Additional Substitution Research Articles

Transformation of a Viral Capsid from Nanocages to Nanotubes and Then to Hydrogels: Redirected Self-Assembly and Effects on Immunogenicity.

The ability to manipulate the self-assembly of proteins is essential to understanding the mechanisms of life and beneficial to fabricating advanced nanomaterials. Here, we report the transformation of the MS2 phage capsid from nanocages to nanotubes and then to nanotube hydrogels through simple point mutations guided by interfacial interaction redesign. We demonstrate that site 70, which lies in the flexible FG loop of the capsid protein (CP), is a "magic" site that can largely dictate the final morphology of assemblies. By varying the amino acid at site 70, with the aid of a cysteine-to-alanine mutation at site 46, we achieved the assembly of double-helical or single-helical nanotubes in addition to nanocages. Furthermore, an additional cysteine substitution on the surface of nanotubes mediated their cross-linking to form hydrogels with reducing agent responsiveness. The hierarchical self-assembly system allowed for the investigation of morphology-related immunogenicity of MS2 CPs, which revealed dramatic differences among nanocages, nanotubes, and nanotube hydrogels in terms of immune response types, antibody levels and T cell functions. This study provides insights into the assembly manipulation of protein nanomaterials and the customized design of nanovaccines and drug delivery systems.

Iodine-Catalyzed Cascade Annulation of 4-Hydroxycoumarins with Aurones: Access to Spirocyclic Benzofuran-Furocoumarins.

An attractive approach for the preparation of spirocyclic benzofuran-furocoumarins has been developed through iodine-catalyzed cascade annulation of 4-hydroxycoumarins with aurones. The reaction involves Michael addition, iodination, and intramolecular nucleophilic substitution in a one-step process, and offers an efficient method for easy access to a series of valuable spirocyclic benzofuran-furocoumarins in good yields (up to 99%) with excellent stereoselectivity. Moreover, this unprecedented protocol provides several advantages, including readily available materials, an environmentally benign catalyst, a broad substrate scope, and a simple procedure.

Genomic surveillance of emerging SARS-CoV-2 Omicron variations in Tianjin Municipality, China 2022

The coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has severely impacted public health. In 2022, the Omicron variant of SARS-CoV-2 rapidly became the dominant circulating variant in the local COVID-19 outbreaks in Tianjin Municipality, China. To gain a deeper understanding of the genetic variations of the Omicron variant in Tianjin, specimens from individuals who tested positive for SARS-CoV-2 between December 2021 and November 2022 were used for virus whole genome sequencing and phylogenetic analysis. A total of 1,674 high-quality Omicron sequences were obtained, consisting of 1,339 sequences from local cases belonging to 20 Phylogenetic Assignment of Named Global Outbreak (PANGO) lineages and 335 sequences from imported cases belonging to 70 lineages. Tianjin experienced five waves of local outbreaks, accompanied by multiple substitutions among subvariants, ranging from the initial BA.1.1 lineage to the subsequent BA.2, BF.7, and BA.5.2 lineages. The evolutionary rate of local strains, estimated to be 28.999 substitutions per year, and the evolutionary rate of imported strains, estimated to be 24.946 substitutions per year, were lower than that of the strains circulating globally. The additional substitutions and deletions of local strains have been used to identify and disrupt the virus transmission chains. The subvariants such as BA.5.2.48, BA.5.2.49, BF.7.14, and XBB.1 circulating in the fifth epidemic wave presented criterial immune escape mutations including S: R346T, S: L452R and S: F486V. It is essential to implement genomic surveillance strategies to investigate further the development of genomic mutation characteristics in the SARS-CoV-2 variant. This ongoing monitoring will contribute to a better understanding of the virus's genetic changes and aid in effective control measures.

Use of Bacillus spp. as beneficial fermentation microbes in baking

The development of minimally processed baked goods is dependent on new “clean label” functional ingredients that allow substitution of additives without compromising quality. We investigated the use of fermentation with Bacillus spp. as a novel approach to improve bread quality. Bacillus velezensis FUA2155 and Bacillus amyloliquefaciens Fad WE ferments were prepared using white wheat flour, wheat bran or buckwheat, and were added at a level of 2.5–20 % to bread dough. Ropy spoilage of bread was controlled by sourdough addition at a level of 10 or 20 %. The volume of white wheat bread and wheat bran bread increased by 47.4 and 62.5 % respectively with 2.5 % Bacillus ferments. Bread shelf-life was prolonged by the Bacillus ferment only at higher dosages that also reduced bread volume. The use of unfermented or sourdough fermented buckwheat improved bread volume and delayed mould spoilage. The characterization of water-soluble polysaccharides from sourdoughs and Bacillus ferments revealed that solubilization of arabinoxylans contributed to the increase in volume after fermentation of wheat but not after fermentation of buckwheat. In conclusion, Bacillus fermentation can be used to improve bread quality, adding to the diversity of microbes that are suitable for baking applications.

EMCDDA framework and practical guidance for naming cathinones.

Cathinones are often sold as "legal" alternatives to controlled stimulants such as amphetamine, MDMA and cocaine. Cathinones are the second largest group of new psychoactive substances (NPS), with close to 170 monitored by the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA). Although all cathinones are related to the parent compound cathinone, one of the psychoactive principles in khat, assigning consistent, informative and user-friendly common names to these substances is challenging. Over time different naming approaches have been applied, leading to cathinones being known by several names. This work provides a framework and practical examples for the consistent naming of cathinones which is easy to understand and can be applied by the forensic community, researchers, clinical practitioners, and policy makers. The scope of the issue and rationale for earlier naming approaches are also discussed. The new naming framework has been developed based on established naming approaches and centered around the common "cathinone," and "phenone" motifs/scaffolds. The proposed framework establishes clear rules to derive the EMCDDA framework names for cathinones. Each name is, in turn, composed by a principal name containing a parent letter, derived after the "cathinone" or the "phenone" scaffold. Additional substitutions are prepended to the principal name. The framework also provides for exceptions for several cathinones and structural analogs scheduled under UN and EU legislation.

Transactivation of Met signaling by oncogenic Gnaq drives the evolution of melanoma in Hgf-Cdk4 mice

Recent pan-cancer genomic analyses have identified numerous oncogenic driver mutations that occur in a cell-type and tissue-specific distribution. For example, oncogenic mutations in Braf and Nras genes arise predominantly in melanocytic neoplasms of the epidermis, while oncogenic mutations in Gnaq/11 genes arise mostly in melanocytic lesions of the dermis or the uvea. The mechanisms promoting cell-type and tissue-specific oncogenic events currently remain poorly understood. Here, we report that Gnaq/11 hotspot mutations occur as early oncogenic drivers during the evolution of primary melanomas in Hgf-Cdk4 mice. Additional single base substitutions in the Trp53 gene and structural chromosomal aberrations favoring amplifications of the chromosomal region containing the Met receptor gene accumulate during serial tumor transplantation and in cell lines established in vitro. Mechanistically, we found that the GnaqQ209L mutation transactivates the Met receptor. Overexpression of oncogenic GnaqQ209L in the immortalized melanocyte cell line promoted in vivo growth that was enhanced by transgenic Hgf expression in the tumor microenvironment. This cross-signaling mechanism explains the selection of oncogenic Gnaq/11 in primary Hgf-Cdk4 melanomas and provides an example of how oncogenic driver mutations, intracellular signaling cascades, and microenvironmental cues cooperate to drive cancer development in a tissue-specific fashion.

Gelation of crocodile myofibrillar protein – κ-carrageenan mixtures in two low-NaCl solution

Crocodile meat is a novel reptile meat source, but its processing method is rare. This study investigated the effect of κ-carrageenan addition and partial substitution of NaCl on the gel properties of crocodile myofibrillar protein (CMP). Result showed that CMP formed gel when temperature above 60 ℃. The water-holding capacity, gel strength, denaturation degree, sulfhydryl content covalent bond and hydrophobic bond of gel in KCl solution were significantly higher than those in CaCl2 solution (P < 0.05). K+ induced CMP to form a tight network structure with uniform small pores though covalent and hydrophobic bonds, but the gel properties were reduced by κ-carrageenan. In CaCl2 solution, κ-carrageenan improved the gel structure by filling the protein network through hydrogen bonding. Therefore, it can be concluded that KCl is better than CaCl2 in the manufacturing of low-sodium crocodile foods. Moreover, κ-carrageenan was only beneficial to gel quality in CaCl2 solution.

A Three‐Component Domino Reaction Enabled by Phase‐Transfer Catalysis for the Assembly of 3‐Thioquinoline‐2,5‐Diones

AbstractA three‐component phase‐transfer catalytic domino reaction involving cyclohexane‐1,3‐dione‐derived enaminones, 5‐alkenyl rhodanines, and haloalkanes has been developed. This protocol produces a wide range of 3‐thioquinoline‐2,5‐diones in yields of 52–81%. The construction of a C−S bond at the C‐3 position of the quinoline‐2,5‐dione framework expands its structural diversity. Studies into the reaction mechanism revealed that the reaction undergoes a conjugate addition, ammonolysis, elimination, and nucleophilic substitution sequence. The synthetic potential of the reaction was demonstrated by the gram‐scale syntheses of representative products. Chloroalkyl chains were installed on the sulfur atoms of most products obtained in this reaction. Diversified product derivatives were obtained by exploiting the favorable leaving nature of the chloride moiety.

Fine-tuning of radiative properties by "mild" substituents: searching for a perfectly soft chromophore.

Controlling spectral properties to achieve desired characteristics is an attractive goal in application-oriented research, e.g., in the design of fluorescence sensors. "Soft" chromophores, molecules with strong spectral responses to internal or external perturbations are good candidates for such studies. In this work, absorption, fluorescence, and magnetic circular dichroism (MCD) spectra were obtained for a series of porphyrins, substituted at the meso-positions with n-hexyl groups. As the number of substituents increases from 1 to 4, significant changes are observed. The intensity of the S0-S1 transition (Qx) in the 0-0 region strongly decreases in mono-substituted porphyrin, but upon additional substitutions it increases to values larger than in the parent, unsubstituted molecule. Such behavior can be explained, using the perimeter model, by changes in the energy splittings between the two highest (HOMO) and two lowest (LUMO) frontier molecular orbitals. Single substitution makes porphyrin a nearly perfect soft chromophore, but upon introduction of a larger number of n-hexyl groups it is transformed into a hard one. DFT simulations incorrectly predict a continuous transition from a soft to hard chromophore, because the calculated ordering of two HOMO orbitals is opposite to that obtained by experiment. On the other hand, for those porphyrins that can be classified as hard chromophores, the calculations nicely reproduce contributions of Franck-Condon and Herzberg-Teller terms to absorption and fluorescence spectra.

Design and Preparation of a Bifunctional Nanobiohybrid Catalyst by Combining Palladium and α‐Amylase Enzyme: Application in One‐pot Chemoenzymatic Catalysis

AbstractA chemoenzymatic approach that combines chemical and bio‐catalyst has proven very useful in synthetic chemistry, however, mutual deactivation of chemical and bio‐catalyst when employed in the same pot is still a challenge. In this context, the development of nanobiohybrid catalysts has played an important role and overcoming the issue of mutual deactivation between catalysts to a certain extent. Herein, we design and synthesize a novel heterogeneous recyclable nanobiohybrid catalyst comprising palladium nanoparticles and α‐amylase from Aspergillus oryzae immobilized onto halloysite nanotubes as a solid heterogeneous support. Further, the wider applicability of the developed nanobiohybrid catalyst is revealed in the one‐pot chemoenzymatic synthesis of functionalized biphenyls and bis(indolyl)methanes which consists of Pd‐catalyzed Suzuki‐Miyaura coupling and α‐amylase mediated aza‐Michael addition or electrophilic substitution reactions respectively. Further, the robustness and generality of the developed one‐pot chemoenzymatic synthesis are demonstrated by incorporating different substitutions at the starting materials and obtaining the corresponding products in moderate to good yields.

Genetic and potential antigenic evolution of influenza A(H1N1)pdm09 viruses circulating in Kenya during 2009–2018 influenza seasons

Influenza viruses undergo rapid evolutionary changes, which requires continuous surveillance to monitor for genetic and potential antigenic changes in circulating viruses that can guide control and prevention decision making. We sequenced and phylogenetically analyzed A(H1N1)pdm09 virus genome sequences obtained from specimens collected from hospitalized patients of all ages with or without pneumonia between 2009 and 2018 from seven sentinel surveillance sites across Kenya. We compared these sequences with recommended vaccine strains during the study period to infer genetic and potential antigenic changes in circulating viruses and associations of clinical outcome. We generated and analyzed a total of 383 A(H1N1)pdm09 virus genome sequences. Phylogenetic analyses of HA protein revealed that multiple genetic groups (clades, subclades, and subgroups) of A(H1N1)pdm09 virus circulated in Kenya over the study period; these evolved away from their vaccine strain, forming clades 7 and 6, subclades 6C, 6B, and 6B.1, and subgroups 6B.1A and 6B.1A1 through acquisition of additional substitutions. Several amino acid substitutions among circulating viruses were associated with continued evolution of the viruses, especially in antigenic epitopes and receptor binding sites (RBS) of circulating viruses. Disease severity declined with an increase in age among children aged < 5 years. Our study highlights the necessity of timely genomic surveillance to monitor the evolutionary changes of influenza viruses. Routine influenza surveillance with broad geographic representation and whole genome sequencing capacity to inform on prioritization of antigenic analysis and the severity of circulating strains are critical to improved selection of influenza strains for inclusion in vaccines.

Electronic and steric substituent effects on the fluorescence emission of 2-pyrazoline derivatives.

A series of substituted 2-pyrazolines were synthesized, and the steric and electronic effects of substituents on the C3 - and C5 -positions of the heterocyclic ring on their fluorescent ability were investigated. Two different conjugative intramolecular charge transfer (ICT) and intramolecular charge transfer through space (spiro-conjugation) affect the fluorescence intensity of these compounds. The extent of the ICT process and spiro-conjugation depends on the electronic nature of the additional substitution and its position on the attached aryl rings. In addition, the effects of the concentration and the solvent polarity on the fluorescence emission were studied. Density functional theory (DFT) calculations were carried out to gain insight into the geometric, electronic, and spectroscopic properties of the pyrazoline derivatives. The results of both experimental and computational studies explain the effects of the geometrical orientation of the C3 - and C5 -aryl rings toward the heterocyclic ring and also the electronic nature of their additional substitutions on the fluorescence intensity.

Humanization and functional characterization of enhanced coagulation factor IX variants identified through ancestral sequence reconstruction

BackgroundLaboratory resurrection of ancient coagulation factor (F) IX variants generated through ancestral sequence reconstruction led to the discovery of a FIX variant, designated An96, which possesses enhanced specific activity independent of and additive to that provided by human p.Arg384Lys, referred to as FIX-Padua. ObjectivesThe goal of the current study was to identify the amino acid substitution(s) responsible for the enhanced activity of An96 and create a humanized An96 FIX transgene for gene therapy application. MethodsReductionist screening approaches, including domain swapping and scanning residue substitution, were used and guided by one-stage FIX activity assays. In vitro characterization of top candidates included recombinant high-purity preparation, specific activity determination, and enzyme kinetic analysis. Final candidates were packaged into adeno-associated viral (AAV) vectors and delivered to hemophilia B mice. ResultsFive of 42 total amino acid substitutions in An96 appear sufficient to retain the enhanced activity of An96 in an otherwise human FIX variant. Additional substitution of the Padua variant further increased the specific activity 5-fold. This candidate, designated ET9, demonstrated 51-fold greater specific activity than hFIX. AAV2/8-ET9 treated hemophilia B mice produced plasma FIX activities equivalent to those observed previously for AAV2/8-An96-Padua, which were 10-fold higher than AAV2/8-hFIX-Padua. ConclusionStarting from computationally inferred ancient FIX sequences, novel amino acid substitutions conferring activity enhancement were identified and translated into an AAV-FIX gene therapy cassette demonstrating high potency. This ancestral sequence reconstruction discovery and sequence mapping refinement approach represents a promising platform for broader protein drug and gene therapy candidate optimization.

Pengaruh Substitusi Tepung Beras Dan Penambahan Puree Wortel Terhadap Tingkat Kesukaan Kue Onde-Onde Ketawa

Onde-onde ketawa cookies with substitution of rice flour and addition of carrot puree is one of the innovations in making dry cakes made from wheat flour with substitution of rice flour and addition of carrot puree. The aim of this research is to find out; 1) the effect of the interaction between the substitution of rice flour and the addition of carrot puree on the level of liking for onde-onde ketawa cake; 2) the effect of rice flour substitution and the addition of carrot puree on the level of liking for onde-onde ketawa cake; 3) the effect of adding carrot puree on the level of liking for onde-onde ketawa cake; 4) the composition of the onde-onde ketawa cake with the substitution of rice flour with the addition of carrot puree is the most preferred. The research method used is an experimental type of research with the substitution of 10%, 20% and 30% rice flour and the addition of 5% and 10% carrot puree. The liking test was carried out on 50 untrained panelists using a questionnaire as a research instrument. The data obtained was then analyzed using the double ANOVA test and the Duncan test as further tests. The results of this research show that; 1) The interaction between the substitution of rice flour and the addition of carrot puree has a significant influence on the level of liking for onde-onde ketawa cakes. 2) vi Substitution of rice flour has an effect on the level of liking for onde-onde ketawa cakes; 3) The addition of carrot puree has an effect on the level of liking of onde-onde ketawa cake. 4) Substitution of 10% rice flour and addition of 10% carrot puree produces the most preferred characteristics of onde-onde ketawa cake.

Development and molecular cytogenetic identification of a new wheat-rye 6RL ditelosomic addition and 1R (1B) substitution line with powdery mildew resistance

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is a serious disease that critically threatens the yield and quality of wheat (Triticum aestivum L.). Using effective powdery mildew resistance genes is considered to be the optimal choice for controlling this disease. Against the background of high homogeneity among the modern commercial cultivars that are mainly derived from conventional interbreeding, the resistance genes from wheat relatives have especially prominent advantages. Octoploid triticale, produced by common wheat and rye (Secale cereale L.) through distant hybridization, is a new synthetic species and valuable gene donor for wheat improvement. In this study, we developed a wheat-rye line YT5 through the hybridization of octoploid triticale and two wheat lines. YT5 was confirmed to be a 6RL ditelosomic addition and 1R (1B) substitution line using genomic in situ hybridization (GISH), multicolor fluorescence in situ hybridization (mc-FISH), multicolor GISH (mc-GISH) and molecular marker analysis. Genetic analysis showed that the powdery mildew resistance in YT5 was derived from the rye chromosome arm 6RL. After inoculation with different Bgt isolates at the seedling stage, YT5 had compound reaction patterns with both obvious spores and hypersensitivity and gradually became highly resistant until the adult-plant stage, thus showing a resistance response significantly different from the reported Pm genes from rye chromosome 6RL. Meanwhile, YT5 showed promising agronomic performance and hence is expected to be an elite resistance donor for wheat improvement. To promote the transfer of the chromosome arm 6RL of YT5 in marker-assisted selection breeding, we selected and verified two 6RL-specific kompetitive allele-specific PCR markers that can be applied to efficiently detect this chromosome arm in different wheat backgrounds.

Response characteristics of coal microstructure with liquid CO2 acidizing treatment: An experimental study

To study the response characteristics of coal microstructure, especially pores and fractures structure variations with liquid CO2 (LCO2) acidizing treatment, the weak acid attributes and plugging removal effect of coal microstructure are studied by the combination methods of diffraction of X-rays, X-ray fluorescence spectrometer, scanning electron microscope and Fourier transform infrared spectrometer, before and after the coal is treated by acidizing. The results showed that the mineral content in the coal decreased after LCO2 acidification, and the carbonate content decreased by an average rate of 0.79%. Meanwhile, most elements in the coal migrated that performed a pressure sensitive tendency, resulting in the maximum migration rate of Calcium (Ca) is 13.66%, the contents of o-trisubstituted aromatic hydrocarbons (3H) and monosubstituted benzene rings (5H) of organic matter in the coal increased, the contents of benzene ring pentasubstituted (1H) adversely and tetrasubstituted m-phenylene rings (2H) decreased. Furthermore, the contents of aliphatic ethers, CC, CO and C–O functional groups decreased as a whole, while the content of –COOH structure increased significantly. The contents of symmetric CH2 and CH3 and asymmetric CH2 and CH3 decreased as a whole, and the hydroxyl functional groups in components increased significantly. The response characteristics of coal microstructure with LCO2 acidizing dissolution treatment mainly include dissolution, transformation and precipitation, hydration swelling of minerals. Meanwhile, the chemical reactions, such as addition reaction, substitution reaction and bond breaking effect, occurs in the coal microstructure of organic matter. This paper provides theoretical basis for the study of acid plugging removal effect of coal microstructure during LCO2 injection to enhance coalbed methane recovery.

Recent strategies for improving the quality of meat products.

Processed meat products play a vital role in our daily dietary intake due to their rich protein content and the inherent convenience they offer. However, they often contain synthetic additives and ingredients that may pose health risks when taken excessively. This review explores strategies to improve meat product quality, focusing on three key approaches: substituting synthetic additives, reducing the ingredients potentially harmful when overconsumed like salt and animal fat, and boosting nutritional value. To replace synthetic additives, natural sources like celery and beet powders, as well as atmospheric cold plasma treatment, have been considered. However, for phosphates, the use of organic alternatives is limited due to the low phosphate content in natural substances. Thus, dietary fiber has been used to replicate phosphate functions by enhancing water retention and emulsion stability in meat products. Reducing the excessive salt and animal fat has garnered attention. Plant polysaccharides interact with water, fat, and proteins, improving gel formation and water retention, and enabling the development of low-salt and low-fat products. Replacing saturated fats with vegetable oils is also an option, but it requires techniques like Pickering emulsion or encapsulation to maintain product quality. These strategies aim to reduce or replace synthetic additives and ingredients that can potentially harm health. Dietary fiber offers numerous health benefits, including gut health improvement, calorie reduction, and blood glucose and lipid level regulation. Natural plant extracts not only enhance oxidative stability but also reduce potential carcinogens as antioxidants. Controlling protein and lipid bioavailability is also considered, especially for specific consumer groups like infants, the elderly, and individuals engaged in physical training with dietary management. Future research should explore the full potential of dietary fiber, encompassing synthetic additive substitution, salt and animal fat reduction, and nutritional enhancement. Additionally, optimal sources and dosages of polysaccharides should be determined, considering their distinct properties in interactions with water, proteins, and fats. This holistic approach holds promise for improving meat product quality with minimal processing.

The H2S detection based on the combined smartphone technology and cellulose composite film and its application in biological imaging

In this study, flavonoids were used as fluorophores and dinitrobenzenesulfonyl groups as recognition groups. A novel fluorescent probe, LBS-XY, with high sensitivity and selectivity for H2S was prepared by nucleophilic addition and nucleophilic substitution reactions. The LBS-XY enables rapid detection of H2S within 150 s with a limit of detection (LOD) as low as 0.041 μM. With the interference of other ions (or molecules), only H2S was able to cause the probe to fluoresce in a green color visible to the naked eye. The probe can be used to realize the detection of H2S in real water samples by smartphone technology, and the fluorescent composite film prepared from the probe also achieved satisfactory results. In addition, the probe was successfully used to image hydrogen sulfide in A549 cells. The results demonstrate the potential of probe LBS-XY for applications in multiple fields.

High-level ceftazidime/avibactam resistance in Escherichia coli conferred by the novel plasmid-mediated β-lactamase CMY-185 variant.

To characterize a blaCMY variant associated with ceftazidime/avibactam resistance from a serially collected Escherichia coli isolate. A patient with an intra-abdominal infection due to recurrent E. coli was treated with ceftazidime/avibactam. On Day 48 of ceftazidime/avibactam therapy, E. coli with a ceftazidime/avibactam MIC of >256 mg/L was identified from abdominal drainage. Illumina and Oxford Nanopore Technologies WGS was performed on serial isolates to identify potential resistance mechanisms. Site-directed mutants of CMY β-lactamase were constructed to identify amino acid residues responsible for ceftazidime/avibactam resistance. WGS revealed that all three isolates were E. coli ST410. The ceftazidime/avibactam-resistant strain uniquely acquired a novel CMY β-lactamase gene, herein called blaCMY-185, harboured on an IncI-γ/K1 conjugative plasmid. The CMY-185 enzyme possessed four amino acid substitutions relative to CMY-2, including A114E, Q120K, V211S and N346Y, and conferred high-level ceftazidime/avibactam resistance with an MIC of 32 mg/L. Single CMY-2 mutants did not confer reduced ceftazidime/avibactam susceptibility. However, double and triple mutants containing N346Y previously associated with ceftazidime/avibactam resistance in other AmpC enzymes, conferred ceftazidime/avibactam MICs ranging between 4 and 32 mg/L as well as reduced susceptibility to the newly developed cephalosporin, cefiderocol. Molecular modelling suggested that the N346Y substitution confers the reduction of avibactam inhibition due to steric hindrance between the side chain of Y346 and the sulphate group of avibactam. We identified ceftazidime/avibactam resistance in E. coli associated with a novel CMY variant. Unlike other AmpC enzymes, CMY-185 appears to require an additional substitution on top of N346Y to confer ceftazidime/avibactam resistance.

In vitro activity of β-lactamase inhibitors avibanvctam and relebactam in combination with β-lactams against multidrug-resistant Mycobacterium tuberculosis and mutations of resistance genes

Objective: To evaluate the activity of six β-lactams in combination with three β-lactamase inhibitors against mycobacterium tuberculosis(MTB) in vitro. Methods: A total of 105 multidrug-resistant tuberculosis (MDR-TB) strains from different regions of Henan province from January to September 2020 were included in this study. Drug activity of six β-lactams (biapenem, meropenem, imipenem, doripenem, ertapenem and tebipenem) alone or in combination with β-lactamase inhibitors (clavulanic acid, avibactam and relebactam) was examined by minimum inhibitory concentration method (MICs) against 105 clinical isolates. Mutations of blaC, ldtmt1 and ldtmt2 were analyzed by PCR and DNA sequencing. Chi-square test was used to compare the antimicrobial activities of different β-lactam drugs. Results: Out of the β-lactams used herein, tebipenem was the most effective against MDR-TB and had an MIC50 value of 8 mg/L(χ2=123.70,P=0.001). Besides, after the addition of β-lactamase inhibitors, the MICs of most β-lactam drugs were reduced more evidently in the presence of avibactam and relebactam compared to clavulanic acid.Especially, relebactam decreased both the MIC50 and MIC90 of telbipenem by 16-fold, and diluted the MIC of 23 (21.90%) and 41 (39.04%) isolatesby 32-fold and 16-fold.In addition, a total of 13.33% (14/105) of isolates harbored mutations in the blaC gene, with three different nucleotide substitutions: AGT333AGG, AAC638ACC and ATC786ATT. For the strains with Ser111Arg and Asn213Thr substitution in BlaC, the MIC values of the meropenem-clavulanate combination were reduced compared with a synonymous single nucleotide polymorphism (SNP) group. Conclusions: Both avibactam and relebactam had better synergistic effects on β-lactams than clavulanic acid. The combination of tebipenem and relebactam showed the most potent activity against MDR-TB isolates. In addition, the Ser111Arg and Asn213Thr substitution of BlaC may be associated with an increased susceptibility of MDR-TB isolates to meropenem in the presence of clavulanate.