Genomic characterization revealing the high rate of tet(X4)-positive Escherichia coli in animals associated with successful genetic elements.

Introduction: The rapid spread of plasmid-mediated tet(X4) conferring high tigecycline resistance poses a significant threat to public health. Escherichia coli as the most common pathogen which carries tet(X4) has been widely disseminated in China. Thus, comprehensive investigations are required to understand the mechanism of transmission of tet(X4)-positive E. coli. Methods: In this study, a total of 775 nonduplicate samples were collected in Guangdong, China from 2019 to 2020. We screened for tet(X4)-positive E. coli by PCR amplification and species identification. Furthermore, we analyzed the phylogenetics and genetic context of tet(X4)-positive E. coli through whole-genome sequencing and long-reads sequencing. Results: Overall, 146 (18.84%) tet(X4)-positive E. coli were isolated, comprising 2 isolates from humans and 144 isolates from pigs. The majority of tet(X4)-positive E. coli exhibited resistance to multiple antibiotics but all of them were susceptible to amikacin and colistin. Phylogenetic analysis showed that ST877, ST871, and ST195 emerged as the predominant sequence types in tet(X4)-positive E. coli. Further analysis revealed various genetic environments associated with the horizontal transfer of tet(X4). Notably, a 100-kbp large fragment insertion was discovered downstream of tet(X4), containing a replicon and a 40-kbp gene cluster for the bacterial type IV secretion system. Discussion: The high colonization rate of tet(X4)-positive E. coli in animals suggests that colonization as a key factor in its dissemination to humans. Diverse genetic context may contribute to the transfer of tet(X4). Our findings underline the urgent need for controlling the spread of plasmid-mediated tigecycline resistance.

Risk factors for bloodstream infection among patients admitted to an intensive care unit of a tertiary hospital of Shanghai, China.

Blood flow infections (BSIs) is common occurrences in intensive care units (ICUs) and are associated with poor prognosis. The study aims to identify risk factors and assess mortality among BSI patients admitted to the ICU at Shanghai Ruijin hospital north from January 2022 to June 2023. Additionally, it seeks to present the latest microbiological isolates and their antimicrobial susceptibility. Independent risk factors for BSI and mortality were determined using the multivariable logistic regression model. The study found that the latest incidence rate of BSI was 10.11%, the mortality rate was 35.21% and the mean age of patients with BSI was 74 years old. Klebsiella pneumoniae was the predominant bacterial isolate. Logistic multiple regression revealed that tracheotomy, tigecycline, gastrointestinal bleeding, shock, length of hospital stay, age and laboratory indicators (such as procalcitonine and hemoglobin) were independent risk factors for BSI. Given the elevated risk associated with use of tracheotomy and tigecycline, it underscores the importance of the importance of cautious application of tracheostomy and empirical antibiotic management strategies. Meanwhile, the independent risk factors of mortality included cardiovascular disease, length of hospital stay, mean platelet volume (MPV), uric acid levels and ventilator. BSI patients exhibited a significant decrease in platelet count, and MPV emerged as an independent factor of mortality among them. Therefore, continuous monitoring of platelet-related parameters may aid in promptly identifying high-risk patients and assessing prognosis. Moreover, monitoring changes in uric acid levels may serve as an additional tool for prognostic evaluation in BSI patients.

AcrAB-TolC efflux pump overexpression and tet(A) gene mutation increase tigecycline resistance in Klebsiella pneumoniae.

Tigecycline-non-susceptible Klebsiella pneumoniae (TNSKP) is increasing and has emerged as a global public health issue. However, the mechanism of tigecycline resistance remains unclear. The objective of this study was to investigate the potential role of efflux pump system in tigecycline resistance. 29 tigecycline-non-susceptible Klebsiella pneumoniae (TNSKP) strains were collected and their minimum inhibitory concentrations (MIC) were determined by the broth microdilution method. The ramR, acrR, rpsJ, tet(A), and tet(X) were amplified by polymerase chain reaction (PCR). The mRNA expression of different efflux pump genes and regulator genes were analyzed by real-time PCR. Additionally, KP14 was selected for genome sequencing. KP14 genes without acrB, oqxB, and TetA were modified using suicide plasmids and MIC of tigecycline of KP14 with target genes knocked out was investigated. It was found that MIC of tigecycline of 20 out of the 29 TNSKP strains decreased by over four folds once combined with phenyl-arginine-ß-naphthylamide dihydrochloride (PaßN). Most strains exhibited upregulation of AcrAB and oqxAB efflux pumps. The strains with acrB, oqxB, and tetA genes knocked out were constructed, wherein the MIC of tigecycline of KP14∆acrB and KP14∆tetA was observed to be 2 µg/mL (decreased by 16 folds), the MIC of tigecycline of KP14ΔacrBΔTetA was 0.25 µg/mL (decreased by 128 folds), but the MIC of tigecycline of KP14∆oqxB remained unchanged at 32 µg/mL. The majority of TNSKP strains demonstrated increased expression of AcrAB-TolC and oqxAB, while certain strains showed mutations in other genes associated with tigecycline resistance. In KP14, both overexpression of AcrAB-TolC and tet(A) gene mutation contributed to the mechanism of tigecycline resistance.

Fitness cost of tet(A) type I variant-mediated tigecycline resistance in Klebsiella pneumoniae.

OBJECTIVE: The aim of the present study is to explore the impact of the tet(A) type I variant (tetA-v1) on its fitness effect in Klebsiella pneumoniae. METHODS: Clinical K. pneumoniae strains were utilized as parental strains to generate strains carrying only the plasmid vector (pBBR1MCS-5) or the tetA-v1 recombinant plasmid (ptetA-v1). Antimicrobial susceptibility testing was conducted to estimate the contribution of tetA-v1 to drug resistance. Plasmid stability was evaluated by serial passage over 10 consecutive days in the absence of tigecycline. Biological fitness was examined through growth curve analysis, in vitro competition assays and a neutropenic mouse thigh infection model. RESULTS: A 2-4-fold increase in tigecycline MIC was observed following the acquisition of tetA-v1. Without tigecycline treatment, the stability of ptetA-v1 plasmids has been decreasing since day 1. The ptetA-v1 plasmid in Kp89, Kp91, and Kp93 exhibited a decrease of about 20% compared to the pBBR1MCS-5 plasmid. The acquisition of the tetA-v1 gene could inhibit the growth ability of K. pneumoniae strains both in vitro and in vivo. tetA-v1 gene imposed a fitness cost in K. pneumoniae, particularly in the CRKP strain Kp51, with a W value of approximately 0.56. CONCLUSION: The presence of tetA-v1 is associated with a significant fitness cost in K. pneumoniae in the absence of tigecycline, both in vitro and in vivo.

Evaluation of role of Tigecycline among clinically significant multidrug resistant pathogens from a tertiary care hospital.

Background: Tigecycline, a glycylcycline antibiotic is a promising option for the treatment of single or multidrug resistant pathogens. The aim of the study was to evaluate the in-vitro Tigecycline susceptibility of various pathogens from clinical samples received at the tertiary care hospitals in South India. Methods: The analysis of specimens from patients admitted were carried out in this prospective cross sectional study. The identification and antimicrobial susceptibility testing was performed by semi-automated Vitek 2 systems and Kirby Bauer method. Pattern of data analysis was done by descriptive statistics. Results: Among 2574 isolates, 812 isolates were Gram positive pathogens and 1762 isolates were Gram negative pathogens. Resistance to Tigecycline was more common among Gram negative pathogens (18.62%) in comparison to the Gram positive pathogens (0.49%). Among 740 Extended Spectrum Beta Lactamases (ESBL) producers such as Klebsiella species & E coli, 629 isolates were susceptible, and 93 isolates were resistant to the tigecycline. All the methicillin resistant Staphylococcus aureus (MRSA) isolates were susceptible to tigecycline. Conclusion: Multidrug resistant (MDR) pathogens like Acinetobacter species, and Klebsiella species were found to be highly effective in vitro to tigecycline for elimination of infections caused by both Gram positive and Gram negative pathogens. The use of combination therapy becomes crucial to prevent the development of Pan Drug resistance.

Tigecycline-induced pancreatitis in a patient with recurrent malignancy: a case report and literature review.

Introduction and importance: Drug-induced pancreatitis is an important health issue that makes a minority of causes of acute pancreatitis. Tigecycline-induced pancreatitis is a rare condition with poorly understood mechanism and has a small incident compared to other causes of pancreatitis. Case presentation: The authors present a case of a 39-year-old female patient with acute pancreatitis. Tigecycline was the suspected culprit by exclusion. The patient was managed by keeping her nill per os, rehydration, pain management and discontinuation of the drug. The patient improved gradually. Clinical discussion: Tigecycline-induced acute pancreatitis is a rare but known complication that is mostly seen in patients with chronic renal insufficiency combined with high dose of administration. Onset is usually within 14 days of initiation. Discontinuation of the drug is the most effective intervention in addition to supportive management. Conclusion: Acute pancreatitis should be suspected in any patient presenting with vomiting, abdominal pain and acidosis while on tigecycline. Monitoring of amylase and lipase can be beneficial especially in those with chronic renal insufficiency or those receiving a high dose.

Optimizing Antibiotic Therapy for Stenotrophomonas maltophilia Infections in Critically Ill Patients: A Pharmacokinetic/Pharmacodynamic Approach.

Stenotrophomonas maltophilia is an opportunistic, multidrug-resistant non-fermentative Gram-negative bacillus, posing a significant challenge in clinical treatment due to its numerous intrinsic and acquired resistance mechanisms. This study aimed to evaluate the adequacy of antibiotics used for the treatment of S. maltophilia infections in critically ill patients using a pharmacokinetic/pharmacodynamic (PK/PD) approach. The antibiotics studied included cotrimoxazole, levofloxacin, minocycline, tigecycline, cefiderocol, and the new combination aztreonam/avibactam, which is not yet approved. By Monte Carlo simulations, the probability of target attainment (PTA), the PK/PD breakpoints, and the cumulative fraction of response (CFR) were estimated. PK parameters and MIC distributions were sourced from the literature, the European Committee on Antimicrobial Susceptibility Testing (EUCAST), and the SENTRY Antimicrobial Surveillance Program collection. Cefiderocol 2 g q8h, minocycline 200 mg q12h, tigecycline 100 mg q12h, and aztreonam/avibactam 1500/500 mg q6h were the best options to treat empirically infections due to S. maltophilia. Cotrimoxazole provided a higher probability of treatment success for the U.S. isolates than for European isolates. For all antibiotics, discrepancies between the PK/PD breakpoints and the clinical breakpoints defined by EUCAST (or the ECOFF) and CLSI were detected.

Efficiency of polymyxin B treatment against nosocomial infection: a systematic review and meta-analysis.

Background: Some cohort studies have explored the effects and safety of polymyxin B (PMB) in comparison to other antibiotics for the treatment of nosocomial infections, yielding inconsistent results. This systematic review aims to explore the effectiveness and safety of PMB and compared it with other antibiotics. Methods: A systematic literature search was conducted in PubMed, Embase, the Cochrane Library, and Web of Science, searching specific terms to identify quantitative cohort studies or RCTs that compared the effects of PMB with other antibiotics in terms of their efficacy and safety. The Newcastle-Ottawa Scale (NOS) was conducted to evaluate the risk of bias of observational studies. Odds ratios with 95% confidence intervals were used for outcome assessment. We evaluated heterogeneity using the I 2 test. Results: A total of 22 observational trials were included in the analysis. The PMB group had a higher mortality rate compared to the control group (odds ratio: 1.84, 95% CI: 1.36-2.50, p<0.00001, I 2 = 73%). while, the ceftazidime-avibactam group demonstrated a distinct advantage with lower mortality rates, despite still exhibiting high heterogeneity (odds ratio 2.73, 95% confidence interval 1.59-4.69; p = 0.0003; I 2 = 53%). Additionally, the PMB group had a lower nephrotoxicity rate compared to the colistin group but exhibited high heterogeneity in the results (odds ratio 0.58, 95% CI 0.36-0.93; p = 0.02; I 2 = 73%). Conclusion: In patients with nosocomial infections, PMB is not superior to other antibiotics in terms of mortality, specifically when compared to ceftazidime-avibactam. However, PMB demonstrated an advantage in terms of nephrotoxicity compared to colistin.

A novel multivariate logistic model for predicting risk factors of failed treatment with carbapenem-resistant Acinetobacter baumannii ventilator-associated pneumonia.

Background: This study aimed to explore the risk factors for failed treatment of carbapenem-resistant Acinetobacter baumannii ventilator-associated pneumonia (CRAB-VAP) with tigecycline and to establish a predictive model to predict the incidence of failed treatment and the prognosis of CRAB-VAP. Methods: A total of 189 CRAB-VAP patients were included in the safety analysis set from two Grade 3 A national-level hospitals between 1 January 2022 and 31 December 2022. The risk factors for failed treatment with CRAB-VAP were identified using univariate analysis, multivariate logistic analysis, and an independent nomogram to show the results. Results: Of the 189 patients, 106 (56.1%) patients were in the successful treatment group, and 83 (43.9%) patients were in the failed treatment group. The multivariate logistic model analysis showed that age (OR = 1.04, 95% CI: 1.02, 1.07, p = 0.001), yes. of hypoproteinemia (OR = 2.43, 95% CI: 1.20, 4.90, p = 0.013), the daily dose of 200 mg (OR = 2.31, 95% CI: 1.07, 5.00, p = 0.034), yes. of medication within 14 days prior to surgical intervention (OR = 2.98, 95% CI: 1.19, 7.44, p = 0.019), and no. of microbial clearance (OR = 0.31, 95% CI: 0.14, 0.70, p = 0.005) were risk factors for the failure of tigecycline treatment. Receiver operating characteristic (ROC) analysis showed that the AUC area of the prediction model was 0.745 (0.675-0.815), and the decision curve analysis (DCA) showed that the model was effective in clinical practice. Conclusion: Age, hypoproteinemia, daily dose, medication within 14 days prior to surgical intervention, and microbial clearance are all significant risk factors for failed treatment with CRAB-VAP, with the nomogram model indicating that high age was the most important factor. Because the failure rate of CRAB-VAP treatment with tigecycline was high, this prediction model can help doctors correct or avoid risk factors during clinical treatment.

Efficacy of Tamoxifen Metabolites in Combination with Colistin and Tigecycline in Experimental Murine Models of Escherichia coli and Acinetobacter baumannii.

This study aimed to evaluate the potential of tamoxifen and N-desmethyltamoxifen metabolites as therapeutic agents against multidrug-resistant Escherichia coli and Acinetobacter baumannii, using a repurposing approach to shorten the time required to obtain a new effective treatment against multidrug-resistant bacterial infections. Characterisation and virulence studies were conducted on E. coli (colistin-susceptible C1-7-LE and colistin-resistant MCR-1+) and A. baumannii (tigecycline-susceptible Ab#9 and tigecycline-resistant Ab#186) strains. The efficacy of the metabolite mix (33.3% each) and N-desmethyltamoxifen in combination with colistimethate sodium (CMS) or tigecycline was evaluated in experimental models in mice. In the pneumonia model, N-desmethyltamoxifen exhibited significant efficacy against Ab#9 and both E. coli strains, especially E. coli MCR-1+ (-2.86 log10 CFU/g lungs, -5.88 log10 CFU/mL blood, and -50% mortality), and against the Ab#186 strain when combined with CMS (-2.27 log10 CFU/g lungs, -2.73 log10 CFU/mL blood, and -40% mortality) or tigecycline (-3.27 log10 CFU/g lungs, -4.95 log10 CFU/mL blood, and -50% mortality). Moreover, the metabolite mix in combination with both antibiotics decreased the bacterial concentrations in the lungs and blood for both A. baumannii strains. In the sepsis model, the significant efficacy of the metabolite mix was restricted to the colistin-susceptible E. coli C1-7-LE strain (-3.32 log10 CFU/g lung, -6.06 log10 CFU/mL blood, and -79% mortality). N-desmethyltamoxifen could be a new therapeutic option in combination with CMS or tigecycline for combating multidrug-resistant GNB, specifically A. baumannii.

Tigecycline Opposes Bortezomib Effect on Myeloma Cells Decreasing Mitochondrial Reactive Oxygen Species Production.

Multiple myeloma is an incurable plasma cell malignancy. Most patients end up relapsing and developing resistance to antineoplastic drugs, like bortezomib. Antibiotic tigecycline has activity against myeloma. This study analyzed tigecycline and bortezomib combination on cell lines and plasma cells from myeloma patients. Apoptosis, autophagic vesicles, mitochondrial mass, mitochondrial superoxide, cell cycle, and hydrogen peroxide were studied by flow cytometry. In addition, mitochondrial antioxidants and electron transport chain complexes were quantified by reverse transcription real-time PCR (RT-qPCR) or western blot. Cell metabolism and mitochondrial activity were characterized by Seahorse and RT-qPCR. We found that the addition of tigecycline to bortezomib reduces apoptosis in proportion to tigecycline concentration. Supporting this, the combination of both drugs counteracts bortezomib in vitro individual effects on the cell cycle, reduces autophagy and mitophagy markers, and reverts bortezomib-induced increase in mitochondrial superoxide. Changes in mitochondrial homeostasis and MYC upregulation may account for some of these findings. These data not only advise to avoid considering tigecycline and bortezomib combination for treating myeloma, but caution on the potential adverse impact of treating infections with this antibiotic in myeloma patients under bortezomib treatment.

Genomic insights into in-ICU emergence of last-resort antimicrobial resistance in a rare, carbapenem resistant, ST16 Klebsiella pneumoniae strain from Jodhpur, India.

OBJECTIVES: To investigate the genomic differences between two extensively drug resistant, ST16 strains of Klebsiella pneumoniae recovered from patients in the same ICU, one of which was colistin resistant. METHODS: Antimicrobial susceptibilities of the isolates were determined using VITEK-2. Hybrid assemblies for both strains were generated using Oxford Nanopore and Illumina technologies. The sequence type, capsule type, O-locus type, antimicrobial resistance determinants and plasmids carried by the isolates were inferred from the genome sequence. The phylogenetic placement, antimicrobial resistance, and virulence determinants of the isolates relative to a collection (n = 871) of ST16 isolates were assessed. RESULTS: Both BC16, a colistin-resistant blood stream isolate and U23, a colistin-sensitive urinary isolate displayed near-identical antimicrobial resistance profiles and genome sequences with varying plasmid profiles. The BC16 genome only had 21 SNPs relative to U23 and belonged to the same capsule, O-antigen locus and multi-locus sequence types. The mgrB locus in BC16 was disrupted by an IS5 element. Phylogenetically, U23 and BC16 were placed on a clade with 4 strains belonging to K-type K48 and O-type O2a as opposed to majority (n = 807) of the strains (K-type K51 and O-type O3b). CONCLUSIONS: BC16 was a colistin resistant derivative of U23, which evolved colistin resistance by an IS5-mediated disruption of the mgrB locus, likely during treatment of the index patient with colistin in the ICU. The strains belong to a rare subtype of ST16 with unique capsular and O-antigen types underscoring the utility of genomic surveillance networks and open-access genomic surveillance data in tracking problem clones.

Prevalence and genomic characterization of clinical Escherichia coli strains that harbor the plasmid-borne tet(X4) gene in China.

The tigecycline resistance gene tet(X4) has been widely reported in animals and animal products in some Asian countries including China in recent years but only sporadically detected in human. In this study, we investigated the prevalence and genetic features of tet(X4)-positive clinical E. coli strains. A total of 462 fecal samples were collected from patients in four hospitals located in four provinces in China in 2023. Nine tet(X4)-positive E. coli strains were isolated and subjected to characterization of their genetic and phenotypic features by performing antimicrobial susceptibility test, whole-genome sequencing, bioinformatic and phylogenetic analysis. The majority of the test strains were found to exhibit resistance to multiple antimicrobial agents including tigecycline but remained susceptible to colistin and meropenem. A total of seven different sequence types (STs) and an unknown ST type were identified among the nine tet(X4)-positive strains. Notably, the tet(X4) gene in six out of these nine tet(X4)-positive E. coli strains was located in a IncFIA-HI1A-HI1B hybrid plasmid, which was an tet(X4)-bearing epidemic plasmid responsible for dissemination of the tet(X4) gene in China. Furthermore, the tet(X4) gene in four out of nine tet(X4)-positive E. coli isolates could be successfully transferred to E. coli EC600 through conjugation. In conclusion, this study characterized the epidemic tet(X4)-bearing plasmids and tet(X4)-associated genetic environment in clinical E. coli strains, suggested the importance of continuous surveillance of such tet(X4)-bearing plasmids to control the increasingly widespread dissemination of tigecycline-resistant pathogens in clinical settings in China.

Repurposing harmaline as a novel approach to reverse tmexCD1-toprJ1-mediated tigecycline resistance against klebsiella pneumoniae infections.

BACKGROUND: A novel plasmid-mediated resistance-nodulation-division (RND) efflux pump gene cluster tmexCD1-toprJ1 in Klebsiella pneumoniae tremendously threatens the use of convenient therapeutic options in the post-antibiotic era, including the "last-resort" antibiotic tigecycline. RESULTS: In this work, the natural alkaloid harmaline was found to potentiate tigecycline efficacy (4- to 32-fold) against tmexCD1-toprJ1-positive K. pneumoniae, which also thwarted the evolution of tigecycline resistance. Galleria mellonella and mouse infection models in vivo further revealed that harmaline is a promising candidate to reverse tigecycline resistance. Inspiringly, harmaline works synergistically with tigecycline by undermining tmexCD1-toprJ1-mediated multidrug resistance efflux pump function via interactions with TMexCD1-TOprJ1 active residues and dissipation of the proton motive force (PMF), and triggers a vicious cycle of disrupting cell membrane integrity and metabolic homeostasis imbalance. CONCLUSION: These results reveal the potential of harmaline as a novel tigecycline adjuvant to combat hypervirulent K. pneumoniae infections.

Real-world safety profile of tetracyclines in children younger than 8 years old: an analysis of FAERS database and review of case report.

BACKGROUND: The study aims to obtain the real-world safety profile of tetracyclines in children younger than 8 years old and provide reference for clinical drug applications. RESEARCH DESIGN AND METHODS: We made a disproportionality analysis of the FDA Adverse Event Reporting System (FAERS) database through OpenVigil 2 and conducted a review of case reports regarding adverse drug reactions (ADRs) of tetracyclines in children younger than 8-year-old. RESULTS: FAERS analysis identified 32 ADRs of tetracyclines in children younger than 8-year-old. Respiratory, thoracic, and mediastinal disorders contained the most frequent ADRs among all system organ classes (SOCs). The top three positive signals with the highest proportional reporting ratio (PRR) were laryngeal injury, Horner's syndrome and methaemoglobinaemia. Sixteen published tetracyclines-associated cases in children younger than 8-year-old were identified in the literature, concentrating in three SOCs. Gastrointestinal disorders were the most commonly reported cases (n = 12). CONCLUSIONS: Several ADRs were newly reported only in children younger than 8-year-old in our research, including Horner's syndrome and methemoglobinemia. We recommended that the clinical practitioners should pay attention to the ADRs both in instruction and beyond the label. Take close care of children and timely intervene when the treatment is inevitable.

Molecular epidemiology and resistance mechanisms of tigecycline-non-susceptible Acinetobacter baumannii isolated from a tertiary care hospital in Chongqing, China.

We studied 34 isolates of Tigecycline-Non-Susceptible A. baumannii (TNAB) obtained from clinical specimens at a large tertiary care hospital in Chongqing, China. These 34 strains belonged to 8 different clones including ST195 (35.3%) and ST208 (17.7%). EBURST analysis found that these 8 ST types belonged to the Clonal Complex 92. Tigecycline resistance-associated genes adeR, adeS, adeL, adeN, rrf, rpsJ, and trm were detected in most strains. The expression level of the resistance-nodulation-cell division (RND) efflux pumps in TNAB strains was higher than the reference strain ATCC19606. 58.8% of strains had a decrease in the tigecycline minimum inhibitory concentration (MIC) after the addition of carbonyl cyanide 3-chlorophenylhydrazone (CCCP). The TNAB strains in our hospital have a high degree of affinity and antibiotic resistance. Regular surveillance should be conducted to prevent outbreaks of TNAB epidemics.

Evaluation of the in vitro susceptibility of clinical isolates of NDM-producing Klebsiella pneumoniae to new antibiotics included in a treatment regimen for infections.

Background: Due to the growing resistance to routinely used antibiotics, the search for new antibiotics or their combinations with effective inhibitors against multidrug-resistant microorganisms is ongoing. In our study, we assessed the in vitro drug susceptibility of Klebsiella pneumoniae strains producing New Delhi metallo-ß-lactamases (NDM) to antibiotics included in the Infectious Diseases Society of America (IDSA) and European Society of Clinical Microbiology and Infectious Diseases (ESCMID) recommendations. Methods: A total of 60 strains of NDM-producing K. pneumoniae were obtained from different patients hospitalized at the 4th Military Hospital in Wroclaw between 2019 and 2022 and subjected to drug susceptibility to selected antibiotics, including the effects of drug combinations. Results: Among the tested antibiotics, the highest sensitivity (100%) was observed for cefiderocol, eravacycline (interpreted according to the European Committee on Antimicrobial Susceptibility Testing [EUCAST]), and tigecycline. Sensitivity to intravenous fosfomycin varied depending on the method used. Using the "strip stacking" method, determining cumulative sensitivity to ceftazidime/avibactam and aztreonam demonstrated 100% in vitro sensitivity to this combination among the tested strains. Conclusion: The in vitro susceptibility assessment demonstrated that, the best therapeutic option for treating infections caused by carbapenemase-producing strains seems to be a combination of ceftazidime/avibactam with aztreonam. Due to the safety of using both drugs, cost effectiveness, and the broadest indications for use among the tested antibiotics, this therapy should be the first-line treatment for carbapenemase-producing Enterobacterales infections. Nevertheless, a comprehensive evaluation of the efficacy of treating infections caused by NDM-producing K. pneumoniae strains should include not only in vitro susceptibility assessment but also an analysis of clinical cases.

Molecular mechanisms of tigecycline-resistance among Enterobacterales.

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

Promoter regulatory mode evolution enhances the high multidrug resistance of tmexCD1-toprJ1.

Antibiotic resistance could rapidly emerge from acquiring the mobile antibiotic resistance genes, which are commonly evolved from an intrinsic gene. The emergence of the plasmid-borne mobilized efflux pump gene cluster tmexCD1-toprJ1 renders the last-resort antibiotic tigecycline ineffective, although its evolutionary mechanism remains unclear. In this study, we investigate the regulatory mechanisms of the progenitor NfxB-MexCD-OprJ, a chromosomally encoded operon that does not mediate antibiotic resistance in the wild-type version, and its homologs, TNfxB1-TMexCD1-TOprJ1 mediating high-level tigecycline resistance, and TNfxB3-TMexCD3-TOprJ1. Mechanistic studies demonstrated that in nfxB-mexCD-oprJ, MexCD expression was under a weaker promoter, PmexC and inhibited by a strong repressor NfxB. For tmexCD1-toprJ1, TMexCD1 was highly expressed owing to the presence of a strong promoter, PtmexC1, and an inactive suppressor, TNfxB1, with a T39R mutation that rendered it unable to bind to promoter DNA. In tnfxB3-tmexCD3-toprJ1b, TMexCD3 expression was intermediate because of the local regulator TNfxB3, which binds to two inverted repeat sequences of PtmexC. Additionally, TNfxB3 exhibited lower protein expression and weaker DNA binding affinity than its ancestor NfxB, together with their promoter activities difference explaining the different expression levels of tmexCD-toprJ homologs. Distinct fitness burdens on these homologs-carrying bacteria were observed due to the corresponding expression level, which might be associated with their global prevalence. In summary, our data depict the mechanisms underlying the evolution and dissemination of an important mobile antibiotic resistance gene from an intrinsic chromosomal gene.IMPORTANCEAs antibiotic resistance seriously challenges global health, tigecycline is one of the few effective drugs in the pipeline against infections caused by multidrug-resistant pathogens. Our previous work identified a novel tigecycline resistance efflux pump gene cluster tmexCD1-toprJ1 in animals and humans, together with its various variants, a rising clinical concern. Herein, this study focused on how the local regulation modes of tmexCD1-toprJ1 evolved to a highly expressed efflux pump. Through comparative analysis between three tnfxB-tmexCD-toprJ homologs and their progenitor nfxB-mexCD-oprJ, modes, we demonstrated the evolutionary dynamics from a chromosomal silent gene to an active state. We found the de-repression of the local regulator and an increase of the promoter activity work together to promote a high production of drug efflux machines and enhance multidrug resistance. Our findings revealed that TMexCD1-TOprJ1 adopts a distinct evolutionary path to achieve higher multidrug resistance, urgently needing tight surveillance.