Evaluation of Disk Potentiation Test (DPT) and Double Disk Synergy Test (DDST) for The Detection of Metallo-β-Lactamases (MBLs) in Clinical Isolates of Bangladesh

Objective: Increasing the emergence of Metallo-β-lactamase (MBL) producing gram-negative bacteria and their dexterous horizontal transmission demands rapid and accurate detection. This study was conducted to determine a suitable method to promptly detect MBL-producing gram-negative bacteria. Methods: A total of 103 gram-negative bacteria were identified from various clinical samples at a tertiary care hospital in Dhaka city. MBL producers were detected by two phenotypic methods, the Disk Potentiation Test (DPT) and the Double Disk Synergy Test (DDST) based on β-lactam chelator combinations where EDTA/SMA has been used as an inhibitor and Imipenem, Ceftazidime as substrates. Results: 103 isolates which were identified as Escherichia coli spp, Klebsiella spp, Pseudomonas spp, Acinetobacter spp, Proteus spp, Providencia spp were found to be multidrug-resistant in antibiogram test. Isolates showed complete resistance (100%) to Imipenem, Meropenem, and Amoxiclav. The highest carbapenem-resistant etiological agents were Acinetobacter spp 40 (38.8%) followed by Pseudomonas spp 27 (26.2%), Klebsiella spp 26 (25.2%), Escherichia coli 8 (7.8%), Proteus spp 1 (1%) and Providencia spp 1 (1%). DPT method detected significantly (p = 0.000009) a higher number of MBL-producers (Imipenem with 0.5 M EDTA n = 61, 59.2% & Ceftazidime with 0.5 M EDTA n = 56, 54.4%) compared to the DDST method (Imipenem -0.5 M EDTA n = 43, 41.7%, Imipenem – SMA n = 38, 36.9% & Ceftazidime -0.5 M EDTA n = 15, 14.6%). Conclusion: Pieces of evidence suggest that DPT is a more sensitive method than DDST and could be recommended for identifying MBL-producing bacteria in Bangladeshi hospitals for the proper management of patients, to reduce time constraints and treatment costs.

Test of subcritical crack growth and fracture toughness under water-rock interaction in three types of rocks

The subcritical crack growth and fracture toughness in peridotite, lherzolite and amphibolite were investigated with double torsion test. The results show that water-rock interaction has a significant influence on subcritical crack growth. With water-rock interaction, the crack velocity increases, while the stress intensity factor declines, which illustrates that water-rock interaction can decrease the strength of rocks and accelerate the subcritical crack growth. Based on Charlse theory and Hilling & Charlse theory, the test data were analyzed by regression and the correlation coefficients were all higher than 0.7, which shows the correlation is significant. This illustrates that both theories can explain the results of tests very well. Therefore, it is believed that the subcritical crack growth attributes to the breaking of chemical bond, which is caused by the combined effect of the tensile stress and the chemical reaction between the material at crack tip and the corrosive agent. Meanwhile, water-rock interaction has a vital effect on fracture toughness. The fracture toughness of samples under atmospheric environment is higher than that of samples immersed in water. And water-rock interaction has larger influence on fracture toughness in amphibolite than that in peridotite and lherzolite.

Anchorage performance of large-diameter FRP bolts and their application in large deformation roadway

In underground coal mines, fibre reinforced polymer(FRP) bolt is ideal for mined rib reinforcements as it can prevent gas explosions caused by shearer frictional spark. With increasing mining depth, small diameter FRP bolts used in shallow underground mining cannot fulfil the rib support requirements. Under the engineering background of deep underground shortwall mining in Wudong coal mine, this paper systematically studies Φ27 mm FRP bolt support for large deformation coal rib. Specimens with a fan-shaped cross-section were used to enable the tensile testing of the bolt rod, the measured average tensile strength of the studied FRP bolt was(486.1 ± 9.6) MPa with a maximum elongation of 5.7%±0.6%.The shear strength of the bolt was measured as approximately 258 MPa using a self-made double shear testing apparatus. Based on the equivalent radial stiffness principle, a laboratory short encapsulation pullout test(SEPT) method for rib bolting has been developed undertaken consideration of the mechanical properties of the coal seam. Results showed that the average peak anchorage forces of the Φ27 mm FRP bolt and Φ20 mm steel rebar bolt were 108.4 and 66.4 k N, respectively, which were agreed with the theoretical calculations and field measurements. Based on theoretical analysis of the loading states of the bolt under site conditions, bolting method of full-length resin grouting was adopted to offset the weaknesses of the FRP bolt. Numerical method was employed to compare the bolting effect using Φ27 mm FRP bolts and steel rebar bolts. Large diameter FRP bolting was determined as the optimum rib support scheme to increase the productivity of the coal mine and to enhance the ground control capability for+425 level mining roadways. This study provides the laboratory testing design and theoretical prediction of large diameter FRP bolts used for rib support in large deformation roadways.

Critical Transient Processes of Enhancement-mode GaN HEMTs in High-efficiency and High-reliability Applications

Wide-bandgap devices,such as silicon-carbide metal-oxide-semiconductor field-effect transistors(MOSFETs)and gallium-nitride high electron mobility transistors(HEMTs),exhibit an excellent figure of merits compared to conventional silicon devices.Challenges of applying such fast switches include accurate extraction and optimization of parasitics especially when 6high-efficiency operation,all of which require the comprehensive understanding of such switch especially its interaction with peripheral circuits.Particularly for the enhancement-mode GaN HEMTs without the intrinsic body diode,when reverse conducting,its high voltage drop causes a high dead-time loss,which has rarely a concern in silicon devices.This paper focuses on 650V/30~60A enhancement-mode GaN HEMTs provided by GaN Systems,analytically models its switching behaviors,summarizes the impact of parasitics and dead time,and applies it in two DC/DC converters.Systematic design rules are generated not only for soft switching but also for hard switching applications.

Occurrence of Extended Spectrum Beta Lactamase Encoding Genes among Urinary Pathogenic <i>Escherichia coli</i>and <i>Klebsiella pneumoniae</i>Isolates Obtained from a Tertiary Hospital in Gombe Nigeria

This study was conducted to assess the occurrence and nature of extended-spectrum beta lactamase (ESBL) producing Escherichia coli and Klebsiella pneumoniae isolates from patients who presented with urinary tract infection at Federal Teaching Hospital Gombe. Isolates collected were recovered on MacConkey agar at 35°C and were identified as members of Enterobacteriaceae, and further screened for antimicrobial susceptibility and resistance by disc diffusion method. Isolates resistant to oxyimino-cephalosporins were confirmed as ESBL producers using Double Disks Synergy Test (DDST). The study shows 66% resistance to ceftriaxone (30 μg) in K. pneumoniae, which was the highest value recorded and a 51% resistance to cefpodoxime (10 μg) in E. coli. The sensitivity of E. coli and K. pneumoniae isolates to cefpodoxime (10 μg) were 49% and 33.9% respectively. ESBLs were detected among 40% (40/100) of E. coli and 54.13% (59/109) of K. pneumoniae isolates. Molecular characterization of ESBL encoding genes among E. coli isolates using multiplex-PCR showed 10% prevalence of SHV gene and 5% prevalence for CTX-M gene while TEM gene was not detected. In K. pneumoniae isolates, 5% prevalence was recorded for each of the three genes screened. The study revealed a co-occurrence of SHV and CTX-M in 75% of the E. coli and 70% of the K. pneumoniae isolates;the occurrence of all the three genes was seen in 10% and 5% of K. pneumoniae and E. coli respectively. Multiplex-PCR method provided an efficient and rapid detection of ESBL related genes, hence could be used in epidemiological studies among ESBL isolates. Monitoring dissemination and transmissions of ESBL producers are highly recommended for optimum patient care and preventing the spread of multidrug resistant (MDR) pathogens.

Insight into multiple-triggering effect in DTSCRs for ESD protection

The diode-triggered silicon-controlled rectifier（DTSCR） is widely used for electrostatic discharge（ESD） protection in advanced CMOS process owing to its advantages, such as design simplification, adjustable trigger/holding voltage, low parasitic capacitance. However, the multiple-triggering effect in the typical DTSCR device may cause undesirable larger overall trigger voltage, which results in a reduced ESD safe margin. In previous research, the major cause is attributed to the higher current level required in the intrinsic SCR. The related discussions indicate that it seems to result from the current division rule between the intrinsic and parasitic SCR formed in the triggering process. In this letter, inserting a large space into the trigger diodes is proposed to get a deeper insight into this issue. The triggering current is observed to be regularly reduced along with the increased space, which confirms that the current division is determined by the parasitic resistance distributed between the intrinsic and parasitic SCR paths. The theoretical analysis is well confirmed by device simulation and transmission line pulse（TLP） test results. The reduced overall trigger voltage is achieved in the modified DTSCR structures due to the comprehensive result of the parasitic resistance vs triggering current, which indicates a minimized multipletriggering effect.

A new method of studying collapsibility of loess

A new triaxial testing system that could control suction in wetting-induced collapsible tests was success-fully developed to study the suction effects on wetting-induced collapsible deformation.The pedestal of the triaxial cell was made up of two parts,and the equipment not only could control suction but also could make water accessible to soil.A pressure/volume-controlled equip-ment was combined with the triaxial system to measure the water volume absorbed by samples accurately and to add pressure on water to filtrate into the sample.The apparatus could measure volume change precisely and keep the deviator stress unvaried,as well as measure the volume of water filtrating into the samples exactly.A triaxial collapsible testing procedure was described using the new apparatus for undisturbed collapsible loess with controlled suction.Furthermore,a series of double triaxial collapsible tests were conducted under different suctions and the same net cell pressure,and tests under different net cell pressures and the same suction were also done.It was indicated that the collapsible deformation increased with the increasing suction,and the effect of the net cell pressure on collapsible deformation was remarkable.The new triaxial apparatus was a useful facility to study the collapsible behavior of loess.