Evolution of blaKPC Under the Pressure of Carbapenems and Ceftazidime/Avibactam in a Patient With Persistent Bacteremia Caused by Klebsiella pneumoniae.

A 30-year-old Korean man with myelodysplastic syndrome admitted hospital due to undifferentiated fever and recurrent skin lesions. He received combination therapy with high doses of meropenem, tigecycline and amikacin, yielding carbapenem resistant Klebsiella pneumoniae (CRKP) harboring K. pneumoniae carbapenemase (KPC)-2 from blood cultures on hospital day (HD) 23. Ceftazidime/avibactam was started at HD 37 and CRKP was eradicated from blood cultures after 5 days. However, ceftazidime/avibactam-resistant CRKP carrying KPC-44 emerged after 26 days of ceftazidime/avibactam treatment and then ceftazidime/avibactam-resistant, carbapenem-susceptible K. pneumoniae carrying KPC-135 was isolated on HD 65. The 3-D homology of KPC protein showed that hot spot changes in the omega loop could be attributed to ceftazidime/avibactam resistance and loss of carbapenem resistance. Whole genome sequencing of serial isolates supported that phenotypic variation was due to clonal evolution than clonal replacement. The treatment regimen was changed from CAZ/AVI to meropenem-based therapy (meropenem 1 g iv q 8 hours and amikacin 600 mg iv per day) starting with HD 72. CAZ/AVI-susceptible CRKP was presented again from blood cultures on HD 84, and the patient expired on HD 85. This is the first Korean report on the acquisition of ceftazidime/avibactam resistance through the emergence of blaKPC variants.

Evaluating the antibacterial effect of meropenem-loaded chitosan/sodium tripolyphosphate (TPP) nanoparticles on Acinetobacter baumannii isolated from hospitalized patients.

BACKGROUND: Acinetobacter baumannii is a health threat due to its antibiotic resistance. Herein, antibiotic susceptibility and its association with the Toxin-antitoxin (TA) system genes in A. baumannii clinical isolates from Iran were investigated. Next, we prepared meropenem-loaded chitosan nanoparticles (MP-CS) and investigated their antibacterial effects against meropenem-susceptible bacterial isolates. METHODS: Out of 240 clinical specimens, 60 A. baumannii isolates were assessed. Antibiotic resistance of the isolates against conventional antibiotics was determined alongside investigating the presence of three TA system genes (mazEF, relBE, and higBA). Chitosan nanoparticles were characterized in terms of size, zeta potential, encapsulation efficiency, and meropenem release activity. Their antibacterial effects were assessed using the well diffusion method, minimum inhibitory concentration (MIC), and colony-forming unit (CFU) counting. Their cytotoxic effects and biocompatibility index were determined via the MTT, LDH, and ROS formation assays. RESULTS: Ampicillin, ceftazidime, and colistin were the least effective, and amikacin and tobramycin were the most effective antibiotics. Out of the 60 isolates, 10 (16.7%), 5 (8.3%), and 45 (75%) were multidrug-resistant (MDR), extensively drug-resistant (XDR), and pandrug-resistant (PDR), respectively. TA system genes had no significant effect on antibiotic resistance. MP-CS nanoparticles demonstrated an average size of 191.5 and zeta potential of 27.3 mV alongside a maximum encapsulation efficiency of 88.32% and release rate of 69.57%. MP-CS nanoparticles mediated similar antibacterial effects, as compared with free meropenem, against the A. baumannii isolates with significantly lower levels of meropenem. MP-CS nanoparticles remarkably prevented A549 and NCI-H292 cell infection by the A. baumannii isolates alongside demonstrating a favorable biocompatibility index. CONCLUSION: Antibiotic-loaded nanoparticles should be further designed and investigated to increase their antibacterial effect against A. baumannii and assess their safety and applicability in vivo settings.

Enhancing resistance, but not virulence attributed to the high mortality caused by carbapenem-resistant Klebsiella pneumoniae.

Carbapenem-resistant Klebsiella pneumoniae (CRKP) has emerged as a global threat due to its high mortality in clinical patients. However, the specific mechanisms underlying this increased mortality remain unclear. The objective of this study is to investigate how the development of a resistance phenotype contributes to the significantly higher mortality associated with this pathogen. To achieve this, a collection of isogeneic strains was generated. The clinical carbapenem-susceptible K. pneumoniae (CSKP) strain HKU3 served as the control isolate, while HKU3-KPC was created through conjugation with a blaKPC-2-bearing plasmid and served as clinical CRKP strain. Using a sepsis model, it was demonstrated that both HKU3 and HKU3-KPC exhibited similar levels of virulence. Flow cytometry, RNA-seq, and ELISA analysis were employed to assess immune cell response, M1 macrophage polarization, and cytokine storm induction, revealing that both strains elicited comparable types and levels of these immune responses. Subsequently, meropenem was utilized to treat K. pneumoniae infection, and it was found that meropenem effectively reduced bacterial load, inhibited M1 macrophage polarization, and suppressed serum cytokine production during HKU3 (CSKP) infection. However, these effects were not observed in the case of HKU3-KPC (CRKP) infection. These findings provide evidence that the high mortality associated with CRKP is attributed to its enhanced survival within the host during antibiotic treatment, resulting in a cytokine storm and subsequent host death. The development of an effective therapy for CRKP infections could significantly reduce the mortality caused by this pathogen.

In vitro activity of human defensins HNP-1 and hBD-3 against multidrug-resistant ESKAPE Gram-negatives of clinical origin and selected peptidoglycan recycling-defective mutants.

The use of immune compounds as antimicrobial adjuvants is a classic idea recovering timeliness in the current antibiotic resistance scenario. However, the activity of certain antimicrobial peptides against ESKAPE Gram-negatives has not been sufficiently investigated. The objective of this study was to determine the activities of human defensins HNP-1 and hBD-3 alone or combined with permeabilizing/peptidoglycan-targeting agents against clinical ESKAPE Gram-negatives [Acinetobacter baumannii (AB), Enterobacter cloacae (EC), Klebsiella pneumoniae (KP), and acute/chronic Pseudomonas aeruginosa (PA)]. Lethal concentrations (LCs) of HNP-1 and hBD-3 were determined in four collections of multidrug resistant EC, AB, KP, and PA clinical strains (10-36 isolates depending on the collection). These defensins act through membrane permeabilization plus peptidoglycan building blockade, enabling that alterations in peptidoglycan recycling may increase their activity, which is why different recycling-defective mutants were also included. Combinations with physiological lysozyme and subinhibitory colistin for bactericidal activities determination, and with meropenem for minimum inhibitory concentrations (MICs), were also assessed. HNP-1 showed undetectable activity (LC > 32 mg/L for all strains). hBD-3 showed appreciable activities: LC ranges 2-16, 8-8, 8->32, and 8->32 mg/L for AB, EC, KP, and PA, being PA strains from cystic fibrosis significantly more resistant than acute origin ones. None of the peptidoglycan recycling-defective mutants showed greater susceptibility to HNP-1/hBD-3. Combination with colistin or lysozyme did not change their bactericidal power, and virtually neither did meropenem + hBD-3 compared to meropenem MICs. This is the first study comparatively analyzing the HNP-1/hBD-3 activities against the ESKAPE Gram-negatives, and demonstrates interesting bactericidal capacities of hBD-3 mostly against AB and EC. IMPORTANCE: In the current scenario of critical need for new antimicrobials against multidrug-resistant bacteria, all options must be considered, including classic ideas such as the use of purified immune compounds. However, information regarding the activity of certain human defensins against ESKAPE Gram-negatives was incomplete. This is the first study comparatively assessing the in vitro activity of two membrane-permeabilizing/peptidoglycan construction-blocking defensins (HNP-1 and hBD-3) against relevant clinical collections of ESKAPE Gram-negatives, alone or in combination with permeabilizers, additional peptidoglycan-targeting attacks, or the blockade of its recycling. Our data suggest that hBD-3 has a notable bactericidal activity against multidrug-resistant Acinetobacter baumannii and Enterobacter cloacae strains that should be considered as potential adjuvant option. Our results suggest for the first time an increased resistance of Pseudomonas aeruginosa strains from chronic infection compared to acute origin ones, and provide new clues about the predominant mode of action of hBD-3 against Gram-negatives (permeabilization rather than peptidoglycan-targeting).

Activated mesenchymal stem cells increase drug susceptibility of methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa.

Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa are major causes of hospital-acquired infections and sepsis. Due to increasing antibiotic resistance, new treatments are needed. Mesenchymal stem cells (MSCs) have antimicrobial effects, which can be enhanced by preconditioning with antibiotics. This study investigated using antibiotics to strengthen MSCs against MRSA and P. aeruginosa. MSCs were preconditioned with linezolid, vancomycin, meropenem, or cephalosporin. Optimal antibiotic concentrations were determined by assessing MSC survival. Antimicrobial effects were measured by minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and antimicrobial peptide (AMP) gene expression. Optimal antibiotic concentrations for preconditioning MSCs without reducing viability were 1 µg/mL for linezolid, meropenem, and cephalosporin and 2 µg/mL for vancomycin. In MIC assays, MSCs preconditioned with linezolid, vancomycin, meropenem, or cephalosporin inhibited MRSA or P. aeruginosa growth at lower concentrations than non-preconditioned MSCs (p ≤ 0.001). In MBC assays, preconditioned MSCs showed enhanced bacterial clearance compared to non-preconditioned MSCs, especially when linezolid and vancomycin were used against MRSA (p ≤ 0.05). Preconditioned MSCs showed increased expression of genes encoding the antimicrobial peptide genes hepcidin and LL-37 compared to non-preconditioned MSCs. The highest hepcidin expression was seen with linezolid and vancomycin preconditioning (p ≤ 0.001). The highest LL-37 expression was with linezolid preconditioning (p ≤ 0.001). MSCs' preconditioning with linezolid, vancomycin, meropenem, or cephalosporin at optimal concentrations enhances their antimicrobial effects against MRSA and P. aeruginosa without compromising viability. This suggests preconditioned MSCs could be an effective adjuvant treatment for antibiotic-resistant infections. The mechanism may involve upregulation of AMP genes.

Metabolomics Method in Understanding and Sensitizing Carbapenem-Resistant Acinetobacter baumannii to Meropenem.

Carbapenem-resistant Acinetobacter baumannii (CRAB) strains are prevalent worldwide and represent a major threat to public health. However, treatment options for infections caused by CRAB are very limited as they are resistant to most of the commonly used antibiotics. Consequently, understanding the mechanisms underlying carbapenem resistance and restoring bacterial susceptibility to carbapenems hold immense importance. The present study used gas chromatography-mass spectrometry (GC-MS)-based metabolomics to investigate the metabolic mechanisms of antibiotic resistance in clinically isolated CRAB. Inactivation of the pyruvate cycle and purine metabolism is the most typical characteristic of CRAB. The CRAB exhibited a reduction in the activity of enzymes involved in the pyruvate cycle, proton motive force, and ATP levels. This decline in central carbon metabolism resulted in a decrease in the metabolic flux of the α-ketoglutarate-glutamate-glutamine pathway toward purine metabolism, ultimately leading to a decline in adenine nucleotide interconversion. Exogenous adenosine monophosphate (AMP) and adenosine triphosphate (ATP) enhance the killing efficacy of Meropenem against CRAB. The combination of ATP and Meropenem also has a synergistic effect on eliminating CRAB persisters and the biofilm, as well as protecting mice against peritonitis-sepsis. This study presents a novel therapeutic modality to treat infections caused by CRAB based on the metabolism reprogramming strategy.

Comparative in vitro activities of eravacycline in combination with colistin, meropenem, or ceftazidime against various Achromobacter spp. strains isolated from patients with cystic fibrosis.

The Achromobacter species is an emerging pathogen causing chronic bacterial infections in patients with certain conditions, such as cystic fibrosis (CF), hematologic and solid organ malignancies, renal failure, and certain immune deficiencies. In the present study, we assessed the in vitro bactericidal activities of eravacycline, either alone or in combination with colistin, meropenem, or ceftazidime, using 50 Achromobacter spp. strains isolated from CF patients. We also investigated the synergistic interactions of these combinations using microbroth dilutions against 50 strains of Achromobacter spp. Bactericidal, and we assessed the synergistic effects of the tested antibiotic combinations using the time-kill curve (TKC) technique. Our studies show that meropenem alone is the most effective antibiotic of those tested. Based on the TKCs, we found that eravacycline-colistin combinations display both bactericidal and synergistic activities for 24 h against 5 of the 6 Achromobacter spp. strains, including colistin-resistant ones, at 4xMIC of colistin. Although we did not observe synergistic interactions with eravacycline-meropenem or eravacycline-ceftazidime combinations, we did not observe antagonism with any combination tested.This study's findings could have important implications for antimicrobial therapy with tested antibiotics.

In vitro effect of the iron chelator deferiprone on the antimicrobial susceptibility and biofilms of Burkholderia pseudomallei.

This study evaluated the effect of the iron chelator deferiprone (DFP) on antimicrobial susceptibility and biofilm formation and maintenance by Burkholderia pseudomallei. Planktonic susceptibility to DFP alone and in combination with antibiotics was evaluated by broth microdilution and biofilm metabolic activity was determined with resazurin. DFP minimum inhibitory concentration (MIC) range was 4-64 µg/mL and in combination reduced the MIC for amoxicillin/clavulanate and meropenem. DFP reduced the biomass of biofilms by 21 and 12% at MIC and MIC/2, respectively. As for mature biofilms, DFP reduced the biomass by 47%, 59%, 52% and 30% at 512, 256, 128 and 64 µg/mL, respectively, but did not affect B. pseudomallei biofilm viability nor increased biofilm susceptibility to amoxicillin/clavulanate, meropenem and doxycycline. DFP inhibits planktonic growth and potentiates the effect of ß-lactams against B. pseudomallei in the planktonic state and reduces biofilm formation and the biomass of B. pseudomallei biofilms.

In vitro susceptibility of nonfermenting Gram-negative rods to meropenem-vaborbactam and delafloxacin.

Aim: Meropenem-vaborbactam and delafloxacin activities were not assessed against Achromobacter spp. (Achr), Burkholderia cepacia complex (Bcc) and Stenotrophomonas maltophilia (Smal). Methodology: A total of 106 Achr, 57 Bcc and 100 Smal were tested with gradient diffusion test of meropenem-vaborbactam, delafloxacin and comparators. Results: Meropenem-vaborbactam MIC50 were 4 µg/ml for Achr, 1 µg/ml for B. cepacia, 2 µg/ml for B. cenocepacia and B. multivorans, and 32 µg/ml for Smal. Delafloxacin MIC50 were 4 µg/ml for Achr, 0.25 µg/ml for B. cepacia and B. multivorans, 2 µg/ml for B. cenocepacia, and 0.5 µg/m for Smal. meropenem-vaborbactam MICs were fourfold lower than meropenem for 28.3% Achr, 77.2% B. cepacia, 53.8% B. cenocepacia and 77.2% B. multivorans. Conclusion: Meropenem-vaborbactam and delafloxacin are in vitro active against Bcc and Achr.

We assess the efficacy of two new antibiotics, meropenem­vaborbactam and delafloxacin, to kill rarely encountered bacteria. These bacteria, Achromobacter, Burkholderia and Stenotrophomonas maltophilia, mainly cause respiratory tract infections. Both antibiotics are found active against Achromobacter and Burkholderia, but not S. maltophilia.

In Vitro and In Vivo Development of a ß-Lactam-Metallo-ß-Lactamase Inhibitor: Targeting Carbapenem-Resistant Enterobacterales.

ß-lactams are the most prescribed class of antibiotics due to their potent, broad-spectrum antimicrobial activities. However, alarming rates of antimicrobial resistance now threaten the clinical relevance of these drugs, especially for the carbapenem-resistant Enterobacterales expressing metallo-ß-lactamases (MBLs). Antimicrobial agents that specifically target these enzymes to restore the efficacy of last resort ß-lactam drugs, that is, carbapenems, are therefore desperately needed. Herein, we present a cyclic zinc chelator covalently attached to a ß-lactam scaffold (cephalosporin), that is, BP1. Observations from in vitro assays (with seven MBL expressing bacteria from different geographies) have indicated that BP1 restored the efficacy of meropenem to ≤ 0.5 mg/L, with sterilizing activity occurring from 8 h postinoculation. Furthermore, BP1 was nontoxic against human hepatocarcinoma cells (IC50 > 1000 mg/L) and exhibited a potency of (Kiapp) 24.8 and 97.4 µM against Verona integron-encoded MBL (VIM-2) and New Delhi metallo ß-lactamase (NDM-1), respectively. There was no inhibition observed from BP1 with the human zinc-containing enzyme glyoxylase II up to 500 µM. Preliminary molecular docking of BP1 with NDM-1 and VIM-2 sheds light on BP1's mode of action. In Klebsiella pneumoniae NDM infected mice, BP1 coadministered with meropenem was efficacious in reducing the bacterial load by >3 log10 units' postinfection. The findings herein propose a favorable therapeutic combination strategy that restores the activity of the carbapenem antibiotic class and complements the few MBL inhibitors under development, with the ultimate goal of curbing antimicrobial resistance.

Transcriptional profiling of Pseudomonas aeruginosa mature single- and dual-species biofilms in response to meropenem.

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen frequently isolated from chronic infections of the cystic fibrosis lung and burn wounds, and is a major cause of antimicrobial-resistant nosocomial infections. P. aeruginosa is frequently co-isolated with the opportunistic fungal pathogen Candida albicans, with the presence of C. albicans in dual-species biofilms promoting tolerance to meropenem. Here, transcription profiling of mature P. aeruginosa single- or dual-species biofilms was carried out to understand the molecular mechanism(s) by which C. albicans enhances meropenem tolerance. C. albicans appeared to have a mild impact on the transcriptome of P. aeruginosa mature biofilms, with most differentially regulated genes being involved in interkingdom interactions (i.e. quorum sensing and phenazine biosynthesis). The addition of meropenem to mature single- or dual-species biofilms resulted in a significant bacterial transcriptional response, including the induction of the beta-lactamase, ampC, genes involved in biofilm formation. P. aeruginosa elicited a similar transcriptional response to meropenem in the presence of C. albicans, but C. albicans promoted the expression of additional efflux pumps, which could play roles in increasing the tolerance of P. aeruginosa to meropenem.

Immunostimulatory Effect of Flagellin on MDR-Klebsiella-Infected Human Airway Epithelial Cells.

Pneumonia caused by multi-drug-resistant Klebsiella pneumoniae (MDR-Kpneu) poses a major public health threat, especially to immunocompromised or hospitalized patients. This study aimed to determine the immunostimulatory effect of the Toll-like receptor 5 ligand flagellin on primary human lung epithelial cells during infection with MDR-Kpneu. Human bronchial epithelial (HBE) cells, grown on an air-liquid interface, were inoculated with MDR-Kpneu on the apical side and treated during ongoing infection with antibiotics (meropenem) and/or flagellin on the basolateral and apical side, respectively; the antimicrobial and inflammatory effects of flagellin were determined in the presence or absence of meropenem. In the absence of meropenem, flagellin treatment of MDR-Kpneu-infected HBE cells increased the expression of antibacterial defense genes and the secretion of chemokines; moreover, supernatants of flagellin-exposed HBE cells activated blood neutrophils and monocytes. However, in the presence of meropenem, flagellin did not augment these responses compared to meropenem alone. Flagellin did not impact the outgrowth of MDR-Kpneu. Flagellin enhances antimicrobial gene expression and chemokine release by the MDR-Kpneu-infected primary human bronchial epithelium, which is associated with the release of mediators that activate neutrophils and monocytes. Topical flagellin therapy may have potential to boost immune responses in the lung during pneumonia.

The Status of Carbapenem Resistance in Cystic Fibrosis: A Systematic Review and Meta-Analysis.

Background: Antibiotic resistance in cystic fibrosis (CF) is a well-known phenomenon. However, the comprehensive epidemiological impact of antibiotic resistance in CF is not clearly documented. So, this meta-analysis evaluated the proportion rates of carbapenem resistance (imipenem, meropenem, and doripenem) in CF based on publication date (1979-2000, 2001-2010, and 2011-2021), continents, pathogens, and antimicrobial susceptibility testing (AST). Methods: We searched studies in PubMed, Scopus, and Web of Science (until April 2021). Statistical analyses were conducted using STATA software (version 14.0). Results: The 110 studies included in the analysis were performed in 25 countries and investigated 13,324 pathogens associated with CF. The overall proportion of imipenem, meropenem, and doripenem resistance in CF were 43% (95% CI 36-49), 48% (95% CI 40-57), 28% (95% CI 23-33), and 45% (95% CI 32-59), respectively. Our meta-analysis showed that trends of imipenem, meropenem, and doripenem-resistance had gradual decreases over time (1979-2021). This could be due to the limited clinical effectiveness of these antibiotics to treat CF cases over time. Among the opportunistic pathogens associated with CF, the highest carbapenem resistance rates were shown in Stenotrophomonas maltophilia, Burkholderia spp., Pseudomonas aeruginosa, and Staphylococcus aureus. The highest and lowest carbapenem resistance rates among P. aeruginosa in CF patients were shown against meropenem (23%) and doripenem (39%). Conclusions: We showed that trends of carbapenem resistance had decreased over time (1979-2021). This could be due to the limited clinical effectiveness of these antibiotics to treat CF cases over time. Plans should be directed to fight biofilm-associated infections and prevent the emergence of mutational resistance. Systematic surveillance for carbapenemase-producing pathogens in CF by molecular surveillance is necessitated.

A simple label-free method reveals bacterial growth dynamics and antibiotic action in real-time.

Understanding the response of bacteria to environmental stress is hampered by the relative insensitivity of methods to detect growth. This means studies of antibiotic resistance and other physiological methods often take 24 h or longer. We developed and tested a scattered light and detection system (SLIC) to address this challenge, establishing the limit of detection, and time to positive detection of the growth of small inocula. We compared the light-scattering of bacteria grown in varying high and low nutrient liquid medium and the growth dynamics of two closely related organisms. Scattering data was modelled using Gompertz and Broken Stick equations. Bacteria were also exposed meropenem, gentamicin and cefoxitin at a range of concentrations and light scattering of the liquid culture was captured in real-time. We established the limit of detection for SLIC to be between 10 and 100 cfu mL-1 in a volume of 1-2 mL. Quantitative measurement of the different nutrient effects on bacteria were obtained in less than four hours and it was possible to distinguish differences in the growth dynamics of Klebsiella pneumoniae 1705 possessing the BlaKPC betalactamase vs. strain 1706 very rapidly. There was a dose dependent difference in the speed of action of each antibiotic tested at supra-MIC concentrations. The lethal effect of gentamicin and lytic effect of meropenem, and slow bactericidal effect of cefoxitin were demonstrated in real time. Significantly, strains that were sensitive to antibiotics could be identified in seconds. This research demonstrates the critical importance of improving the sensitivity of bacterial detection. This results in more rapid assessment of susceptibility and the ability to capture a wealth of data on the growth dynamics of bacteria. The rapid rate at which killing occurs at supra-MIC concentrations, an important finding that needs to be incorporated into pharmacokinetic and pharmacodynamic models. Importantly, enhanced sensitivity of bacterial detection opens the possibility of susceptibility results being reportable clinically in a few minutes, as we have demonstrated.

Cytotoxicity and anti-biofilm activities of biogenic cadmium nanoparticles and cadmium nitrate: a preliminary study.

Wild-type microorganisms have become tolerant to higher antibiotic and antimicrobial agent concentrations due to the global increase in antibiotic consumption. Green-synthesized nanoparticles (NPs) have been proposed as potential antimicrobial agents to overcome the problem. This research prepared cadmium nanoparticles (Cd NPs) using Artemisia persica extract. To clarify the biological behavior of Cd NPs and Cd (NO3)2, cytotoxicity, antibacterial, anti-biofilm, and biocompatible experiments were performed. Since Cd toxicity is associated with liver, kidney damage, and other deficits, HepG2 and HUVEC cell lines were employed as the in vitro cytotoxicity models. Cd NPs had a lower cytotoxic effect than Cd (NO3)2 against both HepG2 and HUVEC cells. The Cd NPs exhibited no hemolysis activity. The antibacterial and anti-biofilm studies were conducted using gram-positive Staphylococcus aureus and gram-negative Proteus mirabilis and Pseudomonas aeruginosa with the ability to form severe adherent biofilms. The antibacterial activity of Cd NPs against clinically isolated S. aureus, P. mirabilis, and P. aeruginosa was above 2560 µg mL- 1. The Cd NPs (640 µg mL- 1) decreased the biofilm formation of S. aureus, P. mirabilis, and P. aeruginosa by 24.6%, 31.6%, and 26.4%, respectively.Moreover, adding Cd NPs (100 µg/disc) to antibiotic discs increased the antibacterial activity of vancomycin, gentamicin, tetracycline, streptomycin, meropenem, and kanamycin against Methicillin-resistant S. aureus, significantly. Due to the emergence of resistant microorganisms, Cd NPs can be used as an exciting material to counterattack global health problems. Further research is needed to clarify the molecular mechanisms underlying Cd NPs' pharmacological and toxicological effects.

A Mycobacterium tuberculosis-Infected Patient Who Could Not Tolerate Oral Intake Successfully Treated Using an Intravenous Tedizolid-Containing Regimen.

BACKGROUND Mycobacterium tuberculosis (M. tuberculosis) is usually treated by oral antimycobacterial agents, including rifampicin, ethambutol, and pyrazinamide, but the treatment regimen with intravenous and/or intramuscular antimycobacterial agents for patients who cannot take medications orally remains unclear. CASE REPORT A 77-year-old man with chronic renal failure had an esophageal-skin fistula after he had surgeries for removal of esophageal and gastric cancers and reconstruction using jejunum, and he showed a cavity, tree-in-bud formation, and pleural effusions in his left upper lung fields on his chest X-ray after treatment of cellulitis and bacteremia/candidemia by meropenem, teicoplanin, and micafungin. M. tuberculosis was isolated from his sputum and exudate fluid from the reconstructed esophageal-skin fistula. Although he could not take antimycobacterial agents orally, treatment was started with intravenous agents combining levofloxacin (LVFX) every other day, isoniazid (INH), and linezolid (LZD). However, his platelets were decreased 21 days after treatment started, and it was thought to be an adverse effect of LZD and/or INH. After changing LZD to tedizolid (TZD), in addition to changing from INH to intramuscular streptomycin twice per week, his platelet counts increased. Intravenous TZD could be continued, and it maintained his condition without exacerbations of thrombocytopenia and renal failure. The M. tuberculosis disappeared, and the abnormal chest X-ray shadows were improved 2 months after the start of treatment. CONCLUSIONS Administration of intravenous TZD, in addition to intravenous LVFX and intramuscular SM in combination, might be a candidate regimen for M. tuberculosis patients who cannot take oral medications.

Meropenem plus Ceftaroline Is Active against Enterococcus faecalis in an In Vitro Pharmacodynamic Model Using Humanized Dosing Simulations.

The standard of care for serious Enterococcus faecalis infections is ampicillin plus ceftriaxone. Ampicillin's inconvenient dosing schedule, drug instability, allergy potential, along with ceftriaxone's high risk for Clostridioides difficile infection and its promotion of vancomycin-resistant enterococci (VRE), led our team to explore alternative options. This work aimed to understand the role of carbapenems in combination with cephalosporins in these infections. We selected two ampicillin and penicillin susceptible E. faecalis strains (AMP-MIC 0.5-2 µg/mL; PCN-MIC 2 µg/mL) and simulated human therapeutic dosing regimens in a 48-h in vitro pharmacodynamic model (IVPD) with ampicillin (2g q4h), ertapenem (1g q24h), meropenem (2g q8h), ceftriaxone (2g q12h), and ceftaroline (600 mg q8h). As expected, ampicillin plus ceftriaxone demonstrated enhanced activity compared with ampicillin monotherapy with no MIC increases in either isolate. Meropenem and ceftaroline demonstrated significant kill against both isolates, with no regrowth or MIC increases occurring. Meropenem plus ceftriaxone also demonstrated significant kill, and while no MIC increases were identified for meropenem, there was minor regrowth and larger standard deviations. Ertapenem combined with either ceftriaxone or ceftaroline enhanced activity at 24 h, but at 48 h, regrowth occurred, and ertapenem MIC increases were noted. Meropenem-based combination therapy against E. faecalis may provide clinicians with another regimen to treat severe E. faecalis infections. Meropenem plus ceftaroline was as active as the standard of care treatment (ampicillin plus ceftriaxone) and may serve as an alternative for serious E. faecalis infections. Further studies are warranted to determine the clinical efficacy.

Population analysis profiling: is it still the gold standard for the determination of heteroresistance in carbapenemase-producing Enterobacteriaceae?

Heteroresistance is the phenomenon wherein subpopulations of presumed isogenic bacteria show varied antibiotic susceptibilities, and the current gold standard for the determination of heteroresistance is population analysis profiling (PAP). However, when conducting PAP to confirm carbapenem heteroresistance in Enterobacteriaceae, the authors found some isolates that did not seem to be heteroresistant, despite meeting PAP criteria. This article elaborates on the validity of PAP for the determination of heteroresistance, especially among carbapenemase-producing Enterobacteriaceae (CPE). Bacterial cells that were originally non-viable on selective agar supplemented with a high concentration of meropenem were found to be occasionally viable, likely due to the hydrolysis of carbapenems by carbapenemases produced by dying cells, mimicking the emergence of subpopulations with enhanced resistance. As such, PAP for CPE is highly affected by carbapenemases produced by dying populations, and may not detect heterogeneity in carbapenem resistance appropriately among seemingly isogenic clones.

The effect of biofilm inhibitor N-acetylcysteine on the minimum inhibitory concentration of antibiotics used in Gram-negative bacteria in the biofilm developed on catheters.

The study determined the effect of N-acetylcysteine (NAC) on the susceptibility of various antibiotics used to treat Gram-negative catheter-related infection in isolates obtained from pediatric patients admitted to the hematology and oncology department of Medical Park Bahçelievler hospital in Istanbul, Turkey. Biofilms were created in vitro utilizing clinical isolates of Escherichia coli, Pseudomonas aeruginosa, Pseudomonas putida, and Proteus mirabilis. 24 h old biofilms were developed on 96-well plate with strains and the minimum biofilm inhibitory concentration (MBIC) of six antibiotics were measured before and after the addition of 75 mg/ml N-acetylcysteine with microplate reader at 450 nm after crystal violet assay. The addition of NAC reduce the MBIC of cefepime, ceftazidime, colistin, meropenem from (16, 16, 8, 4 µg/ml) to (8, 4, 4, 2 µg/ml) respectively in E. coli (isolate 1). In P. aeruginosa (isolate 4), the MBIC of amikacin, ceftazidime, meropenem (64, 32, and 32 µg/ml) reduced to (8, 1, and 0.5 µg/ml) respectively. MBIC of cefepime, colistin, meropenem (32, 16,and 16 µg/ml) reduced to (2, 2,and 0.5 µg/ml) respectively in P. putida (isolate 5). In P. mirabilis (isolate 6), MBIC of amikacin, cefepime, ceftazidime, colisitin and meropenem (64, 128, 32, 4, and 32 µg/ml) reduced to (8, 8, 1, 1, 4 µg/ml). NAC in combination therapy can practically reduce the MBIC of antibiotics used to treat Gram negative bacteria that develop biofilm in medical catheters. As a result, these combinations can be considered as an essential alternative for increasing the antibiotic susceptibility of pathogenic microorganisms and thus increasing treatment success rates.

Bismuth complex of quinoline thiosemicarbazone restores carbapenem sensitivity in NDM-1-positive Klebsiella pneumoniae.

Resistant bacteria represent an urgent worldwide threat. NDM-1-producing strains are rendering the last line antibiotics less effective. Six bismuth complexes of general formula BiLCl2, where L is a thiosemicarbazone bearing a quinoline moiety, have been synthesized and fully characterized, including their X-ray crystal structures. The synergistic relationship between the compounds and meropenem have been tested in a combination therapy in carbapenem-resistant Klebsiella pneumoniae (NTCT14331) carrying the NDM-1 gene. Quinoline-2-carboxaldehyde-N4-phenyl-3-thiosemicarbazone bismuth dichloride and carbapenem showed synergism in a dose dependent manner with negligible antibacterial activity when used in a monotherapy and could restore antibiotic sensitivity in the strain producing NDM-1 enzyme. The minimum inhibitory concentration (MIC) of meropenem lowered down 128 folds up to 2 µgmL-1, a concentration lower to the sensitivity level. The IC50 of the compound against A549 human lung carcinoma cells and HuDe human epithelial tissue was 46.96 ± 16.66 µM and 54.26 ± 9.89 µM respectively. The cytotoxicity against human cells was higher than the effective concentration needed for the synergistic effect in bacterial cells, indicating that a structural optimization of the compounds is needed.