Tigecycline antibacterial activity, clinical effectiveness, and mechanisms and epidemiology of resistance: narrative review

Isoniazid potentiates tigecycline to kill methicillin-resistant Staphylococcus aureus

Therapeutic option for treating methicillin-resistant Staphylococcus aureus (MRSA) infection is urgently required since its resistance to a broad spectrum of currently available antibiotics. Here, we report that isoniazid is able to potentiate the killing efficacy of tigecycline to MRSA. The combination of isoniazid and tigecycline reduces the minimal inhibitory concentration of clinic MRSA strains to tigecycline. The killing activity of tigecycline is further confirmed by killing experiments and murine infection model. We further demonstrate the mechanism that isoniazid increases intracellular accumulation of tigecycline by promoting the influx but limiting the efflux of tigecycline through proton motive force. We also show that isoniazid and tigecycline synergize to increase the abundance of isoniazid-NAD adduct, which in turn damage cell membrane, possibly contributing to the disruption of PMF. Whereas phosphatidylethanolamine and cardiolipin are able to abrogate the synergistic effect of isoniazid plus tigecycline. Thus our study provides a new perspective that antibiotics, e.g. isoniazid, once recognized only to target Mycobacterium tuberculosis, can be repurposed as antibiotic adjuvant to tigecycline, expanding our choice of antibiotic-antibiotic combinations in treating bacterial infectious diseases.

Cross-resistance between tigecycline and cephalosporins regulated by expression of ompK35 and ompK36 in Klebsiella pneumoniae

We investigated the relationship of antibiotic susceptibility changes by subsequent exposure of tigecycline and cephalosporins. In addition to colistin, meropenem, ciprofloxacin, and ampicillin, minimum inhibitory concentrations (MICs) of cephalosporins such as ceftazidime and cefotaxime increased with acquisition of tigecycline resistance. When the K. pneumoniae strains were exposed to cephalosporins, their tigecycline MICs also increased with the acquisition of cephalosporin resistances. The cephalosporin-resistant mutants as well as tigecycline-resistant mutants showed decreased expression of ompK35 and ompK36, despite no genetic alternations. The antibiotic-resistant mutants that have restored the expression level of the genes by cloning of ompK35 or ompK36 recovered their antibiotic susceptibilities, although there were some deviations for each antibiotic. Our findings suggest that the cross-resistance between tigecycline and cephalosporins may be regulated by expression of porin genes. It makes more careful consideration to selecting antibiotics to treat bacterial infections.

Molecular sequence typing of carbapenem-resistant Acinetobacter baumannii clinical isolates: A comprehensive global update

The emergence and spread of antimicrobial resistance (AMR) pose significant challenges to public health worldwide. Understanding the dynamics of AMR within bacterial populations is crucial for devising effective strategies to mitigate its impact. Clonal lineages, representing genetically related group of bacteria, play a vital role in shaping the landscape of AMR dissemination. This review endeavors to provide a comprehensive update on the molecular sequence typing of carbapenem-resistant Acinetobacter baumannii (CRAB) clinical isolates across various geographical regions, with particular emphasis on the application of multilocus sequence typing (MLST). CRAB poses a silent threat in healthcare settings, emerging as a public health concern globally corporate with limited treatment options due to the resistance to carbapenems, the last-line antibiotics, leading to increased mortality rates. This review will serve as invaluable resources, offering in-depth analysis and interpretation of epidemiological data related to CRAB. Through meticulous examination of this data, healthcare professionals will be equipped with a nuanced understanding of the spread and prevalence of this pathogen across diverse geographic regions. Additionally, by incorporating evidence-based strategies informed by epidemiological insights, stakeholders can enhance their ability to effectively combat this formidable pathogen, thereby safeguarding public health and promoting optimal patient outcomes.

Variation of healthcare associated infections at a tertiary hospital in Southwest China over a 5-year period (2019-2023): a retrospective observational study

BACKGROUND

Healthcare-associated infections (HAIs), which are associated with prolonged hospitalization and increased mortality, remain a global challenge. The COVID-19 pandemic paradoxically reduced some HAIs through enhanced hygiene measures but exacerbated others due to resource diversion, with effects after policy changes remaining unclear. Therefore, this study analyzed HAIs distribution, pathogenic microorganisms distribution, and antibiotic susceptibility capturing the period surrounding strict COVID-19 control measures in a southwest China tertiary hospital.

METHODS

We conducted a retrospective study at a tertiary hospital in southwest China from 2019 to 2023. Data were extracted from real-time surveillance system, where HAIs were initially diagnosed by clinicians and subsequently verified by infection control personnel. The HAI incidence rate was calculated per 1000 hospital stays, and negative-binomial regression was used to compare incidence rates across years.

RESULTS

This study enrolled 2808 HAI cases, with 1665 males and 1143 females, averaging 61.37 years old. The incidence rates of HAIs from 2019 to 2023 were 1.75, 1.12, 0.98, 1.31, and 1.30 per 1000 hospital stays, respectively. Hematology (323, 11.50%), cardiology (309, 11.00%), and neurology (262, 9.33%) were the top three departments with the highest HAI rates. Lower respiratory tract (1198, 42.66%), bloodstream (419, 14.92%), and urinary tract (406, 14.46%) were the most common HAI sites. Klebsiella pneumoniae (173, 15.22%), Escherichia coli (155, 13.63%), and Acinetobacter baumannii (136, 11.96%) were the most frequent pathogenic microorganism. Acinetobacter baumannii was resistant to most antibiotics. Klebsiella pneumoniae was most resistant to cefuroxime Axetil, cefuroxime and ceftriaxone. Escherichia coli was most resistant to sulfamethoxazole and trimethoprim, ceftriaxone and cefuroxime. These three pathogenic microorganisms were all susceptible to tigecycline.

CONCLUSIONS

The incidence rates of HAIs fluctuated over the years, peaking in 2019, suggesting potential shifts in infection control dynamics. Klebsiella pneumoniae, Escherichia coli, and Acinetobacter baumannii were the predominant pathogens, and tigecycline may be considered as a potential option against these pathogens. The study highlights the importance of enhancing infection control measures in high-risk departments and sites, optimizing antibiotic stewardship, and continuously monitoring HAI trends to inform evidence-based infection control policies.

CLINICAL TRIAL

Not applicable.

Evaluation of the stability of tigecycline in elastomeric infusion devices used for outpatient parenteral antimicrobial therapy

Background

Tigecycline is increasingly being considered in outpatient parenteral antimicrobial therapy (OPAT) programmes given its spectrum of activity; however, stability data are lacking, necessitating further study.

Objective

To assess tigecycline stability in elastomeric infusers under OPAT conditions, following the UK Yellow Cover Document (YCD) stability testing guidelines.

Methods

Tigecycline was reconstituted with normal saline in Leventon Dosi-Fuser and Baxter-LV10 infusers at doses of 50, 100 and 200 mg in 240 mL. Additionally, a tigecycline intermittent infusion dose (50 mg/100 mL) was reconstituted in Baxter-SV100 infusers. The infusers were stored under refrigerated storage (2°C-8°C) for 7 days, followed by exposure at an in-use temperature of 32°C for 24 h, or at 25°C for 2 hours for the intermittent infusion. Stability was evaluated using a stability-indicating assay, pH measurement, subvisible particle count and visual inspection as per the YCD.

Results

After 7 days of refrigeration followed by 24 h exposure to 32°C, the mean ± SD percentage of tigecycline remaining was 97.9 ± 0.6, 97.3 ± 0.6 and 95.4 ± 0.8 for the Baxter LV10 devices, and 97.2 ± 0.3, 96.9 ± 0.5 and 95.8 ± 0.8 for Dosi-Fuser devices at the low, intermediate, and high dose levels, respectively. For intermittent infusion in Baxter-SV100 devices, the mean ± SD percentage remaining after 7 days of refrigerated storage followed by 2 h at 25°C was 99.7 ± 0.2.

Conclusions

Tigecycline meets the UK YCD criteria of ≤5% degradation limit, indicating its suitability for both intermittent and continuous 24-h infusion in OPAT programs.

Lactobacilli-derived extracellular vesicles as synergistic biomolecules for colistin efficacy against Acinetobacter baumannii

Acinetobacter baumannii (A. baumannii), a gram-negative bacterium resistant to antibiotics, presents substantial medical challenges, causing nosocomial infections with high fatality rates. Colistin (COL) is frequently employed as a last-line defense against these pathogens. Nevertheless, its therapeutic efficacy has been significantly reduced due to the emergence of COL-resistant strains. With the slow development of novel antibiotics, researchers have explored materials to boost the effectiveness of COL against such pathogens. Postbiotics, comprising bioactive compounds derived from probiotic microorganisms, have shown potential antibacterial properties and may work synergistically with certain antibiotics. This study aimed to confirm the role of extracellular vesicles (EVs) as a collection of bioactive molecules that could potentially synergize with COL. EVs from various Lactobacilli strains (LEVs) were evaluated for their effect on COL susceptibility. The findings indicated that, compared to COL treatment alone, LEVs enhanced 4- to 8-fold bactericidal efficacy of COL against A. baumannii strains in the level of minimum inhibitory concentrations (MIC). Additional mechanistic investigations into the synergistic effects of LEVs on established COL mechanisms, including lipopolysaccharide binding, reactive oxygen species (ROS) generation, and biofilm formation, showed that LEVs act as either ROS enhancers or biofilm inhibitors, depending on the bacterial strains. Finally, we demonstrated that repeated use of LEVs did not induce COL resistance in A. baumannii. These results provide the first evidence that LEVs can serve as effective postbiotics, enhancing the susceptibility of A. baumannii strains to COL.

Clinical characteristics and risk factors of tigecycline-induced acute pancreatitis in kidney transplant recipients: a retrospective study

OBJECTIVE

Acute pancreatitis (AP) is a severe but insufficiently recognized adverse effect of tigecycline in kidney transplant (KT) recipients. This study aimed to identify the clinical characteristics and risk factors associated with tigecycline-induced AP in this population.

METHODS

A single-center retrospective study was conducted in KT recipients treated with tigecycline. The clinical characteristics of patients who developed AP were analyzed, and risk factors for tigecycline-induced AP were assessed using univariate analysis and multivariate logistic regression.

RESULTS

80 KT recipients were enrolled, of whom nine developed AP (incidence: 11.25%), and four died. The mean time from tigecycline administration to AP onset was 7.00 days, to symptomatic relief after discontinuation was 4.87 days, and to normalisation of pancreatic enzymes after discontinuation was 8.75 days. The analysis revealed that tacrolimus trough concentration (C0 Tac) and post-transplant acute kidney injury (AKI) were independent risk factors for tigecycline-induced AP in KT recipients. Logistic regression analysis produced a combined predictive expression: Ycombined = AKI + 0.064C0 Tac-2.789. Receiver operating characteristic curve analysis determined that the C0  Tac cut-off was 13.9 ng/mL. The area under the curve for C0  Tac and combined predictor were 0.802 and 0.853, respectively.

CONCLUSION

The incidence of AP following tigecycline treatment was significantly higher in KT recipients than in non-transplant patients. Post-transplant AKI and elevated C0 Tac concentrations were identified as independent risk factors for the development of AP. Close monitoring of renal function and ensuring therapeutic monitoring of C0 Tac levels may help prevent AP.

Evaluating tigecycline dosing for hospital-acquired pneumonia patients: insights from physiologically-based pharmacokinetic modeling of lung exposure

Tigecycline is increasingly used off-label for hospital-acquired pneumonia (HAP), though its efficacy and optimal dosing remain uncertain. Lung exposure to tigecycline may be affected by pulmonary pH changes induced by bacterial infections. This study used a physiologically -based pharmacokinetic (PBPK) model to evaluate the impact of pH shifts on lung exposure and assess the efficacy of various dosing regimens. A lung PBPK model for tigecycline was developed and validated using plasma and lung concentration data from clinical pharmacokinetic studies. Simulations evaluated the impact of pH alterations from 6.6 (healthy) to 5.6 (infection) on lung exposure. Three clinical dosing regimens-standard (100 mg loading dose +50 mg q12h), median (150 mg loading dose +75 mg q12h), and high dose (200 mg loading dose +100 mg q12h)-were assessed by calculating the probability of target attainment (PTA) in lung compartments, including epithelial lining fluid (ELF) and alveolar cells (ACs), across a MIC range of 0.125-32 mg/L. The model reasonably captured tigecycline exposure in plasma and lung. Pulmonary pH alterations had minimal impact on tigecycline AUC in ELF but led to a significant 12.39-fold increase in AUC within ACs at pH 5.6. For pathogens with MIC ≤1 mg/L, all three dosing regimens achieved PTA ≥90% in ELF. However, for MIC >2 mg/L, only the high-dose regimen provided satisfactory PTA. The lung PBPK model provides valuable insights into tigecycline PK in HAP patients and underscores the need to optimize dosing for pneumonia with resistant pathogens.

An overview of potential combination therapies with ceftriaxone as a treatment for gonorrhoea

INTRODUCTION

Ceftriaxone is the last available single dose therapy for gonorrhea that effectively treats infections at all sites. Over a quarter of isolates are now resistant to ceftriaxone in some countries. The introduction of carefully chosen combination therapy with ceftriaxone could retard the emergence of ceftriaxone resistance.

AREAS COVERED

This review summarizes the findings of a PubMed search on the use of partner antimicrobial that could be used with ceftriaxone to prevent the emergence and spread of ceftriaxone resistance. We review 16 antimicrobials that could be partnered with ceftriaxone in terms of pharmacokinetic and pharmacodynamic compatibilities, activity against ceftriaxone resistant isolates and probability of antimicrobial resistance emerging.

EXPERT OPINION

Of these 16 antimicrobials, we reject antimicrobials such as fosfomycin due to poor clinical efficacy and tigecycline due to its considerably longer half-life which would likely select for tetracycline resistance. The most promising agents for combination with ceftriaxone are zoliflodacin, delafloxacin, sitafloxacin, eravacycline and possibly gepotidacin and gentamicin. Clinical studies should be conducted to evaluate the efficacy of these combinations on the eradication of N. gonorrhoeae and their impact on AMR in N. gonorrhoeae and other bacterial species.

Uncovering the Molecular Landscape of Tetracycline Family Natural Products through Bacterial Genome Mining

Tetracycline (TC) family natural products have attracted significant attention due to their diverse chemical structures and important role in drug development. As one of the most successful classes of drugs, TC antibiotics have been used clinically for over 70 years and remain crucial in treating infections. Despite their importance, systematic exploration of novel TC natural products has been limited, leaving the molecular landscape of the TC family poorly understood and hindering further development of these compounds for therapeutic applications. Here, we developed a targeted strategy to identify TC biosynthetic gene clusters (BGCs) based on specific cyclase signatures involved in assembling the TC scaffold. This led to the discovery of 82 representative BGCs with the potential to produce structurally diverse TCs. Among them, we uncovered three groups of novel natural products─misiomycins, varsomycins, and hibarimicins J-L─and identified their biosynthetic pathways. These compounds display distinctive structural features, with misiomycin A and hibarimicin L among the most highly modified TCs identified to date. Misiomycin A biosynthesis involves extensive glycosylation, while biosynthesis of varsomycin A, featuring a unique six-membered lactone ring structure, requires the coordinated action of two TC BGCs. The biosynthesis of hibarimicins J-L, derived from TC monomer dimerization, undergoes complex oxidative modifications involving seven oxygenases. Several TCs exhibited potent activity against drug-resistant Gram-positive pathogens. Our work further expands the structural diversity within the TC family and underscores the potential of these BGCs for generating new TC structures, providing valuable insights for the discovery and development of novel TC-based therapeutics.

The Y58D mutation in rpsJ gene is correlated with tigecycline and eravacycline combined resistance in ST80 vancomycin-resistant Enterococcus faecium isolates

OBJECTIVES

To describe the phenotypic and genetic features of vancomycin-resistant Enterococci (VRE) isolates exhibiting resistance to tetracycline (TET), tigecycline (TGC), and eravacycline (ERV).

METHODS

Between December 2023 and September 2024, 32 VRE were collected from clinical samples at the Policlinico Foggia, Italy. Bacterial identification was carried out by matrix-assisted laser desorption ionization-time of flight mass spectrometry analysis. Antimicrobial susceptibility testing for vancomycin, TET, TGC, and ERV was performed by the reference broth microdilution method. Whole-genome sequencing was carried out to explore the content of tetracycline resistance determinants, and the phylogenetic relationship between isolates (in silico multilocus sequence typing [MLST] and single-nucleotide polymorphisms [SNPs] analysis).

RESULTS

Among the studied isolates, 30 and 2 were vancomycin-resistant Enterococcus faecium (VREfm) and vancomycin-resistant Enterococcus faecalis (VREfs), respectively. Overall, eight isolates (six VREfm and two VREfs) were resistant to TET (8/32, 25%), with four (all VREfm) being resistant to TGC and ERV (4/32, 12.5%), also. The two TET-resistant VREfs strains belonged to sequence type (ST)6 and carried the tet(M) gene only. All the TET-resistant VREfm were ST80 and carried the tet(L) and tet(M) genes. Among these, the four TGC-resistant and ERV-resistant strains showed an uncommon Y58D substitution in the ribosomal S10 protein (rpsJ gene). SNPs analysis revealed that Y58D-carrying strains formed a separate cluster, within ST80 VREfm.

CONCLUSIONS

In this study, we correlated the presence of the Y58D mutation in the rpsJ gene with resistance to TGC and ERV in a cluster of VREfm ST80 clinical strains. The Y58D mutation was invariably found in co-presence with the tet(L) and tet(M) genes.

Phenotypic and in silico characterization of carbapenem-resistant Serratia marcescens clinical strains

BACKGROUND

Serratia marcescens, an opportunistic nosocomial Gram-negative bacterium pathogen, has emerged as an important cause of healthcare-associated infections owing to its acquisition of antimicrobial resistance genes (ARGs) and virulence factor determinants.

METHODS

Four carbapenem-resistant S. marcescens strains were recovered from patients admitted to different hospitals in 2017 and 2018. We assessed the antimicrobial resistance and virulence context, as well as the genetic similarities of four Brazilian S. marcescens strains, and compared the genomes of these S. marcescens isolates with whole genome data of 428 S. marcescens strains available in the NCBI Reference Sequence. Antimicrobial susceptibility testing was performed by disk diffusion and broth microdilution methods according to CLSI recommendations. Whole genome sequencing was performed using Illumina NextSeq 250-bp paired-end sequencing for two isolates, Sm424 and Sm613, which presented representative phenotypes.

RESULTS

The pathogenicity of both sequenced strains was predicted using the Pathogen Finder tool. Both isolates carried efflux system genes (RND, SMR, MFS, ABC-family) and resistance genes (blaSTR-2, aac(6')-Ic, fos). Virulence factor genes involved in motility, regulation, capsule formation, acid resistance, and acriflavine resistance were also found. The Pathogen Finder tool predicted a > 71% probability of being a human pathogen for Sm424 and Sm613.

CONCLUSION

S. marcescens has shown increased adaptive, resistance, and pathogenic potential, being responsible for different nosocomial infections.

Preventable serious drug-disease interactions of reserve antibiotics

INTRODUCTION

Antibiotics that are used exclusively in hospital settings and reserved for treating infections caused by multidrug-resistant or extended-resistant bacterial pathogens are referred to as 'reserved' antibiotics. The purpose of this review article is to provide a better understanding of the risks associated with serious interactions between reserved antibiotics and various diseases, as well as to present key strategies for their prevention.

AREAS COVERED

The literature search was conducted in the MEDLINE, SCOPUS, EBSCO, and GOOGLE SCHOLAR databases without any restrictions on time or language. Only clinical studies, observational human studies, case reports, and case series that reported serious drug-disease interactions were considered.

EXPERT OPINION

Knowledge of the interactions between reserve antibiotics and diseases, that have actually occurred and then been described in the medical literature, is crucial to the safe treatment of critically ill patients with infections caused by multidrug-resistant bacterial strains. Introducing into routine practice the checking of possible interactions with diseases that a patient suffers from, strict monitoring of changes in the function of the excretory organs (kidneys and liver), and measuring the concentration of drugs in the plasma will reduce the possibility of adverse drug-disease interactions.

Genomic plasticity of extensively drug-resistant and multidrug-resistant Acinetobacter baumannii ST208 isolates from a fatal outbreak

BACKGROUND

The prevalence of multidrug-resistant Acinetobacter baumannii (MDRA) has rapidly increased and is linked to severe nosocomial infections. MDRA outbreaks in a Japanese hospital were analysed using whole-genome sequencing.

METHODS

Antibiotic susceptibility testing was performed on clinical isolates from hospitalised patients before and during the 2009 and 2010 outbreaks. Whole-genome sequencing was conducted to identify acquired antibiotic-resistance genes and genetic mutations.

RESULTS

Clinical A. baumannii isolates were resistant to β-lactams (broad-spectrum cephalosporins and carbapenems), aminoglycosides, chloramphenicol, fosfomycin, fluoroquinolones, tetracyclines, and trimethoprim-sulfamethoxazole. MDRA isolates harboured aac(6')-Ib-cr, abaF, armA, blaADC-30, blaTEM-1, and blaOXA-82, or both blaOXA-66 and blaOXA-23, catB8, mphE, msrE, and tet(B). blaOXA-82 genes were recombinationally multiplied. Quinolone resistance was also associated with gyrA S81L and parC S84L mutations. The MDRA isolates belonged to Oxford sequence type (ST) 208 and Pasteur ST2. Three of the 15 isolates developed an extensively drug-resistant (XDR) phenotype, and two isolates harboured an adeS mutation.

CONCLUSIONS

We identified molecular resistance markers in three XDR and one MDR isolate and provided a genomic description of resistance and virulence, as well as the origins of the isolates. The isolates are closely related to MDRA Oxford ST208 and Pasteur ST2, identified in Asia and Australia. MDRA isolates are of concern in both hospital and community settings in the Western Pacific region.

Providencia pseudovermicola sp. nov.: redefining Providencia vermicola and unveiling multidrug-resistant strains from diabetic foot ulcers in Egypt

BACKGROUND

Providencia species are concerning due to their intrinsic resistance to colistin and tigecycline, complicating the treatment of multidrug-resistant (MDR) infections.

METHODS

In the current study, two MDR isolates, DFU6 and DFU52T, were recovered from infected diabetic foot ulcers in Egypt in 2024. Following their initial identification as Providencia stuartii using VITEK® 2 and MALDI-TOF-MS, the isolates were subjected to whole-genome sequencing via DNBseq.

RESULTS

While the 16S rRNA gene showed 100% similarity to that of Providencia vermicola, phylogenomic analysis against the type strains in the TYGS database, including P. vermicola DSM 17385T confirmed that these isolates represent a distinct species within the genus, further supported by overall genome-relatedness indices (ORGIs). This discrepancy prompted us to revise the taxonomy of all published genomes of P. vermicola strains (n = 59) which revealed misidentification of at least 56 strains that are unrelated to the type strain of this species. DFU6 and DFU52T carried novel sequence types (ST29 and ST41, submitted to PubMLST) and harbored multiple resistance genes. Both strains contained the qnrD1 gene on a small, non-mobilizable plasmid. DFU52T possessed a conjugative plasmid encoding blaCMY-6, blaNDM-1, rmtC, aac(6')-Ib10, sul1, aph(3')-Ia, and qacEΔ1. DFU6 carried an ISEcp1-associated blaCTX-M-14, along with aadA, dfrA1, lnuF in a class 2 integron, and armA, msrE, and mphE on a resistance plasmid. Both isolates also featured a pathogenicity island (PAI) integrated into the pheV gene with fimbriae-encoding genes.

CONCLUSION

Following our reassessment of the taxonomic classification of all P. vermicola strains with published genomes, we propose reclassifying certain strains, including DFU6 and DFU52T, into distinct species for which we propose the name Providencia pseudovermicola sp. nov. We recommend DFU52T (= CCASU-2024-72) as the type strain for the novel species. We also shed light on the public health threat of this novel species as a human pathogen that harbours carbapenem and aminoglycoside resistance genes on mobile genetic elements.

Molecular Analysis of Tigecycline Resistance in Carbapenem-Resistant Enterobacterales (CRE) in Mthatha and Surrounding Hospitals

Background: The emergence of carbapenem-resistant Enterobacterales is prevalent and poses a significant threat to health systems worldwide. This study aimed to conduct a molecular analysis of tigecycline resistance in 100 CRE isolates from Mthatha Hospital and surrounding hospitals. Methods: A retrospective study among patients who attended Nelson Mandela Academic Hospital (NMAH) and Mthatha Regional Hospital (MRH), Eastern Cape, South Africa. Enterobacterales isolates were identified using the Vitek2® system (bioMérieux); an E-test was performed on 100 CRE isolates according to the manufacturer's instructions. PCR assays for rapid detection of tet(X) and its variants, including tet(X1) and tet(X2), and high-level tigecycline resistance genes tet(X3), tet(X4), and tet(X5) were developed. Results: The results show a notably high prevalence of CRE infections in neonatal, male surgical, and maternal and pediatric wards, predominantly driven by Klebsiella species (53.4%), followed by Enterobacter species (20.5%) and then Escherichia coli (6.7%), and 7.2% of CRE isolates were resistant to tigecycline (E-test). In this study, tet(X) genes were not identified as the primary mechanism of tigecycline resistance. The risk factors associated with tigecycline resistance in CRE include age, pre-exposure to antibiotics, prolonged hospitalization, and undergoing invasive procedures, indicated by strong r = 0.9501. Conclusions: CRE gradually evolves, posing a significant threat to patients of all ages; early detection of carbapenemase production in clinical infections, carriage states, or both is essential to prevent hospital-based outbreaks.

Restoring tigecycline efficacy with lysine supplementation in tmexCD-toprJ-positive bacteria

OBJECTIVES

Antimicrobial resistance is one of the most pressing challenges to global public health. Tigecycline, a last-resort antibiotic, has been undermined by the emergence of the tmexCD1-toprJ1 gene cluster, a transferable RND-type efflux pump that confers resistance. Metabolite-enabled killing of antibiotic-resistant pathogens by antibiotics is an attractive strategy to tackle antibiotic resistance.

METHODS

The potentiation of lysine to tigecycline was evaluated through a series of in vitro studies, including bacterial viability assays, time-kill kinetics analysis, persister assays, and biofilm eradication experiments, as well as in vivo assessment using a murine systemic infection model. The underlying mechanisms of action were further explored through transcriptomic profiling and biochemical validation.

RESULTS

Herein, we show that lysine synergistically enhances the antibacterial efficacy of tigecycline against tmexCD-toprJ-positive bacteria. Mechanistic studies indicate that lysine supplementation promotes tigecycline uptake by upregulating ∆pH and disrupting membrane permeability. Transcriptomic analysis, coupled with phenotypic experiments, indicates that lysine not only triggers the generation of reactive oxygen species (ROS) by inhibiting hydrogen sulfide (H2S) production but also downregulates energy metabolism pathways essential for efflux pump function. These effects promote intracellular accumulation of tigecycline, thereby overcoming tmexCD-toprJ-mediated resistance. In mouse infection models, the combination of lysine and tigecycline shows improved therapeutic efficacy compared to tigecycline monotherapy.

CONCLUSION

Collectively, our findings indicate that lysine can serve as a promising tigecycline booster to tackle infections caused by tmexCD-toprJ-positive bacteria.

Phenotypical and Molecular Characterization of Acinetobacter baumannii Isolated from Hospitalized Patients During the COVID-19 Pandemic in Brazil

The goal of the present study was to analyze Acinetobacter baumannii strains isolated from hospitalized patients in the period of the COVID-19 pandemic by phenotypic and molecular methods and evaluate their antimicrobial resistance patterns and biofilm production. Forty-seven strains were isolated in 2021-2022 from a hospital in Brazil, and were identified by VITEK®2, MALDI-TOF/MS (VITEK MS® and MALDI Biotyper®), and 16S rRNA sequencing. Fourier-transform infrared (FTIR) spectroscopy was applied for typing and antimicrobial susceptibility testing (AST). In addition, biofilm formation and disinfectant tolerance tests were used. All methods accurately identified all the A. baumannii strains. FTIR typing identified 23 different profiles and 11 clusters, as well as differentiated between the strains from patients with and without COVID-19. Most strains exhibited resistance to the drugs tested, 91.5% of the strains were classified as XDR, 6.4% of the strains were MDR and only 1 strain was classified as non-MDR. Over half of the strains (n = 27, 57.4%) produced biofilms on polystyrene. Sodium hypochlorite (1.0%/15 min) was the best option for effective disinfection. Overall, this study will lay the foundation for further research on effective cleaning protocols for the eradication of A. baumannii biofilms, as well as the use of FTIR for pathogen surveillance in healthcare settings.

Sub-inhibitory concentrations of tigecycline could attenuate the virulence of Staphylococcus aureus by inhibiting the product of α-toxin

Staphylococcus aureus (S. aureus) infection is a serious threat to global health. This study aimed to investigate the anti-virulence efficacy of tigecycline against S. aureus. We used highly virulent S. aureus strains SA75 and JP30 to evaluate the effect of tigecycline on virulence, both of them isolated from the clinic. The MIC value of tigecycline against SA75 was 0.125 µg/mL, and that against JP30 was 0.25 µg/mL. Tigecycline did not affect the growth ability of bacteria at 0.015 µg/mL. Thus, subsequent discussions will focus on the effect of antibiotics at the latter subinhibitory concentrations that did not affect growth. First, the sub-MICs of tigecycline not only enhanced the sensitivity of S. aureus to oxidants and human whole blood but also weakened the hemolytic activity and cell adhesion level of S. aureus. Second, it undermined the survival of S. aureus in RAW264.7 and attenuated the macrophage inflammatory response induced by S. aureus. On the contrary, tigecycline decreased the hemolytic activity, as well as the skin abscess formation and bacterial burden in mice. Most importantly, it significantly decreased the expression of hla, hlgB, hlgC, spa, sbi, saeR, sak, tst, and coa genes by RT-qPCR and the protein expression of α-toxin. Altogether, the sub-MICs of tigecycline might be a promising agent to attenuate the virulence of S. aureus and its host immune response by inhibiting the SaeRS two-component system and the product of α-toxin.IMPORTANCEIn this study, the sub-MICs of tigecycline decreased the resistance of S. aureus to oxidants and human whole blood. Moreover, tigecycline weakened the cell adhesion level of S. aureus and skin abscess formation in mice by reducing bacterial burden. Remarkably, tigecycline decreased the hemolytic activity and significantly downregulated the expression of various virulence genes and α-toxin. This research highlighted that the sub-MICs of tigecycline might be a promising agent to attenuate the virulence of S. aureus by inhibiting the product of α-toxin.

Synthetic approaches and therapeutic applications of FDA-approved antibacterial agents: A comprehensive review from 2003 to 2023

The increasing threat of antibiotic resistance has necessitated the development of new antibacterial agents. 33 novel antibacterial agents have been approved by the U.S. Food and Drug Administration (FDA) within the two-decade timeframe from 2003 to 2023. These novel antibacterial agents included new chemical classes, such as lipopeptides, 18-membered macrolides, diaromatic quinolones, and nitroimidazoles, as well as modified existing classes, such as quinolones, tetracyclines, β-lactams, macrolides, oxazolidinones, and aminoglycosides. Nonetheless, during these twenty years, approval for new antibiotics was notably absent in 6 different years, and the total number of antibiotics approved was considerably less than that of other drug classes, including anticancer drugs. In this review, we provide an extensive analysis of the synthetic approaches and therapeutic applications of these approved antibacterial agents. We believe that this review will help further research on potential antibacterial agents for clinical use and development of next generation of antibacterial agents.

Molecular epidemiology of Escherichia coli in bloodstream infections from a general hospital in Ningxia, China, 2022-2023

OBJECTIVE

To analyse the antibiotic resistance, resistance genes and clonal relationship of Escherichia coli in bloodstream infections in Ningxia from 2022 to 2023.

METHODS

We retrospectively analyzed the antibiotic susceptibilities of 257 isolates. PCR was used to detect blaTEM, blaSHV, blaCTX-M, qnrS, qnrA, qnrB, oqxA, qepA, gyrA, gyrB, parC, and parE, and the clonal relationship through multilocus sequence typing (MLST).

RESULTS

One hundred and twenty-nine of 257 patients were male (50.2%). The 257 E. coli isolates were mainly obtained from the Emergency, Hepatobiliary Surgery, and Haematology Departments, accounting for 56.6%, 7.3%, and 6.2%, respectively. There is no significant difference in sex and genes between the two groups over and under 60 years old (P > 0.05), but there is a significant difference in ST between them(P<0.05). The antimicrobial susceptibility testing showed that the 257 isolates had the highest rates of resistance to ampicillin (82.8%), followed by cefazolin (71.6%), and all isolates were susceptible to tigecycline. Based on the antibiotic susceptibility results for ceftriaxone, we tested 126 isolates of E. coli for extended-spectrum beta-lactamase (ESBL) resistance genes. As a result, blaCTX-M was detected in 76 isolates (60.32%), blaSHV in 26 isolates (20.63%), and blaTEM in 38 isolates (30.16%). Based on the ciprofloxacin and levofloxacin antibiotic susceptibility results, we tested for quinolone resistance genes in 148 isolates, revealing 66 isolates of aac(6')-Ib-cr (44.60%), 3 isolates of oqxA (2.02%), 32 isolates of qnrS (21.62%), and 2 isolates of qepA (1.35%). We did not detect qnrA or qnrB. The detection rates of gyrA, gyrB, parC, and parE were 98%, 42.6%, 91.2%, and 87.8%, respectively and the main amino acid mutations were Ser83 to Leu, Asp87 to Asn(75.2%), Leu417 to Ser, Ser418 to Leu (6.3%), Ser80 to Ile (65.2%), and Ser458 to Ala (21.5%), respectively. MLST revealed that the most common sequence types (STs) were ST69 (12.5%), ST131 (8.2%), and ST1193 (7.8%).

CONCLUSION

In our hospital, E. coli was resistant to most commonly used antibiotics, and cefoperazone/sulbactam, cefotetan, amikacin, and tigecycline were empirically selected for the treatment of bloodstream infections. The predominant ESBL genotype in our hospital was blaCTX-M and the major quinolone resistance gene was aac(6')-Ib-cr. Clonal relationship analysis revealed genetic diversity among the isolates.

Case Report: Management of recurrent UTI with tigecycline in a kidney transplant recipient

This case report describes a 37-year-old man who underwent renal transplantation and subsequently developed complicated recurrent urinary tract infections (UTIs) caused by multidrug-resistant (MDR) Klebsiella pneumoniae. Despite initial treatment with fosfomycin and meropenem, the patient experienced persistent UTIs, leading to multiple hospitalizations. The management of these recurrent infections eventually required the use of tigecycline. Although tigecycline is not typically considered a urinary antibiotic owing to its limited urinary excretion, it was successfully employed in this case to manage the recurrent infections. The patient was treated with tigecycline for several episodes of UTI, which provided a crucial therapeutic option in the context of antibiotic resistance. This case underscores the challenges of managing recurrent MDR UTIs in immunocompromised patients and highlights tigecycline as an effective treatment strategy when standard therapies fail.

Genomic Insights into Colistin and Tigecycline Resistance in ESBL-Producing Escherichia coli and Klebsiella pneumoniae Harboring blaKPC Genes in Ecuador

Introduction: Escherichia coli (E. coli) and Klebsiella pneumoniae (K. pneumoniae) are resistant to third-generation cephalosporins (3GCs), carbapenems, colistin, and tigecycline, making them a major public health priority, mainly within the developing world. However, their genomic epidemiology and possible determinants of resistance remain to be elucidated. Thus, this study aimed to perform a genomic characterization of E. coli and K. pneumoniae, both of which are resistant to last-line antibiotics, isolated from humans, poultry, and a dairy farm environment within Ecuador. Methods: This study analyzed nine 3GC-resistant E. coli isolates harboring the mcr-1 gene (six from poultry farms, two from human infections, and one from dairy farm compost), together with ten isolated colistin- and carbapenem-resistant K. pneumoniae clinical samples. Results: The E. coli isolates of human origin belonged to ST609 and phylogroup A, while the poultry and compost isolates belonged to phylogroups A, B1, E, and F. Diverse STs of the K. pneumoniae isolates included ST13 (five isolates), ST258 (four isolates), and ST86 (one isolate). Within the E. coli isolates, blaCTX-M-55, blaCTX-M-65, blaCTX-M-15, and blaCTX-M-2 genes were identified. This study also identified blaCMY-2 and blaKPC-3 (the latter in a carbapenem-susceptible isolate). In E. coli, the plasmid-borne mcr-1.1 gene was identified across all E. coli isolates within an IncI2 plasmid. Tigecycline-reduced susceptibility or resistance was related to missense amino acid substitutions coded in the marA and acrA genes. Within K. pneumoiae, blaCTX-M-15 and blaCTX-M-65, on the one hand, and blaKPC-2 and blaKPC-3, on the other, were associated with 3GC and carbapenem resistance, respectively. The blaKPC-2 allele was identified in a ~10 kb Tn4401 transposon (tnpR-tnpA-istA-istB-blaKPC-2-tnpA). In K pneumoniae, sequence data and phenotypic analysis linked a nonsense amino acid substitution coded in the mgrB (K3*) gene and missense amino acid substitutions coded in the marA, acrA, arnB, eptA, pmrB, pmrJ, and phoQ genes to colistin resistance. Meanwhile, tigecycline resistance was linked to nonsense and missense amino acid substitutions coded within the ramR sequence. Additionally, this study identified several integron structures, including Int191 (5'CS-dfrA14-3'CS), which was the most prevalent integron (Int) among E. coli and K. pneumoniae isolates in this study, followed by Int0 (5'CS-3'CS) and Int18 (5'CS-dfrA1-3'CS). Conclusions: These results contribute to the genomic epidemiology of MDR E. coli and K. pneumoniae in our setting and to the worldwide epidemiology in the One Health approach.

Stenotrophomonas maltophilia bacteremia in adult patients with hematological diseases: clinical characteristics and risk factors for 28-day mortality

Patients with hematological diseases are at high risk for Stenotrophomonas maltophilia (SM) bacteremia. This study retrospectively analyzed the clinical characteristics and risk factors for 28-day mortality among 140 adult hematological patients diagnosed with SM bacteremia from January 2012 to July 2023. he overall 28-day mortality was 31.43% (44/140), with a median age of 44 years. The median hospital stay before SM bacteremia onset was 25 days, and 69.29% of patients had unresolved neutropenia. All patients had received broad-spectrum antibiotics in the past month, and 69.29% developed breakthrough bacteremia during carbapenem therapy. Independent risk factors for mortality included a Sequential Organ Failure Assessment (SOFA) score ≥5, tigecycline exposure, age ≥60, and pulmonary infection. Patients with ≥2 risk factors were stratified into the high-risk group, with a significantly higher 28-day mortality compared with the low-risk group (56.52% vs 7.04%, P < 0.001). Treatment with trimethoprim-sulfamethoxazole (TMP/SMX) (P = 0.008) or TMP/SMX combined with cefoperazone/sulbactam (CSL) (P = 0.005) was associated with survival benefits among high-risk patients. Overall, SM bacteremia usually occurs in hematological patients with prolonged hospitalization, unresolved neutropenia, and extensive use of broad-spectrum antibiotics, especially carbapenems. Patients with high SOFA scores, advanced age, pulmonary infection, or recent tigecycline exposure are at higher risk of mortality. The preferred treatment is TMP/SMX rather than fluoroquinolones, with combination therapy of TMP/SMX and CSL considered a feasible treatment option.IMPORTANCEThis study, representing the largest cohort of adult hematological patients with SM bacteremia to date, strengthens the validity of existing findings and provides new insights into its clinical management. We identify risk factors for 28-day mortality, revealing that patients with two or more risk factors experience particularly high mortality rates. This highlights the importance of early identification and targeted management of high-risk individuals. Our findings also demonstrate that TMP/SMX is superior to fluoroquinolones and suggest that combining TMP/SMX with CSL may offer additional survival benefits.

Reversal gene expression assessment for drug repurposing, a case study of glioblastoma

BACKGROUND

Glioblastoma (GBM) is a rare brain cancer with an exceptionally high mortality rate, which illustrates the pressing demand for more effective therapeutic options. Despite considerable research efforts on GBM, its underlying biological mechanisms remain unclear. Furthermore, none of the United States Food and Drug Administration (FDA) approved drugs used for GBM deliver satisfactory survival improvement.

METHODS

This study presents a novel computational pipeline by utilizing gene expression data analysis for GBM for drug repurposing to address the challenges in rare disease drug development, particularly focusing on GBM. The GBM Gene Expression Profile (GGEP) was constructed with multi-omics data to identify drugs with reversal gene expression to GGEP from the Integrated Network-Based Cellular Signatures (iLINCS) database.

RESULTS

We prioritized the candidates via hierarchical clustering of their expression signatures and quantification of their reversal strength by calculating two self-defined indices based on the GGEP genes' log2 foldchange (LFC) that the drug candidates could induce. Among five prioritized candidates, in-vitro experiments validated Clofarabine and Ciclopirox as highly efficacious in selectively targeting GBM cancer cells.

CONCLUSIONS

The success of this study illustrated a promising avenue for accelerating drug development by uncovering underlying gene expression effect between drugs and diseases, which can be extended to other rare diseases and non-rare diseases.

Methionine-driven methylation modification overcomes plasmid-mediated high-level tigecycline resistance

Tigecycline is a last-resort antibiotic to treat complicated infections caused by multidrug-resistant pathogens, while the emergence of plasmid-mediated tet(X) family severely compromises its clinical efficacy. Novel antimicrobial strategies not limited to new antibiotics in pharmaceutical pipeline are urgently needed. Herein, we reveal the metabolic disparities between tet(X)-negative and -positive E. coli, including distinct energy demand patterns under tigecycline exposure. In particular, the cysteine and methionine metabolism pathway is remarkably downregulated in tet(X)-positive bacteria. More importantly, we find that the addition of exogenous L-methionine (Met) effectively resensitizes tet(X)-positive pathogens to tigecycline. Our mechanistic analysis demonstrates that exogenous Met promotes intracellular tigecycline accumulation by upregulating bacterial proton motive force. Moreover, Met accelerates the conversion to S-adenosyl-L-methionine, an essential methyl donor, thereby enhancing 5mC methylation modification in the promoter region of tet(X4) gene and reducing its expression. Consistently, the potentiation of Met to tigecycline is abolished in tet(X4)-carrying E. coli Δdcm but restored in dcm-complementary bacteria, which encodes DNA-cytosine methyltransferase. In multiple animal models of infection, Met markedly potentiates the effectiveness of tigecycline against pathogenic E. coli and K. pneumoniae. Overall, this work highlights the therapeutic potential of Met in overcoming plasmid-mediated high-level tigecycline resistance, and provides a new paradigm to enhance antibiotic efficacy by harnessing cellular metabolic networks as well as epigenetic modifications.

Serum concentration threshold and risk factors of tigecycline-induced hypofibrinogenaemia in critically ill patients

OBJECTIVES

Hypofibrinogenaemia is a serious adverse reaction associated with tigecycline (TGC) therapy and may lead to the discontinuation of the treatment. This study aimed to explore the relevant factors of TGC-induced hypofibrinogenaemia and determine the thresholds of serum concentration as a predictive indicator of TGC-induced hypofibrinogenaemia.

METHODS

A retrospective single-centre study was conducted on patients with severe infection who were treated with TGC. Clinical data and serum concentration parameters were extracted from the electronic medical records of these patients. Patients were divided into the hypofibrinogenaemia group (< 2.0 g/L) and the normal fibrinogen group (≥ 2.0 g/L) in order to evaluate risk factors associated with TGC-induced hypofibrinogenaemia. Logistic regression analysis and receiver operating characteristic curves were utilized to identify the risk factors associated with TGC-induced hypofibrinogenaemia and to establish plasma concentration thresholds as predictive indicators.

RESULTS

A total of 114 patients were enrolled in this study, with 59.6% experiencing hypofibrinogenaemia. The multivariate regression analysis indicated that baseline fibrinogen level, trough concentration (Cmin), peak concentration (Cmax), the concentration at 6 h after the dosing (C6h) and the area under the concentration-time curve over a 24-h period (AUC0-24) were significantly associated with hypofibrinogenaemia (P < 0.05). Furthermore, it was found that AUC0-24 is the optimal predictor of TGC-induced hypofibrinogenaemia. The optimal cut-off for the AUC0-24 of TGC in ICU patients was determined to be 17.03 mg h/L.

CONCLUSIONS

TGC exposure is highly predictive of TGC-induced hypofibrinogenaemia. We recommend closely monitoring plasma concentrations of TGC in patients to ensure patient efficacy and safety.

The prevalence of multidrug resistance in Staphylococcus hominis isolated from clinical materials

The treatment of infections caused by Staphylococcus hominis remains a challenge, mainly due to the increasing resistance of these bacteria to antibiotics. The aim of the study was to determine antibiotic resistance in 62 strains S. hominis isolated from clinical materials, and to identify the molecular basis of resistance to antibiotics. Forty-six strains were both methicillin-resistant and harbored the mecA gene. Twenty-three of these strains had mec complex A and ccr complex AB1. Such a combination of the mec and ccr complexes does not correspond to any cassettes that have been demonstrated so far. However, over 80% of the tested strains were multidrug-resistant, of which as many as 12 were resistant to at least seven antibiotics. More than a half of strains harbored the tetK, acc(6')-Ie aph(2''), and ant(4')-I genes. erm(C) was the most common resistant gene to antibiotics from the MLS group. Two strains had as many as five antibiotic resistance genes from the tested groups (erm(C), msr(A), msr(B), mph(C), lnu(A)). The presence of the vga gene encoding resistance to streptogramins A was detected in one strain. All of strains were sensitive to vancomycin. However, 11 of them had reduced sensitivity to this antibiotic and eight of them were characterized by a heterogeneous resistance profile to this antibiotic. Our results clearly shows increasing threat of S. hominis caused by their multi-resistance. Moreover, these bacteria can constitute a reservoir of resistance genes for more pathogenic bacteria.

Treatment Approaches for Carbapenem-Resistant Acinetobacter baumannii Infections

Carbapenem-resistant Acinetobacter baumannii has been associated with over three hundred thousand annual deaths globally. It is resistant to most available antibiotics and associated with high morbidity and mortality. No global consensus currently exists for treatment strategies that balance safety and efficacy because of heterogeneity of treatment regimens in current clinical practice and scarcity of large-scale controlled studies arising from difficulties in establishing robust clinical outcomes. This review outlines the epidemiology and resistance mechanisms of carbapenem-resistant A. baumannii, then summarizes available clinical data on each approved agent with activity against this pathogen. Emerging treatment options such as cefiderocol and sulbactam-durlobactam show promise, but their success hinges on comprehensive clinical validation and access in regions most impacted by this pathogen. New therapeutic modalities that are in various stages of clinical development are also discussed.

AdeABC, AdeFGH, and AdeIJK efflux pumps as key factors in tigecycline resistance of Acinetobacter baumannii: a study from Western Balkan hospitals

PURPOSE

The present study investigated the role of resistance-nodulation-cell division (RND) efflux pumps in tigecycline resistance of Acinetobacter baumannii clinical isolates recovered from three Western Balkan countries (Serbia, Bosnia and Herzegovina and Montenegro).

METHODS

A total of 37 A. baumannii isolates recovered from seven tertiary care hospitals in 2016 and 2022 were tested against tigecycline using broth microdilution method. Then, efflux pump inhibitor carbonyl cyanide 3-chlorophenylhydrazone (CCCP) was used to determine the involvement of efflux pumps in tigecycline resistance. Molecular typing was performed by pulsed-field gel electrophoresis (PFGE) and multiplex PCR-based determination of clonal lineage. Regulators of efflux pumps were analyzed for amino acid substitutions, while reverse transcription-quantitative PCR (RT-qPCR) enabled quantification of RND efflux pumps expression.

RESULTS

All tested isolates were interpreted as resistant to tigecycline and showed reduced tigecycline minimum inhibitory concentration (MIC) values in the presence of CCCP. PFGE analysis showed significant diversity among isolates grouped in cluster I including IC2 (n = 32) and IC3 (n = 1) isolates, while cluster II was comprised of four IC1 isolates. The most prevalent substitutions in AdeR were V120I and A136V and in AdeS G186V and N268H (n = 33). The Q262R substitution was detected in AdeL proteins of IC1 isolates, whereas no alterations were observed within AdeN. The expression of the adeB, adeG, and adeJ genes in selected isolates was upregulated in five (1.16- to 3-fold), sixteen (1.35- to 2.82-fold), and twelve isolates (1.62- to 4-fold) compared to ATCC19606, respectively.

CONCLUSION

This study revealed that overexpression of RND efflux pumps underlies tigecycline resistance in A. baumannii clinical isolates from the Western Balkans.

A rapid liquid chromatography-tandem mass spectrometry based method for the detection of Tet(X) resistance gene in Enterobacteriaceae

There is a major public health threat posed by antibiotic resistance around the world. Tigecycline overcomes the resistance mechanisms of traditional tetracyclines and is often seen as the final resort in combating infections caused by bacteria resistant to multiple drugs. However, the introduction of new mobile tet(X) tetracycline destructases is leading to a notable rise in tigecycline resistance. Therefore, a rapid detection method is needed to monitor the spread of tigecycline resistance. In this study, a novel liquid chromatography-tandem mass spectrometry (LC-MS/MS) method to detect tet(X) in bacterial isolates was developed. This method utilized the analysis by LC-MS/MS of metabolite ratios to determine the presence of tet(X). Bacterial suspensions were co-incubated with tigecycline for 1 h, where tet(X) destructase inactivated tigecycline, making a particular metabolite with a 16-Da change in mass. The characterized quantitative ion pairing of tigecycline in the ESI positive mode was observed at 586.1 → 569.1 m/z. The oxygenated tigecycline detection was established at 602.2 → 529.1 m/z. A model was established using 35 tet(X)-positive and 15 tet(X)-negative Enterobacteriaceae strains in this study to optimize the cutoff value. Applying the model to analyze 70 bacterial isolates, the sensitivity of the LC-MS/MS test was 98.9% compared to polymerase chain reaction (PCR), and specificity was 100%. This method is rapid and easy to operate, providing results within 1 h, making it more suitable for routine use in clinical microbiology laboratories.

Role and mechanism of the outer membrane porin LamB in T-2 mycotoxin-mediated extensive drug resistance in Escherichia coli

The influence of mycotoxins in ecological niches shared with antibiotic-resistant bacteria (ARB) remains underexplored. This study examined the impact of T-2 mycotoxin on the evolution of antibiotic resistance in Escherichia coli, highlighting the role of specific porins. Our findings revealed that exposure to 10 ng/mL of T-2 toxin induced multi-drug resistant (MDR) phenotypes in three E. coli. At 10-5 ng/mL, T-2 toxin caused E. coli ATCC 25922 to develop stable resistance to 13 critical antibiotics, with minimum inhibitory concentrations (MICs) increasing 16- to several thousand-fold. This resistance was linked to the downregulation of the mal gene cluster. Notably, T-2 toxin reduced membrane permeability by downregulating lamB, facilitating its own entry and reducing the intracellular accumulation of both the toxin and antibiotics, thereby enhancing resistance development. LamB mediated the XDR phenotypes in E. coli, particularly by blocking last-resort antibiotics such as cephalosporins, carbapenems, tigecycline, and colistin, complicating treatment strategies. LamB demonstrated high binding affinities for T-2 toxin and various antibiotics, with specific binding sites identified for meropenem (Arg134), imipenem (Ser148, Arg170, Lys129), ceftazidime (Phe106, Lys129), and cefepime (Tyr66, Gln267, Lys269), exhibiting binding energies of -2.93, -2.58, -2.53, and -4.3, respectively. These findings suggest that even low levels of T-2 mycotoxin pose a substantial public health risk. They underscore the urgent need to address these contaminants and open new avenues for antibiotic resistance research.

Evaluating Risk Factors for Clinical Failure Among Tigecycline-Treated Patients

Purpose

Clinical trials have documented that tigecycline has a higher mortality risk than other treatments; it continues to be widely used for various infections in real-world settings, where its associated risk factors for clinical failure are understudied.

Patients and Methods

This retrospective analysis included a prospective 2019-2021 cohort of tigecycline-treated patients, excluding those with multiple infection sites. We assessed the outcomes on day 28, with clinical failure defined by mortality, persistent initial infection symptoms, or the requirement for continued antimicrobial treatment. Multivariable logistic regression was used for the outcome analysis.

Results

Of 253 patients included in the study, 94 experienced clinical failure. The infection foci included pneumonia (46.3%), bloodstream infection (BSI) (25.3%), and skin/soft tissue infections (10.3%). There were no significant differences in high-dose tigecycline administration or monotherapy rates between patients with favorable outcomes and those with clinical failure. A higher Charlson comorbidity index (adjusted odds ratio [aOR] = 1.20, P = 0.001), Pitt bacteremia score (aOR = 1.25, P = 0.007), and BSI (aOR = 3.94, P < 0.001) were significant predictors of clinical failure. Concomitant use of Pseudomonas aeruginosa-active fluoroquinolone (aOR = 1.97, P = 0.03) and carbapenem (aOR = 2.20, P = 0.01) was linked to increased clinical failure.

Conclusion

Multiple comorbidities, BSI, and higher Pitt bacteremia scores are associated with increased risk of clinical failure in tigecycline-treated patients. These results suggest clinicians should consider alternatives to tigecycline for patients with these risk factors. When administering tigecycline, vigilant monitoring is indicated to manage potential clinical failures.

Monte Carlo simulation for dosage optimization of the best available therapy for bloodstream infections secondary to carbapenemase-producing Klebsiella pneumoniae in critically ill patients

OBJECTIVE

We aimed to use Monte Carlo simulation, based on pharmacokinetic/pharmacodynamic targets, to investigate and determine the optimal dosage of the available combination therapies for carbapenem-resistant Klebsiella pneumoniae (CRKP) in critically ill patients.

METHODS

We collected CRKP clinical isolates from Phramongkutklao Hospital between October 2020 and June 2022. A molecular study of resistant genes was performed using polymerase chain reaction. Broth microdilution checkerboards were used to evaluate the mono- and synergistic antibiotic activities. Monte Carlo simulation was used to determine the optimal antibiotic regimens, based on the probability of target attainment (PTA) and cumulative fraction of response.

RESULTS

The 54 CRKP isolates were resistant to tigecycline (100%), colistin (75.9%), amikacin (70.4%), and gentamicin (63.0%). The most common carbapenemase genotype was blaoxacillinases (OXA)-48-like (42.6%), followed by blaNew Delhi metallo beta-lactamase (NDM) (29.6%) and coexistence of blaOXA-48-like and blaNDM (22.2%). Based on the PTA, synergistic and additive activities against CRKP isolates were observed with appropriate dosages of tigecycline-colistin (67.9%), tigecycline-gentamicin (62.2%), and tigecycline-amikacin (51.4%).

CONCLUSIONS

Tigecycline-colistin was the best available combination therapy for critically ill patients with CRKP, especially NDM. When used in combination with tigecycline, a colistin creatinine clearance of <90 mL/min can raise the cumulative fraction of response target and less nephrotoxicity.

Spreading Ability of Tet(X)-Harboring Plasmid and Effect of Tetracyclines as a Selective Pressure

Tigecycline is a last-resort antimicrobial in humans. Tetracyclines are the most widely used antimicrobials in livestock. Mobile tigecycline resistance genes [tet(X)] are disseminated worldwide, and tetracycline use may have promoted the selection of tet(X) genes. Thus, the selective pressure on tet(X) genes and their plasmids in livestock must be elucidated. We performed a retrospective study to clarify the prevalence of tigecycline-resistant Escherichia coli from pigs in Thailand. Screening for tigecycline resistance was performed on 107 E. coli strains from 25 samples, and tet(X)-carrying plasmids were characterized. tet(X) genes were cloned and expressed in E. coli. Bacterial growth rate in the presence of tetracycline as a result of the presence of tet(X) genes was also evaluated. Thirty-two tet(X4)-harboring tigecycline-resistant E. coli strains were detected in 10/25 samples (40%). The tet(X4) genes were carried on various Inc-type plasmids and flanked by ISCR2. The tet(X)-carrying plasmids were transferred to E. coli and Klebsiella pneumoniae. Acquisition of tet(X) genes and their plasmids improved bacterial growth in the presence of tetracycline. In summary, tetracycline use exerts selective pressure on tet(X) genes and their various backbone plasmids; therefore, a reduced amount of tetracycline use is important to limit the spreading of tet(X) genes.

Does Antibiotic Use Contribute to Biofilm Resistance in Sink Drains? A Case Study from Four German Hospital Wards

Backgound. As biofilms are known to harbour (multi-)resistant species, their presence in health settings must be considered critical. Although there is evidence that bacteria spread from drains to the outside, there is still a lack of research data focusing on drain biofilms from hospitals. Methods. We sampled biofilms from various wards of Helios Hospital Krefeld (Germany), where comprehensive antibiotic consumption data were available. Biofilms were analysed by cell counting, isolation of relevant bacterial groups and genetic and phenotypical resistance parameters. Data were correlated with the prescribed antibiotics of the respective ward. Furthermore, an ex situ biofilm model was employed to investigate the influence of sub-inhibitory antibiotics on the bacterial community and the prevalence of class 1 integrons. Results. Our results show that every ward harboured medically relevant bacterial species. While no significant differences were found in cell counts, the median prevalence of the resistance marker gene intI1 correlated with the amount of prescribed antibiotics. In contrast, phenotypical resistances showed no similar tendency. In addition, melting curve analysis data and changes in intI1 prevalence show that the composition of the bacterial community shifted depending on the biofilm and antibiotic. Conclusions. To the best of our knowledge, our study is the first considering possible correlations between the consumption data of hospital wards and resistances in drain biofilms the way we did. Based on our results, we conclude that sub-inhibitory concentrations of antibiotics have no general effect on biofilms in terms of bacterial community shift and occurrence of antibiotic-resistant species. Amongst other things, the effect depends on the initial composition of the bacterial community, the antibiotic used and the intrinsic bacterial resistance, e.g., prevalence of class 1 integrons.

The tigecycline resistance mechanisms in Gram-negative bacilli

Tigecycline, hailed as a pivotal agent in combating multidrug-resistant bacterial infections, confronts obstacles posed by the emergence of resistance mechanisms in Gram-negative bacilli. This study explores the complex mechanisms of tigecycline resistance in Gram-negative bacilli, with a particular focus on the role of efflux pumps and drug modification in resistance. By summarizing these mechanisms, our objective is to provide a comprehensive understanding of tigecycline resistance in Gram-negative bacilli, thereby illuminating the evolving landscape of antimicrobial resistance. This review contributes to the elucidation of current existing tigecycline resistance mechanisms and provides insights into the development of effective strategies to manage the control of antimicrobial resistance in the clinical setting, as well as potential new targets for the treatment of tigecycline-resistant bacterial infections.

Tigecycline Containing Polymethylmethacrylate Cement Against MRSA, VRE, and ESBL-In Vitro Mechanical and Microbiological Investigations

BACKGROUND

The use of antibiotic-loaded bone cements (ALBCs) in arthroplasty has been well established for the prevention and treatment of infections. Tigecycline (Tig), a broad-spectrum antibiotic, has shown efficacy against various pathogens, including vancomycin-resistant strains.

METHOD

ISO and DIN mechanical and microbiological inhibition zone tests were performed on PMMA cement with manually added Tigecycline.

RESULTS

Manually adding 0.5 and 1.0 g Tigecycline to PMMA always meets the mechanical requirements of ISO and DIN standards. Mixtures containing 0.5 g were microbiologically effective for up to 7 days and those containing 1.0 g were effective for 28-42 days.

CONCLUSION

In revision surgery, manually adding Tigecycline in doses of 0.5-1 g to 40 g of PMMA is effective against MRSA, VRE, and ESBL without negatively affecting the cement's properties.

Assessing antimicrobial consumption in public and private sectors within the Costa Rican health system: current status and future directions

BACKGROUND

Antimicrobial resistance is a significant global health threat. Therefore, robust surveillance systems for antimicrobial consumption (AMC) are essential to develop public health strategies. However, Latin American countries, including Costa Rica, face challenges in regularly reporting AMC data. This study aims to estimate and analyse the overall AMC in Costa Rica for 2019.

METHODS

This study is a national-level, retrospective, observational, and descriptive analysis of AMC in Costa Rica from 1 January to 31 December 2019. The study followed the World Health Organization (WHO) guidelines for the Surveillance of National AMC. The Anatomical Therapeutic Chemical (ATC) / Defined Daily Doses (DDD) system was used to analyse types of antimicrobials and DDD per 1000 inhabitants per day (DID). Antimicrobial dispensation data from the Costa Rican Social Security Fund (CCSS) represented the public sector, while the private sector data was sourced from IQVIA. The analysis included data from both inpatient and outpatient sectors.

RESULTS

A total AMC of 14.32 DID, of which 12.75 DID was within the public sector and 4.12 DID was within the private sector. Penicillins had the highest consumption nationally and in the public sector, while macrolides and lincosamides predominate in the private sector. According to the WHO-AWaRe (Access-Watch-Reserve) classification, antibiotics predominantly consumed nationally (74.7%) and in the public (83.0%) sectors are categorized under Access, whereas the private (61.0%) sector predominates the Watch category.

CONCLUSION

This study illustrates the importance of enhancing AMC surveillance by integrating data from both the public and private sectors. The findings indicate an excessive use of "Watch" antimicrobials in the private sector. To address this issue, all sectors and regulatory authorities must play an active and supportive role, in the development of effective, multisectoral policies. The methodology employed in this study is applicable to other Latin American countries, and therefore should be utilized for future analysis AMC in this region.

Tigecycline-induced coagulation gene prognostic prediction model and intestinal flora signature in AML

Infection is among the most common causes of death in patients with acute myeloid leukemia (AML) after chemotherapy. The anti-tumor effect of the intestinal microbiota in patients with AML is increasingly being recognized. Tigecycline, a broad-spectrum antibiotics, plays a vital role in the anti-infection treatment of AML patients with neutropenia and accompanying infections. Previously, this group reported that long-term use of tigecycline caused coagulation dysfunction in patients with hematological malignancies, increasing the risk of casualties. RNA sequencing was performed on CHO cells before and after tigecycline treatment. Further, the combined analysis of AML prognostic differentially expressed genes revealed 13 genes affected by tigecycline and closely related to AML prognosis. These genes were used for modeling analysis, and the results showed that the prepared model significantly improved the prognostic prediction efficiency for AML patients. The model also explored the correlation between prognosis score and immune cells infiltrating tumors and immune therapy targets. Moreover, 16S sequencing was performed on fecal samples from AML patients before and after tigecycline treatment. The results revealed that tigecycline significantly altered the distribution of intestinal microbiota in AML patients - These changes in microbiota are related to chemotherapy resistance. This study emphasizes the importance of intestinal microbiota in AML prognosis. Thus, the findings of this study show that the long-term use of antibiotics can not only cause dysbiosis of the intestinal microbiota but also indirectly affect the sensitivity of chemotherapy drugs, affecting the prognosis of AML patients.

Prevalence and Antibiotic Resistance of Streptococcus agalactiae in Women of Childbearing Age Presenting Urinary Tract Infections from Western Romania

Urinary tract infections (UTIs) are a common bacterial infection in women of childbearing age. Streptococcus agalactiae (Group B Streptococcus-GBS), a rare causative pathogen of UTIs in this population, is particularly important due to the potential risk during pregnancy, when it can lead to life-threatening neonatal infections. The current study analyzed 17,273 urine samples collected from consecutive women aged 18-45 years from Arad County, Western Romania. A total of 2772 samples tested positive for UTIs. In 130 cases, GBS was identified as the causative agent. Univariate logistic regression analysis revealed that women aged 25-34 years were more likely to test positive for GBS than those aged 18-24 years (cOR = 1.91, 95% CI: 1.07-3.43, p = 0.03). Antibiotic sensitivity testing revealed that all GBS strains were fully sensitive to penicillin, ampicillin, and vancomycin. High resistance was observed for clindamycin (77.34%) and tetracycline (88.46%). While GBS was found to be a rare pathogen in UTIs, our results underscore the importance of monitoring GBS in women of childbearing age, especially due to its risks during pregnancy, and emphasize the need for appropriate antibiotic management.

Commercial Day-Old Chicks in Nigeria Are Potential Reservoirs of Colistin- and Tigecycline-Resistant Potentially Pathogenic Escherichia coli

Background: Frequent use of colistin (COL) and tetracyclines in the Nigerian poultry sector potentially triggers bacterial resistance against COL and tigecycline (TIG), which are last-line antibiotics used to treat multidrug-resistant infections. Aim/Objectives: This study aimed to isolate COL- and TIG-resistant E. coli from commercial day-old chicks distributed to poultry farmers in Nsukka Southeastern Nigeria, assess the production of extended-spectrum β-lactamase (ESBL) and carbapenemase by the isolates, and establish their pathogenic potentials. Materials and Methods: Non-duplicate cloacal swabs were systematically collected from 250 randomly selected day-old chicks. MacConkey agar with 1 µg/mL of COL and 16 µg/mL of tetracycline was used for the isolation of putative COL- and tetracycline-resistant E. coli, respectively. E. coli isolates were confirmed biochemically using the API20E Gram-negative identification kit and molecularly by polymerase chain reaction targeting the uidA gene. Phenotypic COL resistance was established using COL agar and COL disc elution tests, while TIG insusceptibility was determined with disc diffusion. ESBL and carbapenemase production was assessed by double-disc synergy and modified carbapenem inactivation methods, respectively. Pathogenic potentials were determined using phenotypic methods. Results: COL- and TIG-resistant E. coli was recovered from 95 (38.0%) and 62 (24.8%) swabs from the 250 chicks, respectively. None of the isolates were potential ESBL or carbapenemase producers. The COL-resistant isolates displayed pathogenic potentials such as biofilm formation, haemagglutination, cell surface hydrophobicity, surface layer, and gelatinase activities at rates of 30.7%, 8.4%, 33.7%, 23.5%, and 17.6%, respectively. Meanwhile, the TIG-resistant isolates exhibited their respective potentials at rates of 47.0%, 21.0%, 35.5%, 58.1%, and 43.6%. Red, dry, and rough (RDAR) was the predominant curli fimbriae, and the cellulose morphotype portrayed by both the COL- and TIG-unsusceptible potential biofilm-producing isolates. Conclusions: This study demonstrates that a significant percentage of commercial day-old chicks distributed to farmers in Nsukka, southeastern Nigeria, are colonized by potentially pathogenic COL- and TIG-resistant E. coli, which could spread to humans and the environment.

Vancomycin-Resistant Enterococci: Current Understandings of Resistance in Relation to Transmission and Preventive Strategies

Due to the limited treatment options and increased mortality rates, infection prevention and control strategies have been implemented for many years to mitigate dissemination of vancomycin-resistant enterococci (VRE) within healthcare settings. The overview provides an insight into the most recent research, particularly the pathogen's resilience in the healthcare environment, and the critical need for infection control strategies, which are currently being scrutinized by some researchers. The notable resilience of enterococci to various environmental conditions highlights the necessity for investigations into innovative technologies capable of effectively targeting the biofilm produced by enterococci on hospital surfaces. A critical approach to traditional infection control strategies is becoming more accepted worldwide, taking into account the epidemiological situation in the given healthcare setting as well as specific characteristics of a patient. For certain high-risk patient populations, traditional infection control strategies including CP and screening should not be omitted. Additionally, further investigation into the resistance mechanisms of available antimicrobial agents is essential, as is research into their potential association with specific successful clones through WGS genotyping, to pre-emptively mitigate their spread before it escalates.

Navigating the Current Treatment Landscape of Metallo-β-Lactamase-Producing Gram-Negative Infections: What are the Limitations?

The spread of carbapenemase-producing gram-negative pathogens, especially those producing metallo-β-lactamases (MBLs), has become a major health concern. MBLs are molecularly the most diverse carbapenemases, produced by a wide spectrum of gram-negative organisms, including the Enterobacterales, Pseudomonas spp., Acinetobacter baumannii, and Stenotrophomonas maltophilia, and can hydrolyze most β-lactams using metal ion cofactors in their active sites. Over the years, the prevalence of MBL-carrying isolates has increased globally, particularly in Asia. MBL infections are associated with adverse clinical outcomes including longer length of hospital stay, ICU admission, and increased mortality across the globe. The optimal treatment for MBL infections not only depends on the pathogen but also on the underlying resistance mechanisms. Currently, there are only few drugs or drug combinations that can efficiently offset MBL-mediated resistance, which makes the treatment of MBL infections challenging. The rising concern of MBLs along with the limited treatment options has led to the need and development of drugs that are specifically targeted towards MBLs. This review discusses the prevalence of MBLs, their clinical impact, and the current treatment options for MBL infections and their limitations. Furthermore, this review will discuss agents currently in the pipeline for treatment of MBL infections.

Development and clinical utility of an ultra performance liquid chromatography - tandem mass spectrometry assay for monitoring omadacycline and tigecycline in severe bacterial infections

Objective

We aimed to develop a rapid, simple, and precise ultra performance liquid chromatography - tandem mass spectrometry (UPLC-MS/MS) technique for simultaneous measurement of omadacycline (OMA) and tigecycline (TGC) in the bloodstream of individuals suffering from serious bacterial infections.

Methods

All analytes were extracted using a 0.2 % formic acid-water dilution and acetonitrile plasma protein precipitation. The quantification was performed by electrospray ionization-triple quadrupole mass spectrometry with selected reaction monitoring and positive ion mode detection. Tetracycline was used as an internal standard in this experiment, with the mobile phase composed of water (with 0.1 % formic acid) and acetonitrile (using gradient elution) flowing at a rate of 0.35 ml/min, and the column temperature set at 30 °C. Each individual analysis was completed in under 3.5 min.

Results

The method was validated based on FDA recommendations, including the assessment of extraction recovery (92.65-101.72 %) and matrix effects (86.22-91.12 %). The standard curve ranges for both OMA and TGC are 0.025 µg/mL to 2.5 µg/mL. The plasma samples were found to be consistent after undergoing three rounds of freezing and thawing at room temperature for 24 h, being placed in an automated sample injector for 24 h, and then frozen for 45 days. Clinical cases were used to demonstrate the application of the therapeutic drug monitoring (TDM) assay, showing how an analytical test can quickly provide information on antibiotic levels in patients and impact their treatment.

Conclusion

Multiplex UPLC-MS/MS assays for the simultaneous measurement of plasma OMA and TGC concentrations are the ideal choice for clinically TDM applications.

Development of a Providencia stuartii multilocus sequence typing scheme

Introduction

The Providencia genus is assuming greater clinical relevance among infections caused by Enterobacterales also because of its intrinsic and acquired resistance to last-resort antibiotics. However, despite having been known and studied for over 50 years, genomics and taxonomy of the Providencia genus are currently undergoing a deep rearrangement. In this study we aim to outline and characterized the P. stuartii species.

Methods

We retrieved from the GenBank database all genomes labelled as Providencia and performed a comprehensive genome-based species definition founded on average nucleotide identity (ANI) and on alignment-free approaches.

Results

After defining the genomes assuredly identifiable as P. stuartii, we devised a MultiLocus Sequence Typing (MLST) and a core-genome MLST (cgMLST) schemes, based on 7 and 2,296 loci respectively.

Discussion

This work hence provides a framework for understanding the role of P. stuartii and of other members of this genus, which should be considered as emerging multidrug-resistant pathogens.

PhoPQ-mediated lipopolysaccharide modification governs intrinsic resistance to tetracycline and glycylcycline antibiotics in Escherichia coli

Tetracyclines and glycylcycline are among the important antibiotics used to combat infections caused by multidrug-resistant Gram-negative pathogens. Despite the clinical importance of these antibiotics, their mechanisms of resistance remain unclear. In this study, we elucidated a novel mechanism of resistance to tetracycline and glycylcycline antibiotics via lipopolysaccharide (LPS) modification. Disruption of the Escherichia coli PhoPQ two-component system, which regulates the transcription of various genes involved in magnesium transport and LPS modification, leads to increased susceptibility to tetracycline, minocycline, doxycycline, and tigecycline. These phenotypes are caused by enhanced expression of phosphoethanolamine transferase EptB, which catalyzes the modification of the inner core sugar of LPS. PhoPQ-mediated regulation of EptB expression appears to affect the intracellular transportation of doxycycline. Disruption of EptB increases resistance to tetracycline and glycylcycline antibiotics, whereas the other two phosphoethanolamine transferases, EptA and EptC, that participate in the modification of other LPS residues, are not associated with resistance to tetracyclines and glycylcycline. Overall, our results demonstrated that PhoPQ-mediated modification of a specific residue of LPS by phosphoethanolamine transferase EptB governs intrinsic resistance to tetracycline and glycylcycline antibiotics.

IMPORTANCE

Elucidating the resistance mechanisms of clinically important antibiotics helps in maintaining the clinical efficacy of antibiotics and in the prescription of adequate antibiotic therapy. Although tetracycline and glycylcycline antibiotics are clinically important in combating multidrug-resistant Gram-negative bacterial infections, their mechanisms of resistance are not fully understood. Our research demonstrates that the E. coli PhoPQ two-component system affects resistance to tetracycline and glycylcycline antibiotics by controlling the expression of phosphoethanolamine transferase EptB, which catalyzes the modification of the inner core residue of lipopolysaccharide (LPS). Therefore, our findings highlight a novel resistance mechanism to tetracycline and glycylcycline antibiotics and the physiological significance of LPS core modification in E. coli.

In vitro evaluation of tigecycline synergy testing with nine antimicrobial agents against Enterobacter cloacae clinical strains

Enterobacterales (especially carbapenem-resistant) are considered an urgent threat to public health. The available antibiotic therapy is limited due to the increase of multidrug-resistant (MDR) strains. Tigecycline, a minocycline derivative, has emerged as a potential key agent in the treatment of MDR isolates. The aim of the study was to evaluate the synergistic effect of tigecycline in combination with nine antimicrobial agents-ceftazidime/avibactam, colistin, ertapenem, gentamicin, imipenem, levofloxacin, meropenem/vaborbactam, polymyxin B, and rifampicin. Eighty clinical Enterobacter cloacae strains were obtained from patients of two University Hospitals in Bialystok, Poland. The E-test method was used to determine synergistic interactions. Among all combinations, synergy was reported in 61% of cases, addition in 32%, and indifference in 7%. The highest synergy rates were observed in tigecycline combinations with: ceftazidime/avibactam (60/80; 75%), imipenem (60/80; 75%), polymyxin B (55/80; 68.75%) and rifampicin (55/80; 68.75%), while the lowest synergy rate was noted in tigecycline-levofloxacin (26/80; 32.5%). The tigecycline-gentamicin showed the highest rate of indifference; antagonism, was not observed in any combination. In conclusion, tigecycline appears more suitable for use in combination therapy rather than as monotherapy and can be effectively paired with various antimicrobial agents against MDR E. cloacae. Further research will be necessary to confirm these results.

Optimizing Treatment Strategies for Carbapenem-Resistant Acinetobacter Baumannii-Associated Pneumonia: A Multicenter Study in Chinese Hospitals

Purpose

To evaluate the clinical outcomes and safety of tigecycline (TGC) plus cefoperazone/sulbactam (CPS) or TGC monotherapy in patients with hospital-acquired pneumonia (HAP) caused by Carbapenem-Resistant Acinetobacter baumannii (CRAB).

Methods

This was a retrospective analysis of multicenter data from 62 Chinese hospitals with CRAB HAP. Risk factors for receiving TGC with CPS therapy and predictors of mortality were assessed using multivariate logistic and Cox regression analyses, respectively. Propensity score matching (PSM) evaluated the efficacy and safety of antimicrobial regimens.

Results

A total of the 180 patients were included, with 95 receiving TGC monotherapy and 85 receiving combination therapy. Multivariate logistic regression analysis revealed that older age (P = 0.011), and intensive care unit (ICU) admission (P = 0.007) were significant risk factors for combination therapy. Multivariate Cox regression demonstrated that combination therapy was associated with a significantly higher risk of 90-day mortality (P = 0.031). Patients in the standard-dose TGC (SDT) plus CPS subgroup had significantly higher rates of SOFA scores ≥ 7 (P = 0.009) and MV used (P = 0.028), as well as higher 30-/90-day mortality compared to high-dose TGC (HDT) plus CPS group. TGC plus CPS significantly reduced CRP levels (P = 0.009), while the variations in ALT, TBIL, Cr, Hb, and PLT levels did not differ between different antimicrobial regimens after PSM.

Conclusion

HDT and CPS combination therapy was more effective in patients with advanced age and more severe condition. Safety profiles of different antimicrobial regimens were similar with liver, kidneys, and coagulation functions.

Population Pharmacokinetics of Tigecycline for Critically Ill Patients Undergoing Continuous Renal Replacement Therapy

Background

Tigecycline is considered one of the last resorts for treating infections caused by multidrug-resistant bacteria. Continuous renal replacement therapy (CRRT) is widely used in critically ill patients, especially those with acute kidney injury or severe infections. However, pharmacokinetic data for tigecycline in patients receiving CRRT are limited.

Methods

This was a single-center prospective clinical study with intensive sampling that included critically ill patients who received tigecycline and CRRT. A population pharmacokinetic (PPK) model was developed and evaluated by goodness-of-fit plots, bootstrap analysis, visual predictive checks, and numerical predictive checks. Pharmacokinetic/pharmacodynamic target attainment and cumulative fraction of response analyses were performed to explore the potential need for dose adjustments of tigecycline in CRRT.

Results

In total, 21 patients with 167 concentrations were included. A two-compartment model adequately described the tigecycline concentration-time points, but no covariates were found to adequately explain the viability in the pharmacokinetic parameters of tigecycline. The typical values of CL, Q, V1 and V2 were 4.42 L/h, 34.8 L/h, 30.9 L and 98.7 L, respectively. For most infections, the standard regimen of 50 mg/12 h was deemed appropriate, expect for skin and soft skin tissue infections and community-acquired pneumonia caused by Acinetobacter baumannii and Klebsiella pneumoniae, which required a dosage regimen of 100 mg/12 h or higher.

Conclusion

A tigecycline PPK model describing critically ill patients undergoing CRRT was successfully developed. The optimized dosage regimens for various infections are recommended.