Presence Of Tetracycline Research Articles

Fluorescence and Colorimetric Dual-Readout Detection of Tetracycline Using Leucine-Conjugated Iron Oxide Quantum Dots.

This study developed a dual-readout system utilizing fluorescence and colorimetry based on iron oxide quantum dots (IO-QDs) for detecting tetracycline (TCy). IO-QDs were synthesized within 6 h using L-leucine as a surface modifier, achieving a more efficient route. Upon interaction with TCy, IO-QDs exhibited a significant decrease in fluorescence response and observable color changes, while fluorescence lifetime remained consistent regardless of TCy presence. Moreover, IO-QDs' fluorescence response remained stable across various temperatures. The Förster resonance energy transfer distance of less than 2 nm and a quenching constant of 2.90 × 1012 M-1s-1 indicated static quenching in the presence of TCy. Additionally, significant changes in observed and corrected fluorescence efficiency suggested the involvement of the inner filter effect in the fluorescence quenching of IO-QDs. The synthesized IO-QDs were then utilized for selective and rapid fluorescence-based TCy detection, showing a linear range of 0.5 to 80 μM. Simultaneously, a colorimetric method for TCy detection was established, demonstrating a good linear relationship within the range of 0.5 to 20 μM. The detection limits for TCy were determined as 0.539 and 0.329 μM using fluorescence and colorimetric approaches, respectively. Furthermore, IO-QDs were applied to detect real samples, and the dual-readout probe exhibited satisfactory recoveries, confirming the practical reliability of the developed method for analyzing milk and drinking water samples.

Novel Antimicrobial Agents Based on Zinc-Doped Hydroxyapatite Loaded with Tetracycline.

In this paper, we present for the first time the development of zinc-doped hydroxyapatite enriched with tetracycline (ZnHApTe) powders and provide a comprehensive evaluation of their physico-chemical and biological properties. Various techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) were used for the sample's complex evaluation. Moreover, the biocompatibility of zinc-doped hydroxyapatite (ZnHAp) and ZnHApTe nanoparticles was evaluated with the aid of human fetal osteoblastic cells (hFOB 1.19 cell line). The results of the biological assays suggested that these nanoparticles hold great promise as potential candidates for the future development of novel biocompatible and antimicrobial agents for biomedical applications. The antimicrobial properties of the ZnHAp and ZnHApTe nanoparticles were assessed using the standard reference microbial strains Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Candida albicans ATCC 10231. The results of the in vitro antimicrobial assay demonstrated that both tested materials exhibited good antimicrobial activity. Additionally, these data also indicated that the antimicrobial effects of the ZnHAp nanoparticles were intensified by the presence of tetracycline (Te). Furthermore, the results also suggested that the antimicrobial activity of the samples increased with the incubation time.

Green and environmentally friendly architecture of starch-based ternary magnetic biocomposite (Starch/MIL100/CoFe2O4): Synthesis and photocatalytic degradation of tetracycline and dye

The presence of tetracycline and dye as organic contaminants has led to the poisoning of wastewater. The aim of this study is to synthesize a novel biocomposite material by decorating natural starch polymer granules with metal-organic framework (MIL100) and cobalt ferrite magnetic (CoFe2O4) nanoparticles. The synthesized ternary magnetic biocomposite (Starch/MIL100/CoFe2O4) was used for the photocatalytic degradation of methylene blue (MB) and tetracycline (TCN) using LED visible light. The synthesis of the biocomposite was confirmed through comprehensive analyses (XRD, SEM, FTIR, BET, EDX, MAP, DRS, pHzpc, TGA, and Raman). The evaluation examined the influence of initial pollutant concentration, catalyst dosage, pH, and the impact of anions on pollutant removal. The results show that the pollutant degradation ability of biocomposite has been significantly improved, so that the base biopolymer, starch, achieved 18% tetracycline degradation, but when decorated with MIL100 and cobalt ferrite, it increased to 91.2%. It was observed that the degradation for methylene blue improved from 12% for starch to 96.6% for the magnetic biocomposite. The tetracycline degradation decreased by more than 20% in the presence of NaCl, NaNO3, and Na2SO4. The finding shows that the biocomposite adheres to first-order kinetics for both pollutants. The scavengers test identified hydroxyl radicals as the most effective active species in the degradation process. High stability, even after passing 5 cycles of recycling was observed for the biocomposite. The results indicated that the facile and green synthesized Starch/MIL100/CoFe2O4 magnetic biocomposite could be used as an effective photocatalyst for the degradation of Tetracycline and dye at room temperature.

Microwave-assisted synthesis of carbon quantum dots and their integration with TiO2 nanotubes for enhanced photocatalytic degradation

This study demonstrates the successful synthesis of carbon quantum dots (CQDs) using the microwave method. Additionally, the hydrothermal method is employed to synthesize CQDs-decorated TiO2 nanotubes (CQDs@TNT) from CQDs decorated TiO2 (CQDs@TiO2). The CQDs induce the quantum confinement effect, observed by employing fluorescence spectroscopy (FL). The decoration of CQDs also results in a 2.92 eV reduction in the band gap in CQDs@TNT. X-ray photoelectron spectroscopy (XPS) reveals the elemental composition of both CQDs and TiO2, including TiO, CO, Ti-O-C, CC, and CO bonds. XRD spectroscopy confirms a reduction in crystallite size and negative microstrain due to compressive strength. The degradation study demonstrates the remarkable photocatalytic activity and stability of CQDs@TNT in the presence of tetracycline (TC) as the target pollutant under simulated visible light. The time dependence of the photodegradation of TC is also studied, and the system is found to be following pseudo second-order kinetics.

Tetracycline and sulphonamide residues in farmed fish in Dar es Salaam, Tanzania and human health risk implications

ABSTRACT In Africa, antibiotic residue investigations in animal food have primarily been focused on meat, neglecting farmed fish. This cross-sectional study conducted in Dar es Salaam, Tanzania, aimed to assess sulphonamide and tetracycline residues in farmed fish, comparing levels with Codex Alimentarius Commission’s acceptable daily intake (ADI) and maximum residue limits (MRLs). A total of 84 farmed fish were sampled and analysed in the presence of tetracycline and sulphonamide residues. All samples were positive for sulphonamide residues (100%; n = 84), and 2.4% (n = 2) were positive for tetracycline and consequently also positive for both compounds. Tetracycline levels were below ADI and MRL, 28.5% (n = 24) surpassed the ADI, and 6% (n = 5) of the samples exceeded the MRL for sulphonamide. Regular monitoring of antibiotic residues in aquaculture products is crucial to mitigate health risks and expanding assessments to include other commonly used compounds is warranted.

Fluorescence sensor based on optimized quantum yield manganese-carbon polymer dots and smartphone-integrated sensing platform for tetracycline detection.

Theone-step synthesis of Mn-doped carbon quantum dots (Mn-CPDs) with a high quantum yield (QY = 45%) is reportedusing the microwave-assisted method. Subsequently, Mn-CPDs were successfully combined with Eu3+ ions to construct an Eu3+@Mn-CPDs fluorescence sensor. The presence of tetracycline (TC) induced a transition of fluorescence emission from blue (434 nm) to red (618 nm), and a robust linear relationship was observed between the ratio of F618 nm / F434 nm and the TC concentration (5 - 50 nmol/L), with a limit of detection (LOD) of 5.76 nmol/L. The underlying mechanism of Eu3+@Mn-CPDs and TC sensing is unveiled as a synergistic effect involving inner filter effect (IFE) and concurrent interactions. Notably, the smartphone-integrated sensing platform based on Eu3+@Mn-CPDs enables rapid and quantitative TC detection within a short time (< 30 s) by monitoring fluorescence color changes, achieving high-detection sensitivities (with a LOD of 6.18 nmol/L). This versatile and efficient sensing platform demonstrates its potential for the determination ofTC concentrations in milk, honey, and tap water samples.

Enhanced Biofilm Formation by Tetracycline in a Staphylococcus aureus Naturally Lacking ica Operon and atl.

Staphylococcus aureus is a major, widespread pathogen, and its biofilm-forming characteristics make it even more difficult to eliminate by biocides. Tetracycline (TCY) is a major broad-spectrum antibiotic, the residues of which can cause deleterious health impacts, and subinhibitory concentrations of TCY have the potential to increase biofilm formation in S. aureus. In this study, we showed how the biofilm formation of S. aureus 123786 is enhanced in the presence of TCY at specific subinhibitory concentrations. S. aureus 123786 used in this study was identified as Staphylococcal Cassette Chromosome mec III, sequence type239 and naturally lacking ica operon and atl gene. Two assays were performed to quantify the formation of S. aureus biofilm. In the crystal violet (CV) assay, the absorbance values of biofilm stained with CV at optical density (OD)540 nm increased after 8 and 16 hr of incubation when the concentration of TCY was 1/2 minimum inhibitory concentration (MIC), whereas at the concentration of 1/16 MIC, the absorbance values increased after 16 and 24 hr of incubation. In tetrazolium salt reduction assay, the absorbance value at OD490 nm of S. aureus 123786 biofilms mixed with 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium solution increased after 8 hr when the concentration of TCY was 1/4 MIC, which may be correlated with the higher proliferation and maturation of biofilm. In conclusion, the biofilm formation of S. aureus 123786 could be enhanced in the presence of TCY at specific subinhibitory concentrations.

Novel electrochemical/fluorescence dual-mode biosensor based on covalent organic framework for tetracycline detection

Excessive antibiotic residues increased the environmental damage and safety of animal products, leading to serious health threats. In this study, a dual-mode probe was developed and applied as an electrochemical/fluorescence sensor for tetracycline (TET) detection. The probe, comprising a fluorescent covalent organic framework, electroactive methylene blue, gold nanoparticles (AuNPs) and single-stranded DNA, was synthesized by self-assembly. A glassy carbon electrode was functionalized with molybdenum disulfide nanosheets, AuNPs, and aptamers. The probe exhibited fluorescent signals in solution and electrochemical signals after being specifically connected to the electrode via hybridization. In the presence of TET, the probe is be competitively expelled from the modified electrode, resulting in an increase in the fluorescent signal and a decrease in the electrochemical signal. The developed electrochemical/fluorescence dual-mode sensor enabled sensitive TET detection in the concentration range of 10 nM–10 mM, with minimum detection limits of 0.03 nM (electrochemical) and 0.05 nM (fluorescence). With its high selectivity, superior reproducibility, and excellent stability, the proposed dual-mode sensor demonstrates high reliability, and excellent application prospects for TET detection in milk and river water samples.

Turn-off/turn-on biosensing of tetracycline and ciprofloxacin antibiotics using fluorescent iron oxide quantum dots.

A fluorescence probe based on iron oxide quantum dots (IO-QDs) was synthesized using the hydrothermal method for the determination of tetracycline (TCy) and ciprofloxacin (CPx) in aqueous solution. The IO-QDs were characterized using high-resolution transmission electron microscopy (HR-TEM), powder X-ray diffraction (P-XRD), vibrating sample magnetometry (VSM), and Fourier-transform infrared spectroscopy (FTIR). The as-prepared IO-QDs are fluorescent, stable, and with a fluorescence quantum yield (QY) of 9.8 ± 0.12%. The fluorescence of IO-QDs was observed to be quenched and enhanced in the presence of TCy and CPx, respectively. The fluorescence intensity ratio shows linearity at concentrations from 1-100 μM and 5-100 μM for TCy and CPx, respectively; the detection limit for TCy and CPx was estimated to be 0.71 μM and 1.56 μM, respectively. The proposed method was also successfully utilized in the spiked samples of drinking water and honey with good recoveries. The method offered convenience, rapid detection, high sensitivity, selectivity, and cost-efficient alternative options for the determination of TCy and CPx in real samples.

Synthesis of water-soluble CdS quantum dots for the fluorescence detection of tetracycline

An effective strategy for combating antibiotic-resistant bacteria (ARB) entails the early detection of antibiotics during the initial stages of water treatment facilities. In this context, cadmium sulfide quantum dots (CdS QDs) were employed for the precise detection of tetracycline (TET), an emerging contaminant, in water. CdS QDs with fluorescence properties were synthesized by culturing Citrobacter freundii bacteria. The CdS QDs were characterized by spectroscopy techniques, and the quantum efficiency was estimated to be 55.8% which is ∼2-fold high compared to the standard rhodamine-B solution. The fluorescence of CdS QDs was quenched at 440 nm in the presence of TET. The linear range of TET was varied from 10 to 100 μM with a lower limit of detection of ∼23 nM. The CdS QDs were used to detect TET in river water, tap water, and milk which showed an excellent recovery rate. Therefore, the novel biosynthesis CdS QDs can be a significant fluorescence probe for the detection of TET that shows exceptional sensitivity and selectivity.

Multi-omics reveals the increased biofilm formation of Salmonella Typhimurium M3 by the induction of tetracycline at sub-inhibitory concentrations

Exposure to sub-inhibitory concentrations (sub-MICs) of antibiotics could induce the biofilm formation of microorganisms, but its underlying mechanisms still remain elusive. In the present work, biofilm formation by Salmonella Typhimurium M3 was increased when in the presence of tetracycline at sub-MIC, and the highest induction was observed with tetracycline at 1/8 MIC. The integration of RNA-sequencing and untargeted metabolomics was applied in order to further decipher the potential mechanisms for this observation. In total, 439 genes and 144 metabolites of S. Typhimurium M3 were significantly expressed after its exposure to 1/8 MIC of tetracycline. In addition, the co-expression analysis revealed that 6 genes and 8 metabolites play a key role in response to 1/8 MIC of tetracycline. The differential genes and metabolites were represented in 12 KEGG pathways, including five pathways of amino acid metabolism (beta-alanine metabolism, tryptophan metabolism, arginine and proline metabolism, phenylalanine, tyrosine and tryptophan biosynthesis, and glutathione metabolism), three lipid metabolism pathways (biosynthesis of unsaturated fatty acids, fatty acid degradation, and fatty acid biosynthesis), two nucleotide metabolism pathways (purine metabolism, and pyrimidine metabolism), pantothenate and CoA biosynthesis, and ABC transporters. Metabolites (anthranilate, indole, and putrescine) from amino acid metabolism may act as signaling molecules to promote the biofilm formation of S. Typhimurium M3. The results of this work highlight the importance of low antimicrobial concentrations on foodborne pathogens of environmental origin.

Full-value preparation of biochar and 2D N-doped CDs@ZIF-L from fermentation residues for sensitive sensing tetracyclines in food samples

The use of thermal conversion to convert Chinese patent medicines (CPM) residues into porous carbon-based materials and carbon dots (CDs) has effectively resolved the challenges associated with resource waste and environmental pollution while enhancing the added value of CPM residues. In this study, biochar and N-doped CDs with high quantum yield (QY) were simultaneously prepared from fermentation residues by employing a hydrothermal carbonization method without any chemical reagents. The obtained biochar had remarkable adsorption capacity, with an iodine adsorption value of 693.22 mg g–1. The QY of N-doped CDs could reach to 36.17 % by the mean of self-doping due to the high nitrogen content of the fermentation residues. Considering the structural integrity and permeable porous structure of the two-dimensional leaf-like zeolitic imidazole framework (ZIF-L), N-doped CDs were encapsulated into ZIF-L to form novel fluorescent composites (N-doped CDs@ZIF-L). Moreover, N-doped CDs@ZIF-L as a novel fluorescent probe could be efficiently quenched in the presence of tetracycline (TC), doxycycline (DOC), and chlortetracycline (CTC) by static quenching and the inner filter effect. Notably, the fluorescent probe exhibited a good linear relationship with the TC, DOC, and CTC at 0–50, 0–50, and 0–45 μM, respectively, with limits of detection of 0.025, 0.033, and 0.027 μM, respectively. This probe could be employed to detect TC antibiotics in honey and milk, suggesting that it had the great potential for applications in environmental monitoring and food safety.

Transcriptional modifications enhance the persistence of resistant plasmids in the presence of tetracycline in an environmentally relevant concentration

Antibiotic resistance genes (ARGs) have captured immense attention due to their widespread existence and remarkable ability to spread across species boundaries. Plasmid carriage promotes the persistence and spread of ARGs in the environment. To investigate the prevalence of plasmids, we conducted serial passage experiments on Pseudomonas putida KT2442 with multidrug-resistant plasmid RP4::gfp in the presence of tetracycline (TC) in an environmentally relevant concentration. The results showed that TC in environmental concentration compensated the fitness cost brought by the plasmid, prolonged the persistence time of the plasmid-bearing strain, and induced the reoccurrence of plasmids after the window time of plasmid loss. Transcriptome sequencing showed that plasmid recovery was compensated by the up-regulation of glyoxylic acid shunt and the down-regulation of ribosome biosynthesis. It is therefore hypothesized that transcriptional modifications may enhance the persistence of resistant plasmids within the population in the presence of TC in an environmentally relevant concentration. This work opens up an avenue for developing a technology based on the window time of plasmid loss to prevent the spread of ARGs.

Heme biosensor-guided in vivo pathway optimization and directed evolution for efficient biosynthesis of heme

BackgroundHeme has attracted much attention because of its wide applications in medicine and food. The products of genes hemBCDEFY convert 5-aminolevulinic acid to protoporphyrin IX (PPIX; the immediate precursor of heme); protoporphyrin ferrochelatase (FECH) inserts Fe2+ into PPIX to generate heme. Biosynthesis of heme is limited by the need for optimized expression levels of multiple genes, complex regulatory mechanisms, and low enzymatic activity; these problems need to be overcome in metabolic engineering to improve heme synthesis.ResultsWe report a heme biosensor-guided screening strategy using the heme-responsive protein HrtR to regulate tcR expression in Escherichia coli, providing a quantifiable link between the intracellular heme concentration and cell survival in selective conditions (i.e., the presence of tetracycline). This system was used for rapid enrichment screening of heme-producing strains from a library with random ribosome binding site (RBS) variants and from a FECH mutant library. Through up to four rounds of iterative evolution, strains with optimal RBS intensities for the combination of hemBCDEFY were screened; we obtained a PPIX titer of 160.8 mg/L, the highest yield yet reported in shaken-flask fermentation. A high-activity FECH variant was obtained from the saturation mutagenesis library. Fed-batch fermentation of strain SH20C, harboring the optimized hemBCDEFY and the FECH mutant, produced 127.6 mg/L of heme.ConclusionWe sequentially improved the multigene biosynthesis pathway of PPIX and performed in vivo directed evolution of FECH, based on a heme biosensor, which demonstrated the effectiveness of the heme biosensor-based pathway optimization strategy and broadens our understanding of the mechanism of heme synthesis.

Cultivation of algal-bacterial granular sludge and degradation characteristics of tetracycline.

Due to the increasing use of antibiotics, tetracycline was frequently detected in wastewater. As a novel technology, algal-bacterial granular sludge process is expected to be widely used in wastewater treatment. However, the degradation effect of tetracycline by algal-bacterial granular sludge process and its degradation path is still unknown. In this study, mature and stable algal-bacterial granular sludge was cultured and the degradation of tetracycline by it was investigated. The results showed that the removal amount of 1~25 mg/L tetracycline by algal-bacterial granular sludge was 0.09~1.45 mg/g VSS, in which the adsorption amount was 0.06~0.17 mg/g VSS and the degradation amount was 0.03~1.27 mg/g VSS. Tetracycline biosorption was dominant at its concentration of 1~3 mg/L, while biodegradation was predominant at 5~25 mg/L of tetracycline. At tetracycline concentration of 3~5 mg/L, the contribution of biosorption and biodegradation to tetracycline removal by algal-bacterial granular sludge process was almost equal. Algal-bacterial granular sludge could effectively degrade tetracycline through demethylation, dehydrogenation, deacylation and deamination or their combination. In addition, the degradation products were non-toxic and hardly pose a threat to environmental health. The research results of this paper provide a solid theoretical basis for tetracycline removal by algal-bacterial granular sludge, and a reference for the development of algal-bacterial granular sludge process for wastewater treatment in the presence of tetracycline.

Construction of F–F@FeVO4/ZnCo2O4 photocatalysts with heterojunction interfacial enhancement and surface oxygen vacancies for the removal of tetracycline, sulfamethoxazole, ciprofloxacin and Cr(VI)

For the purpose of promoting application of green and sustainable photocatalytic materials in real-world composite wastewater remediation, developing stable, efficient and pollution-free treatment devices is necessary and actually urgent. We grew vertical nanosheets consisting of FeVO4/ZnCo2O4 directly on the surface of iron foam (F–F), which intertwined to form F–F@FeVO4/ZnCo2O4 p-n heterojunction catalysts with a three-dimensional framework structure. The F–F@FeVO4/ZnCo2O4 photocatalyst showed excellent photocatalytic performance achieving 96.32%, 92.85%, 95.92% and 97.17% removal efficiencies in the presence of tetracycline (TC), sulfamethoxazole (SMX), ciprofloxacin (CIP) and Cr(VI), respectively. In addition, the photocatalyst was assembled into a simulated photoreactor, enabling the continuous treatment of composite wastewater. The reactor achieved removal efficiencies of 94.81%, 90.02%, 94.17% and 97.15% for TC, SMX, CIP and Cr(VI), respectively, in a 100 min reaction. Furthermore, only after ten photocatalytic cycles under visible light does the catalytic efficiency of the reactor decrease slightly. The excellent performance may be attributed to unique structures that reduce visible light reflection and provide highly reactive reaction centers, as well as surface oxygen vacancies and heterojunctions to accelerate photocarrier separation and free radical generation. The high porosity of F–F also reduces the obstruction of visible light between branches. Moreover, the method of growing FeVO4/ZnCo2O4 active components on F–F overcomes a number of problems (increased interfacial charge transfer impedance, poor structural stability and nonuniform distribution, etc.) associated with conventional methods of combining nanomaterials with recyclable substrates (loading, introduction of adhesives and hybridization, etc.). Density functional theory (DFT) calculations explain the mechanism of interface enhancement.

A ratiometric fluorescence sensor for tetracycline detection based on two fluorophores derived from Partridge tea

Blue fluorescent carbon dots (PCDs) were prepared by hydrothermal method with Partridge tea. The ethanol extract of Partridge tea (PEE) was found to emit red fluorescence. Thus, a novel ratiometric sensor was constructed by simply mixing the two fluorophores derived from Partridge tea. The presence of tetracycline (TET) at lower concentrations enhanced the emission peak at 508nm of PCDs and had a negligible effect on the emission peak at 680nm of PEE. TET at higher concentrations led to quenching both the fluorescence of PCDs and PEE via inner filter effect and fluorescence resonance energy transfer, separately. Good linearities for the detection of TET were obtained in the ranges 0.67 to 15.00μM and 33.33 to 266.67μM, with limit of detection of 0.095μM. The sensor was successfully applied to detect TET in lake water and milk samples with good recoveries ranging from 93.27 ± 4.04% to 107.30 ± 6.16%. This study provided a simple, selective, sensitive, rapid, and environmentally friendly method of monitoring TET residues in the environment and food.

Colloidal Gold Immunochromatography and ELISA Traceability of Tetracycline Residues from Raw Milk to its Dairy Products.

The presence of tetracycline (TC) and its residues in raw milk and milk dairy products poses a threat to human health due to the induction of antibiotic resistance of bacteria that can be transmitted between animals, humans, and the environment. The aim of this study was to investigate the transfer of TC from raw milk to different dairy products: pasteurized milk, boiled milk, sour milk, skimmed milk, and cottage cheese. We analyzed samples of milk from different sources: household farmers, local farms, and milk factories. The analyses of TC in milk and dairy products were performed using colloidal gold immunochromatography assay (GICA) and enzyme-linked immunosorbent assay (ELISA). The highest content of TC was found in the milk purchased from local household farmers; therefore, these samples were chosen for the study of TC transfer to dairy products. TC was also found in sour milk at levels comparable with those obtained in raw milk. The average TC content decreased following heat treatment of the milk, as follows: for pasteurized milk 22.07% and for boiled milk 29.35%. The highest concentrations were determined in cottage cheese in the range 200-620 μg/kg. TC residues are transferred from milk to dairy products in various amounts depending on the preparation conditions, and due to their chemical properties, they accumulate in concentrated derivatives, such as cheese. Therefore, TC can be identified even in cheeses prepared from milk with undetected antibiotic levels.

AMPEROMETRIC BIOSENSORS FOR THE DETERMINATION OF TETRACYCLINE

Amperometric biosensors based on planar graphite electrodes modified by multi-walled carbon nanotubes (CNTs) in chitosan, reduced graphene oxide (RGO), gold nanoparticles (Au NPs) in chitosan, nanocomposites based on them, and immobilized tyrosine enzyme for the determination of tetracycline have been developed. It is shown that tetracycline is a tyrosinase inhibitor, which provides the determination of tetracycline using a tyrosinase biosensor in the concentration range from 1 nM to 1 pM with LOD 0.5 nM. According to the results of kinetic studies of the reaction of the enzymatic conversion of phenol, it is found that in the presence of tetracycline, uncompetitive inhibition is observed on the tyrosinase biosensor. Electrodes modified with nanomaterials can be used as primary transducers of biosensors for fast and accurate determination of the tetracycline concentration. Combination of carbon nanomaterials with metal nanoparticles can form a nanocomposite with a synergistic effect. The use of carbon nanomaterials and metal nanoparticles as modifiers of the electrode surface made it possible to improve the analytical characteristics of the developed sensors: the range of determined concentrations in case of a biosensor modified with CNT/Au NPs and RGO/Au NPs was 1 nM - 1 pM and 0.1 nM - 1 pM, respectively. The correlation coefficient was 0.9925, and the lower limit of the determined concentrations was 50 pM (biosensor with CNT/Au NPs) and 0.7 nM (biosensor with RGO/Au NPs), respectively. The relative standard deviation of the results obtained using biosensors did not exceed 0.078. Methods for the determination of tetracycline using the proposed biosensors in milk and cosmetics have been tested. The compounds present in these samples, structurally unrelated to tetracycline, do not interfere with the determination.

Comparison of Fitness Cost, Stability, and Conjugation Frequencies of tet(X4)-Positive Plasmids in Chicken and Pig Escherichia coli.

The large-scale epidemic of the tet(X4) gene in the livestock and poultry industry is threatening public health; however, there is still a lack of comparative studies on tet(X4)-bearing plasmids in chicken and pig Escherichia coli. To evaluate the prevalence trend of tet(X4)-bearing plasmids and the factors influencing their persistence in the livestock and poultry industry, we examined the fitness cost, stability under tetracyclines pressure, and conjugation frequencies at various temperatures of six tet(X4)-bearing plasmids in four representative pig E. coli isolates and chicken E. coli isolates. Compared with pig E. coli, the plasmid in chicken E. coli showed lower fitness cost, and stronger ability to promote bacterial biofilm formation and motility. Meanwhile, the presence of tetracycline may favor the stability of tet(X4)-bearing plasmids, which was more common in chicken E. coli. Furthermore, the optimal temperature for IncX1 tet(X4)-bearing plasmid conjugation was 42 °C, and its conjugation frequency in chicken E. coli was higher than that in pig E. coli, whereas the optimal temperature for IncFII tet(X4)-bearing plasmid conjugation was 37 °C and it performed better in pig E. coli, suggesting the predominant plasmid types circulating in chicken E. coli and pig E. coli may be distinct. Collectively, although tet(X4) currently appears to be more prevalent in pig E. coli, this is probably independent of the fitness cost caused by tet(X4)-plasmids. To curb the future spread of the tet(X4) gene, reduced tetracyclines usage and tailored interventions should be applied in different breeding industries.