Tigecycline-resistant Klebsiella pneumoniae strains from sewage in Norway carry heavy-metal resistance genes encoding conjugative plasmids

OBJECTIVES

Tigecycline is a last-resort antibiotic used for treatment of infections with carbapenem-resistant Klebsiella pneumoniae. The aim of the study was to understand the genetic mechanism of resistance and the genetic context of resistance genes in two tigecycline-resistant K. pneumoniae strains isolated from sewage in Bergen, Norway.

METHODS

Complete genome sequencing of the two strains was accomplished using a combination of short-read Illumina MiSeq-based and long-read Oxford Nanopore MinION-based sequencing. Conjugation experiments were performed using filter mating and a green fluorescent protein (GFP)-tagged Escherichia coli strain.

RESULTS

The complete genome sequences of strain K6-320.1 and strain K7-325 were assembled into two contigs for each strain, one contig representing the complete circular chromosomes of 5 223 440 bp (K6-320.1) and 5 263 092 bp (K7-325), respectively, and the other representing plasmids with sizes of 276 509 bp (pK6-320.1) and 246 731 bp (pK7-325). Strain K6-320.1 belonged to sequence type (ST)869, whereas strain K7-325 belonged to the pathogenic ST307. Both plasmids belonged to the IncFIB(K)/IncFII(K) group and carried several antibiotic resistance genes (ARGs), including tet(A) and blaCTX-M. Both plasmids (pK6-320.1 and pK7-325) were transferred to a GFP-tagged E. coli strain, leading to the acquisition of resistance against multiple classes of antibiotics. Several heavy-metal resistance genes (HMRGs) encoding resistance against silver (sil), copper (pco), and arsenic (ars) were also present on both plasmids.

CONCLUSIONS

Our study demonstrates the presence of multidrug-resistant K. pneumoniae strains carrying conjugative plasmids encoding both ARGs and HMRGs that have potential for persistence in the environment and human microbiota.

The first tigecycline resistant Enterococcus faecium in Norway was related to tigecycline exposure

OBJECTIVES

We describe the first tigecycline resistant enterococcal isolate in Norway and the mechanisms involved.

MATERIAL AND METHODS

The Norwegian National Advisory Unit on Detection of Antimicrobial Resistance (K-res). received in 2022 an Enterococcus faecium blood culture isolate with decreased susceptibility to tigecycline from a hospitalized patient in the South-Eastern Norway Health region for confirmatory testing. K-res verified a tigecycline-resistant E. faecium (TigR) with broth microdilution MIC of 0.5 mg/L. The patient had received treatment with tigecycline because of an infection with a linezolid- and vancomycin-resistant but tigecycline susceptible E. faecium (TigS) 47 days prior to the detection of the corresponding tigecycline-resistant isolate. Whole-genome comparisons, cgMLST and SNP analyses revealed that the two ST117 strains were closely related.

RESULTS

The TigR isolate showed a novel deletion of 2 amino acids (K57Y58) in a polymorphic region of ribosomal protein S10 previously associated with tigecycline resistance and a deletion of the tet(M) leader peptide previously related to increased expression of tet(M) and tigecycline resistance in enterococci.

CONCLUSIONS

Genomic and epidemiological analyses confirm that the two E. faecium (TigR and TigS) are closely related isolates of the same strain and that the two deletions (in rpsJ and of tet(M) leader peptide) account for the tigecycline resistance in TigR.

Antimicrobial efficacy of eravacycline against emerging extensively drug-resistant (XDR) Acinetobacter baumannii isolates

PURPOSE

Drug-resistant Acinetobacter baumannii is an emerging threat. This study has been conducted to observe the efficacy of eravacycline along with the RND-efflux pump system.

METHODS

A cross-sectional study was done collecting 48 clinical isolates of Acinetobacter baumannii. MICs of 15 antibiotics were detected along with BMD of tigecycline and eravacycline. PCR products of drug-resistant regulatory genes were sequenced and analyzed.

RESULTS

Of the total 48 Isolates, 35 (72.91%) were XDR and 13 (27.08%) were MDR. Out of all, 60.41% of isolates were found to be susceptible to eravacycline by BMD according to both FDA and EUCAST guidelines. A 2-fold decline of MIC50/90 was observed with the use of eravacycline compared to tigecycline. RND-efflux genes like AdeC in 30 (62.5%) isolates and Regulatory gene AdeS in 29 (60.41%) isolates were detected, explaining the existing resistance mechanism.

CONCLUSIONS

XDR Acinetobacter poses an escalating threat due to its resistance to multiple antibiotics, raising serious concerns in healthcare settings. Eravacycline is an encouraging new drug for empirical use in severe infection caused due to the same. Molecular investigation and strict antimicrobial stewardship should be followed to control the emergence, and a better understanding of mechanisms of resistance to prevent the spread of drug-resistant isolates.

Significant Impact of AcrB Amino Acid Polymorphism at Residue 716 on Susceptibility to Tigecycline and Other Antibiotics in Klebsiella pneumoniae

AcrAB-TolC is a multidrug RND-type efflux pump that is widespread in Gram-negative bacteria. As the substrate-binding subunit, AcrB was shown to modulate antimicrobial resistance in Escherichia coli, but the influence of AcrB mutation on Klebsiella pneumoniae, a major clinical pathogen, has not been well-studied. The finding of an R716L mutation in AcrB in a clinical tigecycline-nonsusceptible K. pneumoniae S1 strain inspired us to probe the role of AcrB residue 716 in antimicrobial resistance. This residue was subsequently subjected to saturation mutagenesis, followed by antibiotic susceptibility tests, survival assays, and antibiotic accumulation assays, showing strong influences of AcrB mutation on antimicrobial resistance. In particular, resistance levels to azithromycin, tetracycline, tigecycline, and cefoxitin were significantly changed by AcrB mutation at residue 716. Mutations to charged residues, polar residues, and residues that disrupt secondary structures have particularly reduced the antimicrobial susceptibility of bacteria, except for azithromycin, and the impact is not due to the abolishment of the efflux function of the pump. Therefore, it is concluded that residue 716 is an important residue that significantly influences antimicrobial resistance in K. pneumoniae, adding to our understanding of antimicrobial resistance mechanisms in this key clinical pathogen.

The Mechanism of Tigecycline Resistance in Acinetobacter baumannii under Sub-Minimal Inhibitory Concentrations of Tigecycline

The presence of sub-minimal inhibitory concentration (sub-MIC) antibiotics in our environment is widespread, and their ability to induce antibiotic resistance is inevitable. Acinetobacter baumannii, a pathogen known for its strong ability to acquire antibiotic resistance, has recently shown clinical resistance to the last-line antibiotic tigecycline. To unravel the complex mechanism of A. baumannii drug resistance, we subjected tigecycline-susceptible, -intermediate, and -mildly-resistant strains to successive increases in sub-MIC tigecycline and ultimately obtained tigecycline-resistant strains. The proteome of both key intermediate and final strains during the selection process was analyzed using nanoLC-MS/MS. Among the more than 2600 proteins detected in all strains, we found that RND efflux pump AdeABC was associated with the adaptability of A. baumannii to tigecycline under sub-MIC pressure. qRT-PCR analysis also revealed higher expression of AdeAB in strains that can quickly acquire tigecycline resistance compared with strains that displayed lower adaptability. To validate our findings, we added an efflux pump inhibitor, carbonyl cyanide m-chlorophenyl hydrazine (CCCP), to the medium and observed its ability to inhibit tigecycline resistance in A. baumannii strains with quick adaptability. This study contributes to a better understanding of the mechanisms underlying tigecycline resistance in A. baumannii under sub-MIC pressure.

Emergence of plasmid-mediated high-level tigecycline resistance gene tet(X4) in Enterobacterales from retail aquatic products

The spread of antimicrobial-resistant microbes and genes in various foods poses a significant threat to public health. Of particular global concern is the plasmid-mediated tigecycline resistance gene tet(X4), which, while identified in various sources, has not hitherto been reported in aquatic products. This study aimed to investigate the occurrence and characterization of tigecycline-resistant strains from aquatic products. A total of 73 nonrepetitive seafood samples were purchased from 26 farmers' markets to detect tigecycline-resistant strains. Of these, nine Escherichia coli strains (comprising two ST58, one ST195, ST10, ST48, ST88, ST877, ST1244, ST14462) and one Citrobacter meridianamericanus, recovered from nine (12.33 %, 9/73) seafood samples (fish, n = 7; shrimp, clam and crab, n = 1 respectively), were positive for the tet(X4). Notably, phylogenetic analysis showed that E. coli ST195, a common ST carrying tet(X4), has a close phylogenetic relationship (23∼48 SNPs) with 32 tet(X4)-harboring E. coli ST195 isolates (isolated from pigs, animal foods, vegetable, and humans) deposited in NCBI database. Additionally, E. coli ST58 was closely (2 SNPs) related to one tet(X4)-positive E. coli strain from retail vegetables documented in the NCBI database. Whole genome sequencing and bioinformatic analysis revealed that tet(X4) genes were located on IncX1 (7 E. coli) or hybrid plasmid IncFIA(HI1)/IncHI1B(R27)/IncHI1A (2 E.coli and one C. meridianamericanus). These plasmids displayed high homology with those of plasmids from other sources deposited in GenBank database. These findings underscore the role of epidemic clones and plasmids in driving the dissemination of tet(X4) gene within Enterobacterales of aquatic products origin. To the best of our knowledge, this is the first report of tet(X4)-positive Enterobacterales from aquatic products. The pervasive propagation of tet(X4) gene facilitated by epidemic plasmids and clones across food animals, food products, humans, and the environment presents a serious threat to public health.

Genomic analysis of extensively drug-resistant Acinetobacter baumannii harbouring a conjugative plasmid containing aminoglycoside resistance transposon TnaphA6

The occurrence of multidrug-resistant Acinetobacter baumannii (MDRA) has increased rapidly and is associated with severe nosocomial infections. MDRA has emerged in the hospital setting and has evolved into extensively drug-resistant A. baumannii (XDRA). A clinical XDRA isolate obtained from a hospitalised patient in 2016 was evaluated for antibiotic susceptibility and whole-genome sequence. The XDRA isolate was resistant to β-lactams, including broad-spectrum cephalosporins and carbapenems, and to aminoglycosides, fosfomycin, fluoroquinolones, tetracyclines, tigecycline, and trimethoprim-sulfamethoxazole. The isolate harboured abaF, ant(3″)-II-c, aph(3″)-Ib, aph(6)-Id, armA, blaADC-73, blaTEM-1, blaOXA-66, blaOXA-23, mphE, msrE and tet(B). Quinolone resistance was associated with mutations gyrA S81L and parC S84L. Tigecycline resistance was associated with a mutation in adeS. The isolate belonged to Oxford and Pasteur scheme sequence type 1050 and 2, respectively, and harboured a conjugative plasmid containing the aminoglycoside resistance transposon TnaphA6. Our study demonstrates that the isolate is closely related to a recent MDRA identified in Australia and the USA, in which a similar conjugative plasmid is not observed. Although the MDRA in Australia caused an outbreak, our hospital's surveillance protocol managed to prevent a further outbreak. Our finding suggests that this XDRA isolate is of concern in hospital and community care settings. The gpi allele could be a marker for discriminating this isolate from clonal complex 92 isolates.

Toxicity of tigecycline on the freshwater microalga Scenedesmus obliquus: Photosynthetic and transcriptional responses

Tigecycline (TGC) is a new tetracycline antibiotic medication against multidrug-resistant bacteria. However, the toxicity of TGC to microalgae remains largely unknown. In this study, the toxicity of TGC on Scenedesmus obliquus was examined, focusing on changes in algal growth, photosynthetic activity, and transcriptome. According to an acute toxicity test, the IC10 and IC50 values were 0.72 mg/L and 4.15 mg/L, respectively. Analyses of photosynthetic efficiency and related parameters, such as light absorption, energy capture, and electron transport, identified a 35% perturbation in the IC50 group, while the IC10 group remained largely unaffected. Transcriptomic analysis showed that in the IC10 and IC50 treatment groups, there were 874 differentially expressed genes (DEGs) (220 upregulated and 654 downregulated) and 4289 DEGs (2660 upregulated and 1629 downregulated), respectively. Gene Ontology enrichment analysis showed that TGC treatment markedly affected photosynthesis, electron transport, and chloroplast functions. In the IC50 group, a clear upregulation of genes related to photosynthesis and chloroplast functions was observed, which could be an adaptive stress response. In the IC10 group, significant downregulation of DEGs involved in ribosomal pathways and peptide biosynthesis processes was observed. Kyoto Encyclopedia of Gene and Genomes enrichment analysis showed that treatment with TGC also disrupted energy production, protein synthesis, and metabolic processes in S. obliquus. Significant downregulation of key proteins related to Photosystem II was observed under the IC10 TGC treatment. Conversely, IC50 TGC treatment resulted in substantial upregulation across a broad array of photosystem-related proteins from both Photosystems II and I. IC10 and IC50 TGC treatments differentially influenced proteins involved in the photosynthetic electron transport process. This study emphasizes the potential risks of TGC pollution to microalgae, which contributes to a better understanding of the effects of antibiotic contamination in aquatic ecosystems.

Establishing a synthetic orthogonal replication system enables accelerated evolution in E. coli

The evolution of new function in living organisms is slow and fundamentally limited by their critical mutation rate. Here, we established a stable orthogonal replication system in Escherichia coli. The orthogonal replicon can carry diverse cargos of at least 16.5 kilobases and is not copied by host polymerases but is selectively copied by an orthogonal DNA polymerase (O-DNAP), which does not copy the genome. We designed mutant O-DNAPs that selectively increase the mutation rate of the orthogonal replicon by two to four orders of magnitude. We demonstrate the utility of our system for accelerated continuous evolution by evolving a 150-fold increase in resistance to tigecycline in 12 days. And, starting from a GFP variant, we evolved a 1000-fold increase in cellular fluorescence in 5 days.

A widespread single amino acid mutation in AcrA reduces tigecycline susceptibility in Klebsiella pneumoniae

IMPORTANCE

Tigecycline, a glycecycline antibiotic with broad-spectrum activity against almost all Gram-positive and Gram-negative bacteria, is a highly concerned "last-resort" antibiotic. In addition to plasmid-hosted mobile tet(X) conferring high-level resistance to tigecycline, there are many reports suggesting increased expression of AcrAB-TolC efflux pump leads to tigecycline non-susceptibility. However, the role of mutations in AcrAB-TolC on tigecycline resistance has not been identified. This study reports a novel T188A mutation of the AcrA subunit of AcrAB-TolC complex in a clinical tigecycline-resistant Klebsiella pneumoniae strain and reveals the role of AcrA mutation on tigecycline resistance in K. pneumoniae. High prevalence of A188 type AcrA in hypervirulent multidrug-resistant K. pneumoniae indicates that mutations of the AcrAB-TolC complex may play a larger role in determining bacterial pathogenesis and antibiotic susceptibility than previously expected.

Conjugative plasmids facilitate the transmission of tmexCD2-toprJ2 among carbapenem-resistant Klebsiella pneumoniae

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is a great threat to global public health. The emergence of tmexCD-toprJ greatly weakened the efficacy of tigecycline in the treatment of CRKP infections. In this study, we did a comprehensive investigation of the prevalence and genomic features of tmexCD-toprJ in clinical CRKP from 2018 to 2020 in Henan province, China. The results demonstrated tmexCD-toprJ was at a low prevalence in CRKP from patients (7/2031, 0.34 %). Among the seven tmexCD-toprJ positive CRKP, KP18-29 that carried tmexCD1-toprJ1, blaNDM-1 and mcr-8.2 was resistant to tigecycline, carbapenem and colistin simultaneously. While, tmexCD2-toprJ2 together with one or two carbapenemase genes were detected in the remaining strains. Four strains (KP18-231, KP18-2110-2, KP19-3023 and KP19-3088) isolated at different times but shared the same sequence type (ST) 2667 exhibited high genomic similarity, indicating the clonal dissemination of CRKP ST2667 co-producing KPC-2 and TMexCD-TOprJ. Notably, conjugative transmission of the IncFrepB(R1701) plasmid co-harboring tmexCD2-toprJ2 and blaKPC-2 among clinical CRKP isolates belonging to different STs (ST2667, ST978 and ST147) revealed further propagation of tmexCD-toprJ among K. pneumoniae. Such IncFrepB(R1701) plasmids pose a substantial threat to public health due to their mobile resistance to both tigecycline and carbapenem. Online data mining showed isolates carried both carbapenemase genes and tmexCD-toprJ were dominantly isolated from humans, and isolates of animal origins usually carried mcr genes and tmexCD-toprJ, suggesting that these critical resistance genes co-existed in diverse niches. Global surveillance of K. pneumoniae co-harboring tmexCD-toprJ and mcr/carbapenemase genes in various settings with a One Health strategy was warranted.

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.

Tigecycline-resistance mechanisms and biological characteristics of drug-resistant Salmonella Typhimurium strains in vitro

Increased drug resistance of Gram-negative bacteria to tetracycline caused by the unreasonable overuse of tigecycline has attracted extensive attention to reveal potential mechanisms. Here, we identified a tigecycline-resistant strain called TR16, derived from Salmonella Typhimurium ATCC13311 (AT), and examined its biological characteristics. Compared with AT, the TR16 strain showed significantly higher resistance to amoxicillin but lower resistance to gentamicin. Although the growth curves of TR16 and AT were similar, TR16 showed a significantly increased capacity for biofilm formation and a notably decreased motility compared to AT. Furthermore, transcriptome sequencing and reverse transcription-quantitative PCR (RT-qPCR) were implemented to evaluate the genetic difference between AT and TR16. Whole genome sequencing (WGS) analysis was also conducted to identify single nucleotide polymorphism (SNPs) and screened out two genetic mutations (lptD and rpsJ). The acrB gene of TR16 was knocked out through CRISPR/Cas9 system to further elucidate underlying mechanisms of tigecycline resistance in Salmonella Typhimurium. The up-regulation of acrB in TR16 was verified by RNA-seq and RT-qPCR, and the lack of acrB resulted in a 16-fold reduction in tigecycline resistance in TR16. Collectively, these results implied that AcrB efflux pump plays a key role in the tigecycline resistance of Salmonella, shedding light on the potential of AcrB efflux pump as a novel target for the discovery and development of new antibiotics.

Characterization of class 1 integrons in metallo-β-lactamase-producing Acinetobacter baumannii isolates from hospital environment

BACKGROUND AND OBJECTIVE

The emergence and widespread dissemination of antibiotic resistance in A. baumannii, has become a globally challenge. The increasing hospital outbreaks by multi-drug resistant (MDR) A. baumannii strains, shows the necessity of continuous monitoring to find sources of resistant strains in hospitals. This study aimed to identify the presence of class 1 integrons and metallo-β-lactamase (MBL) related genes in A. baumannii isolates from hospital environment.

METHODS

In order to identify A. baumannii isolates, a total of 297 environmental samples were collected from burn wards and intensive care units (ICUs) of two university hospitals. Resistance to common antibiotics was studied by disk diffusion method and microbroth dilution assay was used to determine the minimum inhibitory concentrations (MICs) of imipenem, colistin and tigecycline. The A. baumannii isolates were studied by polymerase chain reaction (PCR) for the presence of class 1 integrons (intI1, intl CS) and metallo-β-lactamases (MBLs) (blaIMP, blaVIM, blaNDM) genes.

RESULTS

A. baumannii was identified in 68/297 (22.9%) of hospital environment. All A. baumannii strains were multidrug-resistant (MDR), but none of them were resistant to colistin, tigecycline and ampicillin-sulbactam. All (100%) and 38 (95.0%) of A. baumannii isolates from ICUs and burn wards were imipenem resistant respectively. Class 1 integrons was identified in 30/40 (75.0%) and 23/28 (82.1%) isolates from burn wards and ICUs respectively. Two different types of gene cassettes were identified, which included: arr-2, ereC, aadA1, cmlA5 and arr2, cmlA5. MBL genes including blaVIM and blaIMP were detected in 26/28 (92.8%), 27/28(96.4%) and 39/40 (97.5%) and 31/40 (77.5%) of the isolates from the ICUs and the burn wards respectively. None of the isolates contained the blaNDM-1 gene.

CONCLUSION

The findings of the present study showed that the isolation rate of MBL producing carbapenem-resistant A. baumannii (CRAB) was relatively high in the environmental surface of burn wards and ICUs, which can be considered as a potential source of outbreaks in hospitalized patients.

The effect of mitochondria inhibition on natural killer cells cytotoxicity in triple-negative breast cancer cells

Triple-Negative Breast Cancer (TNBC), the most common invasive breast cancer, depicts cancer poor response to conventional therapies. The clinical management of TNBC is a challenging issue. Natural killer (NK) cell therapy in the field of cancer treatment is rapidly growing however, regarding the immunogenicity of breast cancer cells, this type of therapy has shown limited efficacy. Recently, targeting tumor biomarkers has revolutionized the field of cancer therapy. Mitochondria affects apoptosis and innate immunity. Therefore, in this study, mitochondria were inhibited with Tigecycline in stimulating the cytotoxicity of NK cells against TNBC cell lines. MDA-MB-468 and MDA-MB-231 were cultured and treated with IC50 (the half-maximal inhibitory concentration) level of Tigecycline for 48 h and afterward co-cultured with peripheral blood NK cells for 5 h. Lastly, the inhibitory effects of mitochondria on the cytotoxicity of NK cells and apoptosis of TNBC cells were evaluated. Moreover, the expression of apoptotic-related genes was studied. The results showed that mitochondria inhibition increased NK cells cytotoxicity against TNBC cells. Moreover, NK cell/mitochondria inhibition in a combinative form improved apoptosis in TNBC cells by the upregulation of Bad and Bid expression. In conclusion, Tigecycline inhibited mitochondria and sensitized TNBC cells to NK cell therapy. Therefore, mitochondria inhibition could help NK cells function properly.

Tigecycline causes loss of cell viability mediated by mitochondrial OXPHOS and RAC1 in hepatocellular carcinoma cells

BACKGROUND

Despite recent advances in locoregional, systemic, and novel checkpoint inhibitor treatment, hepatocellular carcinoma (HCC) is still associated with poor prognosis. The feasibility of potentially curative liver resection (LR) and transplantation (LT) is limited by the underlying liver disease and a shortage of organ donors. Especially after LR, high recurrence rates present a problem and circulating tumor cells are a major cause of extrahepatic recurrence. Tigecycline, a commonly used glycylcycline antibiotic, has been shown to have antitumorigenic effects and could be used as a perioperative and adjuvant therapeutic strategy to target circulating tumor cells. We aimed to investigate the effect of tigecycline on HCC cell lines and its mechanisms of action.

METHODS

Huh7, HepG2, Hep3B, and immortalized hepatocytes underwent incubation with clinically relevant tigecycline concentrations, and the influence on proliferation, migration, and invasion was assessed in two- and three-dimensional in vitro assays, respectively. Bioinformatic analysis was used to identify specific targets of tigecycline. The expression of RAC1 was detected using western blot, RT-PCR and RNA sequencing. ELISA and flow cytometry were utilized to measure reactive oxygen species (ROS) generation upon tigecycline treatment and flow cytometry to detect alterations in cell cycle. Changes in mitochondrial function were detected via seahorse analysis. RNA sequencing was performed to examine involved pathways.

RESULTS

Tigecycline treatment resulted in a significant reduction of mitochondrial function with concomitantly preserved mitochondrial size, which preceded the observed decrease in HCC cell viability. The sensitivity of HCC cells to tigecycline treatment was higher than that of immortalized non-cancerous THLE-2 hepatocytes. Tigecycline inhibited both migratory and invasive properties. Tigecycline application led to an increase of detected ROS and an S-phase cell cycle arrest. Bioinformatic analysis identified RAC1 as a likely target for tigecycline and the expression of this molecule was increased in HCC cells as a result of tigecycline treatment.

CONCLUSION

Our study provides evidence for the antiproliferative effect of tigecycline in HCC. We show for the first time that this effect, likely to be mediated by reduced mitochondrial function, is associated with increased expression of RAC1. The reported effects of tigecycline with clinically relevant and achievable doses on HCC cells lay the groundwork for a conceivable use of this agent in cancer treatment.

Hierarchy and interconnected networks in the WhiB7 mediated transcriptional response to antibiotic stress in Mycobacterium abscessus

Mycobacterium abscessus is intrinsically resistant to antibiotics effective against other pathogenic mycobacteria largely due to the drug-induced expression of genes that confer resistance. WhiB7 is a major hub controlling the induction of resistance to ribosome-targeting antibiotics. It activates the expression of >100 genes, 7 of which are known determinants of drug resistance; the function of most genes within the regulon is however unknown, but some conceivably encode additional mechanisms of resistance. Furthermore, the hierarchy of gene expression within the regulon, if any, is poorly understood. In the present work we have identified 56 WhiB7 binding sites using chromatin immunoprecipitation sequencing (CHIP-Seq) which accounts for the WhiB7-dependent upregulation of 72 genes, and find that M. abscessus WhiB7 functions exclusively as a transcriptional activator at promoters recognized by σA/σB. We have investigated the role of 18 WhiB7 regulated genes in drug resistance. Our results suggest that while some genes within the regulon (eg. erm41, hflX, eis2 and the ABCFs) play a major role in resistance, others make smaller contributions (eg. MAB_4324c and MAB_1409c) and the observed hypersensitivity ΔMabwhiB7 is a cumulative effect of these individual contributions. Moreover, our CHIP-Seq data implicate additional roles of WhiB7 induced genes beyond antibiotic resistance. Finally, we identify a σH-dependent network in aminoglycoside and tigecycline resistance which is induced upon drug exposure and is further activated by WhiB7 demonstrating the existence of a crosstalk between components of the WhiB7-dependent and -independent circuits.

Study on the Genome and Mechanism of Tigecycline Resistance of a Clinical Chryseobacterium indologenes Strain

Purpose: Chryseobacterium indologenes is a clinically relevant microorganism that has been on the rise, with multidrug-resistant (MDR) strains being reported. C. indologenes carrying tet(X2) has been demonstrated to be resistant to the antibiotic tigecycline, yet, sensitive to all other members of the tetracycline family. This inconsistency in resistance prompts an inquiry into the contribution of tet(X2) to tigecycline resistance in C. indologenes. Materials and Methods: In this study, we report on a comprehensive analysis of the genomic mechanisms underlying tigecycline resistance in a MDR C. indologenes strain (CI3125) that was resistant to tigecycline but sensitive to tetracycline, doxycycline, and minocycline. We used whole-genome sequencing, quantitative reverse transcription PCR, Western blot, antibiotic-degrading tests, and efflux pump inhibiting tests to reveal the mechanism of tigecycline resistance in C. indologenes and elucidate the inconsistency in the antibiotic resistance mechanism for the tetracycline family. Results: Our findings demonstrate that CI3125 carries 60 antibiotic resistance genes distributed on 6 different genetic islands (GIs), with the potential for horizontal transfer. Notably, the tet(X2) gene is located on GI06 of CI3125. Genetic environment analysis of tet(X2) showed that all tet(X2) genes in Flavobacterium and Bacteroides share a conservative and functional ribosome-binding site upstream. Contrary to expectation, our RT-qPCR showed that tet(X2) was not transcribed in CI3125, and Western blot suggested the absence of tet(X2) protein in CI3125. Rather, we demonstrate that minimum inhibitory concentration values for tigecycline decreased two- to eight-folds in the presence of five different efflux pump inhibitors [1-(1-naphthyl- methyl)-piperazine, phenyl-arginine-β-naphthylamide, verapamil, reserpine, and carbonyl cyanide 3-chlorophenylhydrazone]. This finding provides evidence for the involvement of efflux pumps in tigecycline resistance, which is likely to be a universal mechanism among C. indologenes. Our study proposes that the inconsistency in resistance to the tetracycline family in CI3125 may be ascribed to the silence of tet(X2) and the functions of efflux pumps for tigecycline. Conclusions: Overall, our results highlight the importance of genomic approaches in understanding the underlying mechanisms of antibiotic resistance in clinically relevant microorganisms. While tet(X2) in CI3125 is silent, our findings suggest that it may be horizontally spread through GIs. Hence, our findings have significant implications for the management of C. indologenes infections in clinical settings.

Inhibition of mitochondria induces apoptosis and reduces telomere length and activity in acute myeloid leukemia stem cells

Acute myeloid leukemia (AML) is a highly lethal hematological malignancy in adults and children. Abnormal proliferation of leukemia stem cells (LSC) with CD34+ and CD38- phenotypes are the main clinical features of AML. Patients with AML face drug resistance and treatment failure due to a default in stem and progenitor cells. Therefore, defining LSC properties is necessary for targeting leukemia-initiating cells. Mitochondrial mass and activity increase in AML initiating cells compared with normal stem cells. This idea has offered the inhibition of the mitochondrial translation machinery to reduce the number of leukemia-initiating cells in patients with AML Tigecycline is an FDA-approved microbial antibiotic that inhibits oxidative phosphorylation in mitochondria, resulting in the suppression of leukemia cell proliferation with little toxicity to normal cells. Thus, the present study was conducted to evaluate whether LSC is influenced by mitochondrial inhibition. We measured the IC50 of tigecycline in KG-1a AML cell lines. KG-1a AML cell lines were separated into CD34+ and CD34- cells by MACS. In the following, these cells were treated with 20 µM (IC50) tigecycline. The expression of Annexin/PI, Caspase 3, apoptotic genes (BCL2, BCLX, BAX, BAD, and P53) and proteins (P53, BAX, BCL2 and Caspase 9) was evaluated in CD34+ , CD34- and KG-1a AML cells. In addition, the telomere length and expression of hTERT were evaluated in this study. The results indicated that BCl2 (gene and protein) and BCLX gene dramatically decreased. In addition, BAD, BAX, and P53 gene and protein expression significantly increased in CD34+ AML cells compared to CD34- AML cells. The results also suggested that tigecycline induced intrinsic (Cleaved-caspase 9/Pro-Caspase 9 ratio) and p53-mediated apoptosis. Furthermore, hTERT gene expression and telomere length decreased in the tigecycline-treated groups. Taken together, our findings indicate that inhibition of mitochondrial activity with tigecycline can induce apoptosis in cancer stem cells and can be used as a novel method for cancer therapy.

Clinical efficacy and safety of tigecycline based on therapeutic drug monitoring for carbapenem-resistant Gram-negative bacterium pneumonia in intensive care units

BACKGROUND

We investigated the associations between the different doses of tigecycline, its efficacy and safety, and the role of tigecycline therapeutic drug monitoring for patients in the intensive care unit.

METHODS

This study was a single-center cohort including patients infected with multidrug-resistant Acinetobacter baumannii (MDR-AB) and multidrug-resistant Klebsiella pneumoniae (MDR-KP) causing pulmonary infections. The steady-state plasma concentration after tigecycline administration was determined by High-Performance Liquid Chromatography (HPLC) in patients admitted to the ICU between October 2020 and December 2021. Multivariate analyses of tigecycline's clinical efficacy and safety were performed to control confounding factors.

RESULTS

For this study, we included 45 patients and 45 blood samples to determine steady-state trough concentrations of tigecycline. All patients were divided into the High Dose (HD) and Standard Dose (SD) groups. The median trough concentration of tigecycline was 0.56 μg/mL in the HD group, which was higher than in the SD group (0,21 μg/mL), p = 0.000. There was no significant difference between the two groups of patients in terms of bacterial eradication rate, mortality rate, and clinical efficacy. Multiple regression analysis showed that the ICU days were correlated with mortality OR 1.030(1.005-1.056), p = 0.017. APACHE II was significantly associated with clinical efficacy OR 0.870(0.755-1.002), p = 0.045. The level of fibrinogen decline in the HD group was significantly higher than in the SD group (-3.05 ± 1.67 vs -1.75 ± 1.90), p = 0.038. We identified that age and tigecycline treatment duration influenced fibrinogen decline.

CONCLUSIONS

Tigecycline plasma concentrations are significantly increased when using a high dose. However, the plasma concentration of tigecycline is not correlated with clinical efficacy and adverse reactions. Fibrinogen decline appears to be related to the patient's age and days of tigecycline. Large sample data are still needed to confirm the clinical guidance significance of tigecycline TDM.

Safety and effectiveness of tigecycline combination therapy in renal transplant patients with infection due to carbapenem-resistant gram-negative bacteria

Background

Carbapenem-resistant gram-negative bacterial (CRGNB) infections are increasing among kidney transplant recipients, and effective therapeutic options are limited. This study aimed to investigate the efficacy and adverse events associated with combination therapy tigecycline in renal transplant patients with CRGNB infections.

Methods

This study retrospectively analyzed 40 Chinese patients with confirmed or suspected CRGNB infections who received tigecycline therapy. The patients' case features and clinical and microbiological data were analyzed.

Results

A total of 40 renal transplant recipients received tigecycline therapy for a median duration of 9 (range, 3-25) days. CRGNB isolates were obtained from the organ preservation solution of the donor kidney in 28 patients, with confirmed transmission in 4 patients. Infections were detected in the bloodstream, urinary tract, sputum, and wound. The most prevalent isolates were Klebsiella pneumoniae (75%, 30/40), Acinetobacter baumannii (15%, 6/40), and Escherichia coli (10%, 4/40). A clinical response was observed in 32 (80%) patients. The 28-day all-cause mortality rate was 7.5% (3/40), while the one-year all-cause mortality rate was 2.5% (1/40). While one patient died owing to severe pancreatitis, no serious adverse events related to tigecycline therapy were reported. However, multiple indices of liver function and pancreatitis precursors increased after treatment with tigecycline compared to before treatment.

Conclusion

Tigecycline therapy appears to be well tolerated in renal transplant recipients with multidrug-resistant bacterial infections. Nevertheless, attention should be paid to adverse reactions related to tigecycline therapy, especially gastrointestinal reactions, and the related laboratory tests should be closely monitored.

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.

Characterisation of a Novel Tigecycline Resistance Gene tet(X22) and its Coexistence with blaNDM-1 in a Pseudomonas caeni Isolate

OBJECTIVES

The emergence of pathogens that are resistant to both tigecycline and carbapenem poses a threat to public health globally. Continuous emergence of novel tet(X) variants accelerates the tigecycline resistance crisis. This study aimed to characterise the novel tigecycline resistance gene tet(X22) and its coexistence with carbapenem resistance gene blaNDM-1 in Pseudomonas caeni.

METHODS

This P. caeni isolate co-harbouring tet(X22) and blaNDM-1 was systematically investigated using antimicrobial susceptibility testing, conjugation assays, genome sequencing, bioinformatic analyses, cloning of tet(X22) and functional analysis, and protein structure prediction.

RESULTS

The carbapenem-resistant and tigecycline-resistant P. caeni isolate CE14 was obtained from chicken faeces in 2022. CE14 carried multiple antibiotic resistance genes, including the novel tet(X22) and blaNDM-1. Tet(X22) exhibited 64.72-90.48% amino acid identity with other variants [Tet(X) to Tet(X21)]. Cloning of the gene tet(X22) and protein structure prediction revealed that Tet(X22) confers resistance to tetracyclines, including tigecycline. tet(X22) and blaNDM-1 were located in two multidrug-resistant regions of the chromosome.

CONCLUSIONS

The occurrence of the novel ISCR2-flanked tet(X22) in P. caeni suggests that the tet(X) variant has adapted to new hosts and may widely spread to further expand the host range. The future global spread of such pathogens co-harbouring tet(X) and blaNDM variants needs to be continuously monitored according to the One Health approach.