Tigecycline

Silk Sericin and Its Composite Materials with Antibacterial Properties to Enhance Wound Healing: A Review

Wound infections may disrupt the normal wound-healing process. Large amounts of antibiotics are frequently used to prevent pathogenic infections; however, this can lead to resistance development. Biomaterials possessing antimicrobial properties have promising applications for reducing antibiotic usage and promoting wound healing. Silk sericin (SS) has been increasingly explored for skin wound healing applications owing to its excellent biocompatibility and antioxidant, antimicrobial, and ultraviolet-resistant properties. In recent years, SS-based composite biomaterials with a broader antimicrobial spectrum have been extensively investigated and demonstrated favorable efficacy in promoting wound healing. This review summarizes various antimicrobial agents, including metal nanoparticles, natural extracts, and antibiotics, that have been incorporated into SS composites for wound healing and elucidates their mechanisms of action. It has been revealed that SS-based biomaterials can achieve sustained antimicrobial activity by slow-release-loaded antimicrobial agents. The antimicrobial-loaded SS composites may promote wound healing through anti-infection, anti-inflammation, hemostasis, angiogenesis, and collagen deposition. The manufacturing methods, benefits, and limitations of antimicrobial-loaded SS materials are briefly discussed. This review aims to enhance the understanding of new advances and directions in SS-based antimicrobial composites and guide future biomedical research.

Antibiotic-Drug Interactions in the Intensive Care Unit: A Literature Review

Interactions between drugs are a common problem in Intensive Care Unit patients, as they mainly have a critical condition that often demands the administration of multiple drugs simultaneously. Antibiotics are among the most frequently used medications, as infectious diseases are often observed in ICU patients. In this review, the most important antibiotic-drug interactions, based on the pharmacokinetic and pharmacodynamic mechanisms, were gathered together and described. In particular, some of the most important interactions with main groups of antibacterial drugs were observed in patients simultaneously prescribed oral anticoagulants, NSAIDs, loop diuretics, and valproic acid. As a result, the activity of drugs can be increased or decreased, as dosage modification might be necessary. It should be noted that these crucial interactions can help predict and avoid negative consequences, leading to better patient recovery. Moreover, since there are other factors, such as fluid therapy or albumins, which may also modify the effectiveness of antibacterial therapy, it is important for anaesthesiologists to be aware of them.

Molecular mechanisms of tigecycline-resistance among Enterobacterales

The global emergence of antimicrobial resistance to multiple antibiotics has recently become a significant concern. Gram-negative bacteria, known for their ability to acquire mobile genetic elements such as plasmids, represent one of the most hazardous microorganisms. This phenomenon poses a serious threat to public health. Notably, the significance of tigecycline, a member of the antibiotic group glycylcyclines and derivative of tetracyclines has increased. Tigecycline is one of the last-resort antimicrobial drugs used to treat complicated infections caused by multidrug-resistant (MDR) bacteria, extensively drug-resistant (XDR) bacteria or even pan-drug-resistant (PDR) bacteria. The primary mechanisms of tigecycline resistance include efflux pumps' overexpression, tet genes and outer membrane porins. Efflux pumps are crucial in conferring multi-drug resistance by expelling antibiotics (such as tigecycline by direct expelling) and decreasing their concentration to sub-toxic levels. This review discusses the problem of tigecycline resistance, and provides important information for understanding the existing molecular mechanisms of tigecycline resistance in Enterobacterales. The emergence and spread of pathogens resistant to last-resort therapeutic options stands as a major global healthcare concern, especially when microorganisms are already resistant to carbapenems and/or colistin.

Dual-targeting tigecycline nanoparticles for treating intracranial infections caused by multidrug-resistant Acinetobacter baumannii

Multidrug-resistant (MDR) Acinetobacter baumannii (A. baumannii) is a formidable pathogen responsible for severe intracranial infections post-craniotomy, exhibiting a mortality rate as high as 71%. Tigecycline (TGC), a broad-spectrum antibiotic, emerged as a potential therapeutic agent for MDR A. baumannii infections. Nonetheless, its clinical application was hindered by a short in vivo half-life and limited permeability through the blood-brain barrier (BBB). In this study, we prepared a novel core-shell nanoparticle encapsulating water-soluble tigecycline using a blend of mPEG-PLGA and PLGA materials. This nanoparticle, modified with a dual-targeting peptide Aβ11 and Tween 80 (Aβ11/T80@CSs), was specifically designed to enhance the delivery of tigecycline to the brain for treating A. baumannii-induced intracranial infections. Our findings demonstrated that Aβ11/T80@CSs nanocarriers successfully traversed the BBB and effectively delivered TGC into the cerebrospinal fluid (CSF), leading to a significant therapeutic response in a model of MDR A. baumannii intracranial infection. This study offers initial evidence and a platform for the application of brain-targeted nanocarrier delivery systems, showcasing their potential in administering water-soluble anti-infection drugs for intracranial infection treatments, and suggesting promising avenues for clinical translation.

Tigecycline and Hypoglycemia, When and How?

Objective: To describe the clinical characteristics of hypoglycemia that develop with tigecycline therapy and to review and summarize the current evidence of this uncommonly occurring metabolic adverse effect of tigecycline therapy. Underlying risk factors and potential mechanisms are also discussed. Data source: A 3-phase literature search was performed. In phase 1, the Cochrane Central Register of Controlled Trials (CENTRAL) Library, MEDLINE, and Embase electronic databases were searched for hypoglycemia and tigecycline, published from inception until August 2023. In phase 2, MEDLINE was searched for tigecycline randomized controlled trials and results were manually screened for hypoglycemia. In phase 3, the US Food and Drug Administration Adverse Event Reporting System public dashboard was searched for reports on tigecycline and hypoglycemia from June 2005 until July 2023. Study selection and data extraction: Relevant English-language citations and those conducted in humans were considered. Relevance to patient care and clinical practice: Hypoglycemia of various causes is an independent mortality risk. This review raises awareness among clinicians about the possibility of hypoglycemia with tigecycline therapy. Conclusion: Data on tigecycline-related hypoglycemia are scarce. Hypoglycemia may occur at any time during tigecycline therapy and can be severe and persist for days after tigecycline cessation. Renal dysfunction or renal replacement therapy may predispose to severe hypoglycemia during tigecycline therapy. Tigecycline-related hypoglycemia may develop in patients with or without diabetes mellitus and appears independent of insulin or antidiabetic agents. Intravenous dextrose showed efficacy in the restoration of euglycemia. Studies are needed to determine whether tigecycline-related hypoglycemia is iatrogenic or spontaneous.

Conversion to colistin susceptibility by tigecycline exposure in colistin-resistant Klebsiella pneumoniae and its implications to combination therapy

OBJECTIVES

This study investigated the effect of tigecycline exposure on susceptibility of colistin-resistant Klebsiella pneumoniae isolates to colistin and explored the possibility of antibiotic combination at low concentrations to treat colistin-resistant K. pneumoniae isolates.

METHODS

Twelve tigecycline-resistant (TIR) mutants were induced in vitro from wild-type, colistin-resistant, and tigecycline-susceptible K. pneumoniae isolates. Antibiotic susceptibility was determined using the broth microdilution method. The deduced amino acid alterations were identified for genes associated with colistin resistance, lipid A biosynthesis, and tigecycline resistance. Expression levels of genes were compared between wild-type stains and TIR mutants using quantitative real-time polymerase chain reaction (PCR). Lipid A modification was explored using MALDI-TOF mass spectrometry. Time-killing assay was performed to assess the efficiency of combination therapy using low concentrations of colistin and tigecycline.

RESULTS

All TIR mutants except one were converted to be susceptible to colistin. These TIR mutants had mutations in the ramR gene and increased expression levels of ramA. Three genes associated with lipid A biosynthesis, lpxC, lpxL, and lpxO, were also overexpressed in TIR mutants, although no mutation was observed. Additional polysaccharides found in colistin-resistant, wild-type strains were modified in TIR mutants. Colistin-resistant K. pneumoniae strains were eliminated in vitro by combining tigecycline and colistin at 2 mg/L. In this study, we found that tigecycline exposure resulted in reduced resistance of colistin-resistant K. pneumoniae to colistin. Such an effect was mediated by regulation of lipid A modification involving ramA and lpx genes.

CONCLUSION

Because of such reduced resistance, a combination of colistin and tigecycline in low concentrations could effectively eradicate colistin-resistant K. pneumoniae strains.

Antimicrobial Resistance in Commensal Escherichia coli of the Porcine Gastrointestinal Tract

Antimicrobial resistance (AMR) in Escherichia coli of animal origin presents a threat to human health. Although animals are not the primary source of human infections, humans may be exposed to AMR E. coli of animal origin and their AMR genes through the food chain, direct contact with animals, and via the environment. For this reason, AMR in E. coli from food producing animals is included in most national and international AMR monitoring programmes and is the subject of a large body of research. As pig farming is one of the largest livestock sectors and the one with the highest antimicrobial use, there is considerable interest in the epidemiology of AMR in E. coli of porcine origin. This literature review presents an overview and appraisal of current knowledge of AMR in commensal E. coli of the porcine gastrointestinal tract with a focus on its evolution during the pig lifecycle and the relationship with antimicrobial use. It also presents an overview of the epidemiology of resistance to extended spectrum cephalosporins, fluoroquinolones, and colistin in pig production. The review highlights the widespread nature of AMR in the porcine commensal E. coli population, especially to the most-used classes in pig farming and discusses the complex interplay between age and antimicrobial use during the pig lifecycle.

A Review on Analytical Methods for Tigecycline Estimation From Its Bulk and Dosage Form

BACKGROUND

Tigecycline (TIG) is a third-generation glycylcycline derivative used as an antimicrobial and anticancer agent for the past few years. Its intricate structure makes it more vulnerable toward degradation under the influence of various environmental factors and leads to the generation of impurities. Due to its stability issues, TIG is available as a lyophilized powder for injection. The analysis of TIG becomes a cumbersome task for analysts due to its instability in solution form. As TIG works as a life-saving drug, it is important to review its analytical methods for its quality control.

OBJECTIVE

The present review discusses various analytical methodologies for determining TIG from its bulk, lyophilized powder, pharmacopoeial methods and factors responsible for its instability.

METHODS

The present review represents the analysis of data reported in the literature from 1999-2022 for the analysis of TIG.

RESULTS

Numerous alternative analytical techniques such as UV-visible spectrophotometry, spectrofluorimetric methods, RP-HPLC (reversed-phase high-performance liquid chromatography) and FT-IR (Fourier transform infrared), and electrophoresis has been reported for quantification, identification, and characterization of TIG.

CONCLUSIONS

Several analytical techniques are available to be used as a quality control tool for tigecycline, including HPLC without derivatization, whereas the fluorescence technique requires derivatization using acidic dye. A few methods require tedious pre-sample preparation techniques, become time-consuming, and involve using one or more organic solvents; there is a need to develop eco-friendlier methods for analyzing tigecycline.

HIGHLIGHTS

Various analytical methods such as spectrometric, fluorimetric and chromatographic methods have been discussed for estimation of TIG from its bulk and different dosage form.

IS257-mediated amplification of tet(L) variant as a novel mechanism of enhanced tigecycline resistance in Staphylococcus cohnii

The mechanism of enhanced tigecycline MIC in Staphylococcus cohnii after in vitro tigecycline exposure was investigated. S. cohnii 11-B-312 was exposed to incremental concentrations of tigecycline (2-32 mg/L) and the mutants growing at 8, 16 and 32 mg/L were determined by AST and WGS. Copy number and relative transcription level of the tet(L) gene were determined by quantitative PCR. The fitness cost was evaluated by growth kinetics and competition assays. The results revealed that enhanced tigecycline MIC was identified in S. cohnii mutants. Copy number and relative transcription level of tet(L) in the mutants increased 8-, 20-, and 23-fold and 20-, 34-, and 39-fold in the presence of 8, 16, and 32 mg/L tigecycline, respectively. The read-mapping depth ratio analysis indicated that a multidrug resistance region carrying the tet(L) variant has a gradually increased copy number, correlating with the tigecycline selection pressure. S. cohnii strain 11-B-312_32 had a fitness cost, and enhanced tigecycline MIC can revert to the initial level in the absence of tigecycline. In summary, enhanced tigecycline MIC develops with extensive amplification of an IS257-flanked tet(L)-carrying segment in S. cohnii. IS257 seems to play a vital role in the gain and loss of the amplification product.

Antibiotic-Resistant ESKAPE Pathogens and COVID-19: The Pandemic beyond the Pandemic

Antibacterial resistance is a renewed public health plague in modern times, and the COVID-19 pandemic has rekindled this problem. Changes in antibiotic prescribing behavior, misinformation, financial hardship, environmental impact, and governance gaps have generally enhanced the misuse and improper access to antibiotics during the COVID-19 pandemic. These determinants, intersected with antibacterial resistance in the current pandemic, may amplify the potential for a future antibacterial resistance pandemic. The occurrence of infections with multidrug-resistant (MDR), extensively drug-resistant (XDR), difficult-to-treat drug-resistant (DTR), carbapenem-resistant (CR), and pan-drug-resistant (PDR) bacteria is still increasing. The aim of this review is to highlight the state of the art of antibacterial resistance worldwide, focusing on the most important pathogens, namely Enterobacterales, Acinetobacter baumannii, and Klebsiella pneumoniae, and their resistance to the most common antibiotics.

Tigecycline Absorption Improved by Selected Excipients

To investigate the effects of (2,6-di-O-methyl)-β-cyclodextrin (DM-β-CD), (2-hydroxypropyl)-β-cyclodextrin (HP-β-CD), tocopherol polyethylene glycol 1000 succinate (TPGS), sodium desoxycholate (SDOCH), trimethyl chitosan (TMC), and sodium caprate (C10) on the plasma concentration and the oral bioavailability of tigecycline in broiler chickens. To test the effects of the excipients on absorption of tigecycline, a tetracycline that is poorly absorbed from the gastrointestinal tract, broiler chickens were used as an animal model. Tigecycline (10 mg/kg body weight) was administered intravenously, orally, and orally with one of the excipients. Plasma samples were taken after administration. To measure tigecycline concentrations, high-performance liquid chromatography coupled with tandem mass spectrometry was used. Compartmental and non-compartmental analyses were used for pharmacokinetic analyses of mean plasma concentrations versus time. With the exception of sodium caprate, all the excipients significantly increased the area under the curve and bioavailability of tigecycline (p < 0.05). These parameters were approximately doubled by HP-β-CD, TPGS, and SDOCH, with 95% confidence intervals (95% CIs) for the difference that included only increases of 1.5-fold or higher (bioavailability: control, 1.67%; HP-β-CD, 3.24%; TPGS, 3.30%; and SDOCH, 3.24%). The increases in these parameters were smaller with DM-β-CD and TMC (DM-β-CD, 2.41%; TMC, 2.55%), and the 95% CIs ranged from close to no difference to nearly double the values in the control group. These results indicate that HP-β-CD, TPGS, and SDOCH substantially increase the area under the curve and oral bioavailability of tigecycline. They suggest that DM-β-CD and TMC may also substantially increase these parameters, but more research is needed for more precise estimates of their effects.

In vitro susceptibility of common Enterobacterales to eravacycline in Taiwan

BACKGROUND

New tetracycline derivatives exhibit broad-spectrum antimicrobial activities. This study aimed to assess the in vitro activity of eravacycline against common Enterobacterales.

METHODS

Clinical Enterobacterales isolates were collected between 2017 and 2021. The minimum inhibitory concentration (MIC) was determined using a broth microdilution test.

RESULTS

We identified Klebsiella pneumoniae (n = 300), Escherichia coli (n = 300), Klebsiella oxytoca (n = 100), Enterobacter cloacae complex (n = 100), Citrobacter freundii (n = 100), and Proteus mirabilis (n = 100). All P. mirabilis strains were resistant to eravacycline. Excluding P. mirabilis, the susceptibility rates to eravacycline, omadacycline, and tigecycline were 75.2%, 66.9%, and 73%, respectively. The MIC₅₀ and MIC₉₀ (mg/L) of eravacycline were 0.5 and 4 for K. pneumoniae, 0.5 and 1 for E. coli, 0.5 and 1 for K. oxytoca, 0.5 and 2 for E. cloacae complex, and 0.25 and 1 for C. freundii. In cefotaxime non-susceptible and meropenem susceptible Enterobacterales, excluding P. mirabilis, the susceptibility rates of eravacycline, omadacycline, and tigecycline were 69.7%, 57.1%, and 66.2%. We found decreased susceptibility rates of three new tetracycline derivatives against meropenem non-susceptible Enterobacterales (eravacycline: 47.1%, omadacycline: 39.4%, and tigecycline: 39.4%). Eravacycline showed a high susceptibility rate against cefotaxime non-susceptible and meropenem susceptible K. oxytoca (100%), C. freundii (93.2%), E. coli (85.9%), and meropenem non-susceptible E. coli (100%).

CONCLUSION

This study provides the MIC and susceptibility rate of eravacycline for common Enterobacterales. Eravacycline could be a therapeutic choice for cefotaxime non-susceptible or meropenem non-susceptible Enterobacterales, especially K. oxytoca, C. freundii, and E. coli.

Influence of continuous renal replacement therapy on the plasma concentration of tigecycline in patients with septic shock: A prospective observational study

Objective: The influence of continuous renal replacement therapy (CRRT) on the steady-state plasma concentration of high-dose tigecycline was investigated in septic shock patients to provide references for drug dosing.

Methods: In this prospective observational study, 17 septic shock patients presenting with severe infections needing a broad-spectrum antibiotic therapy with high-dose tigecycline (100 mg per 12 h) in the intensive care unit were included and divided into CRRT group (n = 6) or non-CRRT group (n = 11). The blood samples were collected and plasma drug concentration was determined by SHIMADZU LC-20A and SHIMADZU LCMS 8040. The steady-state plasma concentration was compared between groups using unpaired t-test. Furthermore, between-groups comparisons adjusted for baseline value was also done using multivariate linear regression model.

Results: Peak concentration (Cmax) of tigecycline was increased in CRRT group compared to non-CRRT group, but there were no statistical differences (505.11 ± 143.84 vs. 406.29 ± 108.00 ng/mL, p-value: 0.129). Trough concentration (Cmin) of tigecycline was significantly higher in CRRT group than in non-CRRT group, with statistical differences (287.92 ± 41.91 vs. 174.79 ± 33.15 ng/mL, p-value: 0.000, adjusted p-value: 0.000). In safety, Cmin was reported to be a useful predictor of hepatotoxicity with a cut-off of 474.8 ng/mL. In our studies, Cmin of all patients in CRRT group was lower than 474.8 ng/mL.

Conclusion: The plasma concentration of tigecycline was increased in septic shock patients with CRRT treatment and only Cmin shown statistical differences. No dose adjustment seems needed in the view of hepatotoxicity.

Clinical Trial Registration:https://www.chictr.org.cn/, identifier ChiCTR2000037475.

Disrupting the ArcA Regulatory Network Amplifies the Fitness Cost of Tetracycline Resistance in Escherichia coli

There is an urgent need for strategies to discover secondary drugs to prevent or disrupt antimicrobial resistance (AMR), which is causing >700,000 deaths annually. Here, we demonstrate that tetracycline-resistant (Tet^R) Escherichia coli undergoes global transcriptional and metabolic remodeling, including downregulation of tricarboxylic acid cycle and disruption of redox homeostasis, to support consumption of the proton motive force for tetracycline efflux. Using a pooled genome-wide library of single-gene deletion strains, at least 308 genes, including four transcriptional regulators identified by our network analysis, were confirmed as essential for restoring the fitness of Tet^R E. coli during treatment with tetracycline. Targeted knockout of ArcA, identified by network analysis as a master regulator of this new compensatory physiological state, significantly compromised fitness of Tet^R E. coli during tetracycline treatment. A drug, sertraline, which generated a similar metabolome profile as the arcA knockout strain, also resensitized Tet^R E. coli to tetracycline. We discovered that the potentiating effect of sertraline was eliminated upon knocking out arcA, demonstrating that the mechanism of potential synergy was through action of sertraline on the tetracycline-induced ArcA network in the Tet^R strain. Our findings demonstrate that therapies that target mechanistic drivers of compensatory physiological states could resensitize AMR pathogens to lost antibiotics. IMPORTANCE Antimicrobial resistance (AMR) is projected to be the cause of >10 million deaths annually by 2050. While efforts to find new potent antibiotics are effective, they are expensive and outpaced by the rate at which new resistant strains emerge. There is desperate need for a rational approach to accelerate the discovery of drugs and drug combinations that effectively clear AMR pathogens and even prevent the emergence of new resistant strains. Using tetracycline-resistant (Tet^R) Escherichia coli, we demonstrate that gaining resistance is accompanied by loss of fitness, which is restored by compensatory physiological changes. We demonstrate that transcriptional regulators of the compensatory physiologic state are promising drug targets because their disruption increases the susceptibility of Tet^R E. coli to tetracycline. Thus, we describe a generalizable systems biology approach to identify new vulnerabilities within AMR strains to rationally accelerate the discovery of therapeutics that extend the life span of existing antibiotics.

The Blood-Brain Barrier and Pharmacokinetic/Pharmacodynamic Optimization of Antibiotics for the Treatment of Central Nervous System Infections in Adults

Bacterial central nervous system (CNS) infections are serious and carry significant morbidity and mortality. They encompass many syndromes, the most common being meningitis, which may occur spontaneously or as a consequence of neurosurgical procedures. Many classes of antimicrobials are in clinical use for therapy of CNS infections, some with established roles and indications, others with experimental reporting based on case studies or small series. This review delves into the specifics of the commonly utilized antibacterial agents, updating their therapeutic use in CNS infections from the pharmacokinetic and pharmacodynamic perspectives, with a focus on the optimization of dosing and route of administration that have been described to achieve good clinical outcomes. We also provide a concise synopsis regarding the most focused, clinically relevant information as pertains to each class and subclass of antimicrobial therapeutics. CNS infection morbidity and mortality remain high, and aggressive management is critical in ensuring favorable patient outcomes while averting toxicity and upholding patient safety.

Intrathecal or Intraventricular Tigecycline Therapy for Central Nervous System Infection Associated with Carbapenem-Resistant Klebsiella pneumoniae

PURPOSE

Infection with carbapenem-resistant Klebsiella pneumoniae (CRKP) is a great challenge. Central nervous system (CNS) infection caused by CRKP is rarely reported, and effective treatment is limited. Thus, this study aimed to assess intrathecal (IT) or intraventricular (IVT) injection of tigecycline for clearing infection with CRKP in CNS.

PATIENTS AND METHODS

Two patients who had intracranial infection with CRKP after craniotomy were treated in our institution and analyzed retrospectively, summarizing their therapeutic schedules.

RESULTS

They all had a fever with the positive results of cerebrospinal fluid (CSF) test, and CSF culture showed positive for CPKP, which was sensitive only to tigecycline. In addition, the MIC of polymyxin B was not tested due to the limited laboratory conditions. After IT or IVT injection of tigecycline treatment, the temperature of the patients became normal in 3 days, with normal levels of white blood cells, protein, glucose and chlorine concentrations in the CSF. Crucially, twice CSF cultures also became negative with no clinical symptoms of intracranial infection after IT or IVT injection of tigecycline treatment. Moreover, there were no adverse drug reactions observed.

CONCLUSION

IT or IVT injection of tigecycline may be a bright choice to control intracranial infection with CRKP.

Rhamnetin, a Natural Flavonoid, Ameliorates Organ Damage in a Mouse Model of Carbapenem-Resistant Acinetobacter baumannii-Induced Sepsis

In sepsis, the persistence of uncontrolled inflammatory response of infected host cells eventually leads to severe lung and organ failure and, ultimately, death. Carbapenem-resistant Acinetobacter baumannii (CRAB), causative bacteria of sepsis and lung failure in acute cases, belongs to a group of critical pathogens that cannot be eradicated using the currently available antibiotics. This underlines the necessity of developing new modes of therapeutics that can control sepsis at the initial stages. In this study, we investigated the anti-inflammatory activities in vitro and in vivo and the antiseptic effects of rhamnetin, a naturally occurring flavonoid. We found that among its isoforms, the potency of rhamnetin was less explored but rhamnetin possessed superior anti-inflammatory activity with least cytotoxicity. Rhamnetin showed significant anti-inflammatory effects in lipopolysaccharide-, CRAB-, and Escherichia coli (E. coli)-stimulated mouse macrophages by inhibiting the release of interleukin-6 and nitric oxide. In a mouse model of sepsis infected with clinically isolated CRAB or E. coli, rhamnetin significantly reduced the bacterial burden in the organs. In addition, normalized pro-inflammatory cytokine levels in lung lysates and histological analysis of lung tissue indicated alleviation of lung damage. This study implies that a potent natural product such as rhamnetin could be a future therapeutic for treating carbapenem-resistant gram-negative sepsis.

Sweep-Out of Tigecycline, Chlortetracycline, Oxytetracycline, and Doxycycline from Water by Carbon Nanoparticles Derived from Tissue Waste

Pharmaceutical pollution has pervaded many water resources all over the globe. The propagation of this health threat drew the researchers' concern in seeking an efficient solution. This study introduced toilet paper waste as a precursor for carbon nanoparticles (CRNPs). The TEM results showed a particle size range of 30.2 nm to 48.1 nm, the BET surface area was 283 m² g^-1, and the XRD pattern indicated cubical-graphite crystals. The synthesized CRNPs were tested for removing tigecycline (TGCN), chlortetracycline (CTCN), oxytetracycline (OTCN), and doxycycline (DXCN) via the batch process. The adsorption equilibrium time for TGCN, DXCN, CTCN, and OTCN was 60 min, and the concentration influence revealed an adsorption capacity of 172.5, 200.1, 202.4, and 200.0 mg g^-1, respectively. The sorption of the four drugs followed the PSFO, and the LFDM models indicated their high sorption affinity to the CRNPs. The adsorption of the four drugs fitted the multilayer FIM that supported the high-affinity claim. The removals of the four drugs were exothermic and spontaneous physisorption. The fabricated CRNPs possessed an excellent remediation efficiency for contaminated SW and GW; therefore, CRNPs are suggested for water remediation as low-cost sorbent.

Influence of Antibiotics on Functionality and Viability of Liver Cells In Vitro

(1) Antibiotics are an important weapon in the fight against serious bacterial infections and are considered a common cause of drug-induced liver injury (DILI). The hepatotoxicity of many drugs, including antibiotics, is poorly analyzed in human in vitro models. (2) A standardized assay with a human hepatoma cell line was used to test the hepatotoxicity of various concentrations (Cmax, 5× Cmax, and 10× Cmax) of antibiotics. In an ICU, the most frequently prescribed antibiotics, ampicillin, cefepime, cefuroxime, levofloxacin, linezolid, meropenem, rifampicin, tigecycline, and vancomycin, were incubated with HepG2/C3A cells for 6 days. Cell viability (XTT assay, LDH release, and vitality), albumin synthesis, and cytochrome 1A2 activity were determined in cells. (3) In vitro, vancomycin, rifampicin, and tigecycline showed moderate hepatotoxic potential. The antibiotics ampicillin, cefepime, cefuroxime, levofloxacin, linezolid, and meropenem were associated with mild hepatotoxic reactions in test cells incubated with the testes Cmax concentration. Rifampicin and cefuroxime showed significantly negative effects on the viability of test cells. (4) Further in vitro studies and global pharmacovigilance reports should be conducted to reveal underlying mechanism of the hepatotoxic action of vancomycin, rifampicin, tigecycline, and cefuroxime, as well as the clinical relevance of these findings.

Outcomes of Short-Term Tigecycline-Containing Regimens for Mycobacterium abscessus Pulmonary Disease

Short-term intravenous tigecycline therapy during a 1-month initial phase may improve early microbiological response in patients with Mycobacterium abscessus pulmonary disease (PD). However, short-term use of tigecycline did not improve the long-term culture conversion rate of M. abscessus PD. Further studies on the efficacy of prolonged intravenous tigecycline-containing regimens are needed.

Treatment of MDR Gram-Negative Bacteria Infections: Ongoing and Prospective

Antimicrobial resistance is a serious public health concern across the world. Gram-negative resistance has propagated over the globe via various methods, the most challenging of which include extended-spectrum β-lactamases, carbapenemases, and AmpC enzymes. Gram-negative bacterial infections are difficult to treat in critically extremely sick persons. Resistance to different antibiotic treatments nearly always lowers the probability of proper empirical coverage, sometimes resulting in severe outcomes. Multidrug resistance can be combated with varying degrees of success using a combination of older drugs with high toxicity levels and novel therapeutics. The current therapies for multidrug-resistant Gram-negative bacteria are discussed in this review, which includes innovative medications, older pharmaceuticals, creative combinations of the two, and therapeutic targets.

Analysis of the clinical characteristics of tigecycline-induced hypofibrinogenemia

Knowledge regarding the association between hypofibrinogenemia and tigecycline is based mainly on case reports. However, the clinical features of tigecycline-induced hypofibrinogenemia are unclear. We collected 20 patients (16 males and 4 females) with tigecycline-induced hypofibrinogenemia by searching the Chinese and English databases from June 2005 to May 2021, with a median age of 63.5 years (range 39∼90 years). Hypofibrinogenemia developed at a median of 9 days (range 2∼35 days). Most patients had no typical clinical manifestations, and only a few patients had bleeding and ecchymosis. Fibrinogen levels gradually decreased from 3.98 ± 2.05 g/L to 0.87 ± 0.45 g/L (P = 0.000), and the activated partial thromboplastin time (APTT) increased from 38.26 ± 8.80 s to 83.43 ± 47.23 s (P = 0.002). Fibrinogen levels in all patients recovered to the normal range within a median of 4 days (range 1∼12 days) after tigecycline cessation. Our results suggest that fibrinogen levels should be closely monitored in patients treated with tigecycline, specifically patients who may have renal insufficiency or patients with long-term use.

Population Pharmacokinetics of Tigecycline: A Systematic Review

Although tigecycline is widely used in clinical practice, its efficiency and optimal dosage regimens remain controversial. The purpose of this article was to help guide tigecycline dosing in different patient subpopulations through comparing the published population pharmacokinetic models of tigecycline, as well as summarizing and determining the potential covariates that markedly influence tigecycline pharmacokinetics. In this review, literature was systematically searched from the PubMed database from inception to March 2022. The articles focusing on population pharmacokinetics for tigecycline in healthy volunteers or patients were included; finally, a total of eight studies were included in this review. NONMEM methods were used in five studies to generate the population pharmacokinetic models. Tigecycline pharmacokinetics were mostly described by a two-compartment model in these included studies. Estimated clearance and volumes of distribution of tigecycline at steady state (Vss) varied widely in different target patient populations, with a range of 7.5–23.1 L/h and 212.7–1087.7 L, respectively. Body-weight and creatinine clearance were the most important predictors of clearance in these studies, while other predictors include age, gender, bilirubin and aspartate aminotransferase. In conclusion, this review showed the large variability of tigecycline population pharmacokinetics, which can provide guide dosing in different target populations. For clinicians, the individual dosing adjustment should be based not only on the indication and pathogen susceptibility but also on the potential important predictors. However, more studies were needed to confirm the necessity of modified dosage regimens in different patient subpopulations.

Two Cases Report of Intrathecal Tigecycline Therapy for Intracranial Infection with Acinetobacter baumannii and Review of Literatures

OBJECTIVE

To explore the treatment scheme for intracranial infection with Acinetobacter baumannii.

METHODS

We retrospective analyzed two cases of patients of intracranial infection with Acinetobacter baumannii.

RESULTS

The intracranial infection was controlled effectively by the scheme to intravenous"tigecycline + cefperazone-sulbactam"combined with intrathecal tigecycline injection, the two patients recover well with 21 months' follow-up.

CONCLUSIONS

Tigecycline-based drug scheme combined with intrathecal tigecycline injection can achieve the effect of controlling intracranial infection. Lumbar cisterna drainage tube plays a major role in controlling intracranial infection.

Evaluation of antimicrobial susceptibilities of non-tuberculous mycobacteria against linezolid and tigecycline

Mycobacterial susceptibility testing is important for the management of nontuberculous mycobacteria (NTM) infections. The aim of the study is to determine the susceptibilities of tigecycline (TGC) and linezolid (LZD) against NTM. The study was carried out using stocks of NTM strains in the tuberculosis department of the microbiology laboratory. It was designed a retrospective study. LZD and TGC sensitivities of study isolates were analyzed by microdilution. Forty NTM isolates have been studied. LZD and TGC sensitivities varied according to the NTM type. It is concluded that each isolate should be individually evaluated due to variable susceptibilities to LZD and TGC.

The cocrystal 2-(dimethylammonio)-5-nitrobenzoate – 2-(dimethylamino)-5-nitrobenzoic acid, C9H10N2O4

C9H10N2O4, triclinic, P 1 ‾ $P\overline{1}$ (no. 2), a = 9.722(2) Å, b = 10.805(2) Å, c = 10.947(2) Å, α = 67.938(4)°, β = 66.250(4)°, γ = 72.978(4)°, V = 961.8(3) Å3, Z = 4, R gt (F) = 0.0421, wR ref (F 2) = 0.1339, T = 173 K.

Intrathecal Injection of Tigecycline and Polymyxin B in the Treatment of Extensively Drug-Resistant Intracranial Acinetobacter baumannii Infection: A Case Report and Review of the Literature

Purpose

Intracranial infection after neurosurgery is one of the most serious complications, especially extensively drug-resistant (XDR) Acinetobacter baumannii (A. baumannii) seriously affects the prognosis of patients. At present, there is little experience in the treatment of this infection and limited effective treatment options, like tigecycline or polymyxin B. Therefore, this report aims to describe the efficacy of tigecycline combined with polymyxin B by intrathecal (ITH) injection in the treatment of XDR intracranial infection with A. baumannii.

Methods

We report a case of intracranial infection with XDR A. baumannii after ventricular drainage, treated by daily ITH and intravenous (IV) tigecycline, combined with polymyxin B ITH route. Moreover, tigecycline and polymyxin B treatments for XDR intracranial infection with A. baumannii that were reported in the literature were also reviewed and summarized.

Results

The white blood cells (WBCs) of the patient’s cerebrospinal fluid dropped to normal, and the symptoms of intracranial infection disappeared. The patient finally obtained good clinical results and transferred to the local hospital.

Conclusion

The polymyxin B ITH route is an ideal treatment strategy for XDR A. baumannii. The IV plus ITH tigecycline may be an effective treatment option. However, more researches should be conducted to confirm our observation.

Metformin Reverses tmexCD1-toprJ1- and tet(A)-Mediated High-Level Tigecycline Resistance in K. pneumoniae

Tigecycline (TIG) is one of the last effective options against multidrug resistance bacteria. Recently, the RND (resistance–nodulation–division) efflux pump gene cluster, tmexCD1-toprJ1, and the tetracycline-efflux pump tet(A) mutation were reported to mediate high level resistance to TIG in clinically important pathogens, weakening the efficacy of TIG. In this study, we report the potent synergistic effect of the antidiabetic drug metformin in combination with TIG against tet(A) mutant and tmexCD1-toprJ1 positive K. pneumoniae. The fractional inhibitory concentration index (FICI) of TIG and metformin were less than 0.05 for all the tested isolates. The time–kill curve assay showed that the combination of TIG and metformin exhibited much better antimicrobial effect than TIG alone. The synergistic effect was also confirmed in vivo using a well-studied Galleria mellonella larvae model. Mechanistic studies demonstrated that metformin disrupted the important component of proton motive force, the electric potential (Δψ) and the function of efflux pump, thereby increasing the intracellular concentration of TIG. This finding revealed that metformin might be a possible adjuvant of TIG for combating with superbugs carrying the tet(A) mutant and tmexCD1-toprJ1 genes.

The Monte Carlo Simulation of Three Antimicrobials for Empiric Treatment of Adult Bloodstream Infections With Carbapenem-Resistant Enterobacterales in China

Introduction: The aim of this study was to predict and evaluate three antimicrobials for treatment of adult bloodstream infections (BSI) with carbapenem-resistant Enterobacterales (CRE) in China, so as to optimize the clinical dosing regimen further.

Methods: Antimicrobial susceptibility data of blood isolates were obtained from the Blood Bacterial Resistance Investigation Collaborative Systems in China. Monte Carlo simulation was conducted to estimate the probability target attainment (PTA) and cumulative fraction of response (CFR) of tigecycline, polymyxin B, and ceftazidime/avibactam against CRE.

Results: For the results of PTAs, tigecycline following administration of 50 mg every 12 h, 75 mg every 12 h, and 100 mg every 12 h achieved > 90% PTAs when minimum inhibitory concentration (MIC) was 0.25, 0.5, and 0.5 μg/mL, respectively; polymyxin B following administration of all tested regimens achieved > 90% PTAs when MIC was 1 μg/mL with CRE; ceftazidime/avibactam following administration of 1.25 g every 8 h, 2.5 g every 8 h achieved > 90% PTAs when MIC was 4 μg/mL, 8 μg/mL with CRE, respectively. As for CFR values of three antimicrobials, ceftazidime/avibactam achieved the lowest CFR values. The highest CFR value of ceftazidime/avibactam was 77.42%. For tigecycline and ceftazidime/avibactam, with simulated regimens daily dosing increase, the CFR values were both increased; the highest CFR of tigecycline values was 91.88%. For polymyxin B, the most aggressive dosage of 1.5 mg/kg every 12 h could provide the highest CFR values (82.69%) against CRE.

Conclusion: This study suggested that measurement of MICs and individualized therapy should be considered together to achieve the optimal drug exposure. In particular, pharmacokinetic and pharmacodynamic modeling based on local antimicrobial resistance data can provide valuable guidance for clinicians for the administration of empirical antibiotic treatments for BSIs.

Structural and mechanistic basis of the high catalytic activity of monooxygenase Tet(X4) on tigecycline

Background

Tigecycline is a tetracycline derivative that constitutes one of the last-resort antibiotics used clinically to treat infections caused by both multiple drug-resistant (MDR) Gram-negative and Gram-positive bacteria. Resistance to this drug is often caused by chromosome-encoding mechanisms including over-expression of efflux pumps and ribosome protection. However, a number of variants of the flavin adenine dinucleotide (FAD)-dependent monooxygenase TetX, such as Tet(X4), emerged in recent years as conferring resistance to tigecycline in strains of Enterobacteriaceae, Acinetobacter sp., Pseudomonas sp., and Empedobacter sp. To date, mechanistic details underlying the improvement of catalytic activities of new TetX enzymes are not available.

Results

In this study, we found that Tet(X4) exhibited higher affinity and catalytic efficiency toward tigecycline when compared to Tet(X2), resulting in the expression of phenotypic tigecycline resistance in E. coli strains bearing the tet(X4) gene. Comparison between the structures of Tet(X4) and Tet(X4)-tigecycline complex and those of Tet(X2) showed that they shared an identical FAD-binding site and that the FAD and tigecycline adopted similar conformation in the catalytic pocket. Although the amino acid changes in Tet(X4) are not pivotal residues for FAD binding and substrate recognition, such substitutions caused the refolding of several alpha helixes and beta sheets in the secondary structure of the substrate-binding domain of Tet(X4), resulting in the formation of a larger number of loops in the structure. These changes in turn render the substrate-binding domain of Tet(X4) more flexible and efficient in capturing substrate molecules, thereby improving catalytic efficiency.

Conclusions

Our works provide a better understanding of the molecular recognition of tigecycline by the TetX enzymes; these findings can help guide the rational design of the next-generation tetracycline antibiotics that can resist inactivation of the TetX variants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-021-01199-7.

The Development of Third-Generation Tetracycline Antibiotics and New Perspectives

The tetracycline antibiotic class has acquired new valuable members due to the optimisation of the chemical structure. The first modern tetracycline introduced into therapy was tigecycline, followed by omadacycline, eravacycline, and sarecycline (the third generation). Structural and physicochemical key elements which led to the discovery of modern tetracyclines are approached. Thus, several chemical subgroups are distinguished, such as glycylcyclines, aminomethylcyclines, and fluorocyclines, which have excellent development potential. The antibacterial spectrum comprises several resistant bacteria, including those resistant to old tetracyclines. Sarecycline, a narrow-spectrum tetracycline, is notable for being very effective against Cutinebacterium acnes. The mechanism of antibacterial action from the perspective of the new compound is approached. Several severe bacterial infections are treated with tigecycline, omadacycline, and eravacycline (with parenteral or oral formulations). In addition, sarecycline is very useful in treating acne vulgaris. Tetracyclines also have other non-antibiotic properties that require in-depth studies, such as the anti-inflammatory effect effect of sarecycline. The main side effects of modern tetracyclines are described in accordance with published clinical studies. Undoubtedly, this class of antibiotics continues to arouse the interest of researchers. As a result, new derivatives are developed and studied primarily for the antibiotic effect and other biological effects.

Adaptive responses of Pseudomonas aeruginosa to treatment with antibiotics

Pseudomonas aeruginosa is among the highest priority pathogens for drug development, because of its resistance to antibiotics, extraordinary adaptability, and persistence. Anti-pseudomonal research is strongly encouraged to address the acute scarcity of innovative antimicrobial lead structures. In an effort to understand the physiological response of P. aeruginosa to clinically relevant antibiotics, we investigated the proteome after exposure to ciprofloxacin, levofloxacin, rifampicin, gentamicin, tobramycin, azithromycin, tigecycline, polymyxin B, colistin, ceftazidime, meropenem, and piperacillin/tazobactam. We further investigated the response to CHIR-90, which represents a promising class of lipopolysaccharide biosynthesis inhibitors currently under evaluation. Radioactive pulse-labeling of newly synthesized proteins followed by 2D-PAGE was used to monitor the acute response of P. aeruginosa to antibiotic treatment. The proteomic profiles provide insights into the cellular defense strategies for each antibiotic. A mathematical comparison of these response profiles based on upregulated marker proteins revealed similarities of responses to antibiotics acting on the same target area. This study provides insights into the effects of commonly used antibiotics on P. aeruginosa and lays the foundation for the comparative analysis of the impact of novel compounds with precedented and unprecedented modes of action.

Rapid and Accurate Antibiotic Susceptibility Determination of tet(X)-Positive E. coli Using RNA Biomarkers

The emergence and prevalence of novel plasmid-mediated tigecycline resistance genes, namely, tet(X) and their variants, pose a serious threat to public health worldwide. Rapid and accurate antibiotic susceptibility testing (AST) that can simultaneously detect the genotype and phenotype of tet(X)-positive bacteria may contribute to the deployment of an effective antibiotic arsenal, mortality reduction, and a decrease in the use of broad-spectrum antimicrobial agents. However, current bacterial growth-based AST methods, such as broth microdilution, are time consuming and delay the prompt treatment of infectious diseases. Here, we developed a rapid RNA-based AST (RBAST) assay to effectively distinguish tet(X)-positive and -negative strains. RBAST works by detecting specific mRNA expression signatures in bacteria after short-term tigecycline exposure. As a proof of concept, a panel of clinical isolates was characterized successfully by using the RBAST method, with a 3-h assay time and 87.9% accuracy (95% confidence interval [CI], 71.8% to 96.6%). Altogether, our findings suggest that RNA signatures upon antibiotic exposure are promising biomarkers for the development of rapid AST, which could inform early antibiotic choices.

IMPORTANCE Infections caused by multidrug-resistant (MDR) Gram-negative pathogens are an increasing threat to global health. Tigecycline is one of the last-resort antibiotics for the treatment of these complicated infections; however, the emergence of plasmid-encoded tigecycline resistance genes, namely, tet(X), severely diminishes its clinical efficacy. Currently, there is a lack of rapid and accurate antibiotic susceptibility testing (AST) for the detection of tet(X)-positive bacteria. In this study, we developed a rapid and robust RNA-based antibiotic susceptibility determination (RBAST) assay to effectively distinguish tet(X)-negative and -positive strains using specific RNA biomarkers in bacteria after tigecycline exposure. Using this RBAST method, we successfully characterized a set of clinical strains in 3 h. Our data indicate that the RBAST assay is useful for identifying tet(X)-positive Escherichia coli.

Peptostreptococcus anaerobius: Pathogenicity, identification, and antimicrobial susceptibility. Review of monobacterial infections and addition of a case of urinary tract infection directly identified from a urine sample by MALDI-TOF MS

Peptostreptococcus anaerobius is a gram-positive anaerobic coccus (GPAC) found in the gastrointestinal and vaginal microbiota. The organism is mainly found in polymicrobial and scarcely in monobacterial infections such as prosthetic and native endocarditis. Anaerobic bacteria have rarely been reported as the cause of urinary tract infection (UTI). Although GPAC are susceptible to most antimicrobials used against anaerobic infections, P. anaerobius has shown to be more resistant. Herein, we report a case of UTI caused by P. anaerobius from a 62-year-old man with a history of urological disease. Surprisingly, the microorganism was directly identified by Matrix-Assisted Laser Desorption-Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) from the urine sample. The isolate was successfully identified by phenotypic methods, MALDI-TOF MS, and 16S rRNA gene sequencing. P. anaerobius showed no β-lactamase-producing activity, was resistant to penicillin, ampicillin, ciprofloxacin and levofloxacin, and displayed intermediate susceptibility to ampicillin-sulbactam and amoxicillin-clavulanic acid. Successful treatment was achieved with oral amoxicillin-clavulanic acid. Antimicrobial susceptibility testing (AST) should be performed on P. anaerobius isolates due to their unpredictable AST patterns and because empirically administered antimicrobial agents may not be active. This report shows that MALDI-TOF MS, directly used in urine specimens, may be a quick option to diagnose UTI caused by P. anaerobius or other anaerobic bacteria. This review is a compilation of monobacterial infections caused by P. anaerobius published in the literature, their pathogenicity, identification, and data about the antimicrobial susceptibility of P. anaerobius.

High-Dose versus Standard-Dose Tigecycline Treatment of Secondary Bloodstream Infections Caused by Extensively Drug-Resistant Acinetobacter baumannii: An Observational Cohort Study

Background

Extensively drug-resistant Acinetobacter baumannii (XDR-AB) infections have become difficult to treat and are associated with a high mortality rate. Tigecycline is one of the most effective agents used to treat XDR-AB infections, but data from treating bloodstream infection (BSI) in standard dose do not look promising, because of its low plasma concentration. Secondary BSI with primary infection source may indicate tigecycline treatment with a higher dose. Currently, little is known about the application of high-dose tigecycline among patients with secondary BSI caused by XDR-AB. We aimed to investigate the outcomes for high-dose (HD) tigecycline treatment versus standard-dose (SD) treatment of these patients.

Methods

An observational cohort study was conducted at four university affiliated hospitals in mainland China. Adult inpatients who were confirmed as having secondary BSI caused by XDR-AB and received definitive tigecycline treatment were consecutively included. Patients who were treated with 50 mg every 12 h were defined as the SD group, and a twice dose was defined as the HD group.

Results

Of the enrolled patients, 63 received SD and 88 received HD tigecycline treatment. Patients in the two groups had similar with regard to baseline clinical conditions. The 30-day survival was affected by the source of the primary infection. Survival was significantly better in patients with non-pulmonary-infection-related BSI than in patients with pulmonary-infection-related BSI. Multivariate Cox regression confirmed that HD had a protective effect only observed in patients with non-pneumonia-related BSI.

Conclusion

A tigecycline dose that is twice its standard dose is better for the treatment of XDR-AB infection only in BSI associated with non-pulmonary infection.

Benzydamine Reverses TMexCD-TOprJ-Mediated High-Level Tigecycline Resistance in Gram-Negative Bacteria

Recently, a novel efflux pump gene cluster called tmexCD1-toprJ1 and its variants have been identified, which undermine the antibacterial activity of tigecycline, one of the last remaining options effective against multidrug-resistant (MDR) Gram-negative bacteria. Herein, we report the potent synergistic effect of the non-steroidal anti-inflammatory drug benzydamine in combination with tigecycline at sub-inhibitory concentrations against various temxCD-toprJ-positive Gram-negative pathogens. The combination of benzydamine and tigecycline killed all drug-resistant pathogens during 24 h of incubation. In addition, the evolution of tigecycline resistance was significantly suppressed in the presence of benzydamine. Studies on the mechanisms of synergism showed that benzydamine disrupted the bacterial proton motive force and the functionality of this kind of novel plasmid-encoded resistance-nodulation-division efflux pump, thereby promoting the intracellular accumulation of tigecycline. Most importantly, the combination therapy of benzydamine and tigecycline effectively improved the survival of Galleria mellonella larvae compared to tigecycline monotherapy. Our findings provide a promising drug combination therapeutic strategy for combating superbugs carrying the tmexCD-toprJ gene.

Identification and antimicrobial susceptibility profiles of Nocardia species clinically isolated in Japan

The aims of the present study were to profile the antimicrobial susceptibility patterns of a diverse range of Nocardia species isolated in Japan, and to determine the ability of matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) for species/complex identification. Identification of 153 clinical isolates was performed by full-length 16S rRNA gene sequencing as a reference method to evaluate the usefulness of MALDI-TOF MS identification. Antimicrobial susceptibility testing (AST) for 14 antibiotics was performed using the broth microdilution method against 146 of the isolates. Among the total 153 clinical isolates, Nocardia farcinica complex (25%) was the most common species, followed by Nocardia cyriacigeorgica (18%), Nocardia brasiliensis (9%), Nocardia nova (8%), and Nocardia otitidiscaviarum (7%). Among 150 isolates identified to the species/complex level by 16S rRNA gene sequencing, MALDI-TOF MS with the use of a supplemental Nocardia library (JMLD library ver.ML01) correctly identified 97.3% (n = 146) to the species/complex level and 1.3% (n = 2) to the genus level. Among the 146 Nocardia isolates that underwent AST, the susceptibilities were 100% to linezolid, 96% to amikacin, 94% to trimethoprim-sulfamethoxazole, and 76% to imipenem. None of the trimethoprim-sulfamethoxazole-resistant isolates carried either plasmid-mediated sulfonamide-resistant genes (sul1, sul2) or trimethoprim-resistant genes (dfrA).

In Vitro Antimicrobial Susceptibilities of Francisella tularensis subsp. holarctica Isolates from Tularemia Outbreaks That Occurred from the End of the 20th Century to the 2020s in Spain

A collection of 177 Francisella tularensis subsp. holarctica clinical isolates (29 from humans and 148 from animals, mainly hares and voles) was gathered from diverse tularemia outbreaks in the Castilla y León region (northwestern Spain) that occurred from the end of the 20th century to the 2020s. Along with four F. tularensis subsp. holarctica reference strains, all of these clinical isolates were tested using a broth microdilution method to determine their susceptibility to 22 antimicrobial agents, including β-lactams, aminoglycosides and one member each of the tetracycline, glycylcycline, quinolone and sulphonamide classes. Many multi-resistance profiles were found among the tested isolates, but especially among those of human origin (all but two isolates showed resistance to at least 13 of 18 antimicrobial agents). Even so, all human isolates were susceptible to gentamicin and tobramycin, while more than 96% of animal isolates were susceptible to these two aminoglycosides. Ciprofloxacin showed activity against more than 92% of animal and human isolates. However, almost 21% of human isolates were resistant to tetracycline, and more than 65% were resistant to tigecycline. Finally, a quite similar activity to other F. tularensis subsp. holarctica isolates collected 20 years earlier in Spain was observed.

Determination of tigecycline in human lung epithelial cells and polymorphonuclear neutrophils by liquid chromatography/tandem mass spectrometry and its application in a cellular pharmacokinetics study

RATIONALE

In order to characterize the intracellular pharmacokinetic properties of tigecycline, we developed and fully validated a liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for quantification of tigecycline in human lung epithelial (BEAS-2B) cells and polymorphonuclear neutrophils (PMNs).

METHODS

Tetracycline was used as an internal standard and chromatographic separation was achieved on a C18 Hypersil Gold aQ column using two mobile phases, a solution of water (containing 0.1% formic acid) and acetonitrile. The flow rate was 0.4 mL/min for 5.0 min. Tigecycline drug uptake was evaluated by incubating the BEAS-2B cells and the PMNs for up to 3 h at tigecycline concentrations of 1 mg/L.

RESULTS

The assay was linear over the tested concentration range of 0.01-2 mg/L for tigecycline in BEAS-2B cells and PMNs (r²  >0.99). The inter- and inter-day precisions (RSD, %) were <10.02% and the accuracies (%) were within the range of 85-115%. The uptake study showed that after incubation with tigecycline (1 mg/L) for 3 h at 37°C, the intracellular peak concentration of BEAS-2B cells was 14.44 ± 7.12 mg/L at 1 h, and 41.43 ± 25.66 mg/L in PMNs at 20 min. The mean intracellular concentrations fluctuated in the range of 0.8-14.44 mg/L in BEAS-2B cells and 10.14-41.43 mg/L in PMNs for 1 mg/L tigecycline exposure.

CONCLUSIONS

Validated LC/MS/MS is a simple, rapid, and sensitive method for determining the intracellular concentration of tigecycline, and tigecycline has good penetrations both in human BEAS-2B cells and PMNs. The method can be efficiently used for future studies of the intracellular pharmacokinetics of tigecycline.

Multidrug-resistant Klebsiella pneumoniae: mechanisms of resistance including updated data for novel β-lactam-β-lactamase inhibitor combinations

Introduction: Multi-drug-resistant Klebsiella pneumoniae is currently one of the most pressing emerging issues in bacterial resistance. Treatment of K.pneumoniae infections is often problematic due to the lack of available therapeutic options, with a relevant impact in terms of morbidity, mortality and healthcare-associated costs. Soon after the launch of Ceftazidime-Avibactam, one of the approved new β-lactam/β-lactamase inhibitor combinations, reports of ceftazidime-avibactam-resistant strains developing resistance during treatment were published. Being a hospital-associated pathogen, K.pneumoniae is continuously exposed to multiple antibiotics resulting in constant selective pressure, which in turn leads to additional mutations that are positively selected.Areas covered: Herein the authors present the K.pneumoniae mechanisms of resistance to different antimicrobials, including updated data for ceftazidime-avibactam.Expert opinion: K.pneumoniae is a nosocomial pathogen commonly implicated in hospital outbreaks with a propensity for antimicrobial resistance toward mainstay β-lactam antibiotics and multiple other antibiotic classes. Following the development of drug resistance and understanding the mechanisms involved, we can improve the efficacy of current antimicrobials, by applying careful stewardship and rational use to preserve their potential utility. The knowledge on antibiotic resistance mechanisms should be used to inform the design of novel therapeutic agents that might not be subject to, or can circumvent, mechanisms of resistance.

Identification of novel tetracycline resistance gene tet(X14) and its co-occurrence with tet(X2) in a tigecycline-resistant and colistin-resistant Empedobacter stercoris

Tigecycline is one of the last-resort antibiotics to treat severe infections. Recently, tigecycline resistance has sporadically emerged with an increasing trend, and Tet(X) family represents a new resistance mechanism of tigecycline. In this study, a novel chromosome-encoded tigecycline resistance gene, tet(X14), was identified in a tigecycline-resistant and colistin-resistant Empedobacter stercoris strain ES183 recovered from a pig fecal sample in China. Tet(X14) shows 67.14-96.39% sequence identity to the other variants [Tet(X) to Tet(X13)]. Overexpression of Tet(X14) in Escherichia coli confers 16-fold increase in tigecycline MIC (from 0.125 to 2 mg/L), which is lower than that of Tet(X3), Tet(X4) and Tet(X6). Structural modelling predicted that Tet(X14) shared a high homology with the other 12 variants with RMSD value from 0.003 to 0.055, and Tet(X14) can interact with tetracyclines by a similar pattern as the other Tet(X)s. tet(X14) and two copies of tet(X2) were identified on a genome island with abnormal GC content carried by the chromosome of ES183, and no mobile genetic elements were found surrounding, suggesting that tet(X14) might be heterologously obtained by ES183 via recombination. Blasting in Genbank revealed that Tet(X14) was exclusively detected on the chromosome of Riemerella anatipestifer, mainly encoded on antimicrobial resistance islands. E. stercoris and R. anatipestifer belong to the family Flavobacteriaceae, suggesting that the members of Flavobacteriaceae maybe the major reservoir of tet(X14). Our study reports a novel chromosome-encoded tigecycline resistance gene tet(X14). The expanded members of Tet(X) family warrants the potential large-scale dissemination and the necessity of continuous surveillance for tet(X)-mediated tigecycline resistance.

Detection of a new tet(X6)-encoding plasmid in Acinetobacter towneri

OBJECTIVES

The aim of this study was to characterise a novel tet(X6)-carrying plasmid detected in a livestock-associated Acinetobacter towneri isolate.

METHODS

PCR screening was performed to detect tet(X) variants in livestock-associated Acinetobacter spp. isolates. The tet(X6)-positive isolate was analysed by whole-genome sequencing. Functional cloning was performed to detect the activity of Tet(X6). Antibiotic susceptibility was determined by broth dilution and microbiological degradation assays. Site-directed mutagenesis was performed to identify the role of 23-Ala residue of Tet(X6) in tigecycline resistance.

RESULTS

The tet(X6) gene was detected on a 159-kb plasmid (pAT205) carried by a tigecycline-susceptible A. towneri isolate recovered from a swine faecal sample. The genetic context of tet(X6) [ΔISVsa3-tet(X6)-abh-guaA-ISVsa3] is highly similar to that of the reported plasmid-borne tet(X) variants, suggesting that it may represent a common structure mediating the dissemination of plasmid-borne tet(X) genes. Additional resistance genes detected on pAT205 were carried by a Tn6205-like region and a disrupted class 2 integron. Gene expression and microbiological degradation assays consistently suggested that the activity of tet(X6) is weaker than that of tet(X3) and tet(X4). The 23-Ala residue of the first FAD-binding site conferred higher activity to Tet(X6) than the Gly reside conserved in the other plasmid-borne tet(X) variants, indicating that the site might be under selection.

CONCLUSION

This study alerts to the silent dissemination possibility of tigecycline resistance mediated by a novel plasmid. Continuous monitoring of plasmid-borne tet(X) is imperative for tackling its dissemination.

A Novel Transferable Resistance-Nodulation-Division Pump Gene Cluster, tmexCD2-toprJ2, Confers Tigecycline Resistance in Raoultella ornithinolytica

We recently identified a novel plasmid-mediated resistance-nodulation-division (RND)-type efflux pump gene cluster, tmexCD1-toprJ1, in Klebsiella pneumoniae that conferred resistance to multiple antimicrobials, including tigecycline. While homologs of tmexCD1-toprJ1 were found encoded in many other bacterial species in GenBank, their functions and transfer mechanisms remain unknown. This study identified another mobile gene cluster, tmexCD2-toprJ2, co-occurring on both a plasmid (pHNNC189-2) and the chromosome of a clinical Raoultella ornithinolytica isolate, strain NC189, producing KPC-2, NDM-1, and RmtC. tmexCD2-toprJ2 shares high similarity at the nucleotide level with tmexCD1-toprJ1, with 98.02%, 96.75%, and 99.93% identities to tmexC1, tmexD1, and toprJ1, respectively. Phylogenetic analysis revealed that tmexCD2-toprJ2 may have originated from the chromosome of a Pseudomonas species. The expression of tmexCD2-toprJ2 in an Escherichia coli strain resulted in an 8-fold increase in the tigecycline MIC and decreased susceptibility to other antimicrobials. Genetic context analyses demonstrated that tmexCD2-toprJ2, together with the adjacent hypothetical site-specific integrase genes, was possibly captured and mobilized by a XerD-like tyrosine recombinase system, forming a putative transposition unit (xerD-like-int3-like-thf2-ybjD-umuD-ΔumuC1-int1-like-int2-like-hp1-hp2-tnfxB2-ISBvi2-tmexCD2-toprJ2-ΔumuC1), which was inserted into umuC-like genes in both the NC189 plasmid pHNNC189-2 and the chromosome. Since tmexCD1-toprJ1 and tmexCD2-toprJ2 could confer multidrug resistance, the spread of these gene clusters, associated with the new recombinase system, calls for more attention.

Drug repurposing for next-generation combination therapies against multidrug-resistant bacteria

Antimicrobial resistance has been a global health challenge that threatens our ability to control and treat life-threatening bacterial infections. Despite ongoing efforts to identify new drugs or alternatives to antibiotics, no new classes of antibiotic or their alternatives have been clinically approved in the last three decades. A combination of antibiotics and non-antibiotic compounds that could inhibit bacterial resistance determinants or enhance antibiotic activity offers a sustainable and effective strategy to confront multidrug-resistant bacteria. In this review, we provide a brief overview of the co-evolution of antibiotic discovery and the development of bacterial resistance. We summarize drug-drug interactions and uncover the art of repurposing non-antibiotic drugs as potential antibiotic adjuvants, including discussing classification and mechanisms of action, as well as reporting novel screening platforms. A pathogen-by-pathogen approach is then proposed to highlight the critical value of drug repurposing and its therapeutic potential. Finally, general advantages, challenges and development trends of drug combination strategy are discussed.

The Plasmid-Borne tet(A) Gene Is an Important Factor Causing Tigecycline Resistance in ST11 Carbapenem-Resistant Klebsiella pneumoniae Under Selective Pressure

The emergence and prevalence of tigecycline-resistant Klebsiella pneumoniae have seriously compromised the effectiveness of antimicrobial agents in the treatment of infections. To explore the role of the plasmid-borne tet(A) gene in tigecycline resistance in carbapenem-resistant K. pneumoniae (CRKP), a total of 63 CRKP isolates were collected from a tertiary hospital in Hangzhou, China. The minimum inhibitory concentration (MIC) of tigecycline, mutation rate of tet(A) gene, genetic surroundings of tet(A)-carrying transmissible plasmid and the contribution of tet(A) mutation to tigecycline resistance were analyzed using antimicrobial susceptibility test, whole-genome sequencing, tigecycline resistance evolution experiment, and plasmid conjugation experiment. Our results showed that 52.4% (33 isolates) of the test isolates carried the tet(A) gene; among them, 75.8% (25 isolates) exhibited a tigecycline non-susceptible phenotype (MIC = 4 mg/L). Three clonal groups (cluster I, cluster II, and cluster III) were identified in these tet(A)-bearing isolates. All 17 isolates belonged to serotype KL21 (cluster I), which differed by only 13 SNPs, suggesting a clonal spread of tet(A)-positive ST11 K. pneumoniae with serotype KL21 occurred in the sampling hospital. The induction of tigecycline resistance experiments showed that 71.4% of strains evolved tet(A) mutations and developed a high-level tigecycline resistance. Eight amino acid substitutions were identified in these mutants. The most common amino acid substitution was A370V, followed by S251A and G300E. Twelve isolates carrying tet(A) mutants succeeded in the filter mating experiment with a conjugation efficiency of 10^-3-10^-8. Tigecycline MICs in E. coli EC600 transconjugants with a mutated tet(A) were 2 to 8-fold higher than those in E. coli EC600 transconjugants with a wild-type tet(A). One ColRNAI/IncFII type and two IncFII type tet(A)-bearing conjugative plasmids were identified in this study, including a class 1 integron containing multiple antibiotic resistance genes, i.e., tet(A), qnrS1, bla _{LAP- 2}, catA2, sul2, and dfrA14. Our study revealed the wide-spread situation of plasmid-borne tet(A) gene in clinical CRKP, and mutation of tet(A) is a potential driven force that lead to tigecycline resistance.

The Antibiotic Resistome: A Guide for the Discovery of Natural Products as Antimicrobial Agents

The use of life-saving antibiotics has long been plagued by the ability of pathogenic bacteria to acquire and develop an array of antibiotic resistance mechanisms. The sum of these resistance mechanisms, the antibiotic resistome, is a formidable threat to antibiotic discovery, development, and use. The study and understanding of the molecular mechanisms in the resistome provide the basis for traditional approaches to combat resistance, including semisynthetic modification of naturally occurring antibiotic scaffolds, the development of adjuvant therapies that overcome resistance mechanisms, and the total synthesis of new antibiotics and their analogues. Using two major classes of antibiotics, the aminoglycosides and tetracyclines as case studies, we review the success and limitations of these strategies when used to combat the many forms of resistance that have emerged toward natural product-based antibiotics specifically. Furthermore, we discuss the use of the resistome as a guide for the genomics-driven discovery of novel antimicrobials, which are essential to combat the growing number of emerging pathogens that are resistant to even the newest approved therapies.

Alternative treatment of fungal infections: Synergy with non-antifungal agents

Fungal infections are responsible for high mortality rates in immunocompromised and high-risk surgical patients. Therapy failures during the last decades due to increasing multidrug resistance demand innovative strategies for novel and effective antifungal drugs. Synergistic combinations of antifungals with non-antifungal agents highlight a pragmatic strategy to reduce the development of drug resistance and potentially repurpose known compounds with other functions to bypass costly and time-consuming novel drug development.

Microbial Resistance Movements: An Overview of Global Public Health Threats Posed by Antimicrobial Resistance, and How Best to Counter

Antibiotics changed medical practice by significantly decreasing the morbidity and mortality associated with bacterial infection. However, infectious diseases remain the leading cause of death in the world. There is global concern about the rise in antimicrobial resistance (AMR), which affects both developed and developing countries. AMR is a public health challenge with extensive health, economic, and societal implications. This paper sets AMR in context, starting with the history of antibiotics, including the discovery of penicillin and the golden era of antibiotics, before exploring the problems and challenges we now face due to AMR. Among the factors discussed is the low level of development of new antimicrobials and the irrational prescribing of antibiotics in developed and developing countries. A fundamental problem is the knowledge, attitude, and practice (KAP) regarding antibiotics among medical practitioners, and we explore this aspect in some depth, including a discussion on the KAP among medical students. We conclude with suggestions on how to address this public health threat, including recommendations on training medical students about antibiotics, and strategies to overcome the problems of irrational antibiotic prescribing and AMR.

Role of nano-selenium in health and environment

In recent years, researches on selenium nanoparticle have gained more attention due to its important role in many physiological processes. Generally, selenium nanoparticle has a high level of absorption in regular supplementation comparative to selenium. Therefore it is all-important to develop new techniques to elevate the transportation of selenium compounds (selenoproteins, selenoenzymes, etc.) by increasing their bioavailability, bioactivity, and controlled release. SeNPs have special attention regarding their application as food additives and therapeutic agents. Selenium nanoparticle has biomedical and pharmaceutical uses due to its antioxidant, antimicrobial, antidiabetic, and anticancer effects. Selenium nanoparticle is also used to antagonize the toxic effect of chemical and heavy metals. SeNPs are beneficial for the treatment of water and soil contaminated with metals and heavy metals as it has adsorption capability. Selenium nanoparticle is synthesized by the bioreduction of selenium species (sodium selenate, sodium selenite, selenium dioxide, and selenium tetrachloride, etc.) by using bacteria, fungi, plant, and plant extracts, which have given hope for the bioremediation of selenium contaminated water and soils. This article reviews the procedure of selenium nanoparticle synthesis (physical, chemical and biological methods), characterization (UV-vis spectroscopy, transmission electron microscopy, Scanning electron microscopy, electron dispersive X-ray spectroscopy, X-ray diffraction, Fourier transform-infrared spectroscopy, etc.), with the emphasis on its role and application in health and environment.

The distribution of mutations and hotspots in transcription regulators of resistance-nodulation-cell division efflux pumps in tigecycline non-susceptible Acinetobacter baumannii in China

OBJECTIVE

Acinetobacter baumannii has emerged as a problematic hospital pathogen and tigecycline is among the few remaining antibiotics retaining activity against multidrug-resistant A. baumannii. This study was aimed to elucidate the tigecycline resistance mechanisms in 28 unique clinical A. baumannii strains from nine provinces in China.

METHODS

Whole genome sequences were obtained via Illumina HiSeq sequencing and regulatory genes of efflux pumps were analyzed. Minimal inhibitory concentrations (MICs) were determined by agar/microbroth dilution according to the guidelines recommended by Clinical and Laboratory Standards Institute (CLSI). Tigecycline susceptibility data was interpreted using breakpoints for Enterobacterales recommended by EUCAST v8.1.

RESULTS

The majority of isolates belonged to the international clonal lineage IC2 (n = 27, 96.4%). Four isolates were considered tigecycline-intermediate (MIC = 2 mg/L), twenty-four isolates were tigecycline-resistant. The insertion of ISAba1 in adeS was found in six isolates and was the most prevalent insertion element (IS). In four isolates we observed an insertion of ISAba1 in adeN, and two of them had IS26 insertions. Two mutations in adeN (deletion and premature stop codon) were observed only in the MIC = 4 mg/L isolates. Other mutations in adeRS (amino acid insertion/substitutions and premature stop codons) were only detected in the MIC ≥ 8 group. The novel substitutions E219 K in adeR and A130 T in adeS were observed in five and four isolates respectively, suggesting a mutational hotspot.

CONCLUSIONS

This study demonstrates that changes in transcription regulators were important mechanisms in tigecycline resistance in A. baumannii. Also, we identified several chromosomal hotspots that can be used for prediction of tigecycline resistance.