Polymyxin B Treatment Research Articles

Deciphering Antibiotic-Targeted Metabolic Pathways in Acinetobacter baumannii: Insights from Transcriptomics and Genome-Scale Metabolic Modeling.

In the ongoing battle against antibiotic-resistant infections, Acinetobacter baumannii has emerged as a critical pathogen in healthcare settings. To understand its response to antibiotic-induced stress, we integrated transcriptomic data from various antibiotics (amikacin sulfate, ciprofloxacin, polymyxin-B, and meropenem) with metabolic modeling techniques. Key metabolic pathways, including arginine and proline metabolism, glycine-serine and threonine metabolism, glyoxylate and dicarboxylate metabolism, and propanoate metabolism, were significantly impacted by all four antibiotics across multiple strains. Specifically, biotin metabolism was consistently down-regulated under polymyxin-B treatment, while fatty acid metabolism was perturbed under amikacin sulfate. Ciprofloxacin induced up-regulation in glycerophospholipid metabolism. Validation with an independent dataset focusing on colistin treatment confirmed alterations in fatty acid degradation, elongation, and arginine metabolism. By harmonizing genetic data with metabolic modeling and a metabolite-centric approach, our findings offer insights into the intricate adaptations of A. baumannii under antibiotic pressure, suggesting more effective strategies to combat antibiotic-resistant infections.

Tetrahydrocurcumin Attenuates Polymyxin B Sulfate-Induced HK-2 Cells Apoptosis by Inhibiting Endoplasmic Reticulum Stress-Mediated PERK/eIF2α/ATF4/CHOP Signaling Pathway Axis.

The clinical application of polymyxin B (PMB) is limited by its nephrotoxic effects, making the reduction of PMB-induced nephrotoxicity has become a pressing concern for clinicians. Tetrahydrocurcumin (THC), known for its beneficial characteristics in biological functions, presents an attractive option for intervention therapy to mitigate PMB-induced nephrotoxicity. However, the underlying mechanism of how THC mitigates PMB-induced nephrotoxicity is still poorly understood. Here, we first evaluated the potential of THC intervention therapy to mitigate PMB-induced nephrotoxicity in an in vitro model of PMB-induced cell injury. Moreover, we demonstrated that THC effectively protected HK-2 cells from PMB-induced apoptosis by using cell counting kit-8 and flow cytometry assay. THC could also suppress PMB-induced endoplasmic reticulum (ER) stress via PERK/eIF2α/ATF4/CHOP pathway. In addition, using PERK inhibitor GSK2606414 to inhibit ER stress also alleviated PMB-induced apoptosis. Taken together, these findings provide novel insights that THC possesses the ability to alleviate PMB-induced nephrotoxicity by inhibiting the ER stress-mediated PERK/eIF2α/ATF4/CHOP axis, which sheds light on the benefits of THC as an intervention strategy to reduce PMB-induced nephrotoxicity, thus providing a potential avenue for improved clinical outcomes in patients receiving PMB treatment.

Lipid A in outer membrane vesicles shields bacteria from polymyxins.

The continuous emergence of multidrug-resistant bacterial pathogens poses a major global healthcare challenge, with Klebsiella pneumoniae being a prominent threat. We conducted a comprehensive study on K. pneumoniae's antibiotic resistance mechanisms, focusing on outer membrane vesicles (OMVs) and polymyxin, a last-resort antibiotic. Our research demonstrates that OMVs protect bacteria from polymyxins. OMVs derived from Polymyxin B (PB)-stressed K. pneumoniae exhibited heightened protective efficacy due to increased vesiculation, compared to OMVs from unstressed Klebsiella. OMVs also shield bacteria from different bacterial families. This was validated ex vivo and in vivo using precision cut lung slices (PCLS) and Galleria mellonella. In all models, OMVs protected K. pneumoniae from PB and reduced the associated stress response on protein level. We observed significant changes in the lipid composition of OMVs upon PB treatment, affecting their binding capacity to PB. The altered binding capacity of single OMVs from PB stressed K. pneumoniae could be linked to a reduction in the lipid A amount of their released vesicles. Although the amount of lipid A per vesicle is reduced, the overall increase in the number of vesicles results in an increased protection because the sum of lipid A and therefore PB binding sites have increased. This unravels the mechanism of the altered PB protective efficacy of OMVs from PB stressed K. pneumoniae compared to control OMVs. The lipid A-dependent protective effect against PB was confirmed in vitro using artificial vesicles. Moreover, artificial vesicles successfully protected Klebsiella from PB ex vivo and in vivo. The findings indicate that OMVs act as protective shields for bacteria by binding to polymyxins, effectively serving as decoys and preventing antibiotic interaction with the cell surface. Our findings provide valuable insights into the mechanisms underlying antibiotic cross-protection and offer potential avenues for the development of novel therapeutic interventions to address the escalating threat of multidrug-resistant bacterial infections.

Clinical, biological and genome-wide comparison of carbapenem-resistant Klebsiella pneumoniae with susceptibility transformation to polymyxin B during therapy

ObjectivesThe emergence of carbapenem-resistant Klebsiella pneumoniae (CRKP) is a major clinical concern, and polymyxin B (PMB) is a ‘last resort’ antibiotic for its treatment. Understanding the effects of drug susceptibility transformation in CRKP-infected patients undergoing PMB treatment would be beneficial to optimize PMB treatment strategies. MethodsWe retrospectively collected data from patients infected with CRKP and treated with PMB from January 2018 to December 2020. CRKPs were collected before and after PMB therapy, and patients were classified into the ‘transformation’ group (TG) and ‘non-transformation’ group (NTG) by the shift of susceptibility to PMB. We compared clinical characteristics between these groups, and further analysed the phenotypic and genome variation of CRKP after PMB susceptibility transformation. ResultsA total of 160 patients (37 in the TG and 123 in the NTG) were included in this study. The duration of PMB treatment before PMB-resistant K. pneumoniae (PRKP) appearance in TG was even longer than the whole duration of PMB treatment in NTG (8 [8] vs. 7 [6] days; p 0.0496). Compared with isogenic PMB-susceptible K. pneumoniae (PSKP), most PRKP strains had missense mutations in mgrB (12 isolates), yciC (10 isolates) and pmrB (7 isolates). The competition index of 82.4% (28/34) of PRKP/PSKP pairs was <67.6% (23/34), and 73.5% (25/34) of PRKP strains showed a higher 7-day lethality in Galleria mellonella and a greater ability to resist complement-dependent killing than their corresponding PSKP, respectively. ConclusionLow dose with longer PMB treatment durations may be associated with the emergence of polymyxin resistance. The evolution of PRKP is predominantly mediated by an accumulation of mutations, including those in mgrB, yciC, and pmrB. Lastly, PRKP exhibited reduced growth and increased virulence compared with parental PSKP.

Baicalein ameliorates polymyxin B-induced acute renal injury by inhibiting ferroptosis via regulation of SIRT1/p53 acetylation

The polypeptide antibiotic Polymyxin B (PMB) can cause acute kidney injury (AKI), we found that ferroptosis is one of the main mechanisms of renal injury caused by PMB. It was reported that baicalein can inhibit ferroptosis. Therefore, in this study we examined whether baicalein could attenuate PMB-induced renal injury by inhibiting ferroptosis. We confirmed that baicalein could reduce PMB-induced renal injury in vivo and in vitro studies. In the in vitro study, baicalein significantly increased the survival rate of human HK2 tubular epithelial cells. The results of HE staining and electron microscopy in mice also showed that baicalein reduced PMB-induced renal injury, and significantly decreased the levels of BUN and Scr. By detecting ferroptosis-related indicators, we found that pre-incubation of baicalein in HK2 cells down-regulated Fe2+ level, lipid peroxidation, MDA and HO-1 which had been increased by PMB. Furthermore, baicalein up-regulated the levels of SCL7A11, GPX4 and GSH that were decreased by PMB. Moreover, intraperitoneal injection of baicalein in the animal model down-regulated kidney iron level, PTGS2 and 4HNE, and increased the GSH level, which suggested that baicalein could inhibit PMB-induced ferroptosis. Finally, by detecting changes in levels of p53 and p53 K382 acetylation, baicalein was observed to decrease elevated p53 K382 acetylation after PMB treatment, further confirming that baicalein inhibits ferroptosis by reducing p53 K382 acetylation via upregulation of SIRT1 expression. In conclusion, these results suggest that baicalein decreases p53 acetylation level by elevating SIRT1, which can then inhibit PMB-induced ferroptosis and ultimately attenuates AKI.

Prevalence and molecular characteristics of polymyxin-resistant Enterobacterales in a Chinese tertiary teaching hospital.

Polymyxin-resistant Enterobacterales poses a significant threat to public health globally, but its prevalence and genomic diversity within a sole hospital is less well known. In this study, the prevalence of polymyxin-resistant Enterobacterales in a Chinese teaching hospital was investigated with deciphering of their genetic determinants of drug resistance. Polymyxin-resistant Enterobacterales isolates identified by matrix-assisted laser desorption were collected in Ruijin Hospital from May to December in 2021. Both the VITEK 2 Compact and broth dilution methods were used to determine polymyxin B (PMB) susceptibility. Polymyxin-resistant isolates were further characterized by molecular typing using PCR, multi-locus sequence typing, and sequencing of the whole genome. Of the 1,216 isolates collected, 32 (2.6%) across 12 wards were polymyxin-resistant (minimum inhibitory concentration (MIC) range, PMB 4-256 mg/ml, and colistin 4 ≥ 16 mg/ ml). A total of 28 (87.5%) of the polymyxin-resistant isolates had reduced susceptibility to imipenem and meropenem (MIC ≥ 16 mg/ml). Of the 32 patients, 15 patients received PMB treatment and 20 survived before discharge. The phylogenetic tree of these isolates showed they belonged to different clones and had multiple origins. The polymyxin-resistant Klebsiella pneumoniae isolates belonged to ST-11 (85.72%), ST-15 (10.71%), and ST-65 (3.57%), and the polymyxin-resistant Escherichia coli belonged to four different sequence types, namely, ST-69 (25.00%), ST-38 (25.00%), ST-648 (25.00%), and ST-1193 (25.00%). In addition, six mgrB specific mutations (snp_ALT c.323T>C and amino acid change p.Val8Ala) were identified in 15.6% (5/32) of the isolates. mcr-1, a plasmid-mediated polymyxin-resistant gene, was found in three isolates, and non-synonymous mutations including T157P, A246T, G53V, and I44L were also observed. In our study, a low prevalence of polymyxin-resistant Enterobacterales was observed, but these isolates were also identified as multidrug resistant. Therefore, efficient infection control measures should be implemented to prevent the further spread of resistance to last-line polymyxin therapy.

Polymyxin B exerts nephrotoxicity effects via inhibition of the Nrf2/NQO1 pathway-mediated antioxidant response.

Polymyxin B (PMB) is a polypeptide antibiotic widely used in treating multidrug-resistant Gram-negative bacteria. However, nephrotoxicity is a serious adverse effect that limits its clinical use. Therefore, clarification of the molecular mechanism of PMB-induced renal injury is essential. Our study aimed to explore possible mechanisms of PMB-induced nephrotoxicity in vivo and in vitro. Mice were treated with PMB to construct the kidney injury model. The antioxidant capacity was assessed by measuring the superoxide dismutase (SOD) and catalase (CAT) activities and the glutathione (GSH)and malondialdehyde (MDA) contents. The pathway of the nuclear factor erythroid 2-related factor 2/NADH quinone oxidoreductase 1 (Nrf2/NQO1) was examined after PMB treatment in NRK-52E cells and mice. Finally, the expressions of genes and proteins (Bax, Bcl-2, Caspase-3, Caspase-9) related to apoptosis were evaluated through quantitative polymerasechain reaction and western blot assay. The study verified PMB-induced nephrotoxicity in mice and NRK-52E cells in a dose- and time-dependent manner. PMB treatment significantly decreased the expression of Nrf2 and its downstream target gene NQO1 and increased the apoptosis-related proteins expression. In summary, our results suggested that PMB-induced oxidative stress damage by inhibiting the Nrf2/NQO1 pathway and promoting apoptosis in kidney tissues.

Antimicrobial peptide antibiotics inhibit aerobic denitrification via affecting electron transportation and remolding carbon metabolism

The harmful effects of antibiotics on biological denitrification have attracted widespread attention due to their excessive usage. Polymyxin B (PMB) as the typical antimicrobial peptides having been regarded as the “last hope” for treatment of multidrug-resistance bacteria, has also been detected in wastewater. However, little is known about the influence of PMB on aerobic denitrification. In this study, the impact of PMB on aerobic denitrification performance was investigated. Results showed 0.50 mg/L PMB decreased nitrate removal efficiency from 97.4% to 85.3%, and drove denitrifiers to transform more nitrate to biomass instead of producing gas-N. The live/dead staining method showed PMB damaged bacterial membrane. Transcriptome analysis further indicated the key enzymes participating in denitrification and aerobic respiratory chains were suppressed by PMB. To resist the PMB stress, denitrifiers formed thicker biofilm to protect cells from PMB damaging and thus remodeling the central carbon metabolism. Further investigation revealed denitrifiers have different preference on various carbon sources when PMB is present. Subsequently, the underlying mechanism of the distinctive carbon sources preference was explored by the combination of transcriptome and metabolism analysis. Overall, our data suggested denitrifiers have distinctive carbon sources preference under PMB treatment conditions, reminding us that carbon source selection should be cautious in practical applications.

Cell Membrane Remodeling Mediates Polymyxin B Resistance in Klebsiella pneumoniae: An Integrated Proteomics and Metabolomics Study.

Polymyxin B (PB) is introduced into the clinic as the last-line therapy against carbapenem-resistant Klebsiella pneumoniae (CRKP). Unfortunately, increased resistance to PB in Klebsiella pneumoniae (K. pneumoniae) has threatened global health. Resistance of K. pneumoniae to PB was induced by passaging in serial concentrations of PB and determined by microbroth dilution method. Growth characteristics of induced strains including growth curve, reversibility of resistance, and biofilm formation (crystal violet staining method) were measured. This study employed TMT-labeled quantitative proteomics and LC-MS/MS metabolomics analysis to investigate the key biological processes associated with PB resistance in K. pneumoniae. A total of 315 differentially expressed proteins (DEPs) were identified, of which 133 were upregulated and 182 were downregulated in the PB-resistant K. pneumoniae. KEGG enrichment analysis revealed that the DEPs were mainly involved in ATP-binding cassette (ABC) transporters and cationic antimicrobial peptide (CAMP) resistance. Proteins related to central carbon metabolism were inhibited in the PB-resistant K. pneumoniae, but proteins mediating LPS modification were activated. Transcriptional levels of CAMP resistance-related proteins were significantly different between PB-susceptible and -resistant K. pneumoniae. PB treatment led to an increase in reactive oxygen species (ROS) levels of K. pneumoniae. Metabolomics data demonstrated that 23 metabolites were significantly upregulated in PB-resistant K. pneumoniae and 5 were downregulated. The differential metabolites were mainly lipids, including glycerophospholipids, sphingolipids, and fatty acids. Exposure to PB resulted in increased level of phospholipid transport gene mlaF in K. pneumoniae. Our study suggested that membrane remodeling and inhibited central carbon metabolism are conducive to the development of PB resistance in K. pneumoniae.

Nephrotoxicity and Efficacy Assessment of Polymyxin B Use in Renal Transplant Patients.

PurposeThis study investigates the nephrotoxicity and efficacy assessment of polymyxin B (PMB) use in renal transplant patients.Patients and MethodsThis retrospective study included adult (>18 years of age) renal transplant patients who received PMB intravenous drip for more than 72 hours. Efficacy assessment of PMB included clinical treatment efficacy, microbiological efficacy at the end of PMB treatment, and in-hospital all-cause mortality. Nephrotoxicity of PMB was evaluated for further group comparison.ResultsWe enrolled 235 renal transplant patients in our study. After PMB treatment, 45 patients occurred PMB-nephrotoxicity, and the nephrotoxicity rate was 19.15%. Among them, 44 patients were RIFLE R stage, and one patient was RIFLE I stage. The dose of PMB used in patients was 40.0 (40.0–50.0) mg q12h with a loading dose of 41.8±9.8 mg. Multivariate logistic regression analysis showed that ICU admission, vasoactive agents, aminoglycosides, creatinine clearance rate before PMB use, and mean total hospital stay were independent risk factors of PMB-nephrotoxicity in kidney transplant patients. The clinical effective rate was 97.9%, and the microbiological clean rate was 66.7%.ConclusionOur study demonstrated that PMB low dose regimens might achieve good efficacy and less nephrotoxicity in renal transplant patients. We should evaluate the severity of the infection and renal function of patients, avoid the combined use of other nephrotoxic drugs, and minimize the course of use to reduce the occurrence of PMB-nephrotoxicity.

Visualizing the Potential Impairment of Polymyxin B to Central Nervous System Through MR Susceptibility-Weighted Imaging.

Polymyxin B (PMB) exert bactericidal effects on the cell wall of Gram-negative bacteria, leading to changes in the permeability of the cytoplasmic membrane and resulting in cell death, which is sensitive to the multi-resistant Gram-negative bacteria. However, the severe toxicity and adverse side effects largely hamper the clinical application of PMB. Although the molecular pathology of PMB neurotoxicity has been adequately studied at the cellular and molecular level. However, the impact of PMB on the physiological states of central nervous system in vivo may be quite different from that in vitro, which need to be further studied. Therefore, in the current study, the biocompatible ultra-uniform Fe3O4 nanoparticles were employed for noninvasively in vivo visualizing the potential impairment of PMB to the central nervous system. Systematic studies clearly reveal that the prepared Fe3O4 nanoparticles can serve as an appropriate magnetic resonance contrast agent with high transverse relaxivity and outstanding biosafety, which thus enables the following in vivo susceptibility-weighted imaging (SWI) studies on the PMB-treated mice models. As a result, it is first found that the blood-brain barrier (BBB) of mice may be impaired by successive PMB administration, displaying by the discrete punctate SWI signals distributed asymmetrically across brain regions in brain parenchyma. This result may pave a noninvasive approach for in-depth studies of PMB medication strategy, monitoring the BBB changes during PMB treatment, and even assessing the risk after PMB successive medication in multidrug-resistant Gram-negative bacterial infected patients from the perspective of medical imaging.

Assessing the predictive performance of population pharmacokinetic models for intravenous polymyxin B in critically ill patients.

Polymyxin B (PMB) has reemerged as a last‐line therapy for infections caused by multidrug‐resistant gram‐negative pathogens, but dosing is challenging because of its narrow therapeutic window and pharmacokinetic (PK) variability. Population PK (POPPK) models based on suitably powered clinical studies with appropriate sampling strategies that take variability into consideration can inform PMB dosing to maximize efficacy and minimize toxicity and resistance. Here we reviewed published PMB POPPK models and evaluated them using an external validation data set (EVD) of patients who are critically ill and enrolled in an ongoing clinical study to assess their utility. Seven published POPPK models were employed using the reported model equations, parameter values, covariate relationships, interpatient variability, parameter covariance, and unexplained residual variability in NONMEM (Version 7.4.3). The predictive ability of the models was assessed using prediction‐based and simulation‐based diagnostics. Patient characteristics and treatment information were comparable across studies and with the EVD (n = 40), but the sampling strategy was a main source of PK variability across studies. All models visually and statistically underpredicted EVD plasma concentrations, but the two‐compartment models more accurately described the external data set. As current POPPK models were inadequately predictive of the EVD, creation of a new POPPK model based on an appropriately powered clinical study with an informed PK sampling strategy would be expected to improve characterization of PMB PK and identify covariates to explain interpatient variability. Such a model would support model‐informed precision dosing frameworks, which are urgently needed to improve PMB treatment efficacy, limit resistance, and reduce toxicity in patients who are critically ill.

Clinical outcomes and safety of polymyxin B in the treatment of carbapenem-resistant Gram-negative bacterial infections: a real-world multicenter study

BackgroundHigh morbidity and mortality due to carbapenem-resistant Gram-negative bacilli (CR-GNB) has led to the resurgence of polymyxin B (PMB) use in the last decade. The aim of our multicenter, real-world study was to evaluate the effectiveness and safety of PMB in the treatment of CR-GNB infections.MethodsThe real-world study included patients treated with intravenous PMB for at least 7 days during the period of October 2018 through June 2019. Associations between these clinical features and 28-day mortality or all-cause hospital mortality were explored through univariate analyses and multivariable logistic regression.ResultsThe study included 100 patients. Many patients presented with combined chronic conditions, septic shock, mechanical ventilation, and the presence of Klebsiella pneumoniae. The mean duration of PMB therapy was 11 days (range 7–38 days). Temperature (38 °C vs 37.1 °C), white blood cells (14.13 × 109/l vs 9.28 × 109/l), C-reactive protein (103.55 ug/l vs 47.60 ug/l), procalcitonin (3.89 ng/ml vs 1.70 ng/ml) and APACHE II levels (17.75 ± 7.69 vs 15.98 ± 7.95) were significantly decreased after PMB treatment. The bacteria eradication rate was 77.65%. The overall mortality at discharge was 15%, and 28-day mortality was 40%. Major adverse reactions occurred in 16 patients. Nephrotoxicity was observed in 7 patients (7%).ConclusionsOur results provide positive clinical and safety outcomes for PMB in the treatment of CR-GNB. Timely and appropriate use of PMB may be particularly useful in treating patients with sepsis in CR-GNB infections.

Genome-Wide Analysis of the Response of Brucella melitensis NI to Polymyxin B.

The ability of pathogenic bacteria to survive Antimicrobial Peptides (AMPs) in various host niches may contribute to their virulence. Polymyxin B is a cationic AMP, and polymyxin drugs are considered to be the "last line of defense" in the clinical treatment of bacterial infections. The objectives of this study were to comprehensively study the response of Brucella melitensis strain NI to polymyxin B treatment and to identify the target genes in Brucella induced by polymyxin B stimulation. Following treatment with polymyxin B, differentially expressed genes in Brucella were detected using RNA-seq and validated using qRT-PCR. In total, 874 differentially expressed genes were identified, including 560 up-regulated and 314 down-regulated genes. Functional annotation and KEGG pathway analysis revealed that many of these genes are involved in metabolism, two-component systems, transcriptional regulation, transport/ membrane proteins, and virulence factors. Expression of genes involved in T4SS and flagellar biosynthesis and assembly, which are important virulence factors in Brucella, were up-regulated by polymyxin B treatment. Additionally, genes encoding the ABC transporters YejABEF and the cold-shock protein CspA were also up-regulated. These genes confer resistance to AMPs and contribute to the virulence of Brucella. The NIΔsufC, NIΔsufD, NIΔompW, NIΔexbB, NIΔtetR, and NIΔcspA mutants were also more sensitive than B. melitensis NI to polymyxin B. The results of this study provide important insights into the comprehensive response of Brucella in response to polymyxin B stimulation.

A novel decoy strategy for polymyxin resistance in Acinetobacter baumannii.

Modification of the outer membrane charge by a polymyxin B (PMB)-induced PmrAB two-component system appears to be a dominant phenomenon in PMB-resistant Acinetobacter baumannii. PMB-resistant variants and many clinical isolates also appeared to produce outer membrane vesicles (OMVs). Genomic, transcriptomic, and proteomic analyses revealed that upregulation of the pmr operon and decreased membrane-linkage proteins (OmpA, OmpW, and BamE) are linked to overproduction of OMVs, which also promoted enhanced biofilm formation. The addition of OMVs from PMB-resistant variants into the cultures of PMB-susceptible A. baumannii and the clinical isolates protected these susceptible bacteria from PMB. Taxonomic profiling of in vitro human gut microbiomes under anaerobic conditions demonstrated that OMVs completely protected the microbial community against PMB treatment. A Galleria mellonella-infection model with PMB treatment showed that OMVs increased the mortality rate of larvae by protecting A. baumannii from PMB. Taken together, OMVs released from A. baumannii functioned as decoys against PMB.

Clinical Efficacy of Polymyxin B in Patients Infected with Carbapenem-Resistant Organisms.

PurposeCarbapenem-resistant organisms (CROs) pose great challenges for clinical treatment. Polymyxin B (PMB) is one of the “last resort” choices of CRO infections. We explored the possible factors affecting PMB efficacy.Patients and MethodsThis retrospective study involved CRO-infected patients treated with PMB for ≥72 h. The endpoint indicator was clinical efficacy. We compared the characteristics (demographics, pathogenic bacteria, PMB treatment) between patients who had “clinical success” (CS) and “clinical failure” (CF).ResultsA total of 191 patients were enrolled: 110 in the CS group and 81 in the CF group. The total cumulative dose for the CS group was higher than the CF group [1100 (700–1443.75) vs 800 (500–1112.5) mg; P = 0.001]. Treatment duration in the CS group was longer than the CF group [11 (8–14) vs 8 (6–11) days; P < 0.000]. Multivariate logistic regression analysis showed mechanical ventilation, vasoactive agents, multiple-site infection, and total cumulative dose to be independently associated with clinical efficacy. Cox survival analysis for 30-day mortality also showed that the use of vasoactive agents and the total cumulative dose of PMB could influence survival time and mortality rate independently.ConclusionPMB had good efficacy and a low prevalence of adverse reactions. The total cumulative dose, duration of PMB treatment, mechanical ventilation, vasoactive agents, and multiple-site infection were factors associated with the clinical efficacy of PMB.

Combined pollution of arsenic and Polymyxin B enhanced arsenic toxicity and enriched ARG abundance in soil and earthworm gut microbiotas

Polymyxin B (PMB) is considered as the last line of antibiotic defense available to humans. The environmental effects of the combined pollution with PMB and heavy metals and their interaction mechanisms are unclear. We explored the effects of the combined pollution with PMB and arsenic (As) on the microbial composition of the soil and in the earthworm gut, as well as the spread and transmission of antibiotic resistance genes (ARGs). The results showed that, compared with As alone, the combined addition of PMB and As could significantly increase the bioaccumulation factor and toxicity of As in earthworm tissues by 12.1% and 16.0%, respectively. PMB treatment could significantly increase the abundance of Actinobacteria in the earthworm gut (from 35.6% to 45.2%), and As stress could significantly increase the abundance of Proteobacteria (from 19.8% to 56.9%). PMB and As stress both could significantly increase the abundance of ARGs and mobile genetic elements (MGEs), which were positively correlated, indicating that ARGs might be horizontally transferred. The inactivation of antibiotics was the main resistance mechanism that microbes use to resist PMB and As stress. Network analysis showed that PMB and As might have antagonistic effects through competition with multi-drug resistant ARGs. The combined pollution by PMB and As significantly promoted the relative abundance of microbes carrying multi-drug resistant ARGs and MGEs, thereby increasing the risk of transmission of ARGs. This research advances the understanding of the interaction mechanism between antibiotics and heavy metals and provides new theoretical guidance for the environmental risk assessment and combined pollution management.

Quantifying the effects of antibiotic treatment on the extracellular polymer network of antimicrobial resistant and sensitive biofilms using multiple particle tracking

Novel therapeutics designed to target the polymeric matrix of biofilms requires innovative techniques to accurately assess their efficacy. Here, multiple particle tracking (MPT) was developed to characterize the physical and mechanical properties of antimicrobial resistant (AMR) bacterial biofilms and to quantify the effects of antibiotic treatment. Studies employed nanoparticles (NPs) of varying charge and size (40–500 nm) in Pseudomonas aeruginosa PAO1 and methicillin-resistant Staphylococcus aureus (MRSA) biofilms and also in polymyxin B (PMB) treated Escherichia coli biofilms of PMB-sensitive (PMBSens) IR57 and PMB-resistant (PMBR) PN47 strains. NP size-dependent and strain-related differences in the diffusion coefficient values of biofilms were evident between PAO1 and MRSA. Dose-dependent treatment effects induced by PMB in PMBSensE. coli biofilms included increases in diffusion and creep compliance (P < 0.05), not evident in PMB treatment of PMBRE. coli biofilms. Our results highlight the ability of MPT to quantify the diffusion and mechanical effects of antibiotic therapies within the AMR biofilm matrix, offering a valuable tool for the pre-clinical screening of anti-biofilm therapies.

Glucose-Induced Cyclic Lipopeptides Resistance in Bacteria via ATP Maintenance through Enhanced Glycolysis.

SummaryCyclic lipopeptide (CLP) antibiotics have a mechanism that causes membrane malfunction. Thus mechanisms of bacterial resistance to CLPs are thought to modify cell surfaces. However, we found that bacterial resistance to CLPs was strongly related to energy metabolism. Using polymyxin B (PB) as a model of CLPs, we showed that PB causes malfunction of respiration and serious depletion of ATP, contributing to PB-induced cell death and carbon starvation. Glucose addition could maintain the intracellular ATP level and reverse the carbon starvation response resulting from PB treatment. Another study revealed that glycolysis was stimulated by the presence of PB and glucose. The mechanism underlying glucose-enabled CLPs' resistance suggests that glucose could maintain the ATP level in PB-treated bacteria by enhancing glycolysis. Similar results were observed in Staphylococcus aureus, where daptomycin resistance was enhanced by glucose. These findings provide insight into the mode of action of CLPs and resistance to these antibiotics.

TLR4‐driven Lymphatic Alterations during IBD are driven in PAMP/DAMP Specific Manners

BackgroundInflammatory bowel disease (IBD) is characterised by both acute and chronic phase inflammation of the gastro‐intestinal (GI) tract that affect a large and growing number of people worldwide with little to no effective treatments. This is in part due to the lack of understanding of the disease pathogenesis and also the currently poorly described involvement of other systems such as the lymphatics. During DSS induced colitis, mice also develop a severe inflammation of both the colon and terminal ileum with many features similar to IBD. As well as inflammation within the intestinal tract we have previously demonstrated lymphatic remodelling within the mesentery and mesenteric lymph nodes of DSS‐treated mice. The lymphatic remodelling includes lymphangiogenesis, lymphatic vessel dilation and leakiness, as well as cellular infiltration into the surrounding tissue and peripheral draining lymph nodes. The aim of the investigation was to delineate the contribution of PAMP‐ and/or DAMP‐driven lymphatic remodelling and inflammation during disease, in respect to Toll‐like receptor 4 (TLR4) activity.MethodsIntestinal inflammation was induced in C57BL/6 mice by administration of 2.5% DSS in drinking water for 7 days. Mice were treated with TLR4 blocker C34 or Polymyxin‐B (PMXB) daily from days 3–7 of DSS treatment via I.P. injection, and their effects on disease activity and lymphatic function were examined. TLR4 activity and subsequent effect on lymphangiogenesis, lymphadenopathy, and mesenteric lymph node (MLN) cellular composition were assessed.ResultsDSS Mice treated with TLR4 inhibitor, C34, had a significantly improved disease phenotype characterised by reduced ileal and colonic insult. The change correlated with significant reduction in colonic and mesenteric inflammation, resolved mesenteric lymphangiectasia, and CD103+ DC accumulation similar to that of healthy control. PMXB treatment did not resolve inflammation within the colon, or associated mesenteric lymphatic dysfunction, but did however prevent lymphadenopathy within the MLN through alteration of CCL21 gradients and CD103+DC migration.ConclusionsTLR4 appears to mediate several changes within the mesenteric lymphatics, more specifically it is shown to have different outcomes whether stimulation occurs through pathogen derived factors such as LPS or tissue derived DAMPs, a novel phenomenon.Support or Funding InformationThis study was supported by the Lymphedema Research and Education Program, Snyder Institute for Chronic Diseases, Cumming School of Medicine, University of Calgary to P.‐Y.v.d.W.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.