Directional evolution of TetR protein and development of a fluoroimmunoassay for screening of tetracyclines in egg

Synthesis of N-doped and P-doped silicon quantum dots and their applications for tetracycline detection in the honey samples and antibacterial properties

The abuse of tetracycline can lead to its residue in animal derived foods, posing many potential hazards to human health. Therefore, rapid and accurate detection of tetracycline is an important means to ensure food safety. Nitrogen doped and phosphorus doped silicon quantum dots (N-SiQDs, P-SiQDs) with remarkable optical stability were fabricated via a one-pot hydrothermal procedure in this study. Upon the excitation at 346 nm, N-SiQDs and P-SiQDs emitted fluorescence at 431 nm and 505 nm, respectively. Two SiQDs had the potential to serve as a probe for detecting low concentrations of tetracycline (TC), employing a mechanism of the static quenching effect. The calibration curves of N-SiQDs and P-SiQDs were linear within the range of 0-0.8 μM and 0-0.4 μM, the limits of detection were low as 5.35 × 10-4 μmol/L and 6.90 × 10-3 μmol/L, respectively. This method could be used successfully to detect TC in honey samples. Moreover, the remarkable antibacterial efficacy of two SiQDs could be attributed to the generation of a large number of intracellular reactive oxygen species. The SEM images showed that the structure of bacterial cell was disrupted and the surface became irregular when treated with both SiQDs. These properties enabled potential usage of SiQDs as excellent antibacterial material for different biomedical applications.

Development of a receptor based signal amplified fluorescence polarization assay for multi-detection of 35 sulfonamides in pork

With the increasing focus on food security, a screening method with high-throughput, ultra-sensitivity, and user-friendly operation is urgently needed for monitoring of sulfonamides residues in animal-derived foods. In this study, the sulfonamides' receptor dihydropteroate synthase of Staphylococcus aureus was subjected to saturate mutation, and a mutant with higher affinities for sulfonamides was obtained. The mutant was then used as recognition material to establish a fluorescence polarization assay for determination of 35 sulfonamides in pork. Due to the use of an enhanced fluorescent tracer containing two fluorophore molecules, the sensitivities for the 35 sulfonamides were improved for 2.8-8.6 folds (LODs 0.03-1.16 ng/mL) in comparison with using conventional fluorescent tracer. The present method outperformed all previous fluorescence polarization (immuno)assays for sulfonamides due to its broader spectrum, higher sensitivity, and shorter assay time. Furthermore, this is the first study reporting an enhanced fluorescence polarization assay for determination of small molecule substance.

Evolution of a natural TetR protein and development of a Fe3O4 assisted semi-homogeneous fluorescent method for determination of tetracyclines in milk

Compared with antibody, the recognition spectrum of a receptor is broader, and its recognition ability can be improved using simple mutagenesis technique. Compared with conventional immunoassay, the magnetic bead based immunoassay is simpler and can be recycled. Compared with colorimetric and luminescent immunoassays, fluoroimmunoassay is simpler because it does not require a substrate. So a method combines these merits is desirable. In this study, two amino acids in the binding pocket of a natural Escherichia coli TetR protein were mutated to produce a mutant, and the molecular docking showed the binding energies and the numbers of contact acid for 10 tetracyclines all increased. The mutant was coupled with Fe3O4 to synthesize a magnetic complex, and a fluorescent tracer was synthesized by coupling quantum dot and minocycline with bovine serum albumin. Under the assistance of 96-well bottom magnet, a semi-homogeneous method based on the two materials was developed on conventional microplate for determination of the 10 tetracyclines in milk. Results showed once assay was finished within 20 min, the limits of detection (drug concentration showing 10% inhibition) for the 10 drugs were in the range of 0.32-0.94 ng/mL, and the magnetic complex could be regenerated for 6 times. Furthermore, the sensitivities were improved for 4-6 folds in comparison with the use of natural TetR. Therefore, this method is simple, sensitive, time-saving and recyclable, and it can be used for routine screening of the 10 tetracyclines in milk.

Microextraction of Tigecycline Using Deep Eutectic Solvents and Its Determination in Milk by LC-MS/MS Method

The occurrence of tigecycline (TGC), a new first glycylcycline antibiotic residues in food products harmfully influences potential human consumers health. Therefore, analysts are forced to develop new microextraction methods connected with modern extractants for effective isolation of this compound. For this purpose, deep eutectic solvents (DES) as the extraction media were used. Liquid-liquid microextraction (LLME) of tigecycline from milk samples with application of the hydrophobic deep eutectic solvents: decanoic acid:thymol (1:1), thymol:camphor (2:1), dodecanoic acid:menthol (2:1), and dodecanoic acid:dodecanol (1:1) was developed. The studied samples were subjected to a deproteinization process using trichloroacetic acid solution and acetonitrile. The optimal microextraction parameters, molar ratio of DES components, amount of extraction solvents, pH of milk sample, shaking, and centrifugation time, were chosen. Tigecycline in the obtained microextracts of deep eutectic solvents was analyzed using a liquid chromatographic technique connected with a tandem mass spectrometry (LC-MS/MS) system. The limits of detection and quantification values for TGC determination followed by DES-LLME-LC-MS/MS method were in the 1.8 × 10^-11 mol L^-1 (0.01 μg kg^-1) to 4.0 × 10^-9 mol L^-1 (2.28 μg kg^-1) and 5.5 × 10^-11 mol L^-1 (0.03 μg kg^-1) to 1.2 × 10^-8 mol L^-1 (6.84 μg kg^-1) ranges, respectively. The RSD values of precision were in the range 1.4-7.8% (intraday) and 5.4-11.7% (interday). The developed procedures were used for the determination of tigecycline in different bovine milk samples.

Identification and Evolution of a Natural Tetr Protein Based on Molecular Docking and Development of a Fluorescence Polari-Zation Assay for Multi-Detection of 10 Tetracyclines in Milk

In this study, the identity of our recently produced natural TetR protein was identified by using the LC-ESI-MS/MS technique, and its recognition mechanisms, including the binding pocket, contact amino acids, intermolecular forces, binding sites, binding energies, and affinities for 10 tetracycline drugs were studied. Then, it was evolved by site-mutagenesis of an amino acid to produce a mutant, and a fluorescence polarization assay was developed to detect the 10 drugs in milk. The sensitivities for the 10 drugs were improved with IC₅₀ values decreasing from 30.8-80.1 ng/mL to 15.5-55.2 ng/mL, and the limits of detection were in the range of 0.4-1.5 ng/mL. Furthermore, it was found that the binding affinity for a drug was the critical factor determining its sensitivity, and the binding energy showed little influence. This is the first study reporting the recognition mechanisms of a natural TetR protein for tetracyclines and the development of a fluorescence polarization assay for the detection of tetracyclines residues in food samples.

Antibacterial properties and in silico modeling perspective of nano ZnO transported oxytetracycline-Zn2+ complex [ZnOTc]+ against oxytetracycline-resistant Aeromonas hydrophila

Emergence of antibiotics resistance has threatening consequences not only for human health but also for animal health issues in agriculture. Several animal pathogenic bacteria have developed antibiotic resistance and managing same has tremendous cost repercussions and may lead to total harvest loss. Hence in the present study, efforts are made to revitalize an old antibiotic molecule, oxytetracycline (OTc), through nanodelivery approaches using zinc oxide nanoparticles (nZnO) to confront OTc resistant fish pathogenic bacteria Aeromonas hydrophila. OTc was impregnated in nZnO through in situ precipitation method to develop OTc loaded ZnO nanoparticles (OTc@nZnO) with average size of 99.42 nm. Spectroscopic investigation of same revealed complexation of Zn²⁺ with amide and aromatic carbonyl moieties of OTc [ZnOTc]⁺. The complex performed better against A. hydrophila with 7-15 mm inhibition zone as compared to nil for bare OTc at same dose. OTc also showed MIC of 150 µg ml^-1 and for OTc@nZnO it was 7.02 µg ml^-1 with faster killing rate (k, -0.95). In silico docking simulation suggest that [ZnOTc]⁺ had low binding affinity (LBE > -5.00 kcal mol^-1) toward TetR(E) and TetA(E) proteins of A. hydrophila as compared to OTc (LBE < -8.00 kcal mol^-1). This study postulates that [ZnOTc]⁺ released from OTc@nZnO can escape TetR(E) and TetA(E) resistance proteins and bind at 30S ribosomal subunit with high affinity (<-11.00 kcal mol^-1) to exert antibacterial properties. In the recent scenario of recurrent antimicrobial resistance, the develop antibiotic-nanocomposites could come out as potential solution, however further study is required for its feasibility for use in animal health care.

Multiplex Detection of Antibiotic Residues in Milk: Application of MCR-ALS on Excitation-Emission Matrix Fluorescence (EEMF) Data Sets

The presence of antibiotics and their metabolites in milk and dairy products is a serious concern because of their harmful effects on human health. In the current study, a novel synergistic bimetallic nanocluster with gold and silver as an emission fluorescence probe was investigated for the simultaneous determination of tetracycline (TC), ampicillin (AMP), and sulfacetamide (SAC) antibiotics in the milk samples using excitation-emission matrix fluorescence (EEMF) spectroscopy. The multivariate curve resolution-alternating least squares (MCR-ALS) method was implemented to analyze augmented EEMF data sets to quantify the multicomponent systems in the presence of interferences with considerable spectral overlap. A pseudo-univariate calibration curve of the resolved emission spectra intensity against the concentration of the mentioned antibiotics was linear in the range of 5-5000 ng mL^-1 for AMP and 50-5000 ng mL^-1 for TC and SAC. The calculated values of the limit of detection ranged between 1.4 and 14.6 ng mL^-1 with a relative standard deviation (RSD) of less than 4.9%. The obtained results show that the EEMF/MCR-ALS methodology using an emission fluorescence probe is a powerful tool for the simultaneous quantification of TC, AMP, and SAC in complex matrices with highly overlapped spectra.

Development of a Dihydropteroate Synthase-Based Fluorescence Polarization Assay for Detection of Sulfonamides and Studying Its Recognition Mechanism

In this study, the dihydropteroate synthase of Staphylococcus aureus was obtained, and its recognition mechanisms for 31 sulfonamide drugs were studied. Results showed that their core structure matched well with the binding pocket of para-aminobenzoic acid, and all the sulfonamide side chains were out of the binding pocket. Hydrogen bonds and hydrophobic interactions were the main intermolecular forces, and the key amino acids were Gly171 and Lys203. The binding sites in sulfonamide molecules were mainly around the para-aminobenzenesulfonamide part. This enzyme was used to develop a fluorescence polarization assay for detection of these drugs in chicken muscles. The change trends of half of inhibition concentrations and cross-reactivities for the 31 drugs were identical with the receptor-ligand affinities. The limits of detection were in the range of 2.0-38.5 ng/g, and one assay could be finished within several minutes. Therefore, this method could be used for multiscreening of sulfonamide residues in meat samples.

Technological Advancements for the Detection of Antibiotics in Food Products

Antibiotics, nowadays, are not only used for the treatment of human diseases but also used in animal and poultry farming to increase production. Overuse of antibiotics leads to their circulation in the food chain due to unmanaged discharge. These circulating antibiotics and their residues are a major cause of antimicrobial resistance (AMR), so comprehensive and multifaceted measures aligning with the One Health approach are crucial to curb the emergence and dissemination of antibiotic resistance through the food chain. Different chromatographic techniques and capillary electrophoresis (CE) are being widely used for the separation and detection of antibiotics and their residues from food samples. However, the matrix present in food samples interferes with the proper detection of the antibiotics, which are present in trace concentrations. This review is focused on the scientific literature published in the last decade devoted to the detection of antibiotics in food products. Various extraction methods are employed for the enrichment of antibiotics from a wide variety of food samples; however, solid-phase extraction (SPE) techniques are often used for the extraction of antibiotics from food products and biological samples. In addition, this review has scrutinized how changing instrumental composition, organization, and working parameters in the chromatography and CE can greatly impact the identification and quantification of antibiotic residues. This review also summarized recent advancements in other detection methods such as immunological assays, surface-enhanced Raman spectroscopy (SERS)-based assays, and biosensors which have emerged as rapid, sensitive, and selective tools for accurate detection and quantification of traces of antibiotics.

Trends using biological target-based assays for drug detection in complex sample matrices

In vivo, drug molecules interact with their biological targets (e.g., enzymes, receptors, ion channels, transporters), thereby eliciting therapeutic effects. Assays that measure the interaction between drugs and bio-targets may be used as drug biosensors, which are capable of broadly detecting entire drug classes without prior knowledge of their chemical structure. This Trends article covers recent developments in bio-target-based screening assays for detecting drugs associated with the following areas: illicit products marketed as dietary supplements, food-producing animals, and bodily fluids. General challenges and considerations associated with using bio-target assays are also presented. Finally, future applications of these assays for drug detection are suggested based upon current needs.