The safety of polymyxin antibiotics

Colistin antibacterial activity, clinical effectiveness, and mechanisms of intrinsic and acquired resistance

Following a period of disuse owing to the emergence of multidrug-resistant Gram-negative bacteria, colistin has regained global attention as an antibiotic of last resort. The resurgence in its utilization has led to a concurrent increase in acquired resistance, presenting a significant challenge in clinical treatment. Predominantly, resistance mechanisms involve alterations in the lipid A component of the lipopolysaccharide (LPS) structure. These alterations are facilitated by the addition of cationic phosphoethanolamine (pEtN) or 4-amino-L-arabinose, often driven by the upregulation of two-component regulatory systems such as PmrAB and PhoPQ. Structural components of bacteria, such as capsules and efflux pumps, can also play an important role in the resistance mechanism. In addition to these biochemical modifications, structural components of bacteria like capsules and efflux pumps also play crucial roles in mediating resistance. Another significant mechanism is the acquisition of the plasmid-mediated mobilized colistin resistance (mcr) gene, which poses a global health threat due to its ability to transfer between different bacterial genera. Contemporary strategies to combat colistin resistance include the development and use of novel drugs and inhibitors. To devise effective interventions, it is imperative to first elucidate the precise mechanisms of colistin resistance and determine the roles of various contributing factors.

Adjuvant strategies to tackle mcr-mediated polymyxin resistance

The emergence of the mobile colistin resistance (mcr) gene is a demonstrable threat contributing to the worldwide antibiotic resistance crisis. The gene is encoded on plasmids and can easily spread between different bacterial strains. mcr encodes a phosphoethanolamine (pEtN) transferase, which catalyses the transfer of the pEtN moiety from phosphatidylethanolamine to lipid A, the head group of lipopolysaccharides (LPS). This neutralises the overall negative charge of the LPS and prevents the binding of polymyxins to bacterial membranes. We believe that the development of polymyxin adjuvants could be a promising approach to prolong the use of this important class of last-resort antibiotics. This review discusses recent progress in the identification, design and development of adjuvants to restore polymyxin sensitivity in these resistant bacteria, and focuses on both MCR inhibitors as well as alternative approaches that modulate polymyxin resistance.

Polymyxin B1 in the Escherichia coli inner membrane: A complex story of protein and lipopolysaccharide-mediated insertion

The rise in multi-drug resistant Gram-negative bacterial infections has led to an increased need for "last-resort" antibiotics such as polymyxins. However, the emergence of polymyxin-resistant strains threatens to bring about a post-antibiotic era. Thus, there is a need to develop new polymyxin-based antibiotics, but a lack of knowledge of the mechanism of action of polymyxins hinders such efforts. It has recently been suggested that polymyxins induce cell lysis of the Gram-negative bacterial inner membrane (IM) by targeting trace amounts of lipopolysaccharide (LPS) localized there. We use multiscale molecular dynamics (MD), including long-timescale coarse-grained (CG) and all-atom (AA) simulations, to investigate the interactions of polymyxin B1 (PMB1) with bacterial IM models containing phospholipids (PLs), small quantities of LPS, and IM proteins. LPS was observed to (transiently) phase separate from PLs at multiple LPS concentrations, and associate with proteins in the IM. PMB1 spontaneously inserted into the IM and localized at the LPS-PL interface, where it cross-linked lipid headgroups via hydrogen bonds, sampling a wide range of interfacial environments. In the presence of membrane proteins, a small number of PMB1 molecules formed interactions with them, in a manner that was modulated by local LPS molecules. Electroporation-driven translocation of PMB1 via water-filled pores was favored at the protein-PL interface, supporting the 'destabilizing' role proteins may have within the IM. Overall, this in-depth characterization of PMB1 modes of interaction reveals how small amounts of mislocalized LPS may play a role in pre-lytic targeting and provides insights that may facilitate rational improvement of polymyxin-based antibiotics.

Factors affecting the effectiveness and safety of polymyxin B in the treatment of Gram-negative bacterial infections: A meta-analysis of 96 articles

PURPOSE

Polymyxin B, with its unique structure and mechanism of action, has emerged as a key therapeutic agent against Gram-negative bacteria. The study aims to explore potential factors to influence its effectiveness and safety.

METHODS

A model-based meta-analysis of 96 articles was conducted, focusing on factors like dosage, bacterial species, and combined antibiotic therapy. The analysis evaluated mortality rates and incidence rate of renal dysfunction, also employing parametric survival models to assess 30-d survival rates.

RESULTS

In the study involving 96 articles and 9716 patients, polymyxin B's daily dose showed minimal effect on overall mortality, with high-dose group mortality at 33.57% (95% confidence intervals [CI]: 29.15-38.00) compared to the low-dose group at 35.44% (95% CI: 28.99-41.88), P = 0.64. Mortality significantly varied by bacterial species, with Pseudomonas aeruginosa infections at 58.50% (95% CI: 55.42-63.58). Monotherapy exhibited the highest mortality at 40.25% (95% CI: 34.75-45.76), P < 0.01. Renal dysfunction was more common in high-dose patients at 29.75% (95% CI: 28.52-30.98), with no significant difference across antibiotic regimens, P = 0.54. The 30-d overall survival rate for monotherapy therapy was 63.6% (95% CI: 59.3-67.5) and 70.2% (95% CI: 64.4-76.2) for association therapy with β-lactam drugs.

CONCLUSIONS

The dosage of polymyxin B does not significantly change death rates, but its effectiveness varies based on the bacterial infection. Certain bacteria like P. aeruginosa are associated with higher mortality. Combining polymyxin B with other antibiotics, especially β-lactam drugs, improves survival rates. Side effects depend on the dose, with lower doses being safer. These findings emphasize the importance of customizing treatment to balance effectiveness and safety.

Drug-Drug Interactions in Nosocomial Infections: An Updated Review for Clinicians

Prevention, assessment, and identification of drug-drug interactions (DDIs) represent a challenge for healthcare professionals, especially in nosocomial settings. This narrative review aims to provide a thorough assessment of the most clinically significant DDIs for antibiotics used in healthcare-associated infections. Complex poly-pharmaceutical regimens, targeting multiple pathogens or targeting one pathogen in the presence of another comorbidity, have an increased predisposition to result in life-threatening DDIs. Recognising, assessing, and limiting DDIs in nosocomial infections offers promising opportunities for improving health outcomes. The objective of this review is to provide clinicians with practical advice to prevent or mitigate DDIs, with the aim of increasing the safety and effectiveness of therapy. DDI management is of significant importance for individualising therapy according to the patient, disease status, and associated comorbidities.

Polymyxin B vs. colistin: the comparison of neurotoxic and nephrotoxic effects of the two polymyxins

BACKGROUND

The study aimed to compare polymyxin B with colistimethate sodium (CMS) regarding neurotoxicity, nephrotoxicity and 30-day mortality in patients with MDR Gram-negatives.

METHODS

All adult patients who received polymyxin B or CMS for at least 24 h for the treatment of MDR microorganisms were evaluated retrospectively.

RESULTS

Among 413 initially screened patients, 147 patients who were conscious and able to express their symptoms were included in the neurotoxicity analysis. 13 of 77 patients with polymyxin B and 1 of 70 with CMS had neurotoxic adverse events, mainly paresthesias. All events were reversible after drug discontinuation. Among 290 patients included in nephrotoxicity analysis, the incidence of acute kidney injury (AKI) was 44.7% and 40.0% for polymyxin B and CMS, respectively (p = 0.425). AKI occurred two days earlier with colistin than polymyxin B without statistical significance (median (IQR): 5 (3-11) vs. 7 (3-12), respectively, p = 0.701). Polymyxin therapy was withdrawn in 41.1% of patients after AKI occurred and CMS was more frequently withdrawn than polymyxin B (p = 0.025). AKI was reversible in 91.6% of patients with CMS and 79% with polymyxin B after the drug withdrawal. Older age, higher baseline serum creatinine and the use of at least two nephrotoxic drugs were independent factors associated with AKI (OR 1.05, p < 0.001; OR 2.99, p = 0.022 and OR 2.45, p = 0.006, respectively). Septic shock, mechanical ventilation, presence of a central venous catheter and Charlson comorbidity index (OR 2.13, p = 0.004; OR 3.37, p < 0.001; OR 2.47, p = 0.004 and OR 1.21, p p < 0.001, respectively) were the independent predictors of mortality. The type of polymyxin was not related to mortality.

CONCLUSIONS

Neurotoxicity is a relatively common adverse event that leads to drug withdrawal during polymyxins, particularly polymyxin B. Nephrotoxicity is very common during polymyxin therapy and the two polymyxins display similar nephrotoxic events with high reversibility rates after drug withdrawal. Close monitoring of AKI is crucial during polymyxin therapy, particularly, for elderly patients, patients who have high baseline creatinine, and using other nephrotoxic drugs.

Alteration in the Morphological and Transcriptomic Profiles of Acinetobacter baumannii after Exposure to Colistin

Acinetobacter baumannii is often highly resistant to multiple antimicrobials, posing a risk of treatment failure, and colistin is a "last resort" for treatment of the bacterial infection. However, colistin resistance is easily developed when the bacteria are exposed to the drug, and a comprehensive analysis of colistin-mediated changes in colistin-susceptible and -resistant A. baumannii is needed. In this study, using an isogenic pair of colistin-susceptible and -resistant A. baumannii isolates, alterations in morphologic and transcriptomic characteristics associated with colistin resistance were revealed. Whole-genome sequencing showed that the resistant isolate harbored a PmrBL208F mutation conferring colistin resistance, and all other single-nucleotide alterations were located in intergenic regions. Using scanning electron microscopy, it was determined that the colistin-resistant mutant had a shorter cell length than the parental isolate, and filamented cells were found when both isolates were exposed to the inhibitory concentration of colistin. When the isolates were treated with inhibitory concentrations of colistin, more than 80% of the genes were upregulated, including genes associated with antioxidative stress response pathways. The results elucidate the morphological difference between the colistin-susceptible and -resistant isolates and different colistin-mediated responses in A. baumannii isolates depending on their susceptibility to this drug.

Pan-drug resistance and hypervirulence in a human fungal pathogen are enabled by mutagenesis induced by mammalian body temperature

The continuing emergence of invasive fungal pathogens poses an increasing threat to public health. Here, through the China Hospital Invasive Fungal Surveillance Net programme, we identified two independent cases of human infection with a previously undescribed invasive fungal pathogen, Rhodosporidiobolus fluvialis, from a genus in which many species are highly resistant to fluconazole and caspofungin. We demonstrate that R. fluvialis can undergo yeast-to-pseudohyphal transition and that pseudohyphal growth enhances its virulence, revealed by the development of a mouse model. Furthermore, we show that mouse infection or mammalian body temperature induces its mutagenesis, allowing the emergence of hypervirulent mutants favouring pseudohyphal growth. Temperature-induced mutagenesis can also elicit the development of pan-resistance to three of the most commonly used first-line antifungals (fluconazole, caspofungin and amphotericin B) in different Rhodosporidiobolus species. Furthermore, polymyxin B was found to exhibit potent activity against the pan-resistant Rhodosporidiobolus mutants. Collectively, by identifying and characterizing a fungal pathogen in the drug-resistant genus Rhodosporidiobolus, we provide evidence that temperature-dependent mutagenesis can enable the development of pan-drug resistance and hypervirulence in fungi, and support the idea that global warming can promote the evolution of new fungal pathogens.

Antimicrobial Peptides towards Clinical Application-A Long History to Be Concluded

Antimicrobial peptides (AMPs) are molecules with an amphipathic structure that enables them to interact with bacterial membranes. This interaction can lead to membrane crossing and disruption with pore formation, culminating in cell death. They are produced naturally in various organisms, including humans, animals, plants and microorganisms. In higher animals, they are part of the innate immune system, where they counteract infection by bacteria, fungi, viruses and parasites. AMPs can also be designed de novo by bioinformatic approaches or selected from combinatorial libraries, and then produced by chemical or recombinant procedures. Since their discovery, AMPs have aroused interest as potential antibiotics, although few have reached the market due to stability limits or toxicity. Here, we describe the development phase and a number of clinical trials of antimicrobial peptides. We also provide an update on AMPs in the pharmaceutical industry and an overall view of their therapeutic market. Modifications to peptide structures to improve stability in vivo and bioavailability are also described.

Recent Advances in the Development of Polymyxin Antibiotics: 2010-2023

The polymyxins are nonribosomal lipopeptides produced by Paenibacillus polymyxa and are potent antibiotics with activity specifically directed against Gram-negative bacteria. While the clinical use of polymyxins has historically been limited due to their toxicity, their use is on the rise given the lack of alternative treatment options for infections due to multidrug resistant Gram-negative pathogens. The Gram-negative specificity of the polymyxins is due to their ability to target lipid A, the membrane embedded LPS anchor that decorates the cell surface of Gram-negative bacteria. Notably, the mechanisms responsible for polymyxin toxicity, and in particular their nephrotoxicity, are only partially understood with most insights coming from studies carried out in the past decade. In parallel, many synthetic and semisynthetic polymyxin analogues have been developed in recent years in an attempt to mitigate the nephrotoxicity of the natural products. Despite these efforts, to date, no polymyxin analogues have gained clinical approval. This may soon change, however, as at the moment there are three novel polymyxin analogues in clinical trials. In this context, this review provides an update of the most recent insights with regard to the structure-activity relationships and nephrotoxicity of new polymyxin variants reported since 2010. We also discuss advances in the synthetic methods used to generate new polymyxin analogues, both via total synthesis and semisynthesis.

Zoledronic acid and ibandronate-induced nephrotoxicity in 2D and 3D proximal tubule cells derived from human and rat

Drug-induced proximal tubule (PT) injury remains a serious safety concern throughout drug development. Traditional in vitro 2-dimensional (2D) and preclinical in vivo models often fail to predict drug-related injuries presented in clinical trials. Various 3-dimensional (3D) microphysiological systems (MPSs) have been developed to mimic physiologically relevant properties, enabling them to be more predictive toward nephrotoxicity. To explore the capabilities of an MPS across species, we compared cytotoxicity in hRPTEC/TERT1s and rat primary proximal tubular epithelial cells (rPPTECs) following exposure to zoledronic acid and ibandronate (62.5-500 µM), and antibiotic polymyxin B (PMB) (50 and 250 µM, respectively). For comparison, we investigated cytotoxicity using 2D cultured hRPTEC/TERT1s and rPPTECs following exposure to the same drugs, including overlapping concentrations, as their 3D counterparts. Regardless of the in vitro model, bisphosphonate-exposed rPPTECs exhibited cytotoxicity quicker than hRPTEC/TERT1s. PMB was less sensitive toward nephrotoxicity in rPPTECs than hRPTEC/TERT1s, demonstrating differences in species sensitivity within both 3D and 2D models. Generally, 2D cultured cells experienced faster drug-induced cytotoxicity compared to the MPSs, suggesting that MPSs can be advantageous for longer-term drug-exposure studies, if warranted. Furthermore, ibandronate-exposed hRPTEC/TERT1s and rPPTECs produced higher levels of inflammatory and kidney injury biomarkers compared to zoledronic acid, indicating that ibandronate induces acute kidney injury, but also a potential protective response since ibandronate is less toxic than zoledronic acid. Our study suggests that the MPS model can be used for preclinical screening of compounds prior to animal studies and human clinical trials.

Battle of polymyxin induced nephrotoxicity: Polymyxin B versus colistin

OBJECTIVES

Nephrotoxicity is the most serious and common adverse effect that limits the use of polymyxins. This study compared polymyxin E (colistin) and polymyxin B regarding drug-related nephrotoxicity.

METHODS

This study was conducted as a retrospective cohort study in a university hospital between January 2020 and July 2022. Patients older than 18 years and who received colistin or polymyxin B were identified using electronic hospital records. Kidney disease improving global outcome criteria were used for assessing nephrotoxicity.

RESULTS

A total of 190 patients, 95 in both groups, were evaluated. The incidence of acute kidney injury during the treatment was higher in the colistin group [52.6% (n = 50) and 34.7% (n = 33), P = 0.013]. In patients who were exposed to high-dose, the rate of nephrotoxicity was higher in patients receiving colistin [25% (n = 3) vs. 76.9% (n = 10); P = 0.017]. Nephrotoxicity was reversible in 64.4% (n = 38) of patients and the reversibility rate was similar (70% and 52.6% for colistin and polymyxin; P = 0.248). In the multivariable analysis, colistin treatment [odds ratio (OR): 3.882, 95% confidence interval (95% CI) = (1.829-8.241)], concomitant vasopressor use (OR = 2.08, CI: 1.036-4.179), and age (OR=1.036, CI: 1.014-1.058) were found to be independent markers of nephrotoxicity.

CONCLUSION

Nephrotoxicity was more common in patients receiving high-dose colistin than polymyxin B. Therefore, the use of appropriate doses of colistin is important in terms of preventing nephrotoxicity. In addition, advancing age and concomitant use of vasopressors contribute to polymyxin-related nephrotoxicity.

Semisynthetic polymyxins with potent antibacterial activity and reduced kidney cell toxicity

The growing incidence of infections caused by multi-drug resistant Gram-negative bacteria has led to an increased use of last-resort antibiotics such as the polymyxins. Polymyxin therapy is limited by toxicity concerns, most notably nephrotoxicity. Recently we reported the development of a novel class of semisynthetic polymyxins with reduced toxicity wherein the N-terminal lipid and diaminobutyric acid residue are replaced by a cysteine-linked lipid featuring a reductively labile disulfide bond. In the present study we further explored the potential of this approach by also varying the amino acid residue directly adjacent to the polymyxin macrocycle. This led to the identification of new semisynthetic polymyxins that maintain the potent antibacterial activity of the clinically used polymyxin B while exhibiting a further reduction in toxicity toward human proximal tubule epithelial cells. Furthermore, these new polymyxins were found to effectively synergize with novobiocin, rifampicin, and erythromycin against mcr-positive, polymyxin resistant E. coli.

In vivo evaluation of nephrotoxicity and neurotoxicity of colistin formulated with sodium deoxycholate sulfate in a mice model

Neurotoxicity and nephrotoxicity are the major dose-limiting factors for the clinical use of colistin against multidrug-resistant (MDR) Gram-negative bacteria. This study aimed to investigate the neurotoxic and nephrotoxic effects of colistin formulated with in-house synthesized sodium deoxycholate sulfate (SDCS) in a mouse model. Male mice C57BL/6 were randomly divided into four groups: control (saline solution), colistin (15 mg/kg/day), colistin:SDCS 1:1, and colistin:SDCS 1:2. In the colistin:SDCS treatment groups, the dosage was 15 mg/kg/day colistin equivalent; all mice were treated for 7 successive days. The thermal tolerance, body weight gain and organ weights were measured. The levels of serum blood urea nitrogen (BUN), creatinine (Cr), superoxide dismutase (SOD), and catalase (CAT) were assessed. Histopathological damages were assessed on mice organ. The colistin:SDCS formulations significantly improved thermal pain response of the mice comparable to the control group. The administration did not impair kidney function as evidence from BUN and Cr results; however, the oxidative stress biomarkers decreased in the colistin and colistin-SDCS treated mice. Several abnormalities were observed in the kidney, liver, spleen, and sciatic nerve tissues following colistin treatment, which indicated evidence of toxicity. The colistin-SDCS formulations were associated with less acute toxicity and fewer nephrotoxic and neurotoxic changes compared with the colistin alone group which indicated that SDCS attenuated colistin nephrotoxicity and neurotoxicity. This study highlights the potential application of colistin formulated with SDCS for safer clinical use against MDR Gram-negative bacteria.

Antimicrobial and Adjuvant Potencies of Di-n-alkyl Substituted Diazalariat Ethers

Lariat ethers are macrocyclic polyethers-crown ethers-to which sidearms are appended. 4,13-Diaza-18-crown-6 having twin alkyl chains at the nitrogens show biological activity. They exhibit antibiotic activity, but when co-administered at with an FDA-approved antibiotic, the latter's potency is often strongly enhanced. Potency enhancements and resistance reversals have been documented in vitro for a range of Gram-negative and Gram-positive bacteria with a variety of antimicrobials. Strains of E. coli and Staphylococcus aureus having resistance to a range of drugs have been studied and the potency enhancements (checkerboards) are reported here. Drugs included in the present study are ampicillin, cefepime, chlortetracycline, ciprofloxacin, doxycycline, kanamycin, minocycline, norfloxacin, oxycycline, penicillin G, and tetracycline. Enhancements of norfloxacin potency against S. aureus 1199B of up to 128-fold were observed. The properties of these lariat ethers have been studied to determine solubility, their membrane penetration, cytotoxicity and mammalian cell survival, and their effect on bacterial efflux pumps. It is shown that in some cases, the lariat ethers have complex antimicrobials with considerable selectivity. Based on these observations, including 1:1 complexation between lariat ethers and antimicrobials and the cytotoxicity of the MeI salts showing a separation index of 32-fold, they hold significant potential for further development.

Role of efflux pumps, their inhibitors, and regulators in colistin resistance

Colistin is highly promising against multidrug-resistant and extensively drug-resistant bacteria clinically. Bacteria are resistant to colistin mainly through mcr and chromosome-mediated lipopolysaccharide (LPS) synthesis-related locus variation. However, the current understanding cannot fully explain the resistance mechanism in mcr-negative colistin-resistant strains. Significantly, the contribution of efflux pumps to colistin resistance remains to be clarified. This review aims to discuss the contribution of efflux pumps and their related transcriptional regulators to colistin resistance in various bacteria and the reversal effect of efflux pump inhibitors on colistin resistance. Previous studies suggested a complex regulatory relationship between the efflux pumps and their transcriptional regulators and LPS synthesis, transport, and modification. Carbonyl cyanide 3-chlorophenylhydrazone (CCCP), 1-(1-naphthylmethyl)-piperazine (NMP), and Phe-Arg-β-naphthylamide (PAβN) all achieved the reversal of colistin resistance, highlighting the role of efflux pumps in colistin resistance and their potential for adjuvant development. The contribution of the efflux pumps to colistin resistance might also be related to specific genetic backgrounds. They can participate in colistin tolerance and heterogeneous resistance to affect the treatment efficacy of colistin. These findings help understand the development of resistance in mcr-negative colistin-resistant strains.

Optimization of Pyrazole Compounds as Antibiotic Adjuvants Active against Colistin- and Carbapenem-Resistant Acinetobacter baumannii

The diffusion of antibiotic-resistant, Gram-negative, opportunistic pathogens, an increasingly important global public health issue, causes a significant socioeconomic burden. Acinetobacter baumannii isolates, despite causing a lower number of infections than Enterobacterales, often show multidrug-resistant phenotypes. Carbapenem resistance is also rather common, prompting the WHO to include carbapenem-resistant A. baumannii as a "critical priority" for the discovery and development of new antibacterial agents. In a previous work, we identified several series of compounds showing either direct-acting or synergistic activity against relevant Gram-negative species, including A. baumannii. Among these, two pyrazole compounds, despite being devoid of any direct-acting activity, showed remarkable synergistic activity in the presence of a subinhibitory concentration of colistin on K. pneumoniae and A. baumannii and served as a starting point for the synthesis of new analogues. In this work, a new series of 47 pyrazole compounds was synthesized. Some compounds showed significant direct-acting antibacterial activity on Gram-positive organisms. Furthermore, an evaluation of their activity as potential antibiotic adjuvants allowed for the identification of two highly active compounds on MDR Acinetobacter baumannii, including colistin-resistant isolates. This work confirms the interest in pyrazole amides as a starting point for the optimization of synergistic antibacterial compounds active on antibiotic-resistant, Gram-negative pathogens.

A new self-immolative colistin prodrug with dual targeting functionalities and reduced toxicity for the treatment of intracellular bacterial infections

Colistin is a potent antibiotic but its severe side effects including nephrotoxicity and neurotoxicity are the roadblock for their wide use in clinics. To solve this problem, we synthesized a new prodrug, mannose-maltose-colistin conjugate, termed MMCC that can reversibly mask the five amines of colistin that are primarily responsible for the toxicity. The deliberated design of disulfide-based self-immolative linker warranted the reversibly release of the pristine amines of colistin on demand without sacrificing antimicrobial efficacy. Once MMCC was delivered in cells, reducing agents cleaves the disulfide bond and release the pristine amines. The targeting ligands of maltose and mannose were grafted on colistin conjugate for targeting delivery of colistin to bacteria and macrophages, respectively. Taken together, MMCC as a new class of antimicrobial biomaterials, demonstrates its great potential for the treatment of intracellular bacterial infections.

Antisense Peptide Nucleic Acid-Diaminobutanoic Acid Dendron Conjugates with SbmA-Independent Antimicrobial Activity against Gram-Negative Bacteria

Precision antisense antibacterial agents may be developed into novel antibiotics in the fight against multidrug-resistant Gram-negative bacteria. In this study, a series of diaminobutanoic acid (DAB) dendrons are presented as novel carriers for the delivery of antisense antibacterial peptide nucleic acids (PNAs). The dendron-PNA conjugates targeting the essential acpP gene exhibit specific antisense antimicrobial bactericidal activity against Escherichia coli and Klebsiella pneumoniae at one-digit micromolar concentrations, while showing low toxicity to human cells. One compound selected from a structure-activity relationship series showed high stability in mouse and human serum (t_1/2 ≫ 24 h) as well as in vivo activity against a multidrug-resistant, extended spectrum beta-lactamase-producing E. coli in a murine peritonitis model. The compound was also well tolerated in mice upon i.v. administration up to a dose of 20 mg/kg, and in vivo fluorescence imaging indicated clearance via renal excretion with slight accumulation in the kidneys and liver. Thus, DAB-based dendrons constitute a promising new chemistry platform for development of effective delivery agents for antibacterial drugs with possible in vivo use.

Preoptimized phage cocktail for use in aerosols against nosocomial transmission of carbapenem-resistant Acinetobacter baumannii: A 3-year prospective intervention study

Using bacteriophages (phages) as environmental sanitizers has been recognized as a potential alternative method to remove bacterial contamination in vitro; however, very few studies are available on the application of phages for infection control in hospitals. Here, we performed a 3-year prospective intervention study using aerosolized phage cocktails as biocontrol agents against carbapenem-resistant Acinetobacter baumannii (CRAB) infection in the hospital. When a CRAB-infected patient was identified in an intensive care unit (ICU), their surrounding environment was chosen for phage aerosol decontamination. Before decontamination, 501 clinical specimens from the patients were subjected to antibiotic resistance analysis and phage typing. The optimal phage cocktails were a combination of different phage families or were constructed by next-evolutionary phage typing with the highest score for the host lysis zone to prevent the development of environmental CRAB phage resistance. The phage infection percentage of the antibiotic-resistant A. baumannii strains was 97.1%, whereas the infection percentage in the antibiotic-susceptible strains was 79.3%. During the phage decontamination periods from 2017 to 2019, the percentage of carbapenem-resistant A. baumannii in test ICUs decreased significantly from 65.3% to 55%. The rate of new acquisitions of CRAB infection over the three years was 4.4 per 1000 patient-days, which was significantly lower than that in the control wards (8.9 per 1000 patient-days) where phage decontamination had never been performed. In conclusion, our results support the potential of phage cocktails to decrease CRAB infection rates, and the aerosol generation process may make this approach more comprehensive and time-saving.

Adsorption-Based Detoxification of Endotoxins by Porous Flexible Organic Frameworks

Bacterial lipopolysaccharides (LPS, endotoxins) cause sepsis that is responsible for a huge amount of mortality globally. However, their neutralization or detoxification remains an unmet medical need. We envisaged that cationic organic frameworks with persistent hydrophobic porosity may adsorb and thus neutralize LPS through a combination of cooperative ion-pairing electrostatic attraction and hydrophobicity. We here report the preparation of two water-soluble flexible organic frameworks (FOF-1 and FOF-2) from tetratopic and ditopic precursors through quantitative formation of hydrazone bonds at room temperature. The two FOFs are revealed to possess hydrodynamic diameters, which range from 20 to 120 nm, depending on the concentrations. Dynamic light scattering and isothermal titration calorimetric and chromogenic limulus amebocyte lysate experiments indicate that both frameworks are able to adsorb and thus reduce the concentration of free LPS molecules in aqueous solution, whereas cytokine inhibition experiments with RAW264.7 support that this adsorption can significantly decrease the toxicity of LPS. In vivo experiments with mice (five males per group) show that the injection of FOF-1 at a dose of 0.6 mg/kg realizes the survival of all of the mice administrated with LPS of the d-galactosamine (d-Gal)-sensitized absolute lethal dose (LD₁₀₀, 0.05 mg/kg), whereas its maximum tolerated dose for mice is determined to be 10 mg/kg. These findings provide a new promising sequestration strategy for the development of porous agents for the neutralization of LPS.

Disulfiram Enhances the Activity of Polymyxin B Against Klebsiella pneumoniae by Inhibiting Lipid A Modification

Background

The use of antibiotic adjuvants is a complementary strategy to the development of new antibiotics. The essential role of the ArnA dehydrogenase domain (ArnA_DH) in the addition of 4-amino-L-arabinose (L-Ara4N) to lipid A makes it a potential target in polymyxin adjuvant design.

Purpose

This study aimed to identify a dehydrogenase inhibitor that enhances the antibacterial effect of polymyxin B (PB) and to further understand the mechanism of this drug combination.

Methods

A susceptible K. pneumoniae strain, ATCC13883, was used to screen a dehydrogenase inhibitor library based on 3-(4,5)-dimethylthiazol(-z-y1)-2,5-diphenyltetrazolium bromide (MTT) and chequerboard assays. The protein- and cell-based effects of disulfiram (DSF) on ArnA activity were assessed, and the transcription levels of genes in the arn operon were evaluated by quantitative real-time polymerase chain reaction (qRT–PCR). Lipid A was isolated, and a structural analysis was performed. The cell wall function was evaluated through membrane integrity and bacterial viability assays. The in vivo antibacterial activity was evaluated using a mouse pulmonary infection model.

Results

We screened a dehydrogenase inhibitor library and found that the anti-alcoholism drug DSF significantly enhanced the antibacterial activity of PB in vitro and in vivo. The protein-based enzyme activity assay showed that DSF exerted no direct effect on the dehydrogenase activity of ArnA. Treatment with the combination of DSF and PB but not with PB alone decreased both the transcription level of genes in the arn operon and the modification level of lipid A. DSF also strengthened the disruption of the cell membrane integrity of PB. Moreover, the enhanced PB antibacterial activity was effective against clinical PB-resistant strains.

Conclusion

We identified a new drug combination that can be used to reduce the necessary dosage of PB and overcome PB resistance, and this drug combination has good prospects for clinical application.

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.

Safety evaluation of current therapies for high-risk severely ill patients with carbapenem-resistant infections

INTRODUCTION

Infections due to carbapenem-resistant Gram-negative bacteria (CR-GNB) are increasingly frequent events, which are associated with a high mortality rate. Traditionally, combination regimens including high doses of "old antibiotics" such as polymyxins, tigecycline, and aminoglycosides have been used to treat these infections, but they were often associated with low efficacy and high excess of side effects and toxicity, especially nephrotoxicity. Along with the development of new compounds, the last decade has seen substantial improvements in the management of CR infections.

AREAS COVERED

In this review, we aimed to discuss the safety characteristics and tolerability of different new options for treatment of CR infections.

EXPERT OPINION

The availability of new drugs showing a potent in vitro activity against CR-GNB represents a unique opportunity to face the threat of resistance, while potentially reducing toxicity. A thorough understanding of the safety profile from clinical trials may guide the use of these new drugs in critically ill patients at high risk for the development of adverse events. Future data coming from real-life studies for drugs targeting CR infections are crucial to confirm the safety profile observed in pivotal trials.

Liposomal delivery systems and their applications against Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus

Liposomal delivery systems have been widely explored for targeting superbugs such as S. aureus and MRSA, overcoming antimicrobial resistance associated with conventional dosage forms. They have the significant advantage of delivering hydrophilic and lipophilic antimicrobial agents, either singularly as monotherapy or in combination as combination therapy, due to their bilayers with action-site-specificity, resulting in improved targeting compared to conventional dosage forms. Herein, we present an extensive and critical review of the different liposomal delivery systems employed in the past two decades for the delivery of both antibiotics of different classes and non-antibiotic antibacterial agents, as monotherapy and combination therapy to eradicate infections caused by S. aureus and MRSA. The review also identifies future research and strategies potentiating the applications of liposomal delivery systems against S. aureus and MRSA. This review confirms the potential application of liposomal delivery systems for effective delivery and specific targeting of S. aureus and MRSA infections.

Studying the surfaces of bacteria using neutron scattering: finding new openings for antibiotics

The use of neutrons as a scattering probe to investigate biological membranes has steadily grown in the past three decades, shedding light on the structure and behaviour of this ubiquitous and fundamental biological barrier. Meanwhile, the rise of antibiotic resistance has catalysed a renewed interest in understanding the mechanisms underlying the dynamics of antibiotics interaction with the bacterial cell envelope. It is widely recognised that the key reason behind the remarkable success of Gram-negative pathogens in developing antibiotic resistance lies in the effectiveness of their outer membrane (OM) in defending the cell from antibacterial compounds. Critical to its function, the highly asymmetric lipid distribution between the inner and outer bilayer leaflets of the OM, adds an extra level of complexity to the study of this crucial defence barrier. Here we review the opportunities offered by neutron scattering techniques, in particular reflectometry, to provide structural information on the interactions of antimicrobials with in vitro models of the OM. The differential sensitivity of neutrons towards hydrogen and deuterium makes them a unique probe to study the structure and behaviour of asymmetric membranes. Molecular-level understanding of the interactions between antimicrobials and the Gram-negative OM provides valuable insights that can aid drug development and broaden our knowledge of this critically important biological barrier.

Clinical and Microbiological Characteristics of a Community-Acquired Carbapenem-Resistant Escherichia coli ST410 Isolate Harbouring blaNDM-5-Encoding IncX3-Type Plasmid From Blood

Objectives: The aim of this research was to investigate the clinical and microbiological characteristics of a case of community-acquired carbapenem-resistant Escherichia coli isolated from a patient with a bloodstream infection in China. Methods: Escherichia coli Huamei202001 was recovered from the first blood culture from a patient hospitalised in China. An antimicrobial susceptibility test was performed, and the genome was sequenced on an Illumina HiSeq X 10 platform with a 150-bp paired-end approach. The generated sequence reads were assembled using Unicycler, and the whole genome sequence data were analysed using bioinformatics tools. Moreover, the patient and her main family members obtained a faecal sample screening test for CRE, the positive strain was further isolated and the identification and antimicrobial susceptibility testing was performed. Results: Escherichia coli Huamei202001 belonged to sequence type 410. In addition, a blaNDM-5-encoding IncX3-type plasmid was responsible for the spreading of carbapenem resistance. Only the patient was detected as having a positive faecal sample screening test for CRE. Strain Fec01 was identified as E. coli, and the antibiotic susceptibility profile was the same as that of E. coli Huamei202001. Conclusions: Escherichia coli Huamei202001 is defined as community-acquired carbapenem-resistant Enterobacteriaceae. The clone ST410 that harbours the blaNDM-5-encoding IncX3-type plasmid is causing new high-risk clones globally. Thus, infection control measures should be strengthened to curb the dissemination of IncX3.

Colistin Dosing Regimens against Pseudomonas aeruginosa in Critically Ill Patients: An Application of Monte Carlo Simulation

Our aims are to assess various colistin dosing regimens against Pseudomonas aeruginosa (P. aeruginosa) infection in critically ill patients and to propose an appropriate regimen based on microbiological data. A Monte Carlo simulation was performed using the published colistin’s pharmacokinetic parameters of critically ill patients, the published pharmacodynamic target from a mouse thigh infection model, and the minimum inhibitory concentration (MIC) results from a Vietnamese hospital. The probability of target attainment (PTA) of 80% and cumulative fraction of response (CFR) of 90% were used to evaluate the efficacy of each regimen. Of 121 P. aeruginosa laboratory datasets, the carbapenem-resistant P. aeruginosa (CRPA) and the colistin-resistant P. aeruginosa rates were 29.8% and 0.8%, respectively. MIC_50,90 were both 0.5 mg/L. The simulated results showed that at MIC of 2 mg/L, most regimens could not reach the PTA target, particularly in patients with normal renal function (Creatinine clearance (CrCl) ≥ 80 mL/min). At MIC of 0.5 mg/L and 1 mg/L, current recommendations still worked well. On the basis of these results, aside from lung infection, our study recommends three regimens against P. aeruginosa infection at MIC of 0.5 mg/L, 1 mg/L, and 2 mg/L. In conclusion, higher total daily doses and fractionated colistin dosing regimens could be the strategy for difficult-to-acquire PTA cases, while a less aggressive dose might be appropriate for empirical treatment in settings with low MIC_50/90.

Effectiveness and Nephrotoxicity of Intravenous Polymyxin B in Chinese Patients With MDR and XDR Nosocomial Pneumonia

Background: Nosocomial pneumonia is a major health and economic burden globally. Multidrug-resistant (MDR) or extensively drug-resistant (XDR) Gram-negative bacteria are the most common causative pathogens in critically-ill patients. Polymyxin B is a salvage therapy for MDR Gram-negative pathogens; however, the current literature on its effectiveness and nephrotoxicity is limited, including in Chinese patients.

Methods: We retrospectively analyzed 107 patients with nosocomial pneumonia caused by MDR or XDR Gram-negative bacteria treated with intravenous polymyxin B (2–3 mg/kg/day). Renal function was evaluated on the day before commencement of polymyxin B therapy and on the third and 7 days of treatment. Univariate and multivariate analyses were conducted to determine risk factors for the effectiveness and nephrotoxicity of polymyxin B. Sixty-seven (62.6%) and sixty-five (60.7%) patients had favorable clinical and microbiological responses, respectively. Acute physiology and chronic health evaluation II (APACHE II) scores, cardio-pulmonary resuscitation (CPR) history, numbers of pathogens per patient and a favorable microbiological response were independently associated with favorable clinical outcomes of polymyxin B treatment in Chinese patients with MDR or XDR nosocomial pneumonia. Initial renal dysfunction was not associated with late nephrotoxicity (on day 7), although early nephrotoxicity (on day 3) was independently associated with late nephrotoxicity (OR = 39.43, 95% CI 7.64–203.62, p = 0.00).

Conclusion: Our findings support polymyxin B treatment for MDR and XDR pneumonia, with the severity of disease and polymicrobial infection being risk factors for a poor clinical outcome. Nephrotoxicity following 3 days of polymyxin B treatment was found to be a reliable risk factor for later nephrotoxicity.

Comparing the Population Pharmacokinetics of and Acute Kidney Injury Due to Polymyxin B in Chinese Patients with or without Renal Insufficiency

Despite excellent bactericidal effect, dosing adjustment of polymyxin B for patients with renal insufficiency and polymyxin B-related nephrotoxicity is still a major concern to clinicians. The aim of this study was to compare the population pharmacokinetics (PK) properties of polymyxin B in Chinese patients with different renal functions and to investigate the relationship between PK parameters and polymyxin B-related acute kidney injury (AKI). A total of 37 patients with normal renal function (creatinine clearance ≥ 80 ml/min) and 33 with renal insufficiency (creatinine clearance < 80 ml/min) were included. In the two-compartment population PK models, the central compartment clearance (CL) (2.19 liters/h versus 1.58 liters/h; P < 0.001) and intercompartmental clearance (Q) (13.83 liters/h versus 10.28 liters/h; P < 0.001) values were significantly different between the two groups. The simulated values for AUC across 24 h at steady state (AUC_ss,24h) for patients with normal renal function were higher than those for patients with renal insufficiency. However, renal dosing adjustment of polymyxin B seemed not to be necessary. In addition, during the treatment, AKI occurred in 23 (32.86%) patients. The polymyxin B AUC_ss,24h in patients with AKI was significantly higher than that in patients without AKI (108.66 ± 70.10 mg · h/liter versus 66.18 ± 34.79 mg · h/liter; P = 0.001). Both the receiver operating characteristic (ROC) curve and logistic regression analysis showed that an AUC_ss,24h of >100 mg · h/liter was a good predictor for the probability of nephrotoxicity.

Acute toxicity is a dose-limiting factor for intravenous polymyxin B: A safety and pharmacokinetic study in healthy Chinese subjects

OBJECTIVES

Polymyxin B is a last-line antibiotic for multidrug-resistant gram-negative bacterial infections. However, limited safety and pharmacokinetic information is available. We investigated the safety and pharmacokinetics of intravenous polymyxin B in healthy subjects.

METHODS

An open-label, single-dose clinical trial was conducted in healthy Chinese subjects. Polymyxin B (sulphate) was administered intravenously at 0.75 or 1.5 mg/kg (n = 10 per dose, 5 males and 5 females) to examine the safety and pharmacokinetics.

RESULTS

One female subject in the 1.5-mg/kg group discontinued due to abdominal pain during administration. The most frequently reported adverse events were perioral paraesthesia, dizziness, and numbness of extremities (7/10 subjects in the 0.75-mg/kg group, all subjects in the 1.5-mg/kg group). All neurotoxicity-related events dissipated without treatment within a maximum of 23 h. Notably, abdominal pain (3/5) and vulvar pruritus (2/5), colpitis (2/5) or abnormal uterine bleeding (1/5) were reported in female subjects receiving the 1.5-mg/kg dose. In the 0.75-mg/kg group, the total clearance, volume of distribution and half-life of polymyxin B were 0.028±0.002 L/h/kg, 0.219±0.023 L/kg and 5.44±0.741 h, respectively; similar values were observed in the 1.5-mg/kg group. Urinary recovery was 3.7 ± 1.1% and 8.1 ± 1.3% in the 0.75- and 1.5-mg/kg groups, respectively. Population pharmacokinetics of polymyxin B was consistent with a three-compartment model. The clearance and distribution of the central compartment were 0.027 L/h/kg and 0.071 L/kg, respectively.

CONCLUSIONS

This study is the first to examine the safety and pharmacokinetics of polymyxin B in healthy subjects. Our results highlight that acute toxicity is a dose-limiting factor for intravenous polymyxin B.

Safety considerations of current drug treatment strategies for nosocomial pneumonia

Introduction: Nosocomial pneumonia unfortunately remains a frequent event for which appropriate antibiotic treatment is central to improving outcomes. Physicians must choose an early and appropriate empirical treatment, basing their decision on the safety profile and possible side effects. Areas covered: In this review, we analyzed the safety profiles of the most common antimicrobials for treating nosocomial pneumonia. Beta-lactams are used most often for these infections, with a high percentage (6% to 25%) of patients reporting allergy or hypersensitivity reactions; however, exhaustive evaluation is key because it seems possible to de-label as many as 90% by proper assessment. Combinations including a beta-lactam are recommended in patients with risk factors for drug-resistant microorganisms and septic shock. Although aminoglycosides are safe for 3-5 days of therapy, renal function should be monitored. Fluoroquinolones must also be used with care given the risk of collagen degradation and cardiovascular events, mainly aneurysm or aortic dissection. Linezolid or vancomycin are both viable for the treatment of methicillin-resistant Staphylococcus aureus, but linezolid seems to be the superior option. Antibiotic stewardships programs must be developed for each center. Expert opinion: Choosing the most appropriate antimicrobial based on information from national and international guidelines, local microbiology data, and stewardship programs may reduce the use of broad-spectrum antibiotics. Daily assessment for the emergence of adverse events related to antimicrobial use is essential.

Polymyxin-induced nephrotoxicity and its predictors: a systematic review and meta-analysis of studies conducted using RIFLE criteria of acute kidney injury

Polymyxins are last-resort antibiotics re-emerged to treat infections caused by multidrug resistant (MDR) and extensively drug-resistant (XDR) Gram-negative bacterial infections. However, polymyxin-associated nephrotoxicity has become the main safety concern. Therefore, we conducted this systematic review and meta-analysis on polymyxin-induced nephrotoxicity and its predictors using studies conducted based on the validated RIFLE (Risk, Injury, Failure, Loss of Function and End-stage renal disease) criteria of acute kidney damage. Literature search was carried out through visiting legitimate databases and indexing services including PubMed, MEDLINE (Ovid®), EMBASE (Ovid®), and Scopus to retrieve relevant studies. Following screening and eligibility evaluation, relevant data were extracted from included studies and analyzed using STATA 15.0 and Rev-Man 5.3. Inverse variance method with random effects pooling model was used for the analysis of outcome measures at 95% confidence interval. Besides, meta-regression, meta-influence, and publication bias analyses were conducted. A total of 48 studies involving 6,199 adult patients aged ≥ 18 years were included for systematic review and meta-analysis. The pooled incidence of polymyxin-induced nephrotoxicity was found to be 45% (95% CI: 41- 49%; I² = 92.52%). Stratifying with RIFLE severity scales, pooled estimates of polymyxin-treated patients identified as 'risk', 'injury' and 'failure' were 17% (95% CI: 14-20%), 13% (95% CI: 11-15%), and 10% (95% CI: 9-11%), respectively. Besides, the pooled incidence of colistin-induced nephrotoxicity was about 48% (95% CI: 42-54%), whereas that of polymyxin B was 38% (95% CI: 32-44%). Likewise, colistin had 37% increased risk of developing nephrotoxicity compared to the polymyxin B treated cohorts (RR = 1.37, 95% CI: 1.13-1.67; I² = 57%). Older age (AOR = 1.03, 95% CI: 1.01-1.05), daily dose (AOR = 1.46, 95% CI: 1.09-1.96), underlying diabetes mellitus (AOR = 1.81, 95% CI: 1.25-2.63), and concomitant nephrotoxic drugs (AOR = 2.31, 95% CI: 1.79-3.00) were independent risk factors for polymyxin-induced nephrotoxicity. Patients with high serum albumin level were less likely (AOR = 0.69, 95% CI: 0.56-0.85] to experience nephrotoxicity compared to those with low albumin level. Despite the resurgence of these antibiotics for the chemotherapy of MDR/XDR-Gram-negative superbugs, the high incidence of nephrotoxicity has become a contemporary clinical concern. Being elderly, high daily dose, having underlying diseases such as diabetes, and use of concomitant nephrotoxic drugs were independent predictors of nephrotoxicity. Therefore, therapeutic drug monitoring should be done to these patients to outweigh the potential benefits of polymyxin therapy from its risk.

The effects of hesperidin on colistin-induced reproductive damage, autophagy, and apoptosis by reducing oxidative stress

This study has been conducted to investigate the effect of hesperidin on colistin-induced reproductive damage in male rats. Twenty-four adult male Sprague Dawley rats were used as animal material. They were divided into four groups: control group, received physiological saline for 7 days by oral gavage; hesperidin group, received 300 mg/kg day hesperidin for 7 days; colistin group, received 73 mg/kg (total dose) colistin during 7 days; and colistin + hesperidin group, received 300 mg/kg day hesperidin following the colistin treatment. At the end of the study, routine spermatological parameters and biochemical evaluations were assayed. Also, apoptosis and autophagy biomarkers in testes were evaluated. Colistin increased oxidative stress, apoptosis and autophagy expression levels in testis. Hesperidin supplementation significantly decreased the oxidative stress levels in the testes of the colistin + hesperidin group when compared to the colistin group. The highest apoptosis and autophagy expression levels were detected in the colistin group. These values were statistically lower in the colistin + hesperidin group when compared to the colistin group. Colistin treatment decreased the percentage of sperm motility and increased sperm abnormality. Hesperidin supplementation mitigated significantly mentioned side effects compared to the colistin group. In conclusion, hesperidin supplementation can be a good strategy to mitigate colistin-induced testicular toxicity.

Is it time to move away from polymyxins?: evidence and alternatives

Increasing burden of carbapenem resistance and resultant difficult-to-treat infections are of particular concern due to the lack of effective and safe treatment options. More recently, several new agents with activity against certain multidrug-resistant (MDR) and extensive drug-resistant (XDR) Gram-negative pathogens have been approved for clinical use. These include ceftazidime-avibactam, meropenem-vaborbactam, imipenem-cilastatin-relebactam, plazomicin, and cefiderocol. For the management of MBL infections, clinically used triple combination comprising ceftazidime-avibactam and aztreonam is hindered due to non-availability of antimicrobial susceptibility testing methods and lack of information on potential drug-drug interaction leading to PK changes impacting its safety and efficacy. Moreover, in several countries including Indian subcontinent and developing countries, these new agents are yet to be made available. Under these circumstances, polymyxins are the only last resort for the treatment of carbapenem-resistant infections. With the recent evidence of suboptimal PK/PD particularly in lung environment, limited efficacy and increased nephrotoxicity associated with polymyxin use, the Clinical and Laboratory Standards Institute (CLSI) has revised both colistin and polymyxin B breakpoints. Thus, polymyxins 'intermediate' breakpoint for Enterobacterales, P. aeruginosa, and Acinetobacter spp. are now set at ≤ 2 mg/L, implying limited clinical efficacy even for isolates with the MIC value 2 mg/L. This change has questioned the dependency on polymyxins in treating XDR infections. In this context, recently approved cefiderocol and phase 3 stage combination drug cefepime-zidebactam assume greater significance due to their potential to act as polymyxin-supplanting therapies.

Polymyxin B prevents the development of adjuvant arthritis via modulation of TLR/Cox-2 signaling pathway

AIMS

Several microbial toll-like receptor (TLR) ligands, bacterial DNA and bacterial cell wall fragments have been identified in the synovium of rheumatoid arthritis (RA) patients, proving bacterial involvement in the pathogenesis of RA. The current study aimed to verify that low dose polymyxin B could prevent the development of chronic inflammatory arthritis.

METHODS

Twelve days post adjuvant injection, Sprague-Dawley rats were treated twice weekly with methotrexate (0.5 mg/kg) or daily with polymyxin B (1 mg/kg) or with combination of both for 1 or 2 weeks. Arthritis progression was assessed by hind paw swelling, serum levels of tumor growth factor-1β (TGF-1β), tumor necrosis factor-alpha (TNF-α), high sensitivity C-reactive protein (HS-CRP) and nuclear factor kappa B (NF-κB) were measured using ELISA. Cyclooxygenase-1 (Cox-1) and Cox-2 activities, as well as mRNA expression of TLR-2 and TLR-4 were determined. Histopathological examination of the ankle joint was performed as well as immunohistochemistry for anti-TLR-4. Histopathological assessment of toxic effects on the kidney was performed.

KEY FINDINGS

Adjuvant arthritis led to a significant swelling of the hind paw and alteration in all serum parameters, TLR-2 and TLR-4 expression, as well as Cox-2 activity. These alterations were associated with histopathological changes of the joints. Polymyxin B reduced significantly all biomarkers of inflammation, showing better effect of the combination in most of the studied parameters, with minimal signs of nephrotoxicity.

SIGNIFICANCE

In conclusion, results showed that polymyxin B possesses significant anti-arthritic activity which may be attributed to inhibition of the TLR-4, NF-κB and Cox-2 signaling pathway.

Polymyxins and Bacterial Membranes: A Review of Antibacterial Activity and Mechanisms of Resistance

Following their initial discovery in the 1940s, polymyxin antibiotics fell into disfavor due to their potential clinical toxicity, especially nephrotoxicity. However, the dry antibiotic development pipeline, together with the rising global prevalence of infections caused by multidrug-resistant (MDR) Gram-negative bacteria have both rejuvenated clinical interest in these polypeptide antibiotics. Parallel to the revival of their use, investigations into the mechanisms of action and resistance to polymyxins have intensified. With an initial known effect on biological membranes, research has uncovered the detailed molecular and chemical interactions that polymyxins have with Gram-negative outer membranes and lipopolysaccharide structure. In addition, genetic and epidemiological studies have revealed the basis of resistance to these agents. Nowadays, resistance to polymyxins in MDR Gram-negative pathogens is well elucidated, with chromosomal as well as plasmid-encoded, transferrable pathways. The aims of the current review are to highlight the important chemical, microbiological, and pharmacological properties of polymyxins, to discuss their mechanistic effects on bacterial membranes, and to revise the current knowledge about Gram-negative acquired resistance to these agents. Finally, recent research, directed towards new perspectives for improving these old agents utilized in the 21st century, to combat drug-resistant pathogens, is summarized.

Multidrug Resistance (MDR) and Collateral Sensitivity in Bacteria, with Special Attention to Genetic and Evolutionary Aspects and to the Perspectives of Antimicrobial Peptides-A Review

Antibiotic poly-resistance (multidrug-, extreme-, and pan-drug resistance) is controlled by adaptive evolution. Darwinian and Lamarckian interpretations of resistance evolution are discussed. Arguments for, and against, pessimistic forecasts on a fatal “post-antibiotic era” are evaluated. In commensal niches, the appearance of a new antibiotic resistance often reduces fitness, but compensatory mutations may counteract this tendency. The appearance of new antibiotic resistance is frequently accompanied by a collateral sensitivity to other resistances. Organisms with an expanding open pan-genome, such as Acinetobacter baumannii, Pseudomonas aeruginosa, and Klebsiella pneumoniae, can withstand an increased number of resistances by exploiting their evolutionary plasticity and disseminating clonally or poly-clonally. Multidrug-resistant pathogen clones can become predominant under antibiotic stress conditions but, under the influence of negative frequency-dependent selection, are prevented from rising to dominance in a population in a commensal niche. Antimicrobial peptides have a great potential to combat multidrug resistance, since antibiotic-resistant bacteria have shown a high frequency of collateral sensitivity to antimicrobial peptides. In addition, the mobility patterns of antibiotic resistance, and antimicrobial peptide resistance, genes are completely different. The integron trade in commensal niches is fortunately limited by the species-specificity of resistance genes. Hence, we theorize that the suggested post-antibiotic era has not yet come, and indeed might never come.

Evaluation of in vitro activity of ceftolozane-tazobactam against recent clinical bacterial isolates from Brazil - the EM200 study

Background

The emergence of antibiotic resistance is increasing and there are few effective antibiotics to treat infections caused by resistant and multidrug resistant bacterial pathogens. This study aimed to evaluate the in vitro activity of ceftolozane–tazobactam against clinical bacterial isolates from Brazil.

Methods

A total of 673 Gram-negative bacterial isolates including Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa and other Enterobacterales collected from 2016 to 2017 were tested, most of them isolated from patients in intensive care units. Minimum inhibitory concentrations (MIC_50/90) were determined by broth microdilution for amikacin, aztreonam, cefepime, cefotaxime, cefoxitin, ceftolozane–tazobactam, ceftazidime, ceftriaxone, ciprofloxacin, colistin, ertapenem, imipenem, levofloxacin, meropenem, and piperacillin-tazobactam using dried panels. Antimicrobial susceptibility results were interpreted according to Clinical and Laboratory Standards Institute criteria.

Results

Susceptibility rates to ceftolozane–tazobactam ranged from 40.4% to 94.9%. P. aeruginosa susceptibility rate to ceftolozane–tazobactam was 84.9% (MIC_50/90, 1/16 μg/mL) and 99.2% to colistin. For E. coli, ceftolozane–tazobactam inhibited 94.9% (MIC_50/90, 0.25/1 μg/mL) of the microorganisms. The susceptibility rate of K. pneumoniae to ceftolozane–tazobactam was 40.4% (MIC_50/90, 16/>32 μg/mL). Other Enterobacterales have shown susceptibility rates of 81.1% (MIC_50/90, 0.5/16 μg/mL) to ceftolozane–tazobactam, 93.9% to meropenem, 90.9% to amikacin (90.9%), and 88.6% to ertapenem. In non-carbapenemase producing isolates, AmpC mutations were found three isolates.

Conclusions

Ceftolozane–tazobactam has shown relevant activity against a large variety of the analyzed microorganisms collected from multiple centers in Brazil, showing promising results even in multidrug resistant strains.

Evaluation of Dose-Fractionated Polymyxin B on Acute Kidney Injury Using a Translational In Vivo Rat Model

We investigated dose-fractionated polymyxin B (PB) on acute kidney injury (AKI). PB at 12 mg of drug/kg of body weight per day (once, twice, and thrice daily) was administered in rats over 72 h. The thrice-daily group demonstrated the highest KIM-1 increase (P = 0.018) versus that of the controls (P = 0.99) and histopathological damage (P = 0.013). A three-compartment model best described the data (bias, 0.129 mg/liter; imprecision, 0.729 mg2/liter2; R2, 0.652,). Area under the concentration-time curve at 24 h (AUC24) values were similar (P = 0.87). The thrice-daily dosing scheme resulted in the most PB-associated AKI in a rat model.

Polymyxin B-Polysaccharide Polyion Nanocomplex with Improved Biocompatibility and Unaffected Antibacterial Activity for Acute Lung Infection Management

The decade-old antibiotic, polymyxin B (PMB), is regarded as the last line defense against gram-negative "superbug." However, the serious nephrotoxicity and neurotoxicity strongly obstruct further application of this highly effective antibiotic. Herein, a charge switchable polyion nanocomplex exhibiting pH-sensitive property is proposed to deliver PMB which is expected to improve the biosafety of PMB on the premise of retaining excellent antibacterial activity. The polyion nanocomplex is prepared through electrostatic interaction of positively charged PMB and negatively charged 2,3-dimethyl maleic anhydride (DA) grafted chitoligosaccharide (CS). The negative charge of CS-DA will convert to positive due to the hydrolysis of amide bonds in acidic infectious environment, leading to the disassembly of CS-DA/PMB nanocomplex and release of PMB. CS-DA/PMB nanocomplex does not show significant toxicity to mammalian cells while retaining excellent bactericidal capability equivalent to free PMB. The nephrotoxicity and neurotoxicity of CS-DA/PMB dramatically decrease compared to free PMB. Moreover, CS-DA/PMB nanocomplex exhibits superior bactericidal activity against Pseudomonas aeruginosa in an acute lung infection mouse model. The pH-sensitive polyion nanocomplexes may provide a new way to reduce the side effects of highly toxic antibiotics without reducing their intrinsic antibacterial activity, which is the key factor to achieve extensive in vivo clinical applications.

Mechanisms of antimicrobial-induced nephrotoxicity in children

Drug-induced nephrotoxicity is responsible for 20% to 60% of cases of acute kidney injury in hospitalized patients and is associated with increased morbidity and mortality in both children and adults. Antimicrobials are one of the most common classes of medications prescribed globally and also among the most common causes of nephrotoxicity. A broad range of antimicrobial agents have been associated with nephrotoxicity, but the features of kidney injury vary based on the agent, its mechanism of injury and the site of toxicity within the kidney. Distinguishing nephrotoxicity caused by an antimicrobial agent from other potential inciting factors is important to facilitate both early recognition of drug toxicity and prompt cessation of an offending drug, as well as to avoid unnecessary discontinuation of an innocuous therapy. This review will detail the different types of antimicrobial-induced nephrotoxicity: acute tubular necrosis, acute interstitial nephritis and obstructive nephropathy. It will also describe the mechanism of injury caused by specific antimicrobial agents and classes (vancomycin, aminoglycosides, polymyxins, antivirals, amphotericin B), highlight the toxicodynamics of these drugs and provide guidance on administration or monitoring practices that can mitigate toxicity, when known. Particular attention will be paid to paediatric patients, when applicable, in whom nephrotoxin exposure is an often-underappreciated cause of kidney injury.

Treatment of Ventilator-associated Pneumonia with High-dose Colistin Under Continuous Veno-venous Hemofiltration

Background and Objectives

High-dose colistin (COL) ensures adequate treatment of pneumonia caused by multidrug resistant gram-negative bacteria (MDR-GNB) but must be weighed against a higher risk of nephrotoxicity. Continuous veno-venous hemofiltration (CVVH) clears COL by filtering and membrane adsorption that permits to avoid dose accumulation and excessively high peak concentrations. We evaluated clinical/microbiological efficacy of the high-dose COL treatment under CVVH in patients with newly diagnosed MDR-GNB ventilator-associated pneumonia (VAP).

Methods

Observational cohort study in critically ill adult patients with MDR-GNB VAP. Colistimethate sodium (CMS) was administered as a 9 million international units (MIU) of loading dose followed by 3 × 4.5 MIU daily. CVVH was performed over a highly adsorptive membrane. Clinical and microbiological efficacies were assessed at the end of therapy. In survivors, serum creatinine level was evaluated before and at the end of therapy.

Results

Fourteen patients (8 male patients, aged 57 ± 14 years) were consecutively included. Isolated pathogens were Pseudomonas aeruginosa in 7, Klebsiella pneumoniae in 5, and other Enterobacteriaceae in 2 patients. A favorable clinical response was observed in 9 patients (64%). Full and presumed microbiological eradication was observed in 12 patients (86%). Two patients were diagnosed with Stage 1 acute kidney injury.

Conclusions

In patients with MDR-GNB VAP, CVVH may represent an interesting option to enable effective high-dose COL treatment.

Countering Gram-Negative Antibiotic Resistance: Recent Progress in Disrupting the Outer Membrane with Novel Therapeutics

Gram-negative bacteria shield themselves from antibiotics by producing an outer membrane (OM) that forms a formidable permeability barrier. Multidrug resistance among these organisms is a particularly acute problem that is exacerbated by the OM. The poor penetrance of many available antibiotics prevents their clinical use, and efforts to discover novel classes of antibiotics against Gram-negative bacteria have been unsuccessful for almost 50 years. Recent insights into how the OM is built offer new hope. Several essential multiprotein molecular machines (Bam, Lpt, and Lol) work in concert to assemble the barrier and offer a swathe of new targets for novel therapeutic development. Murepavadin has been at the vanguard of these efforts, but its recently reported phase III clinical trial toxicity has tempered the anticipation of imminent new clinical options. Nonetheless, the many concerted efforts aimed at breaking down the OM barrier provide a source of ongoing optimism for what may soon come through the development pipeline. We will review the current state of drug development against the OM assembly targets, highlighting insightful new discovery approaches and strategies.