Development and validation of an HPLC confirmatory method for the determination of seven tetracycline antibiotics residues in milk according to the European Union Decision 2002/657/EC

A novel fluorescence ratio probe based on dual-emission carbon dots for highly selective and sensitive detection of chlortetracycline and cell imaging

The novel dual-emission carbon dots (DECDs) for highly selective and sensitive recognition of chlortetracycline (CTC) and cell imaging were synthesized successfully by one-step synthesis. The obtained DECDs possessed two fluorescence peaks (345 nm and 450 nm) and showed specific response to CTC, resulting in a decrease in fluorescence intensity at 345 nm, a blue shift, and an increase in fluorescence intensity at 450 nm. The obtained DECDs exhibited highly selective response to CTC and not to its analogues, such as tetracycline, doxycycline, and oxytetracycline. Thus, an excellent ratiometric probe for the detection of CTC was fabricated successfully and used for the detection of CTC in real samples with the detection limit (LOD) of 16.45 nM. More importantly, the DECDs were used for quantitative detection of CTC in living cells, which demonstrated excellent biocompatibility and broad prospects in biomedicine application. Finally, the excellent selectivity of DECDs toward CTC was attributed to the FRET mechanism and the formation of complexes.

Occurrence of oxytetracycline residues in milk samples from Palakkad, Kerala, India

Background and Aim

Food of animal origin such as milk is vital for nutritional security and should be free of any antibiotic residues due to its public health significance. We designed a study aiming to determine the occurrence of antibiotic residues and in further levels of oxytetracycline residues in pooled raw milk samples from Palakkad district, Kerala.

Materials and Methods

We collected pooled raw milk samples were collected from Alathur, Chittoor, and Palakkad blocks of Palakkad district, Kerala. A total of 215 samples were screened for antibiotic residues by microbial inhibition assay (MIA) and the positive samples were subjected to enzyme-linked immunosorbent assay (ELISA) to determine oxytetracycline residues, this was further confirmed using high-performance liquid chromatography (HPLC).

Results

We found that out of the 215 pooled raw milk samples screened for antibiotic residues using MIA, 22 samples (10.23%) were positive for antibiotic residues from Palakkad, Kerala. Out of these 22 samples, five (2.33%) were positive for oxytetracycline residues. We further calculated the mean concentration of oxytetracycline residues in these five samples and estimated it to be 201.00±41.25 ng/mL and 272.11±53.21 ng/mL using ELISA and HPLC, respectively. On analyzing these five samples, we found that four samples (1.86%) exceeded the maximum residue limits level of 100 ng/mL for oxytetracycline residues in milk as specified by Codex Alimentarius Commission/Food Safety and Standards Authority of India (FSSAI).

Conclusion

This study revealed that the occurrence of oxytetracycline residues in pooled raw milk samples in the Palakkad district of Kerala. Hence, there is a need for surveillance and monitoring of antibiotic residues in milk due to its impact on public health to ensure consumer safety.

Contamination of Animal Feed with Undeclared Tetracyclines-Confirmatory Analysis by Liquid Chromatography-Mass Spectrometry after Microbiological Plate Test

The presence of tetracycline (TC) antibiotics was determined in animal feed that had been previously screened with a microbiological plate test. Feed samples were screened by a microbiological plate test on a pH 6.0 culture medium seeded with Bacillus cereus ATCC 11778 able to pre-reveal the presence of tetracyclines. Subsequently, confirmation and quantification were performed using a validated HPLC method with mass spectrometric detection. In 2013–2018, 353 feed samples were analysed to detect antibacterial substances, of which 186 (52.7%) were suspected to contain tetracyclines. Forty-two out of 186 (22.6%) samples analysed by the chromatographic method contained undeclared tetracyclines, which were determined at concentrations from 0.3 to 49 mg kg⁻¹. The most frequently identified contaminating tetracyclines were doxycycline and chlortetracycline.

Determination of three tetracyclines in bovine milk using magnetic solid phase extraction in tandem with dispersive liquid-liquid microextraction coupled with HPLC

A novel analytical method namely magnetic solid phase extraction in tandem with dispersive liquid-liquid microextraction was developed and used for the extraction/preconcentration of tetracycline (TCN), oxytetracycline (OTC) and doxycycline (DC) from bovine milk sample before HPLC-UV analysis. The β-cyclodextrin functionalized silica-coated magnetic graphene oxide (Fe₃O₄@SiO₂@GO-β-CD) was used as an adsorbent. The adsorbent was fully characterized using FT-IR, SEM, EDX and Zeta potential techniques. The effective parameters on the performance of the method such as extraction solvent type and volume, adsorbent amount, desorption solvent type and volume, disperser solvent type, desorption time, ionic strength and pH value were investigated. The limit of detection (LOD) and limit of quantification (LOQ) were obtained in the ranges of 1.8-2.9 μg L^-1 and 6.1-9.7 μg L^-1, respectively. The linearity was in the range of 10.0-200.0 μg L^-1 with satisfactory determination coefficients (R²) higher than 0.9929 and a good precision (RSD < 8.8%). The recovery percentages for the analytes in real samples (bovine milk and water) were achieved in a range from 70.6 to 121.5%.

Molecularly Imprinted Polymers as Extracting Media for the Chromatographic Determination of Antibiotics in Milk

Milk-producing animals are typically kept stationary in overcrowded large-scale farms and in most cases under unsanitary conditions, which promotes the development of infections. In order to maintain sufficient health status among the herd or promote growth and increase production, farmers administer preventative antibiotic doses to the animals through their feed. However, many antibiotics used in cattle farms are intended for the treatment of bacterial infections in humans. This results in the development of antibiotic-resistant bacteria which pose a great risk for public health. Additionally, antibiotic residues are found in milk and dairy products, with potential toxic effects for the consumers. Hence the need of antibiotic residues monitoring in milk arises. Analytical methods were developed for the determination of antibiotics in milk, with key priority given to the analyte extraction and preconcentration step. Extraction can benefit from the production of molecularly imprinted polymers (MIPs) that can be applied as sorbents for the extraction of specific antibiotics. This review focuses on the principals of molecular imprinting technology and synthesis methods of MIPs, as well as the application of MIPs and MIPs composites for the chromatographic determination of various antibiotic categories in milk found in the recent literature.

Enhanced photocatalytic degradation activity for tetracycline under visible light irradiation of Ag/Bi3.84W0.16O6.24nanooctahedrons

In this work, a Ag/Bi_3.84W_0.16O_6.24nanooctahedron composite photocatalyst was successfully synthesizedviaa green method at room temperature using silver nitrate (AgNO₃) as the silver source.

Biosensors, antibiotics and food

Antibiotics are medicine's leading asset for fighting microbial infection, which is one of the leading causes of death worldwide. However, the misuse of antibiotics has led to the rapid spread of antibiotic resistance among bacteria and the development of multiple resistant pathogens. Therefore, antibiotics are rapidly losing their antimicrobial value. The use of antibiotics in food production animals is strictly controlled by the European Union (EU). Veterinary use is regulated to prevent the spread of resistance. EU legislation establishes maximum residue limits for veterinary medicinal products in foodstuffs of animal origin and enforces the establishment and execution of national monitoring plans. Among samples selected for monitoring, suspected noncompliant samples are screened and then subjected to confirmatory analysis to establish the identity and concentration of the contaminant. Screening methods for antibiotic residues are typically based on microbiological growth inhibition, whereas physico-chemical methods are used for confirmatory analysis. This chapter discusses biosensors, especially whole-cell based biosensors, as emerging screening methods for antibiotic residues. Whole-cell biosensors can offer highly sensitive and specific detection of residues. Applications demonstrating quantitative analysis and specific analyte identification further improve their potential as screening methods.

Ultrasound-assisted dispersive extraction for the high pressure liquid chromatographic determination of tetracyclines residues in milk with diode array detection

Ultrasound assisted matrix solid phase dispersive extraction was applied for the selective isolation and clean-up of tetracyclines (oxytetracycline, tetracycline, epi-chlorotetracycline, chlorotetracycline and doxycycline) from milk. Target analytes were determined by an accurate and sensitive chromatographic analytical method, which was validated to meet the European Legislation criteria. The separation was performed on a LiChroCART-LiChrospher® 100 RP-18 (5μm, 250×4mm) analytical column, operated at ambient temperature, followed by diode array detection. Validation included investigation of linearity, selectivity, stability, limits of detection and quantitation, decision limit, detection capability, trueness, precision and ruggedness according to the Youden's approach. Limits of quantitation of examined tetracyclines were from 14.5 to 56.6μg/kg significantly lower than respective Maximum Residue Limits, whereas recoveries ranged from 82.0% to 108%. The applicability of the method was evaluated using milk samples purchased from local market. Accuracy of the method was additionally proved by analysis of bovine milk certified reference material (BCR®-492).

Production of monoclonal antibody against doxycycline for immunoassay of seven tetracyclines in bovine muscle and milk

The objective of this study was to produce a generic monoclonal antibody for multi-determination of the residues of tetracycline drugs in bovine muscle and milk. Two new immunogens of doxycycline were prepared that were used to produce the monoclonal antibodies. Results showed the obtained antibodies simultaneously recognized seven tetracycline drugs (doxycycline, tetracycline, chlortetracycline, oxytetracycline, minocycline, methacycline, demeclocycline). The obtained antibodies and three coating antigens were arranged into six combinations to optimize the reagents combination. After comparison of the performances of these combinations, a heterologous indirect competitive ELISA was then used to determine the seven tetracyclines in bovine muscle and milk. The crossreactivities to the seven analytes were in the range of 47%-102% and the limits of detection were in the range of 1.5-6.9 ng/mL depending on the compound. The recoveries of the seven drugs from fortified blank samples were in the range of 75.3%-106.8% with coefficients of variation lower than 10.9%. Therefore, this method could be used as a multi-analytes screen tool for routine monitoring of the residues of these tetracycline drugs in bovine muscle and milk.

High throughput detection of tetracycline residues in milk using graphene or graphene oxide as MALDI-TOF MS matrix

In this work, a new pre-analysis method for tetracyclines (TCs) detection from the milk samples was established. As a good accomplishment for the existing accurate quantification strategies for TCs detection, the new pre-analysis method was demonstrated to be simple, sensitive, fast, cost effective, and high throughput, which would do a great favor to the routine quality pre-analysis of TCs from milk samples. Graphene or graphene oxide was utilized, for the first time, as a duel-platform to enrich and detect the TCs by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). All together, four TCs were chosen as models: tetracycline, oxytetracycline, demeclocycline, and chlortetracycline. Due to the excellent electronic, thermal, and mechanical properties, graphene and graphene oxide were successfully applied as matrices for MALDI-TOF MS with free background inference in low mass range. Meanwhile, graphene or graphene oxide has a large surface area and strong interaction force with the analytes. By taking the advantage of these features, TCs were effectively enriched with the limit of detection (LOD) as low as 2 nM.