Disk Test Research Articles

Wear mechanisms of aluminum 5083/6061/7075 with and without T6 treatment

The application of hardened aluminum alloys on the drive elements must be safe and reliable, T6 treatment is often used to improve their mechanical properties and dimensional stability. However, the impact of T6 treatment on operating life is not easy to evaluate. Hence, the effects of T6 treatment on the wear of aluminum 5083/6061/7075 were studied by a steel ball on disk tester. The results showed that T6 treatment tended to reduce the values of the friction coefficient about 9%. Moreover, T6 treatment had no significant effect on the frequency of the change of the friction coefficient of 5083 and 6061, but significantly affected that of 7075. T6 treatment can also reduce the size of wear particles about 16%. Based on the results, the wear mechanisms of aluminum 5083/6061/7075 with and without T6 treatment are described in this paper.

Edge notched disc test for evaluation of mode-I fracture toughness of brittle material

In the current investigation, the fracture toughness of plexiglass specimens was accurately measured employing Edge Notched Disc (END) type specimens. Besides, the Notched Brazilian Discs (NBD) were used in order to validate the results of the conducted END experiments. Moreover, a numerical analysis was carried out on the END tests to verify the accuracy of the measured fracture toughness values. In the first stage, the splitting tensile test was used to accurately calibrate the micro-scale properties of the Flat Joint (FJ) model. In the second phase, the numerical simulation of END and NBD models was created, in which the notch lengths in END and NBD were set to 5, 15, 25, 40 and 10, 20, 30, 40, 50, 60 in millimeters, respectively. According to the obtained results, the considered FJ model is capable of making an accurate determination of the potential crack growth path and crack initiation stress like the experimentally obtained results for plexiglass specimens. It was also derived that lengthening the notch could not have a considerable effect on the fracture toughness of the models. The Tensile stress distribution on the failure surface of END test could be the main cause of the lower fracture toughness levels of END test. Besides, the same fracture extension patterns were seen from the experimental investigations and numerical simulations.

A new function of thymol nanoemulsion for reversing colistin resistance in Salmonella enterica serovar Typhimurium infection.

Adjuvant addition of approved drugs or foodborne additives to colistin might be a cost-effective strategy to overcome the challenge of plasmid-mediated mobile colistin resistance gene emergence, which poses a threat in the clinic and in livestock caused by infections with Gram-negative bacteria, especially carbapenem-resistant Enterobacteriaceae. Chequerboard assay was applied to screen the colistin adjuvants from natural compounds. The killing-time curve, combined disc test and membrane permeation assay were conducted to identify the synergy efficacy of thymol and colistin in vitro. Thin-layer chromatography (TLC), LC-MS and fluorescence spectra were used to indicate the interaction of thymol and MCR-1. The potential binding sites were then investigated by molecular simulation dynamics. Finally, a thymol nanoemulsion was prepared with high-pressure homogenization as the clinical dosage form. Thymol presented an excellent synergistic effect in vitro with colistin against Salmonella enterica serovar Typhimurium and Escherichia coli bacteria. Thymol addition, forming a complex with MCR-1, might interfere with the efficacy of MCR-1. Moreover, thymol strengthened colistin activity associated with potentiating membrane damage, destroying the biofilm and enhancing reactive oxygen species-mediated oxidative damage. Thymol nanoemulsion combined with colistin remarkably prevented the intestinal damage caused by S. Typhimurium infection, resulting in a survival rate higher than 60%. This study achieved a promising thymol oral formulation as colistin adjuvant to combat S. Typhimurium infection, which could be used to extend the lifespan of colistin in clinical veterinary medicine.

Comparison of loop-mediated isothermal amplification, multiplex PCR, and REP- PCR techniques for identification of carbapenem-resistant Acinetobacter baumannii clinical isolates

Background and Objectives: Acinetobacter baumannii, an opportunistic pathogen, is related to hospital-acquired infections and increased mortality. This study aimed to develop the loop-mediated isothermal amplification (LAMP) test for the fast-de- tecting of A. baumannii isolates as well as determining genetic relatedness for these isolates via the REP-PCR technique.
 Materials and Methods: LAMP primers and multiplex PCR primers were designed for recognizing A. baumannii isolates harboring the bla SHV-1 , bla PER-1 , bla , AMPC, qnr, and aac (6)-1 genes, were collected (October 2020 to February 2021) from Shahid Motahari Hospital, Tehran, Iran. Combination disc test (CDT) results were used to assess the phenotypic iden- tification of isolates from ESBL producers. The sensitivity of the LAMP method was evaluated using a range of serial dilu- tions of genomic DNA. Results were compared between the LAMP technique, and multiplex PCR. The genetic diversity of clinical isolates was determined by REP-PCR.
 Results: Among one hundred A. baumannii samples and based on the combined disc test, 56% of isolates were ESBL pro- ducers. The sensitivity of the LAMP technique for the identification of A. baumannii was 4.06 ng/μl whilst the multiplex PCR was (16.2 ng/μl). Regarding multiplex PCR, (68%) of the isolates were bla SHV-1 positive, (40%) bla , (85%) aac (6́)-1, AMPC (67%), bla TEM-1 (63%), and (15%) qnr respectively. While in LAMP, (69%) of isolates were bla positive, (86%) aac (6')-1, and (20%) qnr. The results of AMPC, bla TEM-1 , and bla PER-1 genes showed 100% compatibility between multiplex PCR and LAMP assays. The results of REP-PCR indicated there were 17 clones, clone A at 14% was the most prevalent of the isolates.
 Conclusion: Wherever equipment and financial constraints are crucial, the LAMP test offers a better and more potent detec- tion rate for the identification of A. baumannii isolates than multiplex PCR. Furthermore, the genetic diversity of A. bauman- nii in these clinical isolates showed frequent commonality of genotypes.

Impact and Role of Hypothalamic Corticotropin Releasing Hormone Neurons in Withdrawal from Chronic Alcohol Consumption in Female and Male Mice.

Worldwide, alcohol use and abuse are a leading risk of mortality, causing 5.3% of all deaths (World Health Organization, 2022). The endocrine stress system, initiated by the peripheral release of corticotropin releasing hormone (CRH) from primarily glutamatergic neurons in the paraventricular nucleus of the hypothalamus (PVN), is profoundly linked with alcohol use, abuse, and relapse (Blaine and Sinha, 2017). These PVN CRH-releasing (PVNCRH) neurons are essential for peripheral and central stress responses (Rasiah et al., 2023), but little is known about how alcohol affects these neurons. Here, we show that two-bottle choice alcohol consumption blunts the endocrine-mediated corticosterone response to stress during acute withdrawal in female mice. Conversely, using slice electrophysiology, we demonstrate that acute withdrawal engenders a hyperexcitable phenotype of PVNCRH neurons in females that is accompanied by increased glutamatergic transmission in both male and female mice. GABAergic synaptic transmission was unaffected by alcohol history. We then tested whether chemogenetic inhibition of PVNCRH neurons would restore stress response in female mice with a history of alcohol drinking in the looming disk test, which mimics an approaching predator threat. Accordingly, inhibition of PVNCRH neurons reduced active escape in hM4Di alcohol history mice only. This study indicates that stress-responsive PVNCRH neurons in females are particularly affected by a history of alcohol consumption. Interestingly, women have indicated an increase in heavy alcohol use to cope with stress (Rodriguez et al., 2020), perhaps pointing to a potential underlying mechanism in alcohol-mediated changes to PVNCRH neurons that alter stress response.SIGNIFICANCE STATEMENT Paraventricular nucleus of the hypothalamus neurons that release corticotropin releasing hormone (PVNCRH) are vital for stress response. These neurons have been understudied in relation to alcohol and withdrawal despite profound relations between stress, alcohol use disorders (AUD), and relapse. In this study, we use a variety of techniques to show that acute withdrawal from a history of alcohol impacts peripheral stress response, PVNCRH neurons, and behavior. Specifically, PVNCRH are in a hyperactive state during withdrawal, which drives an increase in active stress coping behaviors in female mice only. Understanding how alcohol use and withdrawal affects stress responding PVNCRH neurons may contribute to finding new potential targets for the treatment of alcohol use disorder.

Effects of laser remelting on microstructure and tribological properties of plasma–sprayed Fe45Mn35Co10Cr10 high–entropy alloy coating

To further improve the Fe45Mn35Co10Cr10 high–entropy alloy coating prepared by plasma spraying, laser remelting was used to improve its structures and tribological properties. The effects of laser remelting on the microstructure, element composition, phase and hardness of obtained coating were investigated using a super depth of field microscope, energy dispersive spectrometer, X–ray diffraction and hardness tester, respectively. The tribological properties were measured via a ball–on–disk tester at room temperature and 500 °C, and the wear mechanisms were also discussed. The results show that the laser–remelted HEA coating is still composed of face–centered cubic structure, and its hardness is increased by ~301.4% compared with the plasma–sprayed coating, which is attributed to the grain refinement and solid solution strengthening effects. The average coefficient of friction and wear rate of laser–remelted HEA coating is superior to the plasma–sprayed HEA coating, showing that the laser remelting process plays the roles of friction reduction and wear resistance. The wear mechanism of plasma–sprayed HEA coating at room temperature is fatigue wear, abrasive wear and oxidative wear; while that of laser–remelted coating is abrasive wear and oxidative wear. Moreover, the wear mechanism of plasma–sprayed coating at 500 °C is adhesive wear, abrasive wear and oxidative wear, while that of laser–remelted HEA coating is adhesive wear and oxidative wear, which is attributed to the reduction of plastic deformation by the softening effect at high temperature.

Cutter Soil Mix-Energywall full-scale test experimental setup

The demand for sustainable heat production is growing worldwide [1]. Classical geothermal borehole installations are costly due to the required boring depth and space demands in the urban environment. Shallow geothermal heat exchangers comprised of thermally-activated geostructures in combination with heat pumps (also known as energy geostructures, EGS) offer an interesting alternative due to a combination of functions [2]. 
 This paper focuses on the thermal properties of the CSM (Cutter-Soil-Mix [3]) Energywall; a novel EGS type in which heat exchanger pipes are installed in a cutter-soil-mix wall to thermally activate it. Therefore, the CSM Energywall serves the dual function of supporting the soil/overlying structure and providing geothermal energy for space heating/cooling. A test site has been setup in Amstelveen, the Netherlands, where this system will be tested for a 1 year period (starting March 2023). A test site picture is shown in Figure 1.The goals of the experiment are to evaluate the thermal efficiency of the system and to assess its thermo-mechanical behaviour by means of numerical models valiated against the data collected from site monitoring. In the first part of the forthcoming paper, test setup and experimental results (both from the field and laboratory tests of the CSM material) will be presented. In the second part, the implementation and validation of the numerical models will be described. Lastly, the paper will focus on the suitability of the CSM-Energywall as a sustainable urban heat source, with particular reference to the Netherlands context.
 The following research questions have been defined for the CSM-Energywall experiments:
 
 What is the heat extraction potential of a CSM-Energywall in sandy and in cohesive soils?
 Does thermal activation affect the mechanical properties of the CSM material?
 What is the long term heat production potential of the CSM-Energywall?
 How accurately can the heat extraction potential be predicted using numerical models?
 
 A test setup at Amstelveen (NL) has been built to answer the above research questions. The test site is located in a building pit of 22 x 13m. CSM-walls were built along the pit perimeter, serving both as a soil retaining structure and as a foundation for the superstructure. The CSM wall has a thickness of 0.55m and is reinforced with IPE steel beams. The bottom of the CSM wall has a level of NAP-18.0m (NAP= Normaal Amsterdamse Peil, vertical reference system of the Netherlands). The bottom of the steel IPE beams is at a level of NAP-15.6m. The ground level at the test site is located at NAP-0.7m and the groundwater table at NAP-1.5m. The building pit has an excavation level of NAP-4.70m. Heat exchanger pipe loops with a diameter of 20mm have been connected to the steel beams representing the CSM wall reinforcement (Figure 1). The loops have a depth of NAP-15.0m or NAP-11.0m. Five main groups of loops are connected to the flow distributer. Each group is then split into six subgroups. Each subgroup consists of two thermoactive steel rebars. The test setup will run for the duration of the building construction. Being able to select the geothermal activation of the shallowest or deepest loops, it will be possible to measure the energy output of both the fine-grained layers (with a bottom depth of NAP-11.0m) and the underlying sandy layers. 
 During the tests the following aspects will be monitored:
 
 Flowrate of fluid through the main loops (FTB4700 Flowmeter)
 Temperature of each main group of loops (PT100 thermowell)
 Flowrate and temperature of heat pump inlet/outlet fluid (Kramstrup Energymeter)
 Temperature of the soil (thermistor strings)
 
 CSM material core samples have been taken for laboratory testing. Cyclic thermal loading, unconfined compression strength (UCS) tests, computerize tomography (CT) scan tests and hot disk tests will be conducted on samples taken from different depths. The goal of the laboratory testing is to evaluate:
 
 The thermal properties of CSM material depending on the original insitu soil composition, needed to assess the thermal efficiency of the system.
 The UCS of the CSM material, and its possible dependency on temperature.
 The macroporisy and density distribution of the CSM material, to gain insight into the material composition.
 The influence of thermal cycling on the material’s mesostructure (e.g. porosity and density distribution).
 
 The full-scale experiment is going to be numerically modelled in 3D using the COMSOL Multiphysics Finite Element software. The model will be validated based on the experimental results of the test after 1 year and calibrated using laboratory measured thermal properties of the CSM material. The model will then be extended to predict the long term efficiency of the CSM- Energywall and its thermo-mechanincal behaviour.

Designing a Multiplex PCR for Rapid and Accurate Detection of Metallobetalactamases Resistant Genes from Acinetobacter baumaniiIsolates in Tehran City, Iran.

Acinetobacter baumannii strains harboring Meallobetalactamases (MBL) pose a significant threat in the context of nosocomial infections. The present investigation was undertaken with the objective of devising a Multiplex PCR methodology for the concurrent detection of MBL genes within A. baumannii strains prevalent in Tehran City, Iran. Between October 2020 and February 2021, 100 strains of A. baumannii were procured from burn specimens of hospitalized patients at Motahhari Hospital in Tehran. The identification of A. baumannii strains involved conventional biochemical techniques, coupled with confirmation of the presence of the bla OXA-51 gene. Antibiotic susceptibility was assessed using the Kirby-Bauer disc diffusion test. MBL-producing strains were characterized through a phenotypic approach employing the combined disk test, alongside Multiplex PCR for the simultaneous identification of bla VIM, bla IMP, bla GIM, and bla NDM genes. Statistical analyses were conducted using the chi-square test, with SPSS version 20.0 employed for data processing. Among 100 strains examined, 96.1% exhibited positivity for MBL, as determined by the combined disk test. The study revealed a predominance of extensively drug-resistant (XDR) strains, with colistin demonstrating the highest level of sensitivity. The genotypic assay unveiled that Multiplex PCR identified bla VIM, bla NDM, and bla IMP in 20 strains, bla VIM and bla NDM in 30 strains, and exclusively the bla NDM gene in 45 strains. Notably, the Multiplex PCR technique exhibited the capacity to concurrently detect MBL genes (bla VIM, bla IMP, bla GIM, bla NDM) in 2 strains. The current investigation underscores prevalence of the bla NDM gene within clinical strains of A. baumannii. Furthermore, Multiplex PCR emerges as a robust and highly sensitive technique for rapid discernment of the MBL genes within in A. baumannii strains.

Characterization of carbapenemase-producing Gram-negative bacilli: first report of blaNDM-1 in Enterobacter cloacae.

The spread of multidrug-resistant bacteria, particularly carbapenem-resistant Gram-negative bacilli (CR-GNB), has become a serious challenge for clinicians due to limited therapeutic options. The aim of the study was to investigate the prevalence of carbapenemase production among clinical isolates recovered from 352 samples collected in Tebessa hospital, Algeria. Bacterial isolates were identified by 16S RNA gene sequencing and susceptibility to antibiotics was determined by disk diffusion method. Carbapenem-resistant isolates were screened for carbapenemase production using modified carba Nordmann-Poirel test, modified Hodge test and imipenem-EDTA combined disc test. Extended-spectrum β-lactamases (ESBL) were detected using double-disk synergy test. Molecular characterization of carbapenemases and ESBL genes was performed by polymerase chain reaction (PCR) and sequencing. A total of 85 Gram-negative bacilli isolates were recovered mainly from urine samples and were identified as: Klebsiella pneumoniae (17.65%), Serratia odorifera (15.29%), Escherichia coli (12.94%), Raoultella ornithinolytica, Enterobacter cloacae (11.76%), Serratia marcescens (10.59%), Morganella morganii (7.06%), Proteus mirabilis (5.88%), Acinetobacter baumannii (4.70%) and Pseudomonas aeruginosa (2.35%). All strains were resistant or intermediate to imipenem and/or ertapenem. ESBL, carbapenemase and metallo-beta-lactamases (MBL) phenotypes were detected in 19 (22.35%), 9 (10.59%) and 2 (2.35%) GNB isolates, respectively. PCR results in nine carbapenemase-producing GNB strains chosen showed the presence of one to four carbapenemase genes (blaGES, blaSME, blaNDM-1, blaVIM, blaGIM, blaSPM, blaOXA-48) in four strains; however, seven strains had at least one ESBL gene (blaTEM-1, blaCTXM-15, blaSHV). In this study, we report the first incidence of blaNDM-1 gene in Enterobacter cloacae isolated from urine sample in Algeria.

A new scaled testing methodology for the analysis of rolling contact fatigue in railway steels.

Twin disc testing is a relatively cost effective and practical method of investigating the damage resistive properties of rail steels in a scaled environment. The loading conditions and dimensions used in testing are scaled in such a way that the Rolling Contact Fatigue (RCF) generated on a twin disc rig are representative of the conditions experienced at the full-scale. Typical methodologies to generate RCF on a twin disc rig involve the application of water to the contact patch throughout the test, with perhaps a few thousand dry cycles being run beforehand. This research explores the use of weather data to reflect the real-world contact conditions more accurately between a wheel and rail. Met Office weather data collected from 1981 to 2010 shows the average annual precipitation in the UK is around 133 days of rain or snow, which is nearly 36 % of the year. In this study, weather data was used to determine the ratio of wet to dry cycles in the testing methodology.  50k dry cycles are run in intervals of 5k and then transitioned to 25k of wet cycles, which is 30% of the total cycles. Intervals were kept at 5k so attaining 36%. If RCF is not initiated after the first 75k cycles, which ends with 25k wet cycles, then the same dry and wet cycles are repeated. RCF data generated using this methodology demonstrated expected differences in the RCF resistive properties of two rail steel grades, R260 and R350HT. In test 1 the point of initiation for each grade was not captured, though cracks were visible around the expected cycles to initiation, which was verified using optical microscopy. The cracks viewed on the softer R260 steel samples, ‘’260’’ referring to the Brinell hardness value of the steel, were more developed at 85k cycles and showed signs of spalling, whilst the cracks on the harder R350HT sample were much smaller. In test 2 the point of initiation was found for each grade. Optical microscopy was also used to show the depth and direction of head check cracks to ensure the damage viewed from the head was RCF and not plastic flow or cyclic wear. This paper shows the necessity for considering the number of wet cycles applied during twin disc testing and demonstrates it is possible to run a high number of wet cycles which are more representative of real-world conditions when generating RCF on twin disc rigs.  

Potential Use of Saga Leaf Extract (Abrus precatorius) as Anti Bacteria Aeromonas hydrophila by in Vitro

Many diseases are caused by bacterial pathogens, for example, Aeromonas hydrophila. One alternative that can be done to overcome this problem is to use saga leaves (Abrus precatorius) which have bioactive ingredients as antibacterial ingredients. The aims of this study were to determine the antibacterial activity of saga (A. precatorius) leaf extract, to study the character and structure of bacteria inhibited by saga (A. precatorius) leaf extract and to study the bioactive components contained in saga (A. precatorius) leaf extract. The results of the disc test showed that the average inhibition zone was 14,29 mm while the MIC test results showed that at the dose 1 mg/L capable of inhibiting bacterial growth (bacteriostatic) and dose 10 mg/L It has been able to kill bacteria (bactericidal). Crude extract of saga leaf extract (A. precatorius) affects the character and structure of A. hydrophila bacteria by damaging the cell walls and cell membranes of bacteria. The results of Infrared Spectrophotometry analysis of saga (A. precatorius) leaf extract and Ultra Violet Spectrophotometry analysis with 96% absorption ethanol were suspected to contain flavonoid compounds

Data-driven enhanced FDEM for simulating the rock mechanical behavior

In this paper, a data-driven enhanced combined finite-discrete element method (DDFDEM) is proposed to simulate the rock mechanical behavior by directly assigning the rock experimental data into mechanical simulations, thus bypassing the empirical constitutive model of rock. To achieve this, a novel data-driven iterative solver with transient dynamic system equilibrium constraint is first proposed and embedded into the FDEM computing framework. Then, the bonding force update algorithm for crack elements is improved to mitigate the error accumulation during the iteration process. After that, a recommended formation for the proper size of the experimental data set is proposed to balance the computational accuracy and efficiency of DDFDEM, and an efficient nearest neighbor search algorithm is introduced to significantly improve the computational efficiency of DDFDEM. After the above improvements, the computational accuracy and efficiency of DDFDEM in simulating the rock deformation and complex failure process are validated by conducting several examples, including the thin plate tension test, uniaxial compression test, and Brazilian disk test. Finally, the advantage of DDFDEM over conventional FDEM in comprehensively presenting the information hidden behind the experimental data sets is validated by reproducing the nonlinear mechanical behaviors of rock samples based on a data set following the nonlinear elastic material law.

Numerical investigation of ice plate fractures upon rigid ball impact

The fracture process and breaking capability of ice cover impacted by high-speed projectiles before underwater explosion is an urgent subject of scientific research in ice engineering applications. This paper presents the results of numerical simulations of the dynamic fracture behaviour induced by the impact of a small spherical projectile on an ice plate. The proposed 3D rate-dependent peridynamics model is validated by the dynamic ring Brazilian disc testing of ice specimens. Good agreements between the present model and the previous experiments are obtained in ice breaking processes and damage patterns of thin, medium and thick ice plates. Several cases are analysed and discussed in terms of various impact velocities, ice thicknesses, and boundary constraint conditions. The simulations identify detailed fracturing characteristics that are not observed in experiments, including the sequence and shape of crack propagation in a short time interval, the crater formation and the damage evolution along the thickness direction. The proposed peridynamics computational model provides new understanding of the potential of using penetrator–ice block impact tests to observe the evolution of complex brittle damage and reveal the failure mechanism.

A dimensional analysis based multi-scale thermal damage framework of brittle materials at elevated temperatures

Research on macro-scale damage prediction and micro-scale damage mechanisms of brittle materials at elevated temperatures is extremelyimportantto the design and application of practical engineering structures. In this study, a multi-scale thermal damage framework is proposed for both describing macro-scale damage evolution and collective micro-scale cracks behavior of brittle materials atelevatedtemperatures. In the framework, the evolution equation of ideal micro-crack system is deduced to establish the relationship between the macro-scale damage and the micro-scale crack nucleation and growth based on dimensional analysis method. To support the multi-scale thermal damage framework, the multi-scale damage of the benchmark fracture test of the Brazilian disk at elevated temperatures is predicted and compared with the experimental results. The results support the effectiveness and ability of the multi-scale thermal damage framework, which can achieve thermal damage prediction of brittle materials in macro-scale as well as physical mechanisms description in micro-scale.

Discovery of isatin-β-methyldithiocarbazate derivatives as New Delhi metallo- β-lactamase-1 (NDM-1) inhibitors against NDM-1 producing clinical isolates

New Delhi metallo-β-lactamase-1 (NDM-1) poses a threat to public health due to its capability to hydrolyze nearly all β-lactam antibiotics, leaving limited treatment options for NDM-1 positive pathogens. Regrettably, there are presently no effective NDM-1 inhibitors in clinical use. This compels us to seek new compounds to combat multi-drug resistant bacterial infections (MDR). In our study, Zndm19 was identified as a new NDM-1 inhibitor through virtual screening and an NDM-1 enzyme activity inhibition assay. Subsequently, we employed the checkerboard method, time-killing assay, and combined disk test to investigate the synergistic bactericidal efficacy of Zndm19 in combination with meropenem (MEM). Meanwhile, molecular docking and site-directed mutagenesis were conducted to uncover the crucial amino acid residues engaged in Zndm19 binding. Finally, we established a mice peritonitis infection model to assess the synergistic effect of Zndm19 and MEM in vivo. Our findings demonstrated that 16 µg/mL of Zndm19 inhibited NDM-1 activity without affecting NDM-1 expression, restoring the bactericidal activity of MEM against NDM-1-positive Escherichia coli in vitro. Furthermore, MET-67, ASP-124, HIS-189, and HIS-250 amino acid residues constituted the active site of Zndm19 in NDM-1. Importantly, this combination therapy exhibited synergistic anti-infection activity in the mice peritonitis infection model, leading to an approximate 60% increase in survival rates and reduction of tissue bacterial load, effectively combating bacterial infection in vivo. In summary, our research validates that the synthetic novel NDM-1 inhibitor Zndm19 holds promise as a drug to treat drug-resistant bacterial infections, especially those harboring NDM-1.

Novel metallo-β-lactamases inhibitors restore the susceptibility of carbapenems to New Delhi metallo-lactamase-1 (NDM-1)-harbouring bacteria.

The production of metallo-β-lactamases is a major mechanisms adopted by bacterial pathogens to resist carbapenems. Repurposing approved drugs to restore the efficacy of carbapenems represents an efficient and cost-effective approach to fight infections caused by carbapenem resistant pathogens. The nitrocefin hydrolysis assay was employed to screen potential New Delhi metallo-lactamase-1 (NDM-1) inhibitors from a commercially available U.S. Food and Drug Administration (FDA) approved drug library. The mechanism of inhibition was clarified by metal restoration, inductively coupled plasma mass spectrometry (ICP-MS) and molecular dynamics simulation. The in vitro synergistic antibacterial effect of the identified inhibitors with meropenem was determined by the checkerboard minimum inhibitory concentration (MIC) assay, time-dependent killing assay and combined disc test. Three mouse infection models were used to further evaluate the in vivo therapeutic efficacy of combined therapy. Twelve FDA-approved compounds were initially screened to inhibit the ability of NDM-1 to hydrolyse nitrocefin. Among these compounds, dexrazoxane, embelin, candesartan cilexetil and nordihydroguaiaretic acid were demonstrated to inhibit all tested metallo-β-lactamases and showed an in vitro synergistic bactericidal effect with meropenem against metallo-β-lactamases-producing bacteria. Dexrazoxane, embelin and candesartan cilexetil are metal ion chelating agents, while the inhibition of NDM-1 by nordihydroguaiaretic acid involves its direct binding to the active region of NDM-1. Furthermore, these four drugs dramatically rescued the treatment efficacy of meropenem in three infection models. Our observations indicated that dexrazoxane, embelin, candesartan cilexetil and nordihydroguaiaretic acid are promising carbapenem adjuvants against metallo-β-lactamases-positive carbapenem resistant bacterial pathogens.

Evaluation of six commercial and in-house phenotypic tests for detection of AmpC β-lactamases: is routine detection possible?

Phenotypic characterization of the prevalent AmpC β-lactamases in clinical isolates is essential for making informed empirical decisions and critical for strengthening antimicrobial stewardship programmes. This study focused on assessing six assays, two in-house and four commercial phenotypic tests for detection of AmpC, to study the feasibility of making its detection a routine diagnostic microbiology laboratory activity. A total of 116 non-duplicate Gram-negative bacteria that were resistant to third-generation cephalosporins and amoxicillin/clavulanic acid, and resistant or susceptible to piperacillin/tazobactam and carbapenems, were screened by cefoxitin discs for AmpC. These isolates were subjected to two in-house (AmpC Tris-EDTA and disc approximation) methods and four commercial tests: D69C AmpC Detection Set; D72C ESBL, AmpC & Carbapenemase Detection Set; combination disc test: ESBL + AmpC Screen Disc Kit; and AmpC MIC Test Strip for confirmation of AmpC production. Ten whole-genome-sequenced AmpC-confirmed Gram-negative isolates were used as positive controls and one as a negative control. The prevalence of AmpC β-lactamases was 16%. Escherichia coli was a major carrier of plasmid-mediated AmpC (26.5%), followed by Klebsiella pneumoniae (23.4%). Phenotypically, 61% of AmpCs were detected by Tris-EDTA (accuracy: 73.8%), 76% by disc approximation (accuracy: 89.2%), 75% by the D69C AmpC Detection Set (accuracy: 95.4%), 74% by the D72C AmpC, ESBL & Carbapenemase Detection Set (accuracy: 95.4%), 76% by the combination disc test (accuracy: 95.4%) and 63% by AmpC MIC Test Strip (accuracy: 87.7%). The sensitivity and specificity of D69C were 97.9% and 88.2%, respectively, and 95.9% and 93.8% for the combination disc test, while for the disc approximation test and D72C they were 93.9% and 75%, and 93.9% and 100%, respectively. Screening by cefoxitin screening was less sensitive (75%) and specific (25%). Disc approximation and the combination disc test detect AmpC in Enterobacterales and also Pseudomonas aeruginosa and Acinetobacter species. We recommend the in-house disc approximation test and the commercial D69C, as well as the combination disc test, as excellent tools for detection of AmpC. The cefoxitin test overcalls AmpC and cannot be considered a good stand-alone test for AmpC detection.

Effect of heat treatment on abrasive wear behaviour of Ni-WC coatings

In this study, an experimental investigation of the abrasive wear behaviour of HVOF-sprayed Ni-10WC metal coatings was conducted. Different heat treatment temperatures, such as 400 °C, 600 °C, and 800 °C, were used to modify the coating. In order to explore microstructure, element analysis, and phase identification were measured by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x-ray diffraction. The porosity and hardness of coatings were performed using a Vickers microhardness tester and image-J software. Abrasive wear tests were performed using a pin on the disc tester against silicon carbide of 100 µm grit as a counter material mounted on a 165 mm circular disc. The outcome demonstrates that coatings' mechanical and microstructure properties are greatly improved by heat treatment. The optimum temperature was determined to be 600 °C, which exhibited maximum hardness as 750 Hv0.3, minimal porosity as 1.8 %, and maximum wear resistance. Heat treatment lowers the development of the W2C amorphous phase, increasing the microstructure's recrystallization and density.

A Comprehensive Study of Phenotypic and Genotypic Techniques to Detect Metallo-β-lactamases in Carbapenem-resistant Escherichia coli (E. coli) and Klebsiella pneumoniae (KP) Strains Derived through Numerous Clinical Specimens in Advanced Health care Facilities

In recent years, an increase in Escherichia coli and Klebsiella pneumoniae resistant to carbapenem was reported globally. Due to their high prevalence and extensive range of medical conditions, Escherichia coli and Klebsiella pneumoniae are both confirmed to be major public health concerns. Furthermore, carbapenem resistance restricts treatment options for individuals infected with these bacteria. Consequently, early detection of carbapenem resistance is essential for starting effective therapy, achieving successful management, and avoiding the infection from spreading further in the future. This study’s objective was to identify the phenotypic and genotypic identification of Metallo-β-lactamases (MBL) in carbapenem-resistant E. coli and K. pneumoniae in advanced healthcare facilities. Meropenem resistance was tested in E. coli and K. pneumoniae using the Kirby-Bauer disc diffusion technique. MBL was discovered using a combination of Disc diffusion testing and the Modified Hodge Test. The Polymerase Chain Reaction was used to determine the genotypes of the bla NDM-1 genes that express these enzymes. Out of 427 strains, including 223 E. coli and 204 K. pneumoniae, 35 (8.2%) consisted of carbapenem-resistant, and 29 (82.85%) showed phenotypically verified as metallo-beta-lactamase producers by using the Combined disc test and 20 (57.14%) using the Modified Hodge test. Polymerase Chain Reaction tests for genes detect those three different strains all showed the bla NDM-1 gene. Carbapenemase production and MBL can be recognized with the help of phenotypic combination disc and MHT tests in labs. Since both tests showed 100% concordance, laboratories may use the less expensive CDT instead of the MHT. The current study supports institutional antibiotic stewardship programmes to manage antibiotic use and prevent CRE worldwide.

Phenotypic methods for detection of metallo-β-lactamase (MBL) production in multidrug resistant gram negative bacilli – comparative study

Introduction: One of the most common mechanism of resistance of bacterial pathogens to β-lactam antibiotics is production of β-lactamase, there are different types of Beta lactamases, which are expressed by drug resistant gram-negative bacteria. Carbapenemases (Metallo beta lactamases/MBL) are the β-lactamases with the widest spectrum of activity. Early detection of MBL-producing organisms is crucial to establish appropriate antimicrobial therapy and to prevent their interhospital and intrahospital dissemination. Several phenotypic methods are available for the detection of MBL producing bacteria. As there is no standardized method present study was done to screen MDR gram negative bacilli isolated from clinical samples for MBL-production by a low cost, convenient and sensitive procedure. Methods: All non-duplicate MDR gram negative isolates obtained from various clinical samples were screened for carbapenam resistance. All carbapenam resistant bacteria were screened for production of MBL by 3 phenotypic tests (Double disc synergy, combined disk test, Hodge test). The results were compared and analyzed on the basis of results obtained by E test. Results: During Study Period, 988 non duplicate gram negative bacilli were isolated, 70.64% (698) were multi drug resistant. Amongst Total number of MDR Isolates to carbapenam resistance was seen in 62(9.28%). These 62 isolates that were resistant to carbapenam were tested for MBL production. 54 (87%) of these 62 isolates showed MBL production by disc potentiation test whereas 41 isolates (66%) gave positive result by DDST. By Modified Hodge test, out of 62, 48 isolates (77.4%) were MBL positive. Compared to E- test, the Sensitivity Specificity and Accuracy for Disc potentiation test was 90%,100% and 90.32%, for Modified Hodge test was 80%,100% and 80.6% and for Double disc synergy test was 68.3%,100% and 69.3%. Conclusion: In our study, in comparison to MBL E test, disc potentiation test is more sensitive than double disc synergy test and Modified Hodge test for detection of MBL phenotypically