Disk Test Research Articles

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

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.

High-throughput screening identification of apigenin that reverses the colistin resistance of mcr-1-positive pathogens.

The plasmid-mediated gene mcr-1 that makes bacteria resistant to the antibiotic colistin is spreading quickly, which means that colistin is no longer working well to treat Gram-negative bacterial infections. Herein, we utilized a computer-aided high-throughput screening drugs method to identify the natural product apigenin, a potential mcr-protein inhibitor, which effectively enhanced the antimicrobial activity of colistin. Several assays, including a checkerboard minimum inhibitory concentration assay, a time-kill assay, the combined disk test, molecular simulation dynamics, and animal infection models assay, were conducted to verify whether apigenin enhanced the ability of colistin to fight Gram-negative bacterial infections. The results showed that apigenin improved the antimicrobial activity of colistin against multidrug-resistant Enterobacteriaceae infection. Moreover, apigenin not only did not increase the toxic effect of colistin but also had the ability to effectively inhibit the frequency of bacterial resistance mutations to colistin. Studies clearly elucidated that apigenin could interfere with the thermal stability of the protein by binding to the mcr-1 protein. Additionally, the combination of apigenin and colistin could exert multiple effects, including disrupting bacterial membranes, the generation of bacterial nitric oxide and reactive oxygen species, as well as inhibiting bacterial adenosine triphosphate production. Furthermore, the addition of apigenin was able to significantly inhibit colistin-stimulated high expression levels of the bacterial mcr-1 gene. Finally, apigenin exhibited a characteristic anti-inflammatory effect while enhancing the antimicrobial activity of colistin against mcr-1-positive Escherichia coli (E. coli) infected animals. In conclusion, as a potential lead compound, apigenin is promising in combination with colistin in the future treatment of mcr-1-positive E. coli infections.IMPORTANCEThis study found that apigenin was able to inhibit the activity of the mcr-1 protein using a high-throughput virtual screening method. Apigenin effectively enhanced the antimicrobial activity of colistin against multidrug-resistant Enterobacteriaceae, including mcr-1-positive strains, in vitro and in vivo. This study will provide new options and strategies for the future treatment of multidrug-resistant pathogen infections.

Antimicrobial Activity of Diverse Chemotypes of Lippia graveolens Against Aeromonas hydrophila Isolated from Oreochromis niloticus

[Objective] This study aimed to evaluate the antimicrobial efficacy of essential oil (EO) from diverse chemotypes of Lippia graveolens against oxytetracycline-resistant Aeromonas hydrophila, which primarily affects the tilapia aquaculture (O. niloticus) in Guatemala. [Methodology] L. graveolens were collected in three departments in Guatemala. The EO was obtained by hydrodistillation and characterized using gas chromatography and mass spectrometry (GC/MS). Subsequently, an antimicrobial assay was conducted using disk and dilution susceptibility tests and evaluation of synergistic interactions among the chemotypes. Each test was performed in triplicate. [Results] The analysis revealed the presence of twenty-seven compounds in the EO obtained from the chemotypes, with the main class being monoterpenes. The major constituents identified were cis-Dihydro-β-terpineol (8.84%) in chemotype I, carvacrol (51.82%) in chemotype II, and thymol (79.62%) in chemotype III. All EO chemotypes of L. graveolens demonstrated the ability to inhibit the A. hydrophila growth. Thymol chemotype exhibited the strongest inhibitory effect against bacterial growth, with a minimum inhibitory concentration (MIC) of 92.4 µg/mL and a minimum bactericidal concentration (MBC) of 184.8 µg/mL. Furthermore, the results suggest that there is no synergistic or additive effect when combining different chemotypes of L. graveolens. [Conclusions] This is the first report of L. graveolens chemotypes exhibiting antimicrobial activity against oxytetracycline-resistant A. hydrophila. The findings suggest that the chemotype thymol could be a potential treatment for infections in the tilapia aquaculture in Guatemala.

Comparative study on the thermal and tribological properties of PA12 and PA11 for coating applications

AbstractIn this study, the performance and potential applicability of polyamide‐12 (PA12) as an alternative to polyamide‐11 (PA11), which is currently used in the coating processes of sliding tools present in cardan shafts, was investigated. The advantages of PA12 powder instead of PA11 in cardan shafts' coating include ease of supply and cost‐effectiveness, while still achieving similar performance. Therefore, PA12 is a more economical choice for coating applications. The PA11 and PA12 neat polymers were characterized via differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA) and dynamic mechanical analysis (DMA). Based on the analyses, PA12 demonstrated substantial advantages over PA11. It showed a 16°C improvement in decomposition temperature and a 50% increase in crystallinity, enhancing stability under operational conditions, whereas PA11 exhibited approximately 6–7% higher values in crystallization and melting temperatures. The wettability behavior of the steel substrates coated with those polyamides was measured via contact angle analysis. Wear properties and morphologies of coatings were examined using a ball‐on disc test and scanning electron microscopy, respectively and comparatively. Furthermore, PA12 typically displays 30% lower wear rates and similar deformation patterns in tests, thereby presenting itself as a cost‐effective and widely accessible option for coating applications in comparison to PA11.

Reconsidering the Determination of the Tensile Strength of Orthotropic Rocks by Means of the Brazilian Disc Test

Reconsidering the Determination of the Tensile Strength of Orthotropic Rocks by Means of the Brazilian Disc Test

Nasopharyngeal carriage, antimicrobial susceptibility patterns, and associated factors of Gram-positive bacteria among children attending the outpatient department at the University of Gondar Comprehensive Specialized Hospital, Northwest Ethiopia.

Gram-positive bacteria residing in the nasopharynx can lead to severe illnesses in children, such as otitis media, pneumonia, and meningitis. Despite the potential threat, there is a lack of comprehensive data regarding the carriage rates of these bacteria among children in outpatient departments in the study area. This study aimed to assess the nasopharyngeal carriage, antimicrobial resistance patterns, and associated factors of Gram-positive bacteria among children attending the outpatient department at the University of Gondar Comprehensive Specialized Hospital, Northwest Ethiopia. A hospital-based cross-sectional study was conducted from May 1, 2023, to August 30, 2023. A total of 424 nasopharyngeal swab samples were collected using sterile nasopharyngeal swabs, inoculated on Blood Agar and Mannitol Salt Agar plates, and identified through colony morphology, Gram stain, and biochemical tests. Antimicrobial susceptibility of the identified bacterial isolates was determined employing both the Kirby-Bauer and modified Kirby-Bauer methods. D-tests were conducted using clindamycin and erythromycin discs to detect inducible clindamycin resistance, while cefoxitin disc tests were utilized to ascertain methicillin resistance. Data entry was executed using Epi-Data version 4.6, and subsequent analysis was performed utilizing SPSS version 25. Bivariable and multivariable logistic regression analyses were employed to identify associated factors. An adjusted odds ratio at a 95% confidence interval with a P-value of < 0.05 was considered statistically significant. The overall nasopharyngeal carriage rate of Gram-positive bacteria was 296/424 (69.8%, 95% CI: 65.3-74.0). Staphylococcus aureus was the most prevalent 122/424 (28.8%), followed by Streptococcus pneumoniae 92/424 (21.7%). Methicillin resistance was observed in 19/122 (15.6%) of S. aureus and 3/60 (5%) of coagulase-negative staphylococcus (CoNS) species. Inducible clindamycin resistance was 10/122 (8.2%) in S. aureus and 4/53 (7.5%) in coagulase-negative staphylococcus species. Multidrug resistance was found in 146/296 (49.3%, 95% CI: 43.6-55.0) of the isolates. Associated factors with a bacterial carriage were large family size (AOR = 3.061, 95% CI: 1.595-5.874, P = 0.001), having siblings under five years old (AOR = 1.991, 95% CI: 1.196-3.313, P = 0.008), indoor cooking (AOR = 2.195, 95% CI: 1.275-3.778, P = 0.005), an illiterate mother (AOR = 3.639, 95% CI: 1.691-7.829, P = 0.001), and hospital visits (AOR = 2.690, 95% CI: 1.405-5.151, P = 0.003). The study found a high nasopharyngeal carriage of Gram-positive bacteria in outpatient children, including notable levels of methicillin-resistant S. aureus and multi-drug-resistant isolates. Clindamycin, rifampin, and erythromycin were the most effective antimicrobials for the tested isolates. Factors contributing to bacterial carriage include visits to healthcare facilities, larger family sizes, having younger siblings, maternal illiteracy, and indoor cooking. This emphasizes the need for methicillin-resistant S. aureus surveillance in pediatric outpatient settings and community health education, especially for children's guardians. Additionally, improving household ventilation by separating kitchens from sleeping areas and regular screening of younger siblings in healthcare environments were recommended to reduce bacterial transmission within family members. The study also called for studies with advanced procedures like minimum inhibitory concentration testing and molecular characterization to better comprehend the resistance patterns and genes in circulating bacteria.

Study on Traction Characteristics of Point Contact State under Oil–Air Lubrication

Oil–air lubrication technology is commonly utilized in the lubrication design of traditional components to reduce friction between contact pairs. This study focuses on testing the point-contact friction pairs of two quantitative valves using a self-made oil–air lubrication traction force machine with a G95Cr18 disk and ball as the friction pairs. The test data are analyzed using a four-parameter exponential model. Additionally, a calculation model of the oil–air lubrication flow field is established, defining boundary conditions and conducting flow field simulation analysis. The results of the ball and disk test show that the traction coefficient increases with load and decreases with entrainment speed. Furthermore, when the air-speed is 12 m/s, the traction coefficient is lower for the oil supply of 6 mL/min than for the oil supply of 1.5 mL/min. According to CFD analysis, the volume fraction of the oil phase in the contact area increases with the increase of entrainment speed when the slip–roll ratio is 0.1. The theoretical values from the four-parameter exponential model align well with the experimental results, and the fitting accuracy is higher than 0.95.