely due to high pulmonary exposure. Plasma-based PK/PD targets should be applied cautiously when inhalation is added.

Infectious diseases remain a persistent global health burden, with bacterial infections predominating. The growing global burden of drug-resistant infections has led to greater emphasis on the discovery and development of novel antibacterial compounds. In an attempt to discover new potent antibacterials, the antibacterial activity of novel 2-substituted benzimidazole derivatives (NR-1 to NR-9) was evaluated in this study against three bacteria, viz. M. smegmatis, B. subtilis and E. coli in vitro using Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC). Among the nine derivatives assessed, two (NR-4 and NR-5) exhibited inhibitory activity against M. smegmatis, while two (NR-5 and NR-7) were active against B. subtilis, with MICs between 62.5 and 250 g/ml. Notably, NR-5 demonstrated antibacterial activity against both M. smegmatis and B. subtilis, with more efficacy against M. smegmatis (MIC: 62.5 g/ml), which was considerably closer to rifampicin (MIC: 31.25 g/ml). Cytotoxicity analysis of these derivatives in Vero cells indicated minimal toxicity for NR-4 and NR-5, and SwissADME evaluation suggested favourable physicochemical properties and drug-likeness, supporting good oral bioavailability. Moreover, the growth kinetics profiling of the NR-5 Benzimidazole derivative demonstrated that it inhibited the growth of M. smegmatis effectively, even after prolonged exposure. These findings highlighted the promise of the active benzimidazole derivative, NR-5, as a potential candidate for developing a more effective and less toxic antimycobacterial drug. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=76 SRC="FIGDIR/small/710429v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@126a0fcorg.highwire.dtl.DTLVardef@1131372org.highwire.dtl.DTLVardef@161a70corg.highwire.dtl.DTLVardef@1e0dbe_HPS_FORMAT_FIGEXP M_FIG C_FIG

APC148 is a novel metallo-beta-lactamase inhibitor with broad activity against Ambler class B enzymes including NDM, VIM and IMP. It is being developed for patients with serious infections caused by multidrug-resistant Gram-negative bacteria. APC148 is combined with the broad-spectrum beta-lactam antibiotic meropenem and the serine-beta-lactamase inhibitor avibactam, which targets Ambler class A, C, and some class D (OXA-48-like) enzymes. In combination with meropenem and avibactam, APC148 demonstrated superior in vitro activity against a global, multidrug resistant collection of Enterobacterales, showing its promising activity against beta-lactamase producing pathogens. In this randomized, placebo-controlled, first-in-human study, the safety, tolerability and pharmacokinetics of APC148 were evaluated in healthy adults. Single doses ranging from 50 mg to 760 mg APC148 were administered intravenously over 3 h to 46 participants across six dose groups. APC148 was well tolerated at all dose levels. All adverse events were of mild intensity, and no serious adverse events or adverse events leading to study- or treatment discontinuation occurred. The pharmacokinetics of APC148 were dose-proportional with low plasma clearance, low to moderate volume of distribution and a mean plasma half-life of 2.6 h. APC148 is well tolerated in humans at therapeutically relevant doses and represents a promising candidate in the fight against antibiotic-resistant bacteria. (This study has been registered at ClinicalTrials.gov under registration number NCT06360640).

BackgroundMetronidazole (MTZ) is a first-line antibiotic for several enteric infections. Its use is common in low-income countries, where most primary-care consultations are conducted by nurses. However, increasing resistance among some enteric pathogens is a growing concern. Using WHO guidelines, we conducted a register-based cross-sectional study to assess MTZ prescribing practices and their determinants in public and private primary healthcare facilities in South Benin. MethodsWe performed a register-based cross-sectional study covering the year 2020 in 11 primary healthcare facilities (5 public and 6 private) in Abomey-Calavi, South Benin, following WHO recommendations. In total, 200 visits per facility were selected using systematic random sampling. The primary outcome was the prevalence of MTZ prescription. Determinants of MTZ prescription were identified using multivariable logistic regression analysis. ResultsIn total, 2,200 medical visits were analyzed. The median age of patients was 19 years, and 57% were female. Antimalarials were prescribed in 52% of visits. Antibacterial agents were prescribed in the majority of visits, with MTZ being the second most frequently prescribed antibiotic (18%), after aminopenicillins (27%). In multivariable analysis, digestive symptoms (adjusted odds ratio [aOR], 8.65; 95% confidence interval [CI], 6.49-11.6), genitourinary symptoms (aOR, 6.84; 95% CI, 3.18-15.0), and skin lesions (aOR, 2.39; 95% CI, 1.58-3.60) were independently associated with increased odds of MTZ prescription. In contrast, fever (aOR, 0.66; 95% CI, 0.49-0.87), respiratory symptoms (aOR, 0.44; 95% CI, 0.26-0.71), and malaria (aOR, 0.21; 95% CI, 0.15-0.28) were associated with decreased odds. Visits in the private sector were also associated with higher odds of MTZ prescription compared with the public sector (aOR, 2.31; 95% CI, 1.78-3.02). ConclusionMTZ is the second most commonly prescribed antibiotic in primary care in the study area, with its use largely driven by digestive symptoms. Further studies are needed to assess the appropriateness of this prescription. Additionally, research is warranted to understand better the determinants of higher antimicrobial prescribing in the private healthcare sector. Highlights- MTZ is the second most prescribed antibiotic in the study area. - MTZ prescription is primarily driven by digestive symptoms. - The private healthcare sector is independently associated with higher MTZ prescription rates. - Antimicrobial prescribing is generally higher in private healthcare facilities than in public facilities.

Many commonly prescribed non-antibiotic medicines have off-target antimicrobial activity, yet their impact on antibiotic efficacy remains poorly understood. In this study, we investigated eight widely used UK prescription medicines and identified simvastatin, amlodipine, and fluoxetine as growth inhibitory towards methicillin-resistant Staphylococcus aureus (MRSA). These drugs disrupt bacterial membranes, with amlodipine and fluoxetine also triggering stress responses linked to cell wall and membrane damage. Further mechanistic analysis using transposon mutant screening revealed that simvastatin impairs cell wall synthesis by inhibiting the mevalonate pathway. Notably, checkerboard assays demonstrated antagonistic interactions: simvastatin reduced the efficacy of {beta}-lactams and vancomycin, amlodipine with vancomycin and daptomycin, and fluoxetine with vancomycin activity. Prolonged exposure to these drugs also accelerated resistance development to vancomycin and daptomycin. Together, these findings underscore the potential for commonly prescribed non-antibiotic medicines to undermine antibiotic therapy, warranting further study given the rising S. aureus treatment failures.

The rise of multidrug-resistant (MDR) bacteria, particularly carbapenem-resistant Enterobacterales (CRE), poses a significant threat to public health. Infections caused by CRE, such as Escherichia coli and Klebsiella pneumoniae, are associated with high rates of antibiotic treatment failure. {beta}-lactam antibiotics, like meropenem, remain crucial in treating these infections, but their efficacy is undermined by {beta}-lactamase production. This study investigates the potential of APC24-7, a novel broad-spectrum {beta}-lactamase inhibitor (BLi) with dual activity, to restore antimicrobial activity of meropenem against CRE clinical isolates. The in-vitro analysis of a diverse panel of clinically relevant E. coli and K. pneumoniae isolates expressing both serine- and metallo-{beta}-lactamases demonstrated that APC24-7 effectively restored meropenem activity by reducing the minimum inhibitory concentrations (MICs) to below breakpoint. Time-kill assays confirmed that the combination therapy showed dose-dependent bacterial killing, with significant potentiation of meropenem activity against isolates expressing both serine- and metallo-{beta}-lactamases. In-vivo efficacy evaluation in a murine thigh infection model further confirmed APC24-7s potential to restore meropenem efficacy against meropenem resistant strains. These findings suggest that APC24-7offers a promising strategy to combat infections caused by {beta}-lactamase-producing Enterobacterales.

BackgroundPatients undergoing hematopoietic stem cell transplantation (HSCT) often receive multiple antibiotics and antifungal agents concurrently, making it crucial to understand potential pharmacokinetic interactions. We report here an interaction between the glycopeptide antibiotic teicoplanin (TEIC) and sulfo-butyl ether-{beta}-cyclodextrin (SBECD), a solubilizing excipient in the intravenous formulation of posaconazole (PSCZ). MethodsWe performed a single-center retrospective analysis of HSCT patients who received oral and intravenous PSCZ during TEIC therapy. Associations between PSCZ administration and TEIC concentration-to-dose (C/D) ratios were evaluated using linear mixed-effects models. In rats, we examined the effects of intravenous PSCZ and SBECD on TEIC pharmacokinetics by assessing the area under the concentration-time curve (AUC) and urinary excretion of total TEIC and its components. Molecular docking and in vitro protein-binding assays were also conducted to investigate the interaction between TEIC and SBECD. ResultsIn HSCT patients, TEIC C/D ratios were significantly lower during intravenous PSCZ administration but not during oral PSCZ use. In rats, both intravenous PSCZ and SBECD decreased TEIC AUC and increased urinary excretion, particularly for the A2 group. Docking simulations indicated that the hydrophobic side chain of TEIC A2-2 fit within the SBECD cavity, and in vitro assays confirmed SBECD concentration-dependent increases in TEIC unbound fractions. ConclusionCo-administration of intravenous PSCZ containing SBECD may reduce TEIC protein binding, thereby enhancing renal elimination.

Ganciclovir (GCV), and its orally available pro-drug valganciclovir (VGCV), are preferred therapies for treating congenital cytomegalovirus (cCMV), however, their use carries a significant risk of neutropenia for the child. This risk limits dosing and effectiveness of VGCV, particularly in the treatment of infants with cCMV infection, who are at increased risk for sensorineural hearing loss (SNHL). We hypothesized that an improved understanding of the pharmacokinetics (PK) and pharmacodynamics (PD) of VGCV in cCMV-infected infants at risk for SNHL would inform strategies for optimizing safe and effective VGCV dosing. Participants were enrolled in one of two clinical studies interrogating the PK, safety, and efficacy of VGCV treatment in cCMV-infected infants at risk for SNHL. GCV exhibited a short median half-life of 2.02 h and the median (range) area under the 24 h concentration-time curve (AUC24) was 60.8 (26.8, 99.4) g*h/mL. An AUC24 > 70 g*h/mL was associated with an elevated risk of neutropenia (Fisher's Exact p = 0.029). No associations between GCV PK and hearing outcomes were observed. Taken together, these results indicate vast inter-individual variability in GCV PK that is associated with dose-related toxicity, supporting the need for individualized dosing in the cCMV-infected population.

The global dissemination of Enterobacterales producing both metallo-{beta}-lactamases (MBLs) and serine {beta}-lactamases (SBLs) represents a critical threat to modern medicine, as no currently marketed antibiotics effectively target MBL-mediated resistance. APC148 is a novel, selective zinc-chelating MBL inhibitor designed to restore {beta}-lactam activity in MBL positive isolates, when used in combination with a broad-spectrum carbapenem. In this study, we evaluated the in vitro efficacy of APC148 in triple combinations with either meropenem-avibactam (APC301) or cefepime-avibactam (APC302) against a diverse global collection (JMI collection) of 176 MBL- and SBL-producing Enterobacterales isolates (including NDM, VIM, and IMP variants). Using broth microdilution, the triple combinations were compared against several newly approved and late-stage pipeline antibiotic products. Both APC301 and APC302 demonstrated superior potency, achieving a MIC90 of 0.12 {micro}g/mL. When applying CLSI breakpoint interpretive criteria for the parent {beta}-lactams, 99.4% of the MBL and SBL-containing isolates were susceptible to APC301, while 97.2% were susceptible to APC302. These results indicate that the addition of a selective MBL inhibitor to an SBL-inhibitor/{beta}-lactam antibiotic effectively bypasses complex co-existing {beta}-lactam resistance mechanisms in multidrug-resistant (MDR) pathogens. Given that MDR Enterobacterales frequently harbor multiple {beta}-lactamase classes simultaneously, these triple combinations constitute a highly promising clinical strategy to address the therapeutic void in MBL-mediated resistance

Background Antibiotic use is prevalent in hospitals, driving the emergence of drug-resistant pathogens. We investigated the contextual influences on antibiotic prescribing behaviour across hospitals in high, middle, and low-income countries in Asia with an aim to provide actionable insights to improve prescribing behaviour. Methods We conducted a large qualitative study across ten institutions in Singapore, Nepal, and Thailand. Semi-structured interviews and ethnographic observations involving physicians, nurses, pharmacists, and management staff were conducted. Data were analysed thematically using QSR NVivo 14. Findings A total of 194 interviews were conducted amongst physicians (54{middle dot}1%), nurses (19{middle dot}6%), pharmacists (12{middle dot}4%), and management staff (13{middle dot}9%). Structural factors such as limited microbiology laboratory capabilities, concerns about antibiotic quality, weak infection prevention and control policies, and the lack of relevant, updated guidelines were prominent drivers for prolonged and broad-spectrum antibiotics prescriptions. Where these system supports were in place, prescribing decisions were less defensive and more targeted, although prescriber responsibility and concerns about immediate patient deterioration continued to influence practice. Across settings, clinicians tended to prioritise short-term perceived benefits of antibiotic treatment over the longer-term risks of antimicrobial resistance.

Urinary tract infections (UTIs) are among the most common infectious diseases worldwide, with Escherichia coli being the predominant uropathogen. The increasing prevalence of extended-spectrum beta-lactamase (ESBL)-producing strains and their association with fluoroquinolone resistance pose a significant challenge to empirical therapy, particularly in community settings. The aim of this study was to determine the epidemiology and predictive factors associated with ESBL-producing E. coli and its concomitant fluoroquinolone resistance in community-acquired clinical isolates. A retrospective cross-sectional study was conducted analyzing 244 clinical E. coli isolates. Demographic and microbiological data were collected, including age, sex, sample type, and antibiotic susceptibility. Associations between variables and ESBL production were assessed using Pearsons chi-squared test, and odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. Of the isolates, 165 (68%) were ESBL-producing. A significant association was observed between age group and ESBL production (p < 0.001), with the highest frequency in the 20-39 age group. Most ESBL-positive isolates were obtained from women (73%), although odds ratio (OR) analysis suggested a non-significant trend toward a higher probability in men (OR = 1.29; 95% CI: 0.72-2.31). High rates of fluoroquinolone resistance were identified among the ESBL-producing isolates, with 30% resistance to levofloxacin and 35% to ciprofloxacin (p < 0.001). Urine samples showed the highest concentration of ESBL-positive isolates, with a significant association between sample type and resistance (p < 0.001). The high prevalence of ESBL-producing E. coli and its concomitant resistance to fluoroquinolones highlight a critical challenge for the empirical treatment of urinary tract infections in Mexico, underscoring the need to strengthen antimicrobial use management and local surveillance strategies.

Objectives: Optimising parenteral antimicrobial use is central to antimicrobial resistance (AMR) control, yet its appropriateness is difficult to assess. We aimed to develop a quantitative indicator to evaluate the appropriateness of parenteral antimicrobial therapy in hospitalised patients with bloodstream infections. Methods: We developed the Susceptibility-Spectrum Discrepancy Index (S2DI), reflecting the discrepancy between antimicrobial susceptibility of blood culture isolates and the spectrum width of prescribed agents. Using a database from 67 National Hospital Organization hospitals in Japan, we identified patients with Staphylococcus aureus or Escherichia coli bacteraemia from 2017 to 2023. An expert panel of 10 infectious disease physicians independently ranked antimicrobial susceptibility (A) and spectrum width of commonly used agents (B). S2DI was defined as B minus A on day 7 after treatment initiation, with values closer to zero indicating more appropriate therapy. S2DI was calculated for individual cases, aggregated at the hospital level, and analysed using linear mixed-effects models with hospital-level random effects. Results: A total of 4,505 S. aureus and 9,563 E. coli bacteraemia cases were included. Median S2DI was 1 (IQR 0-1) for S. aureus and 2 (IQR 0-3) for E. coli. For both pathogens, later calendar years were significantly associated with more favourable S2DI, suggesting gradual improvement in antimicrobial use. In E. coli bacteraemia, female sex and younger age were also associated with more appropriate therapy. Conclusions: Although variation across hospitals persists, appropriateness of parenteral antimicrobial use has improved over time. S2DI is a simple metric that may support optimisation of antimicrobial use.

The emergence of antimicrobial resistance (AMR) has driven the search for alternative therapeutic strategies, including antivirulence approaches targeting bacterial quorum sensing (QS). Azelaic acid (AzA), a naturally occurring dicarboxylic acid with known antimicrobial properties, has not previously been characterized as a QS inhibitor in Gram-negative pathogens. This study evaluated the dual antimicrobial and antivirulence activity of AzA against reference strains and clinical isolates of Pseudomonas aeruginosa, Enterobacteriaceae, and Staphylococcus aureus through in vitro assays and molecular docking analyses. Minimum inhibitory concentration (MIC) values ranged from 250 to 1000 {micro}g/mL, with lower MICs observed in clinical isolates of E. coli and S. aureus. Subinhibitory concentrations (250, 500 and 750 {micro}g/mL) were used to assess QS-regulated virulence factors in P. aeruginosa, including pyocyanin, elastase, alginate, and protease production. AzA exhibited a significant, dose-dependent inhibition of all evaluated virulence factors across both reference and multidrug-resistant (MDR) and pan-drug-resistant (PDR) clinical strains (p < 0.001), achieving inhibition levels exceeding 90% in several cases, particularly for protease activity. Molecular docking analyses revealed that AzA interacts with key QS-related proteins (LasI, LasR, PqsD, and PqsR), showing moderate binding affinities (-5.3 to -6.5 kcal/mol) and stable interactions within conserved ligand-binding domains. These findings suggest a multitarget modulatory mechanism affecting interconnected QS pathways. Overall, this study demonstrates, for the first time, that AzA acts as a quorum sensing inhibitor in P. aeruginosa, attenuating virulence without directly affecting bacterial growth, highlighting its potential as a promising antivirulence therapeutic strategy.

IntroductionAcinetobacter is a highly diverse genus which includes a range of common pathogenic species such as A. baumannii, A. lwoffii etc. Acinetobacter species causes bacteremia, pneumonia, wound infections, Urinary tract infections in community as well as hospital settings. A. baumannii is one of the ESKAPE pathogen which makes it even more lethal as antibiotics cannot action on this. AimTo isolate Acinetobacter species from various clinical samples and to check their antimicrobial susceptibility pattern by VITEK {square} Compact in SGT Hospital, Gururam, Haryana. ResultsOut of total 6673 samples 595 were the positive isolates from which 35 were Acinetobacter isolates which were received from various wards of the hospital. Occurrence of Acinetobacter was seen more in males(57.14%) as compare to females (46.8%). A total of 31 strains were A. baumannii, 3 were A. lwoffi and 1 strain was of A. haemolyticus. Prominent presence of Acinetobacter was seen in Blood (48.57%) specimen along with pus(22.85%), endotracheal (22.85%), tracheal (2.85%) and eye swabs (2.85%). All the isolates were resistant to piperacillin/tazobactam (100%), ceftriazone (100%), amikacin (100%), gentamicin (100%) ciprofloxacin (91.42%), ceftazidime (91.42%), cefepime (88.57%), levofloxacin (88.57%) and trimethoprim/sulfamethoxazole (80%). Colistin susceptibility was observed in 88.57% of the isolates. ConclusionAcinetobacter is a common pathogen in hospital acquired as well as in community acquired infections as it is a opportunistic pathogen hence to identify the Acinetobacter species and to understand their antimicrobial resistance pattern this study was conducted.

BackgroundThere is currently no approved antiviral therapy against measles virus (MeV). Repurposing available compounds with broad antiviral activity may rapidly identify candidate drugs for clinical evaluation. Here we evaluated the antiviral activity of the clinically approved drugs azelastine hydrochloride and zafirlukast as well as the flavonoids quercetin and isoquercetin against MeV in preventative and therapeutic in vitro studies. MethodsCompounds were tested for antiviral activity against MeV in preventative (prophylactic and virucidal) and therapeutic (steady-state and persistent) assays in Vero/hSLAM cells. Viral loads and cell viability were measured 48h post-infection, and dose-response curves were used to calculate EC50 values. Flavonoids were also tested in the presence of 1 mM ascorbic acid. ResultsAzelastine hydrochloride did not show evidence of antiviral activity against MeV under these conditions, whereas zafirlukast, quercetin, and isoquercetin showed therapeutic activity against MeV. The addition of ascorbic acid enhanced the therapeutic potency of quercetin to 4.2-4.8 {micro}M and of isoquercetin to 10.7-10.9 {micro}M. Antiviral activity was dose-dependent when administered post-infection. ConclusionAmong the four compounds tested, quercetin showed the most potent therapeutic antiviral activity against MeV in vitro. Isoquercetin and zafirkulast also showed therapeutic activity. These findings support further evaluation of quercetin, isoquercetin, and zafirlukast as candidate antiviral drugs for MeV and highlight the utility of in vitro platforms for rapid antiviral drug screening.

WHO recommends bedaquiline-pretomanid-linezolid- (BPaL) and BPaL-moxifloxacin (BPaLM) for treatment of rifampicin-resistant tuberculosis, informed by the TB-PRACTECAL results. However, clinical explanatory data of these drugs exposure and Mycobacterium tuberculosis clearance rates and toxicity relationships remain understudied. We therefore investigated the relationship between the patients exposure to anti-TB drugs in TB-PRACTECAL trial investigational regimens and their treatment outcomes. PRACTECAL-PKPD was a prospective pharmacokinetics and pharmacodynamics study nested in TB-PRACTECAL. Patients with rifampicin-resistant pulmonary tuberculosis were enrolled from Belarus and South Africa. The first objective was to develop drug exposure metrics for bedaquiline, pretomanid, linezolid, moxifloxacin and clofazimine. The efficacy objectives were to establish an exposure-response model for each drug and regimen to both bactericidal activity and long-term treatment outcomes. The safety objective was to investigate the exposure-toxicity relationship of each drug. Antimicrobial exposure did not correlate with the speed of sputum bacterial clearance, however there was a 20% increased bacillary killing rate with BPaLM compared to the standard of care arm whilst BPaL and BPaL-clofazimine (BPaLC) displayed a 15% decreased bacillary killing rate compared to the standard of care arm. Linezolid plasma exposure was higher amongst patients with anaemia or neutropenia compared to those without. No other exposure-toxicity relationships were identified for all other drugs. Absence of correlation between drug exposure and bacillary clearance suggest that the dosages used achieve saturation of bacillary killing, while remaining safe.

ObjectivesMultidrug-resistant (MDR) Klebsiella pneumoniae is an increasingly important cause of recurrent urinary tract infections (UTIs), particularly in high-risk patients such as those with neurogenic bladder, where therapeutic options are limited. Bacteriophage therapy represents a promising alternative, but pre-clinical models and characterization of phages active against UTI-derived strains remain scarce. We therefore aimed to isolate and characterize bacteriophages targeting a clinical MDR K. pneumoniae strain causing recurrent UTI and evaluate their activity under urinary conditions. MethodsThree bacteriophages were isolated from environmental samples using an ESBL-producing K. pneumoniae clinical isolate obtained from a neurogenic bladder patient. Phages were characterized by genome sequencing, electron microscopy, stability assays, one-step growth curves, and host-range analysis across 79 clinical UTI isolates. Phage activity was quantified in LB medium and human urine using bacterial growth kinetics and a lytic activity score. ResultsThree lytic phages from the former siphoviridae family (EDIRA083, EDIRA088, and EDIRA092) belonging to distinct genera were identified. Genomic analysis confirmed the absence of lysogeny-associated, virulence, or antibiotic-resistance genes. Latent periods ranged from 8 to 40 minutes and burst sizes from 38 to 170 virions per infected bacterium. Host-range analysis revealed narrow activity for EDIRA083 and EDIRA088, whereas EDIRA092 infected 29% of the 79 clinical isolates tested. In liquid phage infection assays, overall lytic activity was consistently higher and more sustained in human urine than in LB, suggesting reduced fitness of resistant mutants under urinary conditions. ConclusionsThese results identify three genetically distinct lytic phages targeting MDR K. pneumoniae and highlight the importance of testing phage activity under infection-relevant conditions. Their activity in urine supports further evaluation of these phages as candidates for therapeutic development against MDR Klebsiella UTI.

Biofilms pose a significant challenge to antimicrobial therapy. Bacteria in biofilms differ from planktonic counterpart in their altered metabolism, collective behavior, protective role of extracellular matrix and diversified microbial subpopulations. These attributions significantly influence bioavailability and activity of antibiotics. The presence of bacterial aggregates during acute infections expands the problem to many other conditions previously not discussed in the biofilm context. Klebsiella pneumoniae is a leading cause of life-threatening hospital-acquired infections and is included in the WHO Bacterial Priority Pathogens List due to increasing antimicrobial resistance. The combination of antimicrobial resistance and the ability to form biofilms severely limits the efficacy of antibiotic treatments. In this study, we investigated the in vitro susceptibility of mature biofilms to 13 antimicrobials of K. pneumoniae clinical isolates from a single hospital. The resistance profiles of the local clinical isolates were consistent with the global epidemiology of K. pneumoniae. Minimal biofilm eradication concentrations (MBEC) for mature biofilms were defined with two assays (biomass and metabolic activity measurements) and brought into relation with susceptibility breakpoints and plasma (Cmax). Colistin sulfate, tigecycline, cephalosporins and combination of imipenem with cilastatin were the most potent biomass eradicators, while suppression of metabolic activity was barely reachable. Moreover, we observed a notable increase in metabolic activity upon exposure to sub-MBEC concentrations of antibiotics. Finally, our data broach a subject of antibiotic prioritization with respect to biofilm tolerance. IMPORTANCEThis study addresses the critical gap between standard antibiotic susceptibility testing and the tolerance of biofilm and microbial aggregates during infections caused by K. pneumoniae. By systematically evaluating mature biofilms from a significant number of clinical isolates, we demonstrate that colistin and tigecycline show potent activity against both biofilm biomass and metabolic activity, whereas cephalosporins primarily reduce biomass without effectively suppressing bacterial metabolism, and other drugs have only weak effects on biofilms at clinically achievable concentrations. Furthermore, the alarming observation that sub-inhibitory biofilm eradication concentration (sub-MBEC) of antibiotic can paradoxically increase the metabolic activity of biofilms highlights a potential risk factor for therapy failure and resistance development. Our findings contribute to the necessary evidence base for prioritizing existing antibiotics in the limited armamentarium against biofilm-forming K. pneumoniae.

BackgroundVirtual colony count is a kinetic, 96-well turbidimetric assay that has been used since 2003 to determine the antimicrobial activity of antimicrobial peptides including the defensin HNP1. Virtual colony count results differed from traditional colony counting results in studies of the antimicrobial activity of the human cathelicidin LL-37 and related peptides. The difference could possibly have been caused by an inoculum effect. MethodsThe virtual colony count assay was conducted using inocula that varied from 1250 to 1x108 virtual colony forming units (CFUv) per milliliter. ResultsThe virtual colony count assay demonstrated a pronounced inoculum effect of HNP1 against Staphylococcus aureus ATCC 29213, accompanied by biofilm formation observed in the wells of the 96 well plates at all inocula. The S. aureus inoculum effect was not as drastic as previously reported for Escherichia coli. ConclusionsThe inoculum effect is further evidence that biofilm formation is a resistance mechanism used by a variety of bacteria against antimicrobial peptides such as HNP1.

BackgroundMultidrug-resistant (MDR) Gram-negative bacteria have triggered a critical global health crisis. Polymyxin lipopeptide antibiotics are used as a last-line therapy against these problematic pathogens, but their clinical use is largely limited by severe nephrotoxicity. Human oligopeptide transporter 2 (hPepT2) is a membrane transporter mediating the reabsorption of polymyxins in renal proximal tubular cells, substantially contributing to their nephrotoxicity. However, it remains unclear how polymyxins interact with hPepT2. MethodsIn this study, we investigated the structure-interaction relationship (SIR) of polymyxins with hPepT2 by integrating computational, chemical and cell biology approaches. Bioinformatic modelling predicted the residues essential for the binding of polymyxins with hPepT2. Transporter mutagenesis and molecular analysis were employed to explore the role of each residue in the interaction of hPepT2 and polymyxins. Moreover, we synthesised a series of polymyxin-like analogues with altering the moieties that are critical for binding with hPepT2. The antibacterial activity and nephrotoxicity of these analogues were subsequently assessed. ResultsOur bioinformatic modelling proposed an outward-facing structure of hPepT2 with a possible transport pathway that polymyxins bind to the lateral opening site of hPepT2 (e.g. E214, D215, D317, D342, E622). Molecular assays for transporter function and expression confirmed that D215 residue of hPepT2 is critical for polymyxin binding, while several other residues significantly impact on transporter turnover rate and/or protein expression. Our experimental validations showed that the lipopeptide analogues with altering the Dab1, Dab3, Dab5 and Dab9 moieties of polymyxins demonstrated decreased interactions with hPepT2. Among these synthetic analogues, alanine substitution at Dab3 showed reduced nephrotoxicity in mice while reserved antibacterial activity against a range of bacterial strains. ConclusionsOverall, this proof-of-concept study demonstrated that the computationally predicted and experimentally validated polymyxin-hPepT2 SIR model provides a viable approach for the discovery of novel, safer lipopeptide antibiotics.