Synergistic Antibacterial Effects of Meropenem in Combination with Aminoglycosides against Carbapenem-Resistant Escherichia coli Harboring blaNDM-1 and blaNDM-5

Mechanisms, therapeutic strategies, and emerging therapeutic alternatives for carbapenem resistance in Gram-negative bacteria

Carbapenem-resistant Gram-negative bacteria (CR-GNB) have experienced an alarming surge in prevalence in recent years, escalating into a critical global healthcare crisis. As carbapenems represent the last line of defense against such pathogens, infections caused by CR-GNB have become increasingly challenging to treat, given the restricted therapeutic options and heightened mortality risks. The discovery and development of alternative therapeutic strategies that present novel avenues against multi-drug-resistant organisms are gaining increased attention, presenting a pressing need for innovative solutions. Our comprehensive review delves into the multifaceted landscape of carbapenem resistance in Gram-negative bacteria in response to this urgent challenge. The scope of this review aims to provide an up-to-date and in-depth exploration regarding the mode of action of carbapenem and the resisting mechanisms of carbapenem in GNB. Additionally, it discusses the state of the art of some clinical therapies for the treatment of infections caused by CR-GNB. Moreover, it describes several combinational and alternative therapies to combat CR-GNB, including the computational approach of "molecular docking". In light of the conclusions of this review, we call for the implementation of these strategies to develop comprehensive approaches to mitigate carbapenem resistance in Gram-negative bacteria.

Combined therapeutic option for NDM-producing Serratia Marcescens - an in vitro study from clinical samples

BACKGROUND

Treating NDM-producing bacteria poses a significant challenge, especially for those bacteria inherently resistant to polymyxin, such as Serratia marcescens, necessitating combined therapies.

OBJECTIVE

To assess in vitro the synergistic effect of different antimicrobial combinations against NDM-producing S. marcescens.

METHODS

Four clinical isolates were tested with various antibiotic combinations: polymyxin, amikacin, meropenem, and aztreonam. Concentrations used were those maximized by pharmacokinetic and pharmacodynamic assessments. Synergy evaluation involved a static macrodilution test followed by a time-kill curve assay.

RESULTS

All four isolates demonstrated resistance according to CLSI and EUCAST standards for the tested antibiotics (polymyxin, amikacin, meropenem, and aztreonam). In the macrodilution synergy test, the combination of aztreonam and amikacin was active in 2 out of 4 isolates within 24 h, and polymyxin with meropenem in only one isolate, despite of intrinsic resistance to polymyxin. However, time-kill curve analysis revealed no synergism or additive effect for combinations with the tested antimicrobials.

CONCLUSION

Combinations of polymyxin, meropenem, aztreonam, and amikacin at doses optimized by pharmacokinetic/pharmacodynamic were insufficient to demonstrate any synergism in NDM-producing S. marcescens isolates in time-kill curves.

In Vitro Synergistic Effect of Lefamulin with Doxycycline, Rifampin, and Quinupristin/Dalfopristin Against Enterococci

The widespread resistance of enterococci to many commonly used antimicrobial agents is a growing concern. Given that the current treatment options for enterococcal infections are limited, the discovery of new therapies, including combination therapies, is necessary. We evaluated double-drug combinations of lefamulin with doxycycline, rifampin, and quinupristin/dalfopristin for in vitro synergy against strains of Enterococcus faecium (E. faecium) and Enterococcus faecalis (E. faecalis) by using checkerboard and time-kill assays. In the checkerboard assay, the synergistic effect of lefamulin with doxycycline and rifampin was observed in 29 (85.3%) and 33 (97.1%) of the 34 different E. faecium strains tested, respectively. These combinations also showed synergistic effects against 17 (94.4%) of the 18 different vancomycin-resistant E. faecium strains. Among the 33 different E. faecalis strains, the combination of lefamulin with doxycycline, quinupristin/dalfopristin, and rifampin displayed synergistic effects in 31 (93.9%), 26 (78.8%), and 20 (60.6%) strains, respectively. No antagonism was observed in any of the combinations. The time-kill assay confirmed the synergistic effects of all these combinations. These synergistic combinations exhibited bacteriostatic activity. Although lefamulin is not currently used to treat enterococcal infections, we suggest that these combinations may serve as alternative drug regimens.

Comparing the activity of broad-spectrum beta-lactams in combination with aminoglycosides against VIM-producing Enterobacteriaceae

Metallo-beta-lactamase (MBL)-producing carbapenem-resistant Enterobacteriaceae (CRE) infections continue to pose a serious threat to healthcare. Due to their unique active site, MBLs evade the activity of many novel beta-lactam/beta-lactamase inhibitor combinations, which have been specifically targeted toward those carbapenemases with serine active sites. Furthermore, resistance to most, if not all, other clinically relevant antimicrobial classes leaves few reliable therapeutic options. Combination therapy has thus played a vital role in the treatment of MBL-producing CRE infections. In this study, we utilized the static time-kill assay to investigate clinically relevant concentrations of cefepime, piperacillin-tazobactam, and meropenem alone and in combination with either amikacin or the novel plazomicin to determine if combinations of routinely used beta-lactam therapy with an aminoglycoside would achieve bactericidal activity against eight clinically isolated Verona integron-encoded MBL (VIM)-producing CRE. Furthermore, we compared this activity to the combination of aztreonam/avibactam, which has shown potent activity against MBL-producing CRE. Both aztreonam/avibactam and meropenem with either aminoglycoside were rapidly bactericidal within 4 hours and remained bactericidal through 24 hours against all isolates with few exceptions. Combinations including cefepime and piperacillin-tazobactam were also rapidly bactericidal, but activity after 24 hours was inconsistent depending upon the partner aminoglycoside and isolate. Further investigation is warranted to elucidate optimal antibiotic exposures against MBL-producing CRE, including novel agents in the pipeline.IMPORTANCECarbapenem-resistant Enterobacterales (CRE) are one of the most pressing antimicrobial-resistant threats at present. In addition to exhibiting resistance to many, if not all, commonly used antimicrobial agents, CRE achieves these resistant phenotypes through a variety of mechanisms, each of which can uniquely affect available treatment options. The present study is an in vitro investigation of several Verona integron-encoded metallo-beta-lactamase (VIM)-producing CRE isolated from patients at our academic medical center. Because metallo-beta-lactamases (MBLs) are inherently resistant to many of the novel treatments designed to treat CRE due to their different active site composition, we tested several antimicrobial combinations containing routinely utilized broad-spectrum beta-lactams and aminoglycosides. Our results further our understanding of combination therapy options against VIM-producing CRE, including with non-carbapenem-beta-lactams cefepime and piperacillin. By optimizing combinations of existing antimicrobial agents, we hope to expand the available armamentarium against these resistant pathogens.

Clinical risk factors and outcomes of carbapenem-resistant Escherichia coli nosocomial infections in a Chinese teaching hospital: a retrospective study from 2013 to 2020

The emergence of carbapenem-resistant Escherichia coli strains poses a considerable challenge to global public health, and little is known about carbapenemase-producing E. coli strains in Tianjin, China. This study aimed to investigate the risk factors for infections with carbapenem-resistant E. coli (CREC) strains. This retrospective case-control study was conducted at a tertiary teaching hospital. A total of 134 CREC clinical isolates were collected from the General Hospital of Tianjin Medical University between 2013 and 2020. The control group was selected at a ratio of 1:1 from patients with nosocomial carbapenem-susceptible E. coli infection. Risk factors for nosocomial CREC infection and clinical outcomes were analyzed using univariate and multivariate analyses. Multivariate analysis revealed that cephalosporin exposure (odd ratio OR = 2.01), carbapenem exposure (OR = 1.96), glucocorticoid exposure (OR = 32.45), and surgical history (OR = 3.26) were independent risk factors for CREC infection. The in-hospital mortality rate in the CREC group was 29.1%, and age >65 years (OR = 3.19), carbapenem exposure (OR = 3.54), and central venous catheter insertion (OR = 4.19) were independent risk factors for in-hospital mortality in patients with CREC infections. Several factors were identified in the development of nosocomial CREC infections. The CREC isolates were resistant to most antibiotics. Reducing CREC mortality requires a comprehensive consideration of appropriate antibiotic use, underlying diseases, and invasive procedures.IMPORTANCEEscherichia coli is an opportunistic pathogen that causes severe hospital-acquired infections. The spread of carbapenem-resistant E. coli is a global threat to public health, and only a few antibiotics are effective against these infections. Consequently, these infections are usually associated with poor prognosis and high mortality. Therefore, understanding the risk factors associated with the causes and outcomes of these infections is crucial to reduce their incidence and initiate appropriate therapies. In our study, several factors were found to be involved in nosocomial carbapenem-resistant E. coli (CREC) infections, and CREC isolates were resistant to most antibiotics. Reducing CREC mortality needs a comprehensive consideration of whether antibiotics are used appropriately, underlying diseases, and invasive interventions. These findings provide valuable evidence for the development of anti-infective therapy, infection prevention, and control of CREC-positive infections.

Effect of biogenic bismuth nanoparticle on the expression of New Delhi metallo-β-lactamase (NDM) gene in Multidrug-Resistant Klebsiella pneumoniae

Aim and background

The emergence of Multidrug-Resistant Klebsiella pneumoniae is a global concern due to high mortality and treatment challenges. One of the most important genes for resistance is NDM, which makes the organism resistant to most antibiotics. Today, the use of nanoparticles as therapeutic options has stimulated researchers around the world to investigate its effects. The aim of this study was to investigate the effects of biosynthesized bismuth nanoparticles (Bi NPs) on the expression of NDM genes in multidrug-resistant K. pneumoniae.

Materials and methods

In this study, 5 multidrug-resistant K. pneumoniae clinical isolates from patients referred to Afzalipour Hospital in Kerman, Iran, were used. Antibiotic sensitivity test was performed by disc diffusion method. The presence of the NDM gene was checked in isolates using a PCR reaction. The isolates containing the NDM gene were exposed to the biosynthesized and characterized bismuth nanoparticles, and the effects on the expression of the NDM gene was investigated using real-time PCR.

Results

The results showed that 3 isolates of K. pneumoniae had NDM genes. In TEM and SEM analysis showed that the nanoparticles had a spherical structure and an average size of 22.36 nm. The investigation of biogenic Bi NPs on the expression of the NDM gene demonstrated that the samples treated with bismuth nanoparticles decreased the expression of the NDM gene by 1.6 times compared to the control group (p < 0.011).

Conclusion

Our findings showed that biosynthesized Bi NPs have a high potential to deal with antibiotic resistance genes and can be a promising for treatment.

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-β-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.

A review of the mechanisms that confer antibiotic resistance in pathotypes of E. coli

The dissemination of antibiotic resistance in Escherichia coli poses a significant threat to public health worldwide. This review provides a comprehensive update on the diverse mechanisms employed by E. coli in developing resistance to antibiotics. We primarily focus on pathotypes of E. coli (e.g., uropathogenic E. coli) and investigate the genetic determinants and molecular pathways that confer resistance, shedding light on both well-characterized and recently discovered mechanisms. The most prevalent mechanism continues to be the acquisition of resistance genes through horizontal gene transfer, facilitated by mobile genetic elements such as plasmids and transposons. We discuss the role of extended-spectrum β-lactamases (ESBLs) and carbapenemases in conferring resistance to β-lactam antibiotics, which remain vital in clinical practice. The review covers the key resistant mechanisms, including: 1) Efflux pumps and porin mutations that mediate resistance to a broad spectrum of antibiotics, including fluoroquinolones and aminoglycosides; 2) adaptive strategies employed by E. coli, including biofilm formation, persister cell formation, and the activation of stress response systems, to withstand antibiotic pressure; and 3) the role of regulatory systems in coordinating resistance mechanisms, providing insights into potential targets for therapeutic interventions. Understanding the intricate network of antibiotic resistance mechanisms in E. coli is crucial for the development of effective strategies to combat this growing public health crisis. By clarifying these mechanisms, we aim to pave the way for the design of innovative therapeutic approaches and the implementation of prudent antibiotic stewardship practices to preserve the efficacy of current antibiotics and ensure a sustainable future for healthcare.

Genotypic and phenotypic mechanisms underlying antimicrobial resistance and synergistic efficacy of rifampicin-based combinations against carbapenem-resistant Acinetobacter baumannii

Purpose

Carbapenem-resistant Acinetobacter baumannii (CRAB) is an urgent concern to public health. This study focuses on exploring the resistance mechanisms and the in vitro results of using rifampicin in combination with conventional antibiotics for the management of CRAB.

Methods

The synergistic and bactericidal effects of rifampicin with conventional antibiotics were evaluated using chequerboard assay and time-kill assay, while the phenotypic and genotypic characteristics of resistant determinants were performed by efflux pump detection and whole genome sequencing on 29 isolates from ICU patients with underlying health diseases.

Results

The isolates showed multidrug resistance, with over 60% showing addictive responses to rifampicin-based combinations at FICI ranging from 0.6 to 0.8. The time-kill assay revealed 99 % killing for rifampicin and minocycline combination in one isolate at 1/4 MIC rifampicin plus 1/4 MIC minocycline, while a bacteriostatic effect was observed at 1/2 MIC rifampici plus 1/2 MIC for a second isolate. Combination with tigecycline resulted in a 99% killing in two out of three isolates with a 2.5-3 log reduction in CFU at 1/4 MIC rifampicin plus 1/4 MIC tigecycline. Rifampicin plus colistin exhibited bactericidal activity against three out of four isolates. The combinations of rifampicin with ciprofloxacin, chloramphenicol, and trimethoprim-sulfamethoxazole were ineffective against the isolates. In addition, a 4-fold reduction in rifampicin MIC was observed in 2 out of 14 isolates in the presence of an efflux pump inhibitor. The pan-genome study demonstrated a progressive evolution with an accessory genome estimated to cover 58% of the matrix. Seven of the ten sequenced isolates belong to sequence type 2 (ST2), while one isolate each was assigned to ST164, ST16, and ST25. Furthermore, 11 plasmids, 34 antimicrobial resistance (AMR) genes, and 65 virulence-associated genes were predicted from the whole genome data. The blaOXA-23blaADC-25, blaOXA-66, blaPER-7, aph(6)-Id, armA, and arr-3 were prevalent among the isolates. Sequence alignment of the bacteria genome to the reference strain revealed a deleterious mutation in the rpoB gene of 4 isolates.

Conclusion

The study suggests that rifampicin in combination with either minocycline, tigecycline, or colistin might be a treatment option for CRAB clinical isolates. In addition, genotypic analysis of the bacteria isolates may inform the clinician of the suitable drug regimen for the management of specific bacteria variants.

Unraveling resistance mechanisms in combination therapy: A comprehensive review of recent advances and future directions

Antimicrobial resistance is a global health threat. Misuse and overuse of antimicrobials are the main drivers in developing drug-resistant bacteria. The emergence of the rapid global spread of multi-resistant bacteria requires urgent multisectoral action to generate novel treatment alternatives. Combination therapy offers the potential to exploit synergistic effects for enhanced antibacterial efficacy of drugs. Understanding the complex dynamics and kinetics of drug interactions in combination therapy is crucial. Therefore, this review outlines the current advances in antibiotic resistance's evolutionary and genetic dynamics in combination therapies-exposed bacteria. Moreover, we also discussed four pivotal future research areas to comprehend better the development of antibiotic resistance in bacteria treated with combination strategies.

Enhancing bactericidal activities of ciprofloxacin by targeting the trans-translation system that is involved in stress responses in Klebsiella pneumoniae

Although the trans-translation system is a promising target for antcibiotic development, its antibacterial mechanism in Klebsiella pneumoniae (KP) is unclear. Considering that tmRNA was the core component of trans-translation, this study firstly investigated phenotypic changes caused by various environmental stresses in KP lacking trans-translation activities (tmRNA-deleted), and then aimed to evaluate antibacterial activities of the trans-translation-targeting antibiotic combination (tobramycin/ciprofloxacin) in clinical KP isolates based on inhibition activities of aminoglycosides against trans-translation. We found that the tmRNA-deleted strain P4325/ΔssrA was significantly more susceptible than the wild-type KP strain P4325 under environments with hypertonicity (0.5 and 1 M NaCl), hydrogen peroxide (40 mM), and UV irradiation. No significant differences in biofilm formation and survivals under human serum were observed between P4325/ΔssrA and P4325. tmRNA deletion caused twofold lower MIC values for aminoglycosides. As for the membrane permeability, tmRNA deletion increased ethidium bromide (EtBr) uptake of KP in the presence or absence of verapamil and carbonyl cyanide-m-chlorophenylhydrazone (CCCP), decreased EtBr uptake in presence of reserpine in P4325/ΔssrA, and reduced EtBr efflux in P4325/ΔssrA in the presence of CCCP. The time-kill curve and in vitro experiments revealed significant bactericidal activities of the tmRNA-targeting aminoglycoside-based antibiotic combination (tobramycin/ciprofloxacin). Thus, the corresponding tmRNA-targeting antibiotic combinations (aminoglycoside-based) might be effective and promising treatment options against multi-drug resistant KP.

Comparative Investigation into the Roles of Imipenem:Cyclodextrin Complexation and Antibiotic Combination in Combatting Antimicrobial Resistance in Gram-Negative Bacteria

Extensively drug-resistant (XDR), multidrug-resistant (MDR) and pandrug-resistant (PDR) Gram-negative microorganisms (GNBs) are considered a significant global threat. β-lactam and aminoglycoside combinations and imipenem:cyclodextrin inclusion complexes were studied for the treatment of lethal GNBs. This is because of the broad empiric coverage of the two drugs and their possession of different spectra of activity. Two cyclodextrins (β- and hydroxy propyl β-cyclodextrins) were utilized for inclusion complex formation with imipenem using the physical and kneading methods. In silico investigation using the molecular docking and Fourier-infrared spectroscopy (FTIR) were employed to estimate binding constant and confirm complex formation, respectively. The in vitro effects of amikacin and imipenem combination in comparison to the effect of imipenem-β- and hydroxy propyl β-cyclodextrin (CD) complexes against Klebsiella spp. and Acinetobacter baumannii were studied. The isolated microorganisms' antimicrobial responsiveness to various antibiotics (19 antibiotics) was evaluated. It was found that piperacillin/tazobactam and gentamycin (resistance rates were 33.3% and 34%, respectively) were the most effective antimicrobials. The in vitro studies have been performed by the checkerboard technique and time-killing assay. The studied combination of amikacin and imipenem showed a substantial drop in bacterial count (p < 0.05). The in vitro studies demonstrated a synergism for the investigated combination. Conventional PCR was used in molecular studies to identify the resistance genes bla IMP and aac (6')-Ib. The blaIMP and aac (6')-Ib were recorded in 38.2% and 3.6% of the studied isolates, respectively. The in vitro studies showed synergistic effects among the tested antibiotics with FICIs of ≤0.5. Finally, the study compared the reduction in bacterial count between the tested antibiotic combinations and imipenem:CD physical and kneaded mixtures. Imipenem:CD inclusion complexes demonstrated a significant bacterial count reduction over the antibiotic combination. These results highlight the emerging role of CDs as safe biofunctional excipients in the combat against superbug bacterial resistance.

Propranolol restores susceptibility of XDR Gram-negative pathogens to meropenem and Meropenem combination has been evaluated with either tigecycline or amikacin

BACKGROUND

Infection with extensive-drug-resistant (XDR) carbapenem-resistant (CR) Gram-negative bacteria (GNB) are viewed as a serious threat to human health because of the limited therapeutic options. This imposes the urgent need to find agents that could be used as adjuvants or combined with carbapenems to enhance or restore the susceptibility of XDR CR- GNB. Therefore, this study aimed to examine the effect of propranolol (PR) in combination with Meropenem (MEM) on the susceptibility profile of XDR CR-GNB recovered from severely infected patients as well as to evaluate combining MEM with either tigecycline (TGC) or amikacin (AK).

METHODS

A total of 59 non-duplicate CR- GNB were investigated for carbapenemase production by the major phenotypic methods. Molecular identification of five major carbapenemase-coding genes was carried out using polymerase chain reactions (PCR). Antimicrobial susceptibility tests were carried out using standard methods. Phenotypic and genotypic relatedness was carried out using the heatmap and ERIC PCR analysis. PR, 0.5 -1 mg/mL against the resulting non-clonal XDR CR-GNB pathogens were evaluated by calculating the MIC decrease factor (MDF). A combination of MEM with either AK or TGC was performed using the checkerboard assay.

RESULTS

A total of 21 (35.6%) and 38 (64.4%) CR-GNB isolates were identified as enterobacterial isolates (including 16 (27.1%) Klebsiella Pneumoniae and 5 (8.5%) Escherichia coli) and non-fermentative bacilli (including, 23 (39%), Acinetobacter baumannii, and 15 (25.4%) Pseudomonas aeruginosa). The heatmap and ERIC PCR analysis resulted in non-clonal 28 XDR CR isolates. PR, at a concentration of 0.5 mg /ml, decreased MICs values of the tested XDR CR isolates (28; 100%) and restored susceptibility of only 4 (14.3%) isolates. However, PR (1 mg/mL) when combined with MEM has completely (28; 100%) restored the susceptibility of the tested XDR CR- GNB to MEM. The MEM + AK and MEM + TGC combination showed mostly additive effects (92.8% and 71.4%, respectively).

CONCLUSION

PR at a concentration of 1 mg/mL restored the susceptibility of XDR CR- GNB to MEM which is considered a promising result that should be clinically investigated to reveal its suitability for clinical use in patients suffering from these life-threatening pathogens.

A rapid and ultrasensitive dual detection platform based on Cas12a for simultaneous detection of virulence and resistance genes of drug-resistant Salmonella

Accurate, sensitive, and rapid detection of Salmonella and determination of whether it carries drug resistance genes plays an important role in guiding the clinical medication of salmonellosis and laying a foundation for studying the mechanism of drug resistance transmission of Salmonella. Here, a novel nontransferable, ultrasensitive dual detection platform (Cas12a-Ddp) was developed. The round cap allowed for temporary storage of more Cas12a detection solution than flat cap, enabling one-pot assays and reducing aerosol contamination. The results were read out in dual mode by the microplate reader and UV visualization to achieve sensitive dual-target detection of the virulence genes and drug resistance genes of Salmonella simultaneously, with the possibility of onsite detection. Cas12a-Ddp was combined with multiple polymerase chain reactions and recombinase polymerase amplifications successively. An ultrasensitive dual detection limit of 1 CFU/mL was obtained without any cross-reaction within 40 min. This was an improvement of 1-2 orders of magnitude over the existing methods. Cas12a-Ddp overcame the influence of proteins and fat in liquid matrix foods. It was used for the detection of drug-resistant Salmonella in milk and skim milk powder, also with the dual detection limit of 1 CFU/mL and spiked recovery of 68.58%-158.49%. It was also used for the analysis of Salmonella resistance rate analysis. The Cas12a-Ddp provided a reliable, fast, sensitive, and practical multi-CRISPR detection platform.