This study investigated the combined antibacterial and anti-biofilm activity of polymyxin B (PB) with intrinsically acidic N-acetylcysteine (NAC) against Klebsiella pneumoniae. The minimum inhibitory concentrations (MICs) of PB, acidic NAC, and neutralized NAC against 34 K. pneumoniae strains were determined using the broth microdilution. Drug interactions were assessed by checkerboard assays and the fractional inhibitory concentration index (FICI), while biofilm inhibition was quantified using crystal violet staining. Polymyxin B resistance was identified in the reference multidrug-resistant strain K. pneumoniae ATCC BAA-1705. The PB-NAC combination showed an additive effect (FICI 0.53-0.63) against PB-resistant and PB-intermediately susceptible strains, whereas indifferent interactions were observed in PB-susceptible strains. Furthermore, sub-inhibitory concentrations of the combination produced significantly stronger biofilm inhibition than either agent alone. Neutralization of NAC markedly reduced its antibacterial and anti-biofilm activities, with substantial inhibition observed only at concentrations ≥ 32 mg/mL. These findings demonstrate that the combination of PB and acidic NAC exerts additive antibacterial effects, particularly against resistant K. pneumoniae strains, and enhances biofilm inhibition. Notably, the intrinsic acidity of NAC is essential for its antimicrobial and anti-biofilm activity.

Lipopolysaccharide (LPS), also known as an endotoxin, poses serious health risks, such as sepsis, shock, and fever. Detecting LPS is important for hemodiafiltration therapy. In this study, an electrochemical LPS sensor with carbon nanotubes (CNTs) and polymyxin B (PmB) was developed for the first time. Layer-by-layer fabrication was done using dispersed CNTs and a PmB solution. LPS selectively bound to sensing elements and hindered redox reaction of markers, causing the peak current to decrease. As the LPS concentration increased, the number of LPS molecules bound to sensing elements increased, and fewer markers could approach the electrode surface. Consequently, the peak current decreased with increasing LPS concentration. The CNTs contribute to enhance the electrochemical current due to marker ion because of theirs high conductivity and catalytic ability. PmB discriminates LPS, and the CNTs enhance the signal arising from this response. The measurement range was 10fg/mL-10ng/mL. This sensor did not respond to other chemicals, such as human serum albumin, glucose, and bicarbonate, present in biological samples. This performance makes it suitable for water quality management of dialysis fluids, helping reduce the workload of clinical engineers. The CNT-based platform can be expanded to detect other targets and has the potential for widespread application in various areas.

Validation of limited sampling strategies for polymyxin B therapeutic drug monitoring in critical care.

A Vibrio-susceptibility class of antimicrobial peptide Ajapocin via membranolytic pattern to combat "non-cholera" pathogens in vivo infection models.

Antimicrobial resistance, particularly in carbapenem-polymyxin-resistant Klebsiella pneumoniae (CPR-Kp), is a major global concern. This study evaluated the chemical composition and antimicrobial potential of Cinnamomum triplinerve essential oils against CPR-Kp. Essential oils from leaves (CTL) and bark (CTB) were extracted via hydrodistillation and analyzed by gas chromatography-mass spectrometry. Their antimicrobial activity, alone and combined with polymyxin B (PMB), was assessed through checkerboard assays, biofilm inhibition, cell membrane permeability, and scanning electron microscopy (SEM). Reactive oxygen species (ROS) production was also examined. Safety was evaluated via hemolysis and toxicity tests in Caenorhabditis elegans, which was also used as an infection model to attest combinations in vivo efficacy. (E)-Nerolidol was identified as the major component. CTL and CTB reduced the PMB minimum inhibitory concentration by 32-fold, demonstrating synergy and biofilm inhibition in combination. SEM confirmed bacterial death, though intracellular bacterial protein leakage was absent. CTL-PMB induced oxidative stress, unlike CTB-PMB. No hemolysis or toxicity was observed. Infected C. elegans treated with CTL-PMB and CTB-PMB showed survival rates of 77.77% and 27.29%, respectively. These findings highlight the in vitro and in vivo potential of C. triplinerve essential oils as adjuvants to PMB, offering a promising therapeutic strategy against CPR-Kp infections.

BackgroundCarbapenem-resistant Acinetobacter baumannii (CRAB) presents a significant healthcare concern owing to restricted treatment alternatives and elevated mortality rates. This study assesses the in vitro synergistic effects of antimicrobial combinations to determine appropriate treatment alternatives.Table 1In Vitro Synergistic Activity of Antimicrobial CombinationsMethodsSixty non-duplicate CRAB isolates were identified and tested using the VITEK 2 system. Resistance mechanisms were determined via PCR for blaNDM and blaOXA-48. Synergistic activity of Polymyxin B (PB) + Sulbactam (SUL), Tigecycline (TGC) + SUL, Minocycline (MIN) + SUL, Sulbactam + Avibactam (SUL-AVI), and PB + Meropenem (MEM) + SUL was assessed using the Broth Disk Elution (BDE) method.ResultsA total of 60 clinical isolates were tested for in vitro synergy using different antibiotic combinations. Effectiveness was defined as no bacterial growth (-) in the presence of a drug combination. The most effective combinations were SUL+PB and SUL+PB+MEM, showing 100% synergy (no bacterial growth). SUL+TGC and SUL+PB were highly effective (98.33%, CI: 95.09%-101.57%), followed by SUL+MIN (91.67%, CI: 84.67%-98.66%). SUL+AVI was the least effective (65%, CI: 52.93%-77.07%) [Table 1]. Chi-square analysis showed no significant difference between SUL+TGC, SUL+PB, and SUL+PB+MEM (p > 0.05). Advanced pairwise Z-tests also found no statistically significant differences among combinations (all p-values > 0.05).ConclusionPolymyxin B-based regimens, particularly in combination with Meropenem and Sulbactum, appear highly promising for use in critically ill patients where rapid, broad-spectrum activity is paramount.DisclosuresAll Authors: No reported disclosures

Polymyxin B (PMB) is widely used as a last-line antibiotic for treating serious infections caused by multidrug-resistant Gram-negative bacteria. However, its clinical use is restricted by significant nephrotoxicity, which limits dosing flexibility and compromises therapeutic efficacy. Objective The aim of this study was to evaluate the potential nephroprotective effects of telmisartan (TMS) and nicorandil (NIC) in rats treated with polymyxin B (PMB). Methods Rats were randomly allocated into four groups. Normal control; PMB (12 mg/kg/day, S.C. for one week); TMS + PMB (10 mg/kg/day TMS orally (p.o.) for two weeks); and NIC + PMB (3 mg/kg/day NIC, i.p. for two weeks). Both drugs were administered one hour prior to PMB for one week and continued for an additional week. At the end of the treatment period, animals were anesthetized, and blood and kidney tissue samples were collected for histological and immunohistochemical analyses, as well as assessments of renal function, oxidative stress markers, mitochondrial dysfunction, endoplasmic reticulum stress, and apoptotic biomarkers. Results The findings demonstrated that both telmisartan and nicorandil significantly improved renal function and attenuated oxidative stress, mitochondrial dysfunction, ER stress, and apoptosis-related markers. Histopathological findings supported these results. Conclusion The renoprotective effects of telmisartan and nicorandil were mediated through modulation of the Nrf2/NQO1 antioxidant pathway and FAS/FASL apoptotic signaling, along with downregulation of renal expression of p53, cytochrome c, and caspase-3. These observations clearly indicate the protective role of both agents against PMB-induced nephrotoxicity.

Screening for novel therapeutic agents targeting multidrug-resistant Klebsiella pneumoniae.

Evaluation of the relative effectiveness of various antibiotic regimens used to treat hospital-acquired pneumonia induced by drug-resistant Acinetobacter baumannii.

Synergistic antibacterial effect and mechanism of benzalkonium chloride and polymyxin B against Pseudomonas aeruginosa.

The emergence of multidrug-resistant Pseudomonas aeruginosa (P. aeruginosa) infections, particularly those involving biofilm formation, poses a critical challenge to global healthcare. While polymyxin B (PMB) remains a last-line antibiotic against such infections, its efficacy is severely limited by poor biofilm penetration and adaptive resistance mechanisms. In this study, we developed a biomimetic nanoplatform (PMφ-PLGA-NOR) comprising a poly(lactic-co-glycolic acid) (PLGA) core loaded with norharmane (NOR), coated with PMB-modified P. aeruginosa cytoplasmic membrane (PMφ). This design utilizes the homologous targeting of bacterial membrane components and PMB's affinity for Gram-negative pathogens to achieve efficient biofilm penetration. NOR, a β-carboline compound, has been shown to disrupt quorum sensing (QS) by inhibiting PqsA, resulting in significant reduction in biofilm formation. In vitro investigations have demonstrated that PMφ-PLGA-NOR disrupts the integrity of biofilms, thereby enhancing the bactericidal efficacy of PMB by facilitating its deep penetration into the biofilm matrix. In vivo, intraperitoneal administration of Mφ-PLGA-NOR combined with PMB achieved a 2-log reduction in bacterial lung burden. This study underscores the promise of bacterial plasma membrane-based pathogen-mimetic nanoplatforms in potentiating the efficacy of antibiotic adjuvants in conjunction with biofilm-penetrating strategies.

Antimicrobial resistance and genomic characterization of Escherichia coli isolated from mink in northern China.

Background: Nebulized polymyxin B (PMB) therapy is widely used in intensive care units for treating hospital-acquired and ventilator-associated pneumonia caused by multidrug-resistant Gram-negative bacteria, yet its pulmonary delivery performance during invasive mechanical ventilation remains poorly characterized. Methods: An in vitro adult mechanical ventilation model was used. We evaluated two nebulizers (vibrating mesh nebulizer [VMN] and jet nebulizer [JN]) at three positions (standalone nebulizer, 15 cm from the Y-piece, and the humidifier's dry end) with two artificial airway types (endotracheal and tracheostomy tubes). Lung deposition was predicted using the multiple-path particle dosimetry model, incorporating the Yeh/Schum five-lobe adult lung model. Results: In the standalone setup, the percentage of delivered dose of VMN and JN was approximately 40% and 34%, respectively. Mechanical ventilation significantly reduced the delivered dose (all p ≤ 0.0085), with VMN at the humidifier's dry end delivering only 2.14-2.99% of the nominal dose. In all the tested ventilation scenarios, both the use of the JN and positioning the nebulizer 15 cm from the Y-piece significantly increased aerosol delivery (all p ≤ 0.021). While the ventilator circuit reduced the total drug amount, it filtered larger aerosols. This resulted in a smaller mass median aerodynamic diameter and a higher fine particle fraction (all p < 0.0001), which doubled the predicted alveolar deposition fraction (from 13-14% in standalone to 23-28% in ventilation scenarios) and eliminated extrathoracic deposition. Conclusions: This study provides the first in vitro and in silico assessment of PMB aerosol delivery during invasive mechanical ventilation. Nebulizer type, its placement within the circuit, and the artificial airway are critical factors that significantly alter the pulmonary delivery of PMB aerosol and subsequently impact its lung deposition.

The aim of this study was to investigate pharmacokinetics of polymyxin B (PMB) in patients with sepsis and preserved or impaired renal function. Methods . A two-center, prospective, randomized study enrolled patients with sepsis. Blood samples for analysis were collected in a steady state (SS) to assess the pharmacokinetics of PMB. PMB concentration in the patients' serum was measured using a direct competitive ELISA to verify the achievement of target area under the concentration-time curve (AUC 24 ) value of 50–100 mg×h/L. Results . The study included 34 patients with sepsis receiving PMB therapy who were distributed into two groups based on their glomerular filtration rate (GFR): patients with impaired renal function (GFR 80 mL/min, n = 17), and with preserved renal function (GFR 80 mL/min, n = 17). The mean AUC 24 value in 34 patients was 64.02 ± 11.64 mg×h/L, the median volume of distribution was 31.53 (23.79–43.72), and the median clearance was 3.72 (2.73–4.85). In patients with preserved renal function, the median AUC 24 was 48.38 mg×h/L, and the SS concentration was 2.02 mg/mL. In patients with impaired renal function, the AUC 24 was 71.78 mg×h/L, and the SS concentration was 2.99 mg/mL. The clearance of PMB differed considerably depending on GFR: the median clearance in patients with GFR 80 mL/min was 3.28 L/h versus 4.97 L/h in patients with GFR &gt; 80 mL/min (p = 0.012). In 14 of 17 patients with reduced renal function, the AUC 24 values fell in the range of 50–100 mg×h/L. In the group with preserved and increased renal function, only 7 of 17 patients reached the target range, and in 53% of patients (9 of 17), the exposure to PMB was below the therapeutic level (AUC 24 50 mg×h/L). Conclusion . Renal function affects the clearance of PMB and, consequently, the achievement of the target therapeutic range. Standard dosing regimens do not provide achieving the target concentrations of antibiotic in all patients, as some patients with preserved renal function have insufficient PMB exposure, while patients with impaired renal function have enhanced exposure, increasing the risk of drug failure or toxicity. To ensure the effectiveness and safety of treatment, regular therapeutic PMB concentrations monitoring and individual dose adjustments are necessary, especially in patients with altered renal function.

Hybrid vesicles are increasingly employed as nanocarrier systems for drug delivery owing to their versatile functionalities. This study presents a multifunctional vesicle delivery platform, designated PMB@LNV-SyBV, which integrates anti-inflammatory lemon-derived exosomes and attenuated bacterial vesicles to deliver polymyxin B (PMB). The incorporation of exogenous cholesterol enhances the drug-loading capacity of these vesicles. Antimicrobial assays confirm that PMB@LNV-SyBV effectively targets carbapenem-resistant Gram-negative bacteria. By inheriting pathogen-associated molecular patterns from native bacteria, PMB@LNV-SyBV is efficiently recognized and internalized by neutrophils, enabling it to reach infection sites alongside neutrophil recruitment. Subsequently, the vesicles are released from neutrophils in response to inflammatory stimuli. In infection models involving Klebsiella pneumoniae-induced mouse pneumonia and K. pneumoniae/Escherichia coli-induced mouse bloodstream infections, PMB@LNV-SyBV significantly reduces bacterial load, modulates pro-inflammatory cytokine release, and increases sepsis survival rates. With its high yield and favorable biocompatibility, the multifunctional PMB@LNV-SyBV represents a promising therapeutic platform for the clinical management of carbapenem-resistant bacterial infections.

Increased resistance to β-lactams/β-lactamase inhibitors by mutations in β-lactamase genes, porins, and efflux pumps complicates the management of carbapenem-resistant Klebsiella pneumoniae (CRKP). Polymyxin B (PMB)-based combination therapy is the best alternative treatment for middle and low-income countries that cannot access the latest medicines. It is crucial to know both phenotypic and genotypic characteristics of a pathogen to understand the killing effect of each drug and its combinations. Hence, our objective was to incorporate mechanistic insights gained from resistance mechanisms of each isolate to develop a mechanism-based pharmacokinetic/pharmacodynamic model. Six clinical CRKP isolates with diverse genotypic resistance expressing blaKPC, blaNDM, porin, and mgrB mutations were used for static concentration time kill (SCTK) assays to evaluate the rate and extent of killing by monotherapy, double and triple combinations using PMB (0.5-64 mg/L), meropenem (10-120 mg/L), and fosfomycin (75-500 mg/L). Isolate BRKP28 expressed non-functional MgrB (a regulatory protein) and high-level phenotypic resistance (PMB MIC: >128 mg/L). In line with the observed resistance, the model estimated that BRKP28 had a reduced maximum killing rate constant for PMB (3.61 h⁻¹) relative to other isolates. The mechanistic synergy of PMB, due to outer membrane disruption, was incorporated into three isolates with porin mutations. PMB demonstrated 83%-88% mechanistic synergy with meropenem and 81%-98% with fosfomycin. The model further estimated that a very low concentration of PMB (0.49-0.64 mg/L) was sufficient to achieve 50% of the maximum synergy. Simulations using population pharmacokinetic models showed that combination therapy of PMB (1 mg/kg q12h) and fosfomycin (8 g q8h) achieved >73% reduction in area under the bacterial load-versus-time curve across four isolates. The triple combination therapy achieved a 67.7% reduction in non-carbapenamase producing isolate. These findings demonstrates that a low PMB dosing regimen (1 mg/kg q12h) can produce synergistic effects in combination therapy and may be effective in managing infections caused by CRKP, including PMB resistant isolates.

Polymyxins, including polymyxin B (PMB), are last-resort antibiotics against multidrug-resistant Gram-negative infections in humans and livestock. Residual polymyxins from wastewater and manure can accumulate in soil, facilitating the emergence and spread of polymyxin resistance. Paenibacillus polymyxa, a natural polymyxin producer used in crop cultivation, may increase soil polymyxin burden. Since PMB strongly adsorbs to soil, its reliable quantification has been challenging. To address this, the extraction solvent and solid-phase extraction procedure were optimized to improve recovery and reduce matrix effects. We developed and validated a UPLC-MS/MS method to quantify PMB in soil. The method showed linearity (10–1000 ng/g), with a limit of detection of 0.86 ng/g and a limit of quantification of 2.12 ng/g. Method validation confirmed acceptable analytical performance. A 28-day monitoring of PMB in soil inoculated with varying P. polymyxa doses revealed a dose-dependent increase over the first 14 days, followed by a decline; PMB remained detectable on day 28. Ecological risk assessment using the risk quotient (RQ) indicated that PMB levels in the high-dose group (2 × 108 CFU/100 g) approached the high-risk threshold (RQ ≥ 1) on day 14, while lower doses posed low to medium risk. This work provides a soil PMB quantification method and insight into the ecological risk of P. polymyxa application.

BackgroundAntimicrobial resistance is a global concern. Tigecycline (TGC) and polymyxin B (PMB) constitute some of the last treatment options remaining for carbapenem-resistant Klebsiella pneumoniae (CRKP). However, heteroresistance to these two drugs has rarely been reported. In this study, we investigated the prevalence of heteroresistance to TGC and PMB among clinically isolated CRKP strains, and assessed the synergistic activity of TGC plus PMB, TGC plus imipenem (IPM), and PMB plus IPM against heteroresistant CRKP.MethodsA total of 90 nonduplicated CRKP clinical isolates were collected from Tianjin Medical University General Hospital, China,from January 2022 to October 2022. PCR was used to detect the resistance genes. Population analysis profile (PAP) was performed to determine the existence of heteroresistance. Checkerboard assay was carried out on ten randomly selected dual-heteroresistant CRKP strains. Additionally, MIC50 (minimum inhibitory concentration) and MIC90 were calculated, and the concentration-cumulative inhibitory percentage curves were plotted. Time-kill assays were conducted with selected CRKP strains.ResultsAmong them, 48 (55.2%) of the 87 TGC-susceptible and TGC-immediate isolates exhibited heteroresistance phenotypes, and 61 (70.9%) of the 86 PMB-susceptible isolates showed heteroresistance phenotypes. Thirty-two isolates (35.6%) were heteroresistant to TGC and PMB simultaneously. PCR results showed that 96.7% (87/90) not only carried carbapenemase genes, but also co-harbored extended-spectrum β-lactamases (ESBLs) genes. Single time-kill curves demonstrated that PMB monotherapy could rapidly eradicate non-heteroresistant strains within 8 h. Conversely, in heteroresistant strains, there was a sharp reduction in cells numbers initially but ensuing a prompt rebound. Intriguingly, further heteroresistance screening decoded the occurrence of heteroresistance phenomenon. Importantly, Checkerboard assay exhibited TGC combined with PMB exert relatively better effect to overcome dual heteroresistance compared with the other two regimes, with MIC50 and MIC90 of them were significantly declined than single drug and the concentration-cumulative inhibitory percentage curves shifted to the left. Moreover, they can early eliminate single heteroresistance in lower dose. Additionally, combined drug time-kill assays proved synergism effect. Overall, combining TGC and PMB may be a therapeutic approach to overcome counterpart heteroresistance in CRKP.ConclusionThis study provides valuable insights and theoretical support for the clinical therapy of relevant heteroresistance.Supplementary InformationThe online version contains supplementary material available at 10.1186/s12866-025-04554-8.

BackgroundThis study aimed to compare the efficacy and safety of colistimethate sodium (CMS) and polymyxin B (PMB) in treating carbapenem-resistant Gram-negative bacteria (CR-GNB)-induced bloodstream infection (BSI) based on real-world data. While international studies on CMS and PMB have yielded conflicting results, there is a lack of direct comparative data from Chinese cohorts, where the pathogen distribution may influence outcomes.MethodsA retrospective analysis was conducted on 373 Chinese patients with CR-GNB-induced BSI who received CMS-containing therapy (n=132) or PMB-containing therapy (n=241) between Dec 2021 and Dec 2023. Propensity score matching was used to balance the two groups at a ratio of 1:2. The primary outcome was clinical success. The secondary outcomes included inpatient days, in-hospital mortality, 28-day all-cause mortality, and incidence of adverse events. Statistical analysis was performed with Wilcoxon rank sum test, Student’s t-test, chi-square test, and Fisher’s exact test as appropriate.ResultsIn this cohort, Acinetobacter baumannii was the predominant pathogen (53.4%). No significant differences were observed in efficacy outcomes between the two groups (p>0.05). For safety, the difference in hyperpigmentation incidences between the two groups was statistically significant (CMS vs PMB: 0.0% vs 6.36%, p=0.04). Incidences of hypersensitivity, neurotoxicity, and nephrotoxicity were similar between groups (p>0.05). A longer treatment course (>12 days), while associated with a higher incidence of hyperpigmentation, was linked to significantly improved clinical outcomes, including higher success rate, reduced in-hospital mortality, and lower 28-day all-cause mortality (p<0.05).ConclusionThis study provides the first large, real-world comparative evidence from a Chinese cohort with CR-GNB BSIs. In this setting, CMS and PMB demonstrated comparable efficacy. The critical difference lay in the safety profile, with CMS associated with a markedly lower incidence of hyperpigmentation. This finding provides a tangible basis for antibiotic stewardship, positioning CMS as a valuable first-line polymyxin option.

Population pharmacokinetics and dosing optimisation of polymyxin B in patients with severe burns.