Novel bioassay using Bacillus megaterium to detect tetracycline in milk

Development and performance evaluation of a microbiological method for screening and LC-MS/MS for conformation of sulfonamides in animal-derived foods

This study developed a highly sensitive microbiological method utilizing a novel microtiter plate to screen 10 sulfonamides in chicken muscles, eggs, and prawns. This plate was fabricated from agar incorporating trimethoprim and spread with Bacillus megaterium. After residue detection by bioassay, the same test solutions were analyzed by LC-MS/MS for accurate identification and quantification. It also proved eco-friendly compared to using other quantitative methods. The residual drugs were extracted with McIlvaine buffer and purified using an Oasis® MCX cartridge. A triethylamine/methanol/water (0.5:75:24.5, v/v/v) mixture was used as the eluate. The obtained LOD values of the bioassay ranged from 5 to 25 µg kg-1 allowing the detection of the target drugs at the MRLs established in Japan. Adhering to ISO/IEC 17025 standards, the performance of the bioassay was evaluated. Based on the inhibition zone size in bioassay results, quality control yielded a Z score within ±2, indicating reasonable control over the screening process. Proficiency testing of a chicken muscle sample spiked with sulfadimidine demonstrated the inhibition zone detection of the bioassay and quantified value alignment of LC-MS/MS with reference values. In a surveillance study of 91 samples, sulfamethoxazole was detected in one prawn sample.

Validation and application of an immunochromatographic test to detect four macrolides and two lincosamides in raw cow milk

In this study, an immunochromatographic test (using the Charm QUAD2® Test) was used to screen for residual macrolides and lincosamides in raw cow's milk. The validation parameters (selectivity/specificity, detection capability (CCβ), and ruggedness) were in agreement with the requirements of[EC] 2021. The selectivity of the immunochromatographic test was verified by the negative results of microbiological tests. The false-positive rate was 0%. The CCβ values of the immunochromatographic test for various antibiotics in milk were as follows: erythromycin 0.02 mg/kg, spiramycin 0.1 mg/kg, tilmicosin 0.025 mg/kg, tylosin 0.05 mg/kg, lincomycin 0.15 mg/kg, and pirlimycin 0.15 mg/kg. The determined CCβ values were lower than the respective maximum residue limits (MRLs; regulatory limits in Japan) for milk, except for lincomycin (equal to the MRL). The presence of antibiotic groups other than macrolides and lincosamides did not interfere with the specificity of the test. It showed no significant difference in lot-to-lot repeatability. The results obtained by the two researchers showed no significant differences. Finally, the test was applied to milk samples obtained from a tylosin-treated cow. The outcome was positive and in agreement with the results of the chemical analytical and microbiological methods. Therefore, this validated immunochromatographic test is expected to be suitable for routine analysis to ensure milk safety.

A dual-signal fluorescent sensor based on MoS2 and CdTe quantum dots for tetracycline detection in milk

A dual-signal fluorescent sensor was developed for tetracycline (TET) detection in milk with excellent reproducibility and stability. In this protocol, molybdenum disulfide quantum dots (MoS₂ QDs) with blue fluorescence and cadmium telluride quantum dots (CdTe QDs) with yellow fluorescence were synthesized to establish the MoS₂/CdTe-based sensor with two fluorescence emission peaks at 433 nm and 573 nm. With the addition of TET, the fluorescence of MoS₂/CdTe were quenched by photoinduced electron transfer (PET), and the fluorescence of CdTe QDs were quenched more obvious than MoS₂ QDs. With the strategy, a calibration curve was established between the TET concentration in the range of 0.1-1 μM and the ratio of fluorescence intensity at 573 nm and 433 nm (F₅₇₃/F₄₃₃). Furthermore, the dual-signal sensor was applied for TET detection in milk samples with the recovery of 95.53-104.22% and the relative standard deviation (RSD) less than 5%, indicating the strong application potential.

Synergistic SERS Enhancement in GaN-Ag Hybrid System toward Label-Free and Multiplexed Detection of Antibiotics in Aqueous Solutions

Noble metal-based surface-enhanced Raman spectroscopy (SERS) has enabled the simple and efficient detection of trace-amount molecules via significant electromagnetic enhancements at hot spots. However, the small Raman cross-section of various analytes forces the use of a Raman reporter for specific surface functionalization, which is time-consuming and limited to low-molecular-weight analytes. To tackle these issues, a hybrid SERS substrate utilizing Ag as plasmonic structures and GaN as charge transfer enhancement centers is presented. By the conformal printing of Ag nanowires onto GaN nanopillars, a highly sensitive SERS substrate with excellent uniformity can be fabricated. As a result, remarkable SERS performance with a substrate enhancement factor of 1.4 × 1011 at 10 fM for rhodamine 6G molecules with minimal spot variations can be realized. Furthermore, quantification and multiplexing capabilities without surface treatments are demonstrated by detecting harmful antibiotics in aqueous solutions. This work paves the way for the development of a highly sensitive SERS substrate by constructing complex metal-semiconductor architectures.

Ratiometric fluorescent probe for tetracycline detection based on waste printing paper

Tetracycline (TC) is a broad-spectrum antibiotic used to treat bacterial infections. In this study, a ratiometric fluorescence (FL) probe was developed to detect TC in water samples using waste printing paper extract as a FL indicator. For this ratiometric probe, the emission of printing paper extract at 436 nm gradually decreased and the emission of a mixed solution at 538 nm significantly increased with the sequential addition of TC upon excitation at 390 nm, coupled with a marked FL colour change from bright blue to faint yellow. Therefore, a ratiometric F₅₃₈ /F₄₃₆ FL probe was created for TC detection by simply mixing the printing paper extraction and TC. Under the optimized conditions, a linear range from 1 to 100 μM and a detection limit of 0.48 μM (S/N = 3) for TC were obtained. Importantly, the FL probe can be easily prepared with rapid response, high sensitivity, and good selectivity. The application of waste printing paper extract for detection of TC in environmental water samples was demonstrated.

Monitoring of residual antibacterial agents in animal and fishery products in Tokyo from 2003 to 2019: application and verification of a screening strategy based on microbiological methods

Residual antibacterial agents in 5909 animal and fishery products in Tokyo, Japan, were investigated over 17 consecutive years (2003-2019). Monitoring of 32 antibacterial agents (lincosamides, macrolides, penicillins, quinorones and tetracyclines) per product was accomplished via two steps: screening (by microbiological methods) and confirmation (by instrumental methods). Microbiological screening methods identified presumptive groups and determined semi-quantitative values. The instrumental methods quantified 81 residues of 11 different antibacterial agents in 72 samples. The screening strategy based on microbiological methods demonstrated the following: (i) the majority of the samples (over 99%) met Japanese regulations, (ii) using multiple methods provided a reliable inspection system with accurate quantitative values and (iii) there was a constant presence of tetracyclines and unexpected residues (lincomycin and norfloxacin) in various products. Thus, this long-term monitoring and screening strategy provided evidence that the frequencies and trends of residual antibacterial agents not only enhance food safety but also help to prevent antimicrobial resistance.

Development and Evaluation of a Preliminary Screening Assay for Antibiotic Residues in Meat

A preliminary screening assay based on a microbial chromogenic reaction was developed to detect common antibiotic residues in meat rapidly. The assay comprised two bioassays: one for Escherichia coli and another for Geobacillus stearothermophilus. The assay was optimized and evaluated for the simultaneous screening of 30 antibiotics from five common antibiotic classes (tetracyclines, aminoglycosides, macrolides, β-lactams, and quinolones) found in meat. Extraction using phosphate-acetonitrile buffer (pH 7.2) and a delipidating treatment using n-hexane resulted in a high extraction efficacy for the five antibiotics, without affecting the microbial color reaction. A carrier, polyvinyl alcohol (0.1 g/mL); a cross-linking agent, boric acid-sodium tetraborate solution (pH 5.5); and a bacterial suspension with an initial optical density of 1.0 were the optimal embedding conditions for stability, microbial activity, and chromogenic efficiency. The assay exhibited a 6-month shelf life, with detection limits of 40-60, 60-140, 60-100, 20-40, and 40-180 μg/kg for tetracyclines, aminoglycosides, macrolides, β-lactams, and quinolones, respectively, which met the European Commission (37/2010) requirements for antibiotic residue limits. Our assay results were confirmed using LC-MS/MS with 160 samples, revealing a good correlation. This study demonstrates a reliable, easy-to-use, and economical method for preliminary screening of antibiotic residues in meat. This method may find an immediate application in food safety and general testing laboratories.

Tetracyclines in Food and Feedingstuffs: From Regulation to Analytical Methods, Bacterial Resistance, and Environmental and Health Implications

Antibiotics are widely used as growth promoters in animal husbandry; among them, the tetracyclines are a chemical group of relevance, due to their wide use in agriculture, surpassing in quantities applied almost every other antibiotic family. Seeing the considerable amounts of tetracyclines used worldwide, monitoring of these antibiotics is paramount. Advances must be made in the analysis of antibiotics to assess correct usage and dosage of tetracyclines in food and feedstuffs and possible residues in pertinent environmental samples. The tetracyclines are still considered a clinically relevant group of antibiotics, though dissemination of tolerance and resistance determinants have limited their use. This review focuses on four different aspects: (i) tetracyclines, usage, dosages, and regulatory issues that govern their food-related application, with particular attention to the prohibitions and restrictions that several countries have enforced in recent years by agencies from both the United States and the European Union, (ii) analytical methods for tetracyclines, determination, and residues thereof in feedstuffs and related matrices with an emphasis on the most relevant and novel techniques, including both screening and confirmatory methods, (iii) tetracycline resistance and tetracycline-resistant bacteria in feedstuff, and (iv) environmental and health risks accompanying the use of tetracyclines in animal nutrition. In the last two cases, we discuss the more relevant undesirable effects that tetracyclines exert over bacterial communities and nontarget species including unwanted effects in farmers.