Disk Test Research Articles

EVALUATION OF THE APPLICABILITY OF THE O.K.N.V.I. RESIST-5 AND THE KPC&MBL&0XA-48 DISK TESTS IN A ROUTINE MICROBIOLOGY LABORATORY

Background: The global spread of carbapenemase-producing Enterobacterales (CPE) and the increasing emergence of clinical Enterobacterales harboring multiple carbapenemases of different molecular classes have prioritized the use of rapid molecular detection methods in routine microbiology laboratories. The aim of this study was to evaluate the applicability of the immunochromatographic O. K.N.V.I. RESIST-5 and the KPC&MBL&0XA-48 disc tests in a clinical microbiology laboratory. Material and methods: The tests were performed with 50 CPE belonging to 8 species and producing 7 molecularly characterized carbapenemases. Six of these isolates carried two different carbapenemases. To assess the specificity of the assays, 18 non-carbapenemase-producing but carbapenem-resistant Enterobacterales (non-CP CRE) were also included. Both tests were performed from a common overnight culture on Mueller-Hinton agar with inoculum harvested around an ertapenem disk. Results: The O.K.N.V.I. RESIST-5 correctly detected all 56 carbapenemases, including KPC-2 in Klebsiella pneumoniae; OX-48 in Serratia marcescens, Citrobacter freundii, Enterobacter hormaechei and K. pneumoniae; NDM-1 in Escherichia coli, Morganella morganii, E. hormaechei, C. freundii, S. marcescens and K. pneumoniae; VIM-1 in Proteus mirabilis; VIM-4 in C. freundii and S. marcescens; VIM-86 with and without NDM-1 in Providencia stuartii, and NDM-5 with and without OXA-232 in K. pneumoniae. The KPC&MBL&0XA-48 disc tests correctly confirmed KPC, OX-48-like and most MBL except VIM in P. mirabilis. Furthermore, the combination disc tests failed to detect OXA-48-like in pairs with MBL in K. pneumoniae. Conclusions:The O.K.N.V.I. RESIST-5 multiplex lateral assay is an excellent test for rapid diagnostic of CPE in routine microbiology laboratories. It is easy to handle and provides results with 100% sensitivity and specificity when an inoculum around ertapenem disc from routine antibiogram was used.

Genotypic detection of metallo-Beta-Lactamases among multidrug resistant Klebsiella pneumoniae isolated from urine samples of UTI patients

Metallo-beta-lactamases producing bacteria are of public health concern, owning to the fact that bacteria that harbour genes for their production are notably resistant to several antibiotics. This study was carried out to genotypically investigate the prevalence of MBL-production in multidrug resistant K. pneumoniae isolated from urine samples of UTI patients attending a tertiary teaching hospital in Awka, Anambra State, Nigeria. Two hundred (200) mid-stream urine samples were collected from UTI patients, and were analyzed using standard microbiological procedures. Antibiotic susceptibility testing (AST) of the isolates was carried out using Kirby-Bauer disc diffusion method and combination disc test was employed to phenotypically screen the isolates for MBL production. The genotypic screening was performed by Polymerase chain reaction (PCR), using specific primers. Fifty-one (51) K. pneumoniae isolates were recovered from the urine samples. AST revealed that the isolates exhibited high resistance to Amoxicllin-clavulanic acid (100%), Ampiclox (98.04%), Imipenem (98.04%), Cefotaxime (96.08%), Cefuroxime (96.08%), Nitrofurantoin (70.59%), and were relatively susceptible to Ofloxacin (54.91%), Gentamycin (50.98%) and Levofloxacin (47.06%). A 79.02% of the K. pneumoniae isolates showed resistance to more than two classes of antibiotics, thus termed multidrug resistance strains. Of the 38 (41.76%) isolates of K. pneumoniae that were resistant to imipenem, 19 (20.88%) were confirmed as MBL-producers phenotypically, while 19 (20.88%) were non-MBL producers. Genotypically, blaVIM (21.98%) was the most detected MBL gene, followed by blaOXA-48 (18.68%) and blaIMP (15.38%). This study revealed the prevalence of multidrug resistant and MBLs producing K. pneumoniae in urine samples of the selected UTI patients.

Bacterial contamination of mobile handwashing stations in hospital settings in the Democratic Republic of the Congo

BackgroundAs part of the containment of the COVID-19 pandemic, mobile handwashing stations (mHWS) were deployed in healthcare facilities in low-resource settings. We assessed mHWS in hospitals in the Democratic Republic of the Congo for contamination with Gram-negative bacteria.MethodsWater and soap samples of in-use mHWS in hospitals in Kinshasa and Lubumbashi were quantitatively cultured for Gram-negative bacteria which were tested for antibiotic susceptibility. Meropenem resistant isolates were assessed for carbapenemase enzymes using inhibitor-based disk and immunochromatographic tests. Mobile handwashing stations that grew Gram-negative bacteria at counts > 10,000 colony forming units/ml from water or soap were defined as highly contaminated.ResultsIn 26 hospitals, 281 mHWS were sampled; 92.5% had the “bucket with hand-operated tap” design, 50.5% had soap available. Overall, 70.5% of mHWS grew Gram-negative bacteria; 35.2% (in 21/26 hospitals) were highly contaminated. Isolates from water samples (n = 420) comprised 50.3% Enterobacterales (Klebsiella spp., Citrobacter freundii, Enterobacter cloacae), 14.8% Pseudomonas aeruginosa and 35.0% other non-fermentative Gram-negative bacteria (NFGNB, including Chromobacterium violaceum and Acinetobacter baumannii). Isolates from soap samples (n = 56) comprised Enterobacterales (67.9%, including Pluralibacter gergoviae (n = 13)); P. aeruginosa (n = 12) and other NFGNB (n = 6). Nearly one-third (31.2%, 73/234) of Enterobacterales (water and soap isolates combined) were multi-drug resistant; 13 isolates (5.5%) were meropenem-resistant including 10 New Delhi metallo-beta-lactamase (NDM) producers. Among P. aeruginosa and the other NFGNB, 7/198 (3.5%) isolates were meropenem resistant, 2 were NDM producers. Bacteria listed as critical or high priority on the World Health Organization Bacterial Priority Pathogens List accounted for 20.3% of isolates and were present in 12.0% of all mHWS across 13/26 hospitals. Half (50.5%) of highly contaminated mHWS were used by healthcare workers and patients as well as by caretakers and visitors.ConclusionsMore than one third of in-use mobile handwash stations in healthcare facilities in a low resource setting were highly contaminated with clinically relevant bacteria, part of which were multidrug resistant. The findings urge a rethink of the place of mobile handwash stations in healthcare facilities and to consider measures to prevent their contamination.

Completion and Stimulation Design Evolution in Tight Chalk Formations in Offshore Norway

Summary Lower completion and acid stimulation designs for low-permeability chalk formations in a series of North Sea fields were modified from historical/legacy approaches to improve well performance for both production and injection purposes. The modifications included (1) a stimulation change from high-rate matrix acidizing to acid fracturing and (2) optimization of ball-activated sliding sleeve designs. The improvement in well performance was validated by actual productivity comparisons to offset wells. Further improvements are being developed for future extended reach wells. A ball-activated sliding sleeve completion was chosen for a new series of improved horizontal well completions. Sleeve spacing, the number of sleeves, and port sizes were subsequently optimized for targeted stimulated lateral lengths by pipe flow modeling and limited-entry design methods. Optimization of acid fracturing designs was achieved after incorporating critical findings from various laboratory tests including rotating disk tests, acid-etched fracture conductivity tests, and gel shear history simulator tests. The new acid fracturing treatment designs were generated with the help of numerical simulations that were continuously fine-tuned based on new observations made during treatments and rigorous analysis of bottomhole injection pressures during the treatment. As a result of the lower completion design optimization process, different-size nozzles were introduced into the sliding sleeves to treat up to five sleeves per stimulation stage with effective, limited-entry, fluid diversion. This allowed (1) use of available pumping weather windows effectively in the often-challenging North Sea offshore environment, (2) reducing or eliminating time-consuming wireline perforation runs, and (3) limiting acid exposure to mitigate ball/seat zonal isolation loss events (i.e., dissolvable balls were not always compatible with acid). The new and improved acid fracturing design enabled a reduction of the number of gel/acid cycles from five to three, which reduced stimulation cost without losing stimulation effectiveness. The new design also resulted in productivity enhancements depending on the well location within the structure. The largest performance improvement was observed in wells that were placed farther downflank, where stronger reservoir rock and lower permeabilities were found. These wells required a more intensive acid fracturing treatment to generate economical and sustainable production rates. Finally, wells that used the new stimulation techniques also tended to require a lower restimulation frequency. This type of analysis work has not been presented previously and it optimizes lower completion for acid fracturing stimulation on a well-by-well basis. Further improvement is expected as stimulation designs and completion technology continue to evolve.

Ceftazidime-avibactam tolerance and persistence among difficult-to-treat KPC-producing Klebsiella pneumoniae clinical isolates from bloodstream infections.

Tolerance and persistence occur "silently" in bacteria categorized as susceptible by antimicrobial susceptibility testing in clinical microbiology laboratories. They are different from resistance phenomena, not well-studied, and often remain unnoticeable. We aimed to investigate and characterize ceftazidime-avibactam (CZA) tolerance/persistence in 80 Klebsiella pneumoniae isolates from bloodstream infections. We used the Tolerance Disk Test (TDtest) to detect CZA tolerance/persistence and investigate the avibactam (AVI) influence on them, and time-kill assays with minimal duration for killing (MDK) determination to characterize/differentiate CZA tolerance from persistence, for selected isolates. Whole genome sequencing was performed for 49/80 selected isolates to investigate genes related to beta-lactam tolerance/persistence and resistance as well as phylogeny studies. Tolerance/persistence to CZA was detected in 48/80 (60%) isolates, all extensively drug-resistant (XDR) or multidrug-resistant, carbapenem-resistant K. pneumoniae (CRKp), KPC producers, and previously categorized as susceptible (not resistant) to CZA. No heteroresistance was detected. CZA tolerance/persistence occurred due to ceftazidime tolerance/persistence and was not related to AVI in the CZA combination. 5/11 isolates were characterized as CZA-tolerant and 5/11 as CZA-persistent. The single (1/11) XDR and CRKp non-KPC producer was truly susceptible. All the CZA-tolerant/persistent isolates (ST11, ST258, ST340, ST437, ST16, ST17, and ST307) harbored the carbapenemase-encoding gene blaKPC-2. Mutation in only two genes (rpoS and degQ) related to beta-lactam tolerance/persistence was found in only 7/49 CZA-tolerant/persistent isolates, suggesting the presence of yet unknown beta-lactam tolerance/persistence genes. Among the K. pneumoniae bloodstream isolates studied, 60%, previously categorized as susceptible to CZA, were, actually, tolerant/persistent to this antibiotic, all these KPC producers.

Rate-dependent FDEM numerical simulation of dynamic tensile fracture and failure behavior in frozen soil

Considering that the dynamic fracture and failure behaviors of frozen soil play a crucial role in the safety and stability of engineering foundations in cold regions, this study aimed to reveal the dynamic tensile mechanical properties and damage failure mechanisms of frozen soil under impact loading. Dynamic Brazilian disk (BD) tests were conducted on frozen soil at different temperatures and loading velocities using a split Hopkinson pressure bar (SHPB) apparatus, followed by numerical simulations using the finite discrete element method (FDEM), focusing on the dynamic tensile deformation characteristics, failure patterns, tensile strength, and energy dissipation mechanisms of the frozen soil. The experimental results indicated that the dynamic tensile mechanical properties of frozen soil were influenced by both temperature and loading velocity. As the temperature decreased and loading velocity increased, the tensile strength of frozen soil significantly increased and showed a linear correlation with the loading velocity. At lower loading velocities, the cracks tended to propagate along the paths of least resistance, forming fewer but longer macrocracks. With increasing loading velocities, the number of cracks markedly increased, and their distribution became more diffuse, leading to a greater extent of failure in the frozen soil. An exponential damage cohesive interface model that considers rate effects was proposed to describe the dynamic tensile fracture mechanical behavior of frozen soil accurately. This model addresses the rate sensitivity of frozen soil and effectively accounts for the temperature effect by considering the volume of ice content and cryogenic suction. A comparison of the FDEM numerical simulation results with the experimental data indicated a good consistency in the overall trends, thus validating the effectiveness and applicability of the FDEM in simulating the dynamic tensile mechanical behavior of frozen soil.

Experimental comparison between flattened Brazilian disc and ring tests in evaluating indirect tensile strength of two types of Gondwana sandstone

Experimental comparison between flattened Brazilian disc and ring tests in evaluating indirect tensile strength of two types of Gondwana sandstone

Expression of MBL Genes and Biofilm Genes among Clinical Isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa, a versatile Gram-negative bacterium, poses a serious threat due to its adeptness at developing resistance mechanisms. Metallo-beta-lactamases produced by P. aeruginosa are pivotal in conferring resistance to beta-lactam antibiotics, compromising treatment effectiveness. The bacterium’s proficiency in forming biofilms further enhances its persistence, especially in clinical settings. In this study conducted at Krishna Hospital and Medical Research Center, Karad, 205 clinical isolates of Pseudomonas aeruginosa were investigated for their metallo-beta-lactamase (MBL) production and biofilm-forming capabilities. The phenotypic detection of MBL production was carried out using the Imipenem-EDTA combination disc test, while biofilm formation was assessed through the microtiter plate technique. Genotypic detection involved conventional polymerase chain reaction targeting MBL and biofilm genes. Results showed that 28.29% of isolates produced MBL phenotypically, with 16.59% possessing MBL genes, notably the blaNDM-1 gene in 15.12% of isolates. Regarding biofilm production, 85.85% of isolates were biofilm producers, and biofilm-encoding genes were present in 80.49% of isolates. The most frequently encoded genes were algD (79.51%), pelF (58.0%), and pslD (46.34%). Comparing phenotypic and genotypic methods for MBL detection, a statistically significant average agreement was observed. While there was an increasing trend in biofilm genotypic positive patterns with stronger biofilm phenotypic patterns, the correlation was not statistically significant. The study concludes that every resistant clinical isolate should be screened for MBL and biofilm production using simple phenotypic tests, with confirmation by PCR if possible. This comprehensive analysis provides insights into the prevalence and genetic basis of MBL and biofilm in P. aeruginosa clinical isolates, contributing to strategies for combating antibiotic resistance.

MOLECULAR CHARACTERIZATION OF MBL IN UROPATHOGENIC E. COLI ISOLATED FROM PATIENTS OF TERTIARY CARE HOSPITAL

Background: Antibiotic resistance is on an increasing trend, particularly in gram-negative bacteria. The production of metallo β-lactamase (MBL) puts the health sector at great risk as it further limits the treatment option for MDR strain. MBL is mostly reported in Enterobacteriaceae, which poses resistance to almost all β-lactam antibiotics except monobactam. The current study aims to determine the prevalence, antibacterial sensitivity pattern, and molecular characterization of MBL in Uropathogenic E. coli from clinical samples of hospitalized patients in Khyber Pakhtunkhwa. Methods: From tertiary care hospitals in Peshawar, 250 Urine samples were collected from indoor hospitalized patients. Gold standard microbiological methods were used to identify UPEC from these clinical samples.For that,urine samples was inoculated onto Cysteine Lactose Electrolyte. Deficient (CLED) agar plate, and MacConkey Agar.Positive growth of E.coli identified through Gram staining, colony morphology, Biochemical Tests and E.coli 16srRNA gene amplification .Antibiotic sensitivity was determined by the disc diffusion method on Muller Hinton agar. For the detection of MBL production double disc synergy, and a combination disc test of the antibiotics were used. Furthermore, multiplex PCR was used for the molecular characterization of the MBL (blaIMP, blaVIM, and blaNDM) genes. Results: Of the 250 samples, only 110 samples were confirmed as Uropathogenic E. coli based on colonial morphology, biochemical testing, and molecular level by targeting the 16SrDNA. Female was found more susceptible to UTI compared to male. High prevalence was found in the age group 45-65 years. UPEC was found highly resistance to Ciprofloxacin (90%), followed by Cefotaxime and Ceftriaxone (86%), Ceftazidime and Augmentin (81%), Tazobactam (61%). while the lowest resistance was reported against Meropenum (20%) Imipenem (18%) and Amikacin (37%). PCR-based confirmed prevalence of MBL encoding genes was blaNDM (42%), blaVIM (32%), and blaIMP (26%). Conclusion: The study proposed a higher prevalence of urinary tract infections (UTIs) in females aged group 54-65 years compared to males. An analysis of antibiotic sensitivity revealed Imipenem and Meropenem to be the most effective antimicrobial agents, while Ciprofloxacin, Cefotaxime and Amoxicillin were found to be the less effective. UPEC were found highly resistance to Ciprofloxacin 91%, and ceftazidime 86%, while comparatively less resistance to meropenem, and imipenem,20% and 18% respectively. Genotype BlaNDM of the MBL is highly prevalent (42%) among UPEC.Furthermore, the presence of MBL genes was detected in over 19% of UPEC, and in different combinations.The upraise of the MBLs resistance in uropathogenic E. coli is an alarming sign for clinicians to decide on treatment options for complicated UTIs.

Population of giant planets around B stars from the first part of the BEAST survey

Exoplanets form from circumstellar protoplanetary disks whose fundamental properties (notably their extent, composition, mass, temperature, and lifetime) depend on the host star properties, such as their mass and luminosity. B stars are among the most massive stars and their protoplanetary disks test extreme conditions for exoplanet formation. This paper investigates the frequency of giant planet companions around young B stars (median age of 16 Myr) in the Scorpius-Centaurus (Sco-Cen) association, the closest association containing a large population of B stars. We systematically searched for massive exoplanets with the high-contrast direct imaging instrument SPHERE using the data from the BEAST survey, which targets a homogeneous sample of young B stars from the wide Sco-Cen association. We derived accurate detection limits in the case of non-detections. We found evidence in previous papers for two substellar companions around 42 stars. The masses of these companions are straddling the sim 13 Jupiter mass deuterium burning limit, but their mass ratio with respect to their host star is close to that of Jupiter. We derived a frequency of such massive planetary-mass companions around B stars of $11_ $<!PCT!>, accounting for the survey sensitivity. The discoveries of substellar companions b and B happened after only a few stars in the survey had been observed, raising the possibility that massive Jovian planets might be common around B stars. However, our statistical analysis shows that the occurrence rate of such planets is similar around B stars and around solar-type stars of a similar age, while B-star companions exhibit low mass ratios and a larger semi-major axis.

Employing miniaturized test methods to determine high-temperature strength of carbon-bonded alumina

The Brazilian disc test (BDT) and the ball-on-three-ball (B3B) test, both adapted for utilizing miniaturized specimens, are used to characterize the strength of ceramic filter materials made from carbon-bonded alumina (Al2O3-C) at temperatures up to 1500 °C. Conventionally manufactured Al2O3-C and environmentally friendly coal tar pitch-free variations of filter materials are investigated. To determine the fracture stresses and the Weibull distribution of the material’s strength, finite element models and the maximum likelihood method are used. Scanning electron microscopy of fracture surfaces gives insight into the microstructure of tested samples. The material strength of the pitch-free Al2O3-C was found to be inferior to the conventional alternative. The volume-related Weibull stress distributions revealed that the uniaxial strength of the conventional filter materials exhibited an increasing trend as temperature increased, which was contrary to the biaxial strength.

Detection of Carbapenemase-Producing Enterobacterales: A Comparative Analysis of Available Phenotypic Methods

Background: Carbapenems serve as a critical last-line defence against infections from multidrug-resistant Enterobacterales. The increasing prevalence of CRE (carbapenem-resistant Enterobacterales) poses significant challenges in clinical settings. This greatly complicates the handling of gram-negative bacilli (GNB) infections and represents a significant global health threat. Aim: This study evaluates and contrasts different phenotypic techniques used to identify carbapenemase-producing Enterobacterales isolated from various clinical samples. Objectives: To compare the accuracy and reliability of Combined Disc Test (CDT) and Modified Carbapenem Inactivation Method/EDTA - Carbapenem Inactivation Method (mCIM/eCIM) in identifying Metallo-beta-lactamase (MBL)-producing Enterobacterales. Methods: All clinical specimens submitted for culture and sensitivity testing at the Department of Microbiology were analysed to isolate and identify Enterobacterales. Carbapenemase production was assessed through using the phenotypic CDT Confirmation was carried out using the mCIM and eCIM in accordance with Clinical and Laboratory Standards Institute (CLSI) guidelines. Results: During a two-year period, 254 strains of Enterobacterales were isolated. Among those, 80/254 (31.49%) isolates exhibited resistance to the Imipenem (IMP) disc. The CDT identified 30/80 (37.5%) isolates as serine carbapenemase producers and 50/80 (62.5%) isolates as MBL producers. In comparison, the mCIM/eCIM methods detected 26/80 (32.5%) isolates as serine carbapenemase producers, 48/80 (60.0%) isolates as MBL producers, and 6/80 (7.5%) isolates were tested negative for carbapenemase production. Conclusion: This study evaluates the precision and effectiveness of the mCIM/eCIM and CDT methods for identifying CRE. The combination of the mCIM and eCIM tests may be a more reliable phenotypic method for detecting carbapenemase compared to the CDT.

Enterobacterales Producing ESBLs and AmpC in Fresh Vegetables from Tebessa City, Algeria.

This study aimed to evaluate the contamination levels of fresh products by ESBLs-producing Enterobacterales (ESBLs-E) or AmpC-producing Enterobacterales and characterize ESBLs genes. A total of 132 samples (67 vegetables and 65 fruits) were collected from markets in Tebessa, eastern Algeria. Among the samples, 16 third-generation cephalosporin-resistant Enterobacterales isolates were identified with a prevalence of 19.40% in vegetable samples, while there was no positive finding in fruit samples. Isolates showed resistance to most β-lactams, and all of them displayed multidrug resistance. Phenotypic tests for ESBLs detection, using double-disk synergy test and double-disk test were positive for 14 strains, including Klebsiella pneumoniae (n = 5), Klebsiella oxytoca (n = 4), Klebsiella terrigena (n = 2), Kluyvera spp. (n = 2), and Enterobacter cloacae (n = 1). Two AmpC-producing strains (Citrobacter freundii and E. cloacae) were identified through the AmpC disk test. Contamination rates of vegetables by ESBLs-E and AmpC-producing Enterobacterales were 19.40% and 2.98%, respectively. PCR results showed the presence of at least one ESBL gene in seven selected strains, with the dominance of blaCTX-M gene. Notably, K. pneumoniae strains showed the co-occurrence of two or three genes. Sequencing identified uncommon variants of ESBLs genes for the first time in Algeria, including blaCTX-M-79 (2/7), blaCTX-M-107 (2/7), blaCTX-M-117 (2/7), blaTEM-112 (1/7), blaTEM-125 (2/7), blaTEM-194 (1/7), and blaSHV-176 (3/7).

Subclinical variability in visual function modulates visual dependence - independent of age

Paradoxically visual dependence is reported to increase with age, contributing to falls risk, whereas visual function typically declines. This study assesses the relationship between age, objective and subjective measures of visual function and visual dependence, in healthy young and older adults. Forty-four healthy Young (YA; n = 32; 18 males, aged 26.2 ± 5.3 yrs.) and Older (OA; n = 12; 3 males, aged 62.4 ± 6.7 yrs.) adults were assessed for objective (visual acuity, contrast sensitivity, depth perception, and lower peripheral vision), and subjective visual function (VFQ-25) along with motion sickness susceptibility. Subjective Visual Vertical (SVV) and induced nausea and vection were assessed using the Rod and Disc Test (RDT). Groups were compared using Mann-Whitney U, whilst determinants of SVV variability were evaluated using Multiple regression modelling. Visual acuity (p < 0.01) and contrast sensitivity (p = 0.04) were lower in OA. Visual dependence (SVV tilt errors) was not associated with ageing (p = 0.46). YA experienced greater RDT-induced vection (p = 0.03). Visual acuity and contrast sensitivity accounted for modest proportions of variance in SVV tilt errors (VA; R2 = 0.14, F(1,42) = 8.00, p < 0.01; β = 6.37) and (CS; R2 = 0.06, F(1,42) = 3.93, p = 0.05; β = −4.97), respectively. Our findings suggest that subclinical differences in visual acuity and contrast sensitivity contribute to SVV tilt error variability, among both healthy young and older adults. Further studies are needed to define the inter-relationship between age-related visual function, non-visual factors (including vestibular and somatosensory fidelity, activity levels, fear of falling and cognitive function) and visual dependence.

Assessment of lefamulin 20 µg disk versus broth microdilution when tested against common respiratory pathogens

ObjectiveTo evaluate the performance of the disk diffusion test with lefamulin 20 µg compared with the Clinical and Laboratory Standards Institute (CLSI) reference broth microdilution (BMD) method. MethodsA total of 572 clinical stains, including 240 Staphylococcus aureus, 211 Streptococcus pneumoniae, and 121 Haemophilus influenzae, isolated from 71 medical centres from the China Antimicrobial Surveillance Network in 2020. BMD method and disk diffusion methods were performed according to CLSI. Categorical agreement (CA), major error (ME), and very ME (VME) were calculated. ResultsLefamulin showed potent activity against S. aureus, S. pneumoniae, and H. influenzae. Using the BMD method, lefamulin inhibited 97.1% of S. aureus isolates at 0.25 mg/L; seven isolates were not susceptible. For S. pneumoniae and H. influenzae, the percentage of susceptibility to lefamulin was 100% and no non-susceptible strains were found in this study. Compared with the reference BMD method, the CA of the lefamulin 20 µg disk testing was 99.8% (571/572), with 14.3% (1/7) VME and no ME. In our study, VME was determined in S. aureus. For S. pneumoniae and H. influenzae, the VME was not determined due to the lack of lefamulin non-susceptible strains. ConclusionsThe lefamulin 20 µg disk diffusion testing showed excellent CA and ME with the reference BMD method for S. aureus, S. pneumoniae, and H. influenzae. The VME exceeding CLSI recommendations may be a bias due to fewer lefamulin non-susceptible isolates. Our results suggest that lefamulin non-susceptible isolates detected by disk diffusion should be confirmed by the reference BMD.

Differential frequency of persister cells in clinically derived isolates of Pseudomonas aeruginosa after exposure to cefiderocol and ceftolozane/tazobactam.

Bacterial persistence is a phenomenon whereby a subpopulation of bacteria survive high concentrations of an active antibiotic in the absence of phenotypic alterations. Persisters are associated with chronic and recurrent infections for pathogens including Pseudomonas aeruginosa. Understanding persister profiles of newer antibiotics such as cefiderocol and ceftolozane/tazobactam against P. aeruginosa is warranted as these agents generally target difficult-to-treat infections. Persister formation was assessed using in vitro assays against nine clinical P. aeruginosa isolates exposed to cefiderocol or ceftolozane/tazobactam. Quantitative persister assays were performed using a stationary phase of bacteria challenged with 10-fold MIC drug concentrations. Persisters were quantitated as the percent persisters at 24 h and the log ratio (LR) difference in AUC for cfu for each antibiotic alone compared with growth control. The tolerance disc test (TDtest) was used to qualitatively detect persisters. Percent persisters at 24 h was lower with cefiderocol compared with ceftolozane/tazobactam for six of the nine tested isolates. Eight of the nine isolates had higher reduction in LR for cefiderocol groups, suggesting an overall higher and more rapid bacterial reduction in cefiderocol groups. For cefiderocol, five of the nine tested isolates lacked regrowth after replacement with glucose disc, suggesting no persistence via the TDtest. For ceftolozane/tazobactam, three isolates lacked persister formation. Cefiderocol resulted in less bacterial persistence relative to ceftolozane/tazobactam against nine clinical P. aeruginosa isolates. Cefiderocol's siderophore mechanism may be advantageous over ceftolozane/tazobactam through enhanced anti-persister effects. Clinical correlation of these findings is warranted as persisters can lead to antibiotic resistance and treatment failure.

Wear properties of a new Al80Mg10Si5Cu5 multicomponent alloy

The present study investigates the tribological properties of a newly developed multicomponent aluminium weight-light multicomponent alloy for wear based on the Al80Mg10Si5Cu5 system for lightweight automotive applications, especially back drum discs. The samples were manufactured by High-Pressure Die Casting (HPDC) employing cast alloy returns and secondary aluminium ingots and were tested at room temperature (RT) and 200 °C. It has been observed that the Al80Mg10Si5Cu5 alloy offers a higher hardness and wear resistance at RT and especially at 200 °C compared with the AlSi9Cu3 reference alloy (x10 times reduction in wear rate). The impact of maintaining the external surface layer (skin) of HPDC cast parts has been studied for the ball-on disc test, showing improved tribological properties and the possibility of avoiding the machining of contact surfaces. The as-cast Al80Mg10Si5Cu alloy with the surface layer showed a wear rate coefficient of 5 × 10−4 mm3/N.m2 at RT, a 50 % lower than that of the sample without skin. Solution heat-treated samples (72 h at 440 °C, water quenching at 75 °C, and natural aging) with the surface layer showed a wear rate coefficient of 11 × 10−4 mm3/N.m2, approximately 20 % lower than the sample without a surface layer. The wear rate of AlSi9Cu3 alloy decreased by more than 50 % in the samples without skin at RT. At 200 °C, wear rate coefficients were lower in the samples with the surface layer.

Prevalence of Metallo β-Lactamase Genes Among MDR Pseudomonas &lt;i&gt;Aeruginosa&lt;/i&gt; Isolated from Different Sources in Baghdad

Background: Pseudomonas aeruginosa is a gram-negative apportunistic pathogen that has ability to couse different type of infections and charecterised by their high resistance to commonly used antibiotics via different stratiges. Objective: The objective of this study is to detect the prevalence rate of MβL gene among MDR Pseudomonas aeruginosa. Methods: Forty clinical isolates of Pseudomonas aeruginosa were obtained from different hospitials in Baghdad/Iraq. Their identification was confirmed by using 16s rDNA as a housekeeping gene (reference gene). Specific primers were used to detect 3 types of Metallo β-lactamase (MβL) genes vim, spm1, and imp1 genes followed by sequencing the amplified fragment which was analyzed by Geneious software. Antibiotic sensitivity test for 15 antimicrobial agents was done using the Kirby-Bauer disc diffusion method. Results: The revealed resistance pattern was as following: 100% for the combination of Trimethoprim/Sulphamethoxazole and Nitrofurantoin, 95% for Tigecycline, 82.5% for Ciprofloxacin, 67.5% for Cefepime, 60% for Levofloxacin, 57.5% for Carbenicillin, 55% for Piperacillin, 50% for Amikacin, 47.5% for Tobramycin, 45% for both Imipenem and Ceftazidime, 27.5% for piperacillin/tazobactam, 22.5% for Aztreonam and 7.5% for Colistin. More than half (55%) of isolates were positive for MβL enzymes production during phenotypically assessed by combined disc test. The MIC of meropenem ranged from 16µg/ml to 32 µg/ml. The percentage of MβL genes among the total isolates during conventional PCR was as follows: 95% for vim, 25% of the isolates harbored both vim and imp1, while spm 1 are negative in all isolates. The result of the study explained that 10 isolates from the antibiotic susceptibility test were resistant to 10-14 antimicrobial agents that harbored both vim and imp1 genes. Conclusions: MβL gene could be used as a genetic marker to determine the degree of resistance in MDR P. aeruginosa which are more resistant than other isolates that have one gene of MβL responsible for break the β-lactam ring then inactivating the β-lactam antibiotic.

Evaluation of the Expression of SIM and NDM Genes in Pseudomonas Aeruginosa Isolated from Clinical Sources

Pseudomonas aeruginosa has recently been labeled a major threat to public health due to its resistance to almost all commonly used antibiotics. Many factors have been suggested for P. aeruginosa's antibiotic resistance. The goal of this study is to find out what role SIM and NDM, which are related to carbapenem resistance, play in P. aeruginosa isolates from local clinical sources. In this study, out of 110 different clinical specimens, 50 were identified as P. aeruginosa from hospitalized patients. All of the isolates were characterized based on the biochemical test and confirmed using the VitekII compact system. P. aeruginosa isolates were tested for antibiotic susceptibility using 8 antibiotics, including: amikacin, tobramycin, ciprofloxacin, levofloxacin, imipenem, meropenem, piperacillin/tazobactam, ticarcillin, and clavulanate. Susceptibility testing results revealed that every isolate was highly resistant to Piperacillin/Tazobactam, with lower resistance to Ticarcillin/clavulanate (TCC). Using the broth dilution method, the minimum inhibitory concentration (MIC) of P. aeruginosa isolates resistant to meropenem ranged from 32µg/100µl to 128 µg/100µl. The EDTA combined disc test was used to detect the ability of P. aeruginosa isolates to produce carbapenemase, and the results showed that all isolates were carbapenemase producers. Additionally, conventional PCR confirmed the identification of P. aeruginosa using 16S. Real-time PCR was adopted to assess the expression of the NDM and SIM genes in 25 of the identified P. aeruginosa isolates. The mean of gene expression results for NDM showed increased expression compared to the control sample of 1.74, while the SIM gene showed expression of 0.95. These genes, SIM and NDM in class B (which are important for resistance in Pseudomonas aeruginosa), result from chromosomal changes that mutate the membrane permeability flow pump, causing excessive expression.

Characterizing carbapenemase production in Enterobacterales through combined disk test and genetic profiling

Objectives: Carbapenem-resistant Enterobacterales (CRE) are a major organism among the critical group of drug-resistant bacteria and are associated with high morbidity and mortality. With limited treatment options, the detection and characterization of carbapenemase are important for appropriate management. This study aims to characterize carbapenemase produced by Enterobacterales using a combined disk test and molecular profiling. Materials and Methods: All CRE isolated from various clinical samples were included in the study. Carbapenemase production was characterized by observing synergy on combining meropenem disk with beta-lactamase inhibitors such as phenylboronic acid, ethylenediaminetetraacetic acid, and cloxacillin, following which genetic profiling was done using multiplex polymerase chain reaction. Statistical analysis: Statistical analyses were done using the Statistical Package for the Social Sciences Statistics and Microsoft Excel. The data were presented in tables, charts, and graphs to elucidate the findings comprehensively. Results: Out of 445 Enterobacterales isolated, 104 (23.4%) were carbapenem-resistant. The most common CRE isolated was Klebsiella pneumoniae (62 out of 104), followed by Escherichia coli (40 out of 104), and two out of 104 CRE isolates were Enterobacter species. Coproduction of NDM and OXA-48-like enzymes (39.4%) was the most common mechanism, followed by NDM alone (19.2%) and OXA-48 alone (16.3%). NDM was the most common gene detected overall, with 72 out of 104 CRE (69.2%) isolates showing its presence, followed by OXA-48 present in 63 of 104 (60.6%) isolates. Conclusions: Metallo-beta-lactamases (NDM) were the predominant type of carbapenemase gene detected among the Enterobacterales isolates, with the coproduction of NDM and OXA-48 enzymes being the most common mechanism of resistance.